Acrolink Mexcel 7N-PC9900 Power Cord

Introduction

The 7N-PC9900 is the latest version of Acrolink's flagship power cord, replacing the PC9700. According to Acrolink, the PC9900 is an upgraded version of the PC9700 and features new special shielding technology. 

Description

Visually and reading off the specifications sheet, the PC9900 and PC9700 are near identical twins. The Live and Neutral conductors are the same D.U.C.C. Stressfree 7N wires consisting of 50 strands of 0.32 mm diameter conductors, while the ground is similar except the wires are made from super-anneal 4.5N copper. 

The shield is described as polyurethane enameled 4N copper braid with special shielding technology - carbon fabric sleeves. In comparison, the PC9700 uses the same copper braid combined with semi-conductive carbon tape. 

Otherwise the PC9900 looks and feels the same, with a diameter of 16 mm and identical resistance and capacitance values. 

I no longer had the PC9700 on hand so I could not compare the two models. Instead, I used the 8N-PC8100 as a baseline for comparison instead.

Sound Quality

Acrolink Mexcel users expect the finest levels of resolving power and suppressed noise floor, which the PC9900 delivers in spades. 

The PC9900 has extremely high levels of resolution across the frequency range, with tight and powerful bass lines, and high frequencies that are extended and clean. In typical Mexcel fashion, this is delivered in very quick and focused transients, with a natural decay. Due to the very low noise floor, the PC9900 is almost like delivering a jolt to your system, giving it a sudden boost in contrast and dynamic range. 

Tonally, the PC9900 sounds similar to the PC9700 (based on memory). A quick read of my previous review of the PC9700 provides more insight into the character of both the PC9700 and PC9900. However, the PC9900 offers subtly improved resolving power with a little bit more focus and drive. I noticed that the Mexcel twins differ in how the human voice is presented. While both cables have more sweetness in the midrange compared to other Mexcel models, the PC9900 has a silkier and more fluid delivery. However, this comes at the expense of some snap and presence.

Comparisons to the PC8100 proved interesting. Unlike the PC9700, I would consider both the PC8100 and PC9900 to be on par with each other. The PC9900 is like using a computer monitor with higher resolution. The PC8100 makes do with lower resolution, but with more colour contrast, and a slightly warmer hue. Your choice of poison boils down more to taste. If you like a bolder presentation with more meat and flavour, the PC8100 fits the bill. The PC9900 is perfect for the palate that favours microdetail and a more refined and sophisticated presentation. If you like your Japanese whisky, think of the PC8100 as Nikka, and PC9900 as Yamazaki.

Conclusion

Acrolink Mexcel power cords are one of the finest products in the industry and come with a strong personal recommendation. While they are expensive, the level of performance delivered is very reasonable. I would have hesitated to say this some years ago, but a quick look at audio magazines and websites shows that flagship cables from the competition can even cost multiples of the PC9900 - Highly Recommended.

A big thanks goes out to X-Audio for arranging for the review sample.

Acrolink Mexcel 7N-PC9900 Power Cord
Price : S$ 5,500

X-Audio
1 Jalan Anak Bukit 
#01-01S, Bukit Timah Plaza
Tel : 64662642
  

     

 

AGD Audion Monoblock Power Amplifier

Introduction

AGD Productions Inc is the new kid on the high-end audio block. The brainchild of Alberto Guerra, AGD Productions Inc produces products that are distinctive and different from the competition.

For one, their amplifiers use their proprietary GaNTube™ technology. A friend of mine mentioned, "It looks like a tube, lights up like a tube, and sounds like a tube". The photo of the GaNTube™ below shows that a transistor based circuit housed in a vacuum tube like envelope. From the octal base, to the getter flashing on top, this looks like a typical 6550 or KT88 tube.

The GaNTube™ is a class D circuit, utilising Gallium Nitride MOSFET transistors in lieu of conventional silicon transistors. Gallium Nitride is being touted as the next big thing in semiconductor manufacturing, boasting superior performance in more compact packages. They are superior in terms of power efficiency, thermal stability, RF production and immunity. 

Alberto Guerra enjoyed a long and illustrious career in companies like Infineon and more than knows his way around Gallium Nitride technology, holding ten patents to his name (including two in Gallium Nitride know-how).

Description

The Audion comes in a really big Pelican case. Opening the case reveals the the pair of monoblocks, product literature and a pair of power cords. The amplifiers are compact and light at 2.5 kg each. In fact, the Pelican case feels heavier than the amplifier. 

Finishing is of high quality, with a solid indestructible feel. You can opt for the brushed finish, or a chrome finish for a premium. My review sample came with the brushed finish. The company logo is engraved into the front panel, while all inputs and the power inlet are located at the rear. The excellent speaker binding posts (a pair of WBT Nexgen 5-way posts) are located on the top of the amplifier, behind the GaNTube™. If you are using spade terminated speaker cables, this all fits very nicely. However, if you are using banana plug terminations like me, your cables will arch gracefully (like my flexible speaker cables), or suspend your Audion amplifier in mid-air in a worst-case scenario.

The power switch is located directly above the IEC inlet and will be partially blocked by monstrous power plugs that ship with any serious garden hose. Otherwise operation is event-free. The GaNTube™ glows orange like a vacuum tube except very little heat is produced. I demonstrated this to a visiting audiophile by resting my finger on the GaNTube™ in the middle of a listening session. No start-up noises or power-down thumps - excellent manners for this house guest. 

The Audion packs plenty of power, delivering 85 WPC into 8 ohms and 170 WPC into 4 ohms. It can deliver more than 30A of current which should be more than enough for most of the speakers out there in the wild. The input impedance of both the RCA and XLR input is 40 kohms (600 ohm inputs can be custom ordered). Noise is an astonishingly low -130db. The GaNTube™ switches at a frequency of 400 kHz.

 

I tried the Audion with three DACs with digital volume control (the Chord Dave, Totaldac D-1 Six and Antelope Audio Zodiac Platinum DAC). I also tried using a Music First Audio TVC preamp. Although the specifications do not specify the input sensitivity / gain of the Audion, it is definitely quite high. All three DACs were being used between -30db to -20db. In the case of a DAC with digital volume control, that is sufficient attenuation to potentially result in resolution loss. If you are using an active preamp with high amounts of gain, you have been warned ! In fact, this is one of the very few power amplifiers I've used that sound really good driven directly from the source. Save your pennies by skipping the preamp ! Another noteworthy point is that Audion sounds good through both the RCA and XLR input - no worries if your source is single-ended only.

Sound Quality

Let's get this out of the way first - Class D amplifiers get a bad rap from audiophiles. Conventional wisdom is that Class D amplifiers are sterile and lifeless. I have owned and auditioned enough Class D amplifiers to understand their appeal and their strengths. Many years ago, I bought a pair of monoblock amplifiers from a Japanese company called Flying Mole. They are no longer in business, but the product showed great promise. I have also owned a number of Class T amps (i.e. based on the Tripath chip), and amplifiers with both B&O ICEPower and Hypex modules. Each generation of module showed steady improvement, and a number were of high enough quality to challenge traditional amplifier designs.

The Audion need not make any excuses for itself. The sound quality easily surpasses most traditional amplifier designs and can even be considered as a serious challenger to the top amplifiers on the market. 

First up is the bass authority you get from the Audion. Class D amplifiers typically have superb control over your woofers. In some cases, you get a tight bottom-end that seems artificial with a lack of shading or texture. The Audion breathes freely here - as an example, double bass notes flow with timbre and life. The bass has just the right amount of wetness for me, although I did feel that there was a slight midbass emphasis, which resulted in a weightier and warmer tone.

The midrange has an inner glow quality that good single-ended triode amplifiers possess. However, this glow is even-handed and avoids the thick luscious tone that some tube amplifiers aim for. Some equipment smooth over the midrange to portray a more "musical" tone, but the Audion retains plenty of microdetail. 

The Audion's high-frequency performance must have delivered the greatest surprise during my review experience. Even the best class D modules I have heard (with the exception of the Orchard Audio BOSC - a story for another day) subtly reduce the top-end air in the recordings. While they do not by any means sound dull or rolled-off, you could sense a slight reduction in the scale of acoustic space. I always assumed that this was a necessary evil resulting from the low-pass filter required in class D designs to filter out ultrasonic noise. The Audion come through clear and extended. Neither is there any glare or harshness in the reproduction - cymbals crash and bells ring in a clear and extended manner, with a firm but crisp tone. 

Solid state amplifiers excel in staging precision but often cannot match tube amplifiers in dimensionality - the acoustic space around voices and instruments, and the perception of depth and height. The Audion could very well have been of vacuum tube pedigree in this regard, delivering convincing reproductions of each voice and instrument in the recording mix. Marry this with solid state speed and low frequency control, compactness and lack of heat - you truly get the best of both worlds here ! 

Prior to my experience with the Audion, discussions about Class D amplifiers with friends have always been caveated to a degree, e.g. "They deliver a lot of clean power for the price and are very accurate, but you really need a good preamplifier to flesh out the tone and complete the picture.", or "They really deliver bang for the buck, but if you spend a lot more, you can get even higher sonic performance." 

My caveats here are altogether different. Firstly, the high amounts of gain requires some care in matching with preamplifiers and sources. Secondly, the Audion is not affordable although it delivers exceptional sound quality for the price. The price tag puts it out of reach of most audiophiles but quality is never cheap. 

You could also make the argument that the Audion is not neutral. It isn't and to me it was almost certainly a deliberate design choice. Instead, it chose to be musical and delicate, while having the speed, power and control to bring realism to large-scale works. You can now have your cake and eat it ! 

Conclusion

The Audion is a truly revolutionary product. I understand that AGD already has several different GaNTube™ designs in the making, including a higher powered version, and a lower powered one for headamp use. The new modules may be installed in place of the current GaNTube™, which shows that the socketed GaNTube™ is not merely a whimsical fashion choice. 

Keep you eye on AGD, this is a truly special product that will redefine your notions of Class D and solid state technology - Highly Recommended.

This review was made possible with the kind assistance of Horizon Acoustics, sole distributor of AGD Productions Inc in Singapore. 

AGD Audion Monoblock Power Amplifier

Price : SGD 12,800

Horizon Acoustics

1 Pemimpin Drive

#08-11, One Pemipin

Singapore 576151

http://www.horizonacoustics.com

The Quick and Dirty 300B tube shoot-out

Introduction

The 300B vacuum tube must be one of the most talked-about vacuum tube models, especially in Asia. Critics like to pan it as hyped-up, before introducing their own favourite directly heated triode tube. Others on the other hand revere it as the lighted path to sonic bliss.

The 300B tube was introduced in 1938 by Western Electric to amplify telephone signals. It is a large directly heated triode tube, with a typical power of 8-9 watts for a single-ended design, and about double the power for a push-pull or paralleled design. I recall that it's popularity was at its peak in the 1990s and 2000s, coinciding with the surge in popularity of single-ended triode amplifiers. 

The Shoot-Out

One of my audiophile pals recently bought an Elekit 8600R integrated amplifier and loves it to bits. His set has the works, including upgraded resistors, premium coupling caps (V-Cap CuTF), Lundahl output transformers and a TKD potentiometer. He recently bought a pair of Elrog 300B tubes and I offered to "help" (more like push him down the slippery slope) with some tube rolling activities.

The Elekit 8600R is an affordable 300B integrated tube amplifier, with a single 12AX7 and two 12AU7 tubes used in the input and driver stages. It uses solid state rectification and is available with a variety of upgrade options. The catch ? You have to build it yourself. The circuit is laid out on PCBs, but there are a lot of parts to solder, and some of the solder pads are small and very close together. This is definitely not a kit for a beginner and you should have a bit of soldering experience and good soldering equipment before tackling this. Your reward is a great sounding amplifier at a fraction of the cost of a completed product.

Here is a group picture of our contestants :-

(Clockwise from top left) - Shuguang Treasure 300B-Z, Elrog, Takatsuki, Genalex, Sophia Electric Royal Princess.

As a disclaimer, none of these tubes have considerable time on them, with about 25-50 hours of playtime except for the Sophia Electric which is used and has at least a few hundred hours on them. Some claim that these premium tubes may need about 500 hours of burn-in time to sound their best. Secondly, the logistics and timing of this get-together only permitted us to warm up the tubes for about 10 minutes before playing 3-4 tracks. There were three other participants besides myself (one person left after the Elrog and Takatsuki comparison - he was too deeply traumatised to continue having sold off his Takatsukis during a moment of foolishness !).

Elrog ER-300B

There were reports of unreliability in the early days, but things are said to have improved significantly after Thomas Mayer took over. The Elrog stands tall and proud. The taller than usual height meant that the Elekit tube cage could not fit and had to be removed. 

The Elrog retails for EUR 1,240 per pair including VAT and shipping within Europe. These tubes have a maximum plate voltage of 600V and 40W dissipation ! The re-issue Western Electric 300B in comparison has a maximum plate voltage of 450V.

I really liked this tube. It has a Teutonic precision to it, with very tight and controlled bass and a linear sound throughout the frequency range. Among all the tubes tested, I found it to have the best dynamics and speed. The soundstaging is laidback and the tonality is slightly dark. 

Here are the comments from the other participants :-

"Neutral, dynamic, tight bass, good extension of highs and lows. Suitable for fast music and rock."

"Open sounding. Linear and muscular. Detailed sounding as well."

".... pushed the vocals and focus "in front", towards the listener. The soundstage was more intimate, but may actually be more transparent- it had a precise and narrow focus to the sound made the ANJ's sound more like other ANJs I've heard ..."

Takatsuki TA-300B 

Kyoto isn't just great for sight seeing and eating Japanese sweets and snacks. It is also home to Takatsuki Electric Industry Co Ltd. Currently they only produce two models of vacuum tubes, the 300B and the 274B rectifier. 

Like any high-end Japanese product, the Takatsuki comes in exquisite packaging with the tubes packed securely in a wooden box, full literature on the product including individual test results from their Amplitrex tube tester. A pair of Takatsukis will set you back about USD 1,500-2000 per pair.

This was definitely a crowd favourite and elicited plenty of excited superlatives. The Takatsuki is a very clear and open tube with the widest and deepest soundstage. The top end has incredible amounts of air, which created the most realistic acoustic space among the tubes on test here. I found the staging to be slightly forward, with noticeable midrange projection, contrary to the findings of one of the participants who felt that it had recessed soundstaging.

It had less tonal density and heft compared to the Elrog, and careful matching is required to avoid excessive brightness. Otherwise, it was the clear leader in terms of detail retrieval, imaging and soundstage precision. The crowd begged for the Valvo Heerlen 12AX7 to be put in place of the Telefunken (more details below), but I politely declined to maintain a consistent test base for our shootout. 

Here are the comments from the other participants :-       

"Big soundstage, airy, good extension of highs and lows, slightly colored compared to elrog. Suitable for vocals and recitals."

"Open, lit, detailed. Excellent soundstage and so holographic sounding"

"Voicing "behind" the speakers, incredible microdetail and filled out the space. Extremely holographic, clean, and refined. the Takatsuki opened up the sound and removed the ANJ flavouring."

Sophia Electric Royal Princess

This tube was generously on loan from TC. Although he did not participate, he had very high hopes for his tube. 

This tube had two big problems, the Elrog and the Takatsuki. While the Royal Princess was more open sounding that the Genalex, this came with a subtle grit at high-frequencies. There is also more midrange glow compared to the rest of the tubes here. Objectively, this is a decent tube but viewed against the very high price it commands, it was underwhelming. According to the Sophia Electric website, these tubes cost USD 1,200 per pair. 

"Shuguang Treasure/Sophia Princess-both are good tubes. Good details. But a bit of sibilance can be heard."

"Sophia was noticeably less open, but still detailed sounding. As mentioned by Eric, the sibilant treble was a minus. Still quite holographic"

"Good soundstage, falling behind the Takatsukis, clear warmer focus and more bassy than the other two. However lack of refinement compared to both the Takatsuki and Elrog."

Shuguang 300B-Z Black Treasure

Shuguang of China makes tubes, a lot of them ! Their tubes are supplied as stock by many equipment manufacturers. In recent years, they launched their premium offering - the Treasure Series. 

Apart from differences in construction and materials, only senior technicians are deployed to assemble these. The most visually striking part of Treasure Tubes are their polymer carbon coating with gives the glass their characteristic blacked appearance.

I have previously used Black Treasure tubes, their KT88s and the CV-181. I lost one KT88 after about 500 hours, but otherwise they have held up reasonably well.

These tubes sit squarely in the middle price wise between standard and premium offerings. They typically sell for about USD 300-400 per pair. 

I found these tubes to be very good value for money. They did everything the Genalex did, with a slight but noticeable improvement. Tonally, they are warmer and denser than the Genalex, while maintaining good levels of detail retrieval. There was a bit of midrange harshness in the beginning, but this was missing by the time we reached the last test track. I suspect this tube may be a dark horse as my previous Black Treasure tubes sounded their best after more than 500 hours of burn-in.

Here are the comments from the other participants :-     

"Good tube. Good details. But a bit of sibilance can be heard."

"Shuguang was Genalex level up. Meaty and full sounding while retaining an acceptable amount of details. More refined than the Genalex."

Genalex Gold Lion PX-300B

These Russian tubes are made in the old Reflektor plan in Saratov, but under foreign ownership. New Sensor Corporation now owns the rights to a lot of the big trade names of the past and churns out an impressive line of tubes under various labels. Locally, they cost about USD 300 per pair. 

These tubes are to me perfectly listenable and very good all-round performers. You are unlikely to get any sonic wows, but there are no nasty surprises either. Tonally, they are slightly on the warm side of neutral. I thought that they had good staging and projection, but the Takatsuki showed how much was being left on the table. 

I would rate their field reliability to be similar to the Shuguang Treasure. I lost a KT-88 years ago, so that makes one death count each. Alternatively, maybe I just have bad luck with KT-88 tubes ?

Here are the comments from the other participants :-     

"Perfectly listenable if I didn't hear the rest. But after hearing the rest, it was meaty but flat sounding."  

"Good all rounder. Value-for-money."

The Unsung Heroes

We also took some time to roll the 12AX7 tube. Our host had Telefunken smooth plates installed. Changing this tube had as much effect as the 300B tubes. We tried a JJ ECC83S, and two vintage Valvo tubes, one produced in Heerlen, and another from the Hamburg plant. All three tubes had a warmer and denser tone compared to the Telefunken (no surprise really), and the host liked the Valvo Heerlen tube the best. The above shoot-out was carried out with the Telefunken tubes installed.

Conclusion

Your mileage will vary. Each tube will sound different when deployed in another system, due to circuit differences, as well as system synergy. 

Also to be clear, none of these tubes made the system unlistenable or objectionable in any way. As one participant pointed out, we could have had a happy outing with the Genalex if we did not hear the rest of the tubes. So please experiment for yourself and happy rolling ! 

Don't forget to let us know your favourite 300B by leaving a comment. 

Musical Paradise MP-701 Mk II Tube Preamp

Introduction

Musical Paradise is a cheerful company that serves up tantalising components to audiophiles on a modest budget. According to their website, they state the following, "Our mission is to design and manufacture high quality audio equipment to fulfill critical audiophiles' demand with competitive prices." 

This is the first Musical Paradise product that I've owned and so far I have been impressed by their innovation, quality of build, sound quality and totally outrageous value-for-money. 

Description

Looking like a very tall oversized shoebox, the MP-701 Mk II measures 31 cm (W) x 39 cm (D) x 14.5 cm (H). Construction is really good, with a solid aluminium alloy faceplate and panels. Weight is a reassuring 12 kg. 

The MP-701 Mk II is said to be the product of two years of research and development. It is a three tube design with zero negative feedback. The power supply is tube rectified. There are plenty of conveniences, including XLR sockets in addition to the usual RCA sockets, as well as a remote control.

Parts quality is very good throughout, with a 150 W shielded toroidal transformer, Vishay resistors, Nichicon and Rubycon electrolytic capacitors, and Obbligato Gold film coupling capacitors. There is also an option to upgrade the coupling capacitors to Mundorf Silver/Gold/Oil capacitors for a premium.   
This is the point where the usual list of features ends and things really get interesting. 

Want to roll your own capacitors but don't know which end of the soldering iron to hold ? No problem, just undo the binding posts and change the capacitors yourself. 

Can't get the gain matched properly in your system ? No problem, just change the gain settings by flipping a DIP switch. 

Want to roll different tube types ? No problem, change your preamp or rectifier tube heater voltage settings by accessing a switch too.

Here is a list of rectifier and preamp tubes that can be used in the MP-701 Mk II :-

Rectifier tubes

6.3 V - 6Z5P, 6X5
5 V -  5R4, 5U4G, 5AR4, GZ33, GZ34, 274B, 5Y3, 5Z3P

Preamp tubes 

6.3 V - 6N11, 6N1P, E88CC, E188CC, CCA, 6922, 6H23, 6H6, 6H30, (6SN7 with 6SN7 to 6922 adapter).

12.6 V - 12AU7, 12BH7, E80CC, (12SN7 with 6SN7 to 6922 adapter).

Don't forget that as each rectifier type has a different voltage drop, the resulting plate voltage will also change. As this shifts the operating point of the tube, the rectifier choice will alter the sound. This means that the possibilities on tweaking the sound are endless ! Similarly, you can get a more classic tube tone with tubes like the 12AU7, or a more modern and linear sound with the 6N1P or 6H30 tube. 

Both the two output coupling capacitors and two film capacitors that bypass the main electrolytic power supply capacitors are mounted on speaker binding posts that unscrew to allow easy replacement.

Impedance is specified at 100 Kohms (input) and 2 Kohms (output) with a recommended pairing with a power amp with a minimum 10 Kohms. I personally think that is a bit too liberal, and at least 47 kohms may be more appropriate.

Operation

The MP-701 has no mute relay to suppress start-up noise, so please remember to switch on the unit at least two minutes before switching on your power amp, and remember to switch off your power amp first before powering down the MP-701. 

There is also no power LED, although the prominent tube rectifier should serve as enough visual indication. I also found that the knob markings to be too discreet to be seen - time to get out your felt marker.

The XLR inputs and outputs are there merely for convenience. This is not a balanced circuit design, but at least you do not need to use an adapter if your source or power amp only have balanced connections.

Lastly, do bear in mind that you need a lot of height clearance on your rack if you choose to use very tall tube rectifiers.  

Sound Quality

The stock Chinese tubes supplied had a very subtle high-pitched whine, so I replaced them with some vintage Voskhod 6N1P-EB tubes instead. Otherwise everything else was stock, include the rectifier tube and film capacitors.

In my system, I got the best results with the lowest gain setting (my Totaldac D1-Six DAC has higher than usual output voltage). My set was pre-owned, but I still put in an additional 24 hours of use before doing any serious listening. 

The MP-701 in stock form has a confident tone, with very firm and powerful bass. The midrange has a subtle warmth to it, with a little bit more body and projection to it than my Conrad Johnson GAT S2 preamplifier. 

High-frequencies have very nice openness and sparkle, with good transient strike and decay. 

Dynamically, this is one powerful and agile little tank, with a hefty and tight bass, with plenty of articulation and speed too. Fast-paced music never caught it flat-footed, although separation does suffer a bit compared to my much more costly preamps on hand.

From a price-performance perspective, the MP-701 does very well and easily takes on contenders at double or triple the price. It does not play the overt tube card, and has plenty of resolution and dynamics to please listeners.

You can read below to find out how far you can push the MP-701.

Taking into account its asking price and tuning options, this is a no-brainer save for two caveats. Firstly, you should avoid pairing this with power amplifiers with low input impedance. Secondly, this is not a balanced design - the XLR sockets are there for convenience only and are wired in parallel with the single-ended inputs / outputs.   

Tuning Options

Accessing the gain switches is quite easy. A long bamboo skewer or toothpick is able to reach the switches through the top most tube cut-out. If you are clumsy, removing the tube makes this even easier. Similarly, the rectifier heater voltage switch can be accessed in the same manner. The signal tube heater voltage switch does require removal of the top-cover though.

Changing out the coupling or power supply bypass capacitors should only be done by users with a certain degree of technical skills and understanding of electricity. After unplugging the set from the mains and depressing the power switch to drain the capacitors, I measured close to 100V DC on the coupling capacitors and more than 180V on the power supply capacitors. The capacitors discharged to a safe level after a few hours, so I highly recommend that you take necessary precautions to check the residual voltages and to drain the capacitors safely before working on the set.  

According to Musical Paradise, the coupling capacitors should be between 1.5 uF to 4.7 uF and have a DC rating of at least 350 V, while the power supply filter bypass capacitors should be between 0.1 uF - 10 uF and have DC rating of at least 350 V.

My unit came with Obbligato gold coupling capacitors of 2.2 uF and Bennic power supply capacitors of 6.8 uF. I would advise users to use power supply filter bypass capacitors of at least 400 V DC. I measured about 350 V DC across these capacitors although this will vary depending on your choice of tube rectifier and your local mains power supply. 

The value of your coupling capacitor is dependent on the input impedance of your partnering power amplifier and is inversely related. You can use this handy calculator at VH Audio's website to calculate the minimum value of your coupling capacitor :- https://www.v-cap.com/coupling-capacitor-calculator.php

The two power supply bypass capacitors at the bottom of the board are wired in parallel with each other. The theory of power supply bypass capacitors is that the performance of the large electrolytic power supply capacitors can be improved by adding small film capacitors in parallel. Film capacitors have much lower ESR and would "speed up" the power supply. 

The jury is still out, so feel free to remove these film capacitors altogether. You can also add two different capacitors. The common practice is to use a capacitor of 1 % or 0.1 % of the value of the capacitor being bypassed. If you are upgrading the coupling capacitors, feel free to move the stock Obbligato capacitors down to the power supply also.

Musical Paradise also advises that different signal tubes (so long as they have the same heater voltage) can be mixed too. The lower two tubes handle the left and right signal, and have to be the same tube, but a different tube can be used in the top position. The circular cut-out for the tubes is quite large, so you can also use large rectifier tubes that use "coke-bottle" envelopes.  

The Works ! 

While the MP-701 is perfectly listenable in stock form, is it worth upgrading, and how well can it perform ? 

Using some parts on hand, I changed the output coupling capacitors to VH Audio's excellent TFTF capacitors, and the power supply bypass capacitors were changed to a Mundorf Supreme and a Multicap RTX. I left my Voskhod 6N1P-EB tubes in place (I tested and matched them for tight section and pair matching BTW), although I did change the stock rectifier for a vintage GE 5U4G tube.

You can expect a significant upgrade, with a marked improvement in transparency, speed and control. The warmth and body I previously noted were absent, and in place was a sparkling clean and clear midrange. The uplift in resolution and soundstaging dimensionality to me far outweigh the cost spent. Consider this a wholehearted endorsement to lavish attention on your MP-701. 

Conclusion

The MP-701 is an incredibly versatile preamp with outrageous performance for the money. The tuning options means that tweaking options are limited only by your imagination. Devoting a modest sum of money also allows you to lift the performance of the MP-701 from excellent to outstanding !

The Musical Paradise just goes to show you that you really can have it all without breaking the bank (rest assured I didn't miss out any digits in the price below). Having a relook at their mission statement, I can only say, "Mission Accomplished !" - Best Buy.

Musical Paradise MP-701 II

Price : USD 699 with free worldwide shipping

http://www.musicalparadise.ca

Pass Labs ACA Power Amplifier

Introduction

The Amp Camp Amplifier ("ACA") is a simple amplifier that was designed to be built in a single afternoon. It was created by Nelson Pass for an event called "Amp Camp" in which a small group of people turn up and by the end of the day, they would have built a small amplifier.

This means that the build has to be straightforward, even for the first-timer. Indeed, the build is quite easy, and the very detailed build guides on the internet will certainly ensure that you get this up and running in no time at all.

A complete kit with everything you need is available at the Diyaudio Store - just be quick, because they sell out really fast !

Description

The ACA is a low power Class A power amplifier which is able to deliver 8W per channel into an 8 ohm load (at 3 % distortion), or 15W if operated as a monoblock. It is built in a very compact chassis, with a separate power brick supplying 24V DC to the ACA. This is a great idea for a first-time project as you don't have to mess around with potentially lethal voltages.  

The current version of the kit at the time of this post is V 1.6, which was the version I built. Other important specifications :-

Input impedance - 10 Kohm
Gain                    - 14 db
Damping factor  - 10
Output noise       - 100 uV

For a detailed description of the circuit, you can read what Papa Pass (as he is affectionately called in the DIY audio scene) has to say here.

Build Experience

I highly recommend this for the beginner. Like any kit, it would be helpful if you practice your soldering on a practice or waste board first. Everything you need is in the kit, except for soldering iron, solder and a multi-meter. I assume of course that you have basic tools around the house, like screwdriver set, pliers and a cutters to snip of the component leads.

This is a PCB kit, and the very low parts count means that you really can finish this in half a day if you are minded to do so. 

The kit includes both blue and red LEDs - choose your favourite colour. I friction fit those LEDs for fun, and settled for red LEDs.

Like any Class A circuit, this runs quite hot. It settles down at about 18-20 degrees C above ambient temperature.

Like anything in life, things can go wrong if you do not take due care. This kit is straightforward enough that your possibility of messing things up are quite low. The most difficult part of assembly is likely to be affixing the transistors to the heatsinks (installing the insulation pads wrongly could either short out your transistors, or cause them to overheat. The second most difficult part (for a beginner) is biasing the transistors. Well, for me the most difficult part was aligning up the chassis as one of the rails arrived bent out of shape.

In operation, the ACA runs hot - it needs every square inch of those heatsinks ! After about two hours of operation, the faceplate is quite hot to the touch too. There is no anti-thump circuit, and the ACA will make rude sounds when powering off, and a loud thump when switched off. If you are using sensitive speakers, this is loud enough to scare both pets and probably their owner too.   

Sonic Quality

The limited power requires careful partnering. If you have typical speakers (e.g. 86-89 db sensitivity), you certainly can’t go very loud with the ACA. However, the few watts on tap will suffice for background music, and even reasonable listening levels if you are sit close to your speakers and listen to less complex music. To extract the most out of this amplifier, high-efficiency speakers are highly recommended.

The ACA has a very pleasant smooth and warm quality that makes listening very pleasurable. I spent more than a week during this lock-down, paired with my Vivid Giya G4 speakers (hardly the easiest load). Used within its power limitations, the ACA actually sounds very good for the money invested (Let's face it - pickings are slim for Class A amplifiers below USD 500).

Soundstaging is reasonably good, with good dimensionality. The ACA has a very nice grain-free and refined sound that eludes most solid state designs. The only obvious weakness was a lack of bass control with a flabby and loose low-end. Given the low damping factor of the ACA and the unsympathetic load, this was hardly surprising. Time to try out the ACA with more suitable speakers !

A pair of Tannoy Kensington GR speakers proved to be a better match although it was evident that more power was needed. Although they are rated at 93 db sensitivity, the Tannoys are not known to be an easy load either. They sound quite good at background music levels, with a usable limit at a volume in between my usual listening levels and that. Pushed harder, and the amp begins to harden in sound, as well as lose its limited grip on the woofers. Perhaps my very easy to drive Zu Dirty Weekend II speakers would be a perfect match ? I'll update this post once I've tried that.

Conclusion

The ACA is a pleasant amp that is easy to build and an excellent introduction to the wonderful world of DIY. If you have reasonable expectations and a suitable partnering pair of speakers, you could end up with sonic bliss at a very modest budget. If you are expecting something really special with a sound that rivals First Watt or Pass Lab's offerings, you are going to walk away disappointed. 

Pass Labs ACA Power Amplifier
Available direct from diyaudiostore.com
USD 327

Topping D90 MQA DAC

Introduction

Topping is well known for their low-cost audio electronics, ranging from amplifiers to DACs and headamps. They have become increasingly upmarket and their top-of-the-line DAC, the D90 was released last year. 

The buzz around the D90 was centered around the decoding chip used, the Asahi Kasei AK4499. The DAC chip alone does not maketh the final output. The quality of the power supplies and the output stage play a part too, not to mention the implementation of the digital receiver, clocks etc. 

The AK4499 is Asahi Kasei’s premium offering in their Velvet Sound range. It is described as a 4 channel switched resistor DAC with top-notch measurements like a dynamic range of 137 db (stereo) and THD+N of -124 db. 

Description

The D90 MQA DAC is an update of the D90 DAC with MQA decoding and a change of the USB chip from the XMOS XU208 to the XU216. The rest of the features list of the D90 MQA reads like any premium DAC, including fully balanced outputs, DSD 512 decoding, I2S input and dual Accusilicon Femto clocks. The best feature is left for last - a retail price comfortably below USD 1,000 (USD 799.99) !

In a nod to modern conveniences, the D90 MQA includes a Bluetooth receiver, with support for Bluetooth 5.0 and LDAC/AAC/S-BC/APTX/APTX LL/APTXHD protocol. In other words, you can stream 24 bit / 96 kHz music with the right source. If you believe that a receiver and antenna is the work of the hi-fi devil, you can disable the function from the front panel. 

The rear panel has all the usual inputs, including Toslink and AES. I2S input is in the form of a HDMI socket, and the pin settings can be configured to maximise compatibility with your source. 

Both single ended and balanced outputs are provided. The RCA jacks are spaced quite close, so be careful if you have cables with very large RCA plugs. 

Easy access to the voltage selector at the bottom of the unit.

Looking at Topping’s internal pictures, a single power transformer is used in the linear power supply (the mains voltage is easily switchable by the user), with lots of goodies like Nichicon FW power supply capacitors, TI OPA1612 chips for I/V conversion, and healthy voltage regulation (including 6 independent regulated power supplies). Bear in mind that all this is packed in an enclosure that is small and light enough to be held in the palm of your hand. The Topping's external dimensions are 22.2 cm x 16 cm x 4.5 cm (W x D x H), and the unit weighs 1.4 kg.

The Topping is a fully balanced design, with two outputs from the AKM4499 DAC chip paralleled to achieve better performance. The AK4118 receiver chip supports up to 24 bit / 192 kHz sampling rates through the Optical, Coaxial and AES digital inputs. USB and I2S inputs support up to 768 kHz sampling rate, as well as DSD 64 - DSD512. USB decoding is handled by an XMOS XU216 chip, which contains two xCORE tiles with up to 2000 MIPS processing power (double that of the XU208). You may also choose to have simultaneous output from both the RCA and XLR analog outputs, or only have one output active.

The digital volume control can be operated in 0.5 db steps, which permits you to skip a separate pre-amplifier if required. The Topping also has a choice of six FIR digital filters for PCM and two settings for DSD.  A plastic remote control is also provided with close to full functionality. The remaining functions can be accessed by pressing the left button and switching on the unit. 

I liked the front OLED panel, which uses large fonts that can be seen across the room. All necessary information is displayed, including the active input and output(s), sampling rate, volume and whether the stream decoded is PCM, DSD and MQA processed. The brightness of the display can be controlled, but not switched off entirely - take note if you are an audiophile bat.

Build quality is impressive and the look and feel of the Topping far exceeds my expectations, especially at its price level.  

MQA - A Primer

MQA, or Master Quality Authenticated is a process that was established by Meridian Audio, the well-known British hi-fi company. MQA allows high-resolution audio to be packed into a compact data stream. It also digitally fingerprints files so that you can be assured that your file has not been tampered with in any way.  

MQA files are backward compatible with any equipment capable of playing back red-book CDs or digital files, and can be encoded on popular files formats like WAV, FLAC or ALAC. In a process that is termed as "Audio-Origami", the high-resolution signal is folded into either a 44.1 kHz or 48 kHz sampled format depending on the sampling rate of the original file. Lossy compression is then applied to the ultra-sonic frequency range (which has little amounts of energy). The most practical benefit to this is reduced data bandwith required if you are streaming (e.g. from Tidal), and much smaller file size.

MQA is also able to do digital compensation to the encoded signal based on the recording equipment. If your DAC has a full MQA decoder, there is also further compensation for the playback device.

The first level decoding (MQA Core Decoder) of the signal enables the signal to be unfolded into a high resolution stream (MQA Core Stream) of either 88.2 kHz or 96 kHz. You may use Roon, or any other compatible software decoder to extract the MQA Core Stream. 

The Topping is a full MQA decoder which will perform the full unfolding, authentication of the stream, and apply file and DAC specific compensation to achieve the highest possible sound quality. To be clear, no software decoder is required for full MQA decoders, and MQA encoded files can be played from any source. In my case, the files were streamed from my Melco N1/ZH2 NAS and TIDAL. For users that do not own a DAC with MQA decoding, a software decoder upstream will at least allow them to enjoy high-resolution audio, but without the final unfolding to either 172.4 kHz or 196 kHz sampling, nor DAC compensation.    
I high recommend watching this video on "The Hans Beekhuyzen Channel" which explains how MQA works. 

Sound Quality

In comparison to their upmarket relatives, my experience is that budget to mid-range DACs generally lag behind in microdetail retrieval, low frequency authority and dimensionality. They do deliver most of the goods, but that fraction left on the table is what motivates audiophiles to open their wallets.

Serious listening was done after a week of burn-in and experimenting with the different inputs (I'll come back to that later).

The Topping delivers very good sound quality with excellent detail retrieval. It has tight bass which is delivered with punch when required. Midrange reproduction is good with a sweet tonality that is comfortable to listen to. High frequencies are extended too, with a sparkle and decay that is able to recreate a spacious and convincing portrayal of the acoustic space of the recording. Its star quality to me is staging and imaging, which is done with very good depth, width, and space around voices and instruments.

I would describe the Topping as tonally close to neutral with a touch of warmth. The staging and vocals have a laidback character to it, while transients are clear but with a soft edge to it. If you like your music to have a crisp snap and edge, you are probably not going to like the Topping. 

The Topping likes to play nice, and the softer presentation does flatter poor recordings, especially bright and harsh ones. I actually find this to be a desirable character, considering that the Topping will most likely be used with other affordable equipment, which may have weaknesses and flaws best not laid bare for all to see.    

I also did some listening tests to sample MQA files available from 2L. I preferred the MQA encoded files of both the original high-resolution recording, and the CD quality file. I was not sure about the merits of MQA prior to this, but consider me sold.   

As good as the Topping may be, it is not going to dent the sales of high-end DACs. While it does embarrass a lot of the competition, as well as many mid-range DACs, the Topping is unable to match the best out there in detail retrieval, dynamics and other audiophile niceties that the enthusiast seeks. To be clear, I am very comfortable recommending the Topping for the price, and even if your budget is a multiple or two of that. However, don't rush out to sell your flagship DAC in favour of the Topping !

A Word About Inputs

I have a general preference for using SPDIF over USB inputs, relying on an outboard USB / SPDIF bridge as I find it delivers better sound quality. In the case of the Topping, the USB input was superior, with SPDIF sounding a bit more gray and vague. I use a Weiss INT204 bridge, powered with an Uptone JS-2 power supply. It was a surprise then that the much simpler (and cheaper) route sounded better.

I also tried connecting my Melco N1/ZH2 NAS to the I2S input of the Topping using a Singxer SU-1 USB / SPDIF bridge. Despite careful study of the pinouts of the Topping, and appropriate setting of the DIP switches on the Singxer, I was unable to get any sound although the appropriate sampling rate was displayed on the Topping. 

The Bluetooth connection actually works quite well, and I was very comfortable using my Samsung Galaxy S10+ phone to stream music from Tidal to the Topping. The quality is more than decent and the slight loss in quality is more than acceptable. 

Most of my listening was done using the USB input.

Glitches

While switching from non-MQA to MQA encoded files, there was a brief, but loud burst of static through my system. The Topping locked-up on the two occasions that it happened, and the unit had to be powered down and restarted before everything was back to normal. I was not able to recreate this again, and I am unsure whether the problem lies with the Topping, or the rest of the equipment in the chain. Do leave a comment on this post if you have had similar experiences with your Topping.

Conclusion

The Topping D90 MQA is an excellent way to get your feet wet in the MQA pool for a modest outlay. I am pleasantly surprised at the very high quality delivered for the price and this is definitely an outstanding value-for-money product - Best Buy. 

P.S. The Topping was a personal purchase by me at full retail price. 

Second Opinion (From TC)

Description

I was pleasantly surprised when i received the package from Eric. It comes in a large black cardboard box with the words "TOPPING" on top. The DAC is snuggly fit in between the thick foam compartments and it would survive any kind of rough handling during shipment. The DAC is the most light weight and smallest that i have come across in this hobby with the Calyx 24/192 coming in second place in terms of size but on the other hand very heavy due to the casing.

Being conditioned that bigger and heavier equipment means more good stuff are packed inside, frankly when i lifted the Topping i thought "is it really as good as what all the reviews say ?" With the D90 placed on top of the Oppo 205, i hooked it up and started playing songs using the Cambridge Audio CXC as a CD transport. I sent a photo to Eric and promptly got a reply back that the DAC looks like it's floating! I looked closely and realised that it's front is being lifted up due to the heavy power cord it's connected to. I removed the Oppo 205 from the rack and placed the DAC back on the rack space this time ensuring that the DAC is fully resting on the rack shelf and powered it on. Wow! the sound is lifted up by a few notches right away! Important tip to note. Though the Dac is small and lightweight, it's still sensitive to placement and deserves a good spot in your rack and try not to stack it on top of other equipment to get the maximum potential out of it.


Sound

True to the AKM "Velvet Sound", the DAC does sound very refined and smooth without any rough edges. Music flows like a water stream and you can just sit back and let the DAC perform its magic. 

Be patient and let the DAC warm up at least 30 minutes and you will be rewarded with spades of details and layering. Bass is tight, in control and not excessive. It's not a forward sounding and grips you in the seat type of sound but i would say the character is an even handed with a deep soundstage. As i keep listening to the DAC, fluidity, naturalness and musical comes to my mind.  

Just for the fun of it, I have tried to tweak the sound with the cloned Ceraball footers but find that it tipped the high frequencies too much and wasn't to my liking. Overall, the presentation is still neutral with just a tinge of warmth.


Other comments- despite its small size and light weight, resist the temptation to stack it on top of other equipment to save space. It's sensitive to placement and deserves a proper spot on your rack. Warm up is critical and give it at least 30 mins to let the music soar!RCA cable users might face problem with the tight spacing between the connectors

At this price point, it's a very good performance DAC with a myriad of connectivity options and is even able to handle MQA.

The D90 is highly sensitive to the source equipment that it pairs up with. Compared to the Cambridge Audio CXC, the sound quality coming out from the Mac mini is still very good but just a tad softer and rounded. Layering and micro details are not as transparent but overall
it's still highly enjoyable if you are not out to "dissect" the music. The bass attack is strong and big. I think a dedicated streamer will do more justice to the D90.

I was unable to to turn on the Bluetooth until i sought help from Eric who informed me of the magic menu that will appear when you press the standby button together with the power switch behind the DAC. So for anxious users like me who just like to jump headon to test the DAC without reading the instruction manual, please take note. The Bluetooth function is highly interesting and all you need is your mobile phone. Detecting the D90 on the mobile phone is a breeze and it brings with it a myriad of music sources at your disposal. You could
stream Tidal, Spotify, music files on your mobile and even local radio stations. 

Music quality is slightly below using mac mini but it ups the fun and convenience factor. All you need is a mobile phone, D90, a power amp and you are good to go. Just think of the space that can be saved with a simple setup like this. I have tried out the connectivity distance and i could achieve about 10 metres before I experienced sound dropouts streaming FLAC files. That's quite good already if you like to move around your house multi-tasking doing chores while you listen to music to keep the boredom away.

Final words

The D90 impressed me greatly with its small form factor, multi-functionality and very good sound quality for its price. It banished the common thinking that for good sound quality, the equipment must be big and chock full of components inside. If i could reverse my audiophile
journey a few years back and not be "burdened" with so much equipment, I would get this in a heartbeat. 

Just maybe, if your girlfriends and spouses (Note from Eric - I advise only having one girlfriend or spouse at a time please !) can see how small this D90 is, they will surely "approve" the indulgence in this hobby right away !