Friday, September 18, 2020

AGD Audion Monoblock Power Amplifier


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

For one, their amplifiers use their proprietary GaNTubeTM 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 GaNTubeTM 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 GaNTubeTM 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).


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 is 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 GaNTubeTM. 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. 

To be continued ...

Monday, August 24, 2020

The Quick and Dirty 300B tube shoot-out


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.


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. 

Saturday, July 11, 2020

Musical Paradise MP-701 Mk II Tube Preamp


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. 


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.


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 :-

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. 


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