Eastern Electric Minimax Tube DAC Plus

Eastern Electric Minimax Tube DAC Plus

The 4 op-amps in clear view. The two white plastic capacitors are coupling caps for the tube output stage

A closer view. The OEM M2Tech USB board is at the rear of the unit

The subject of this review is the Eastern Electric MiniMax Tube DAC Plus (which I will refer to as the “Plus”), which is an upgraded version of the original Minimax DAC. The original Minimax DAC was based on the Sabre ES9018 DAC chip and was unusual in offering a choice of both a solid state and tube based output stage (using a single 12AU7 tube), and volume control.

In comparison, the Plus loses the volume knob and upgrades its crippled USB input (red book only for the original version!). There are also a number of component changes, including an upgrade to separate power transformers to handle its digital and analog sections, and some fine tuning in the power supply and tube output stage.

Input flexibility remains excellent with a total of 5 inputs, USB, BNC, RCA, Optical and AES / EBU. The USB port (sourced from M2Tech) now supports up to 24/192 kHz sampling rates and is asynchronous.
Output is single-ended only. Why no balanced outputs considering the ease of implementing this out of the ES9018 ? I presume this is because of the single tube stage. Having a tube stage for balanced operation would require a second tube at the very least.

The front panel (like the original version) also offers on-the-fly switching between the tube and solid state output stage, as well as phase inversion. The unit does not remember user settings and will revert to the tube output stage as a default when switched on.

The tube output stage is constantly energised once the unit is switched on, so you can forget about leaving the unit on permanently unless you listen to the solid state output stage, and remove the tube from its socket all together.

Physically smaller than standard component dimensions, the Plus is best described as a slightly shrunk 2/3 scale model. Fit and finish are very high for the price and operation of knobs and buttons always feels solid and reliable.

Thankfully, tube replacement is relatively easy, as the tube is accessible from the rear panel. However, it is a bit fiddly as there is a tube damper / shield to remove first. The tube sockets are very tight and physical space is limited to pry the tube out from. Users are best advised to remove the top cover first before trying to remove the tube - the additional space on top makes this a far easier task.

This unit is well run in having been bought second-hand. The Plus replaced the Calyx 24/192 DAC on my equipment rack. Both units were setup in the same way, fed by a 2011 Mac mini running Pure Music 1.84. The digital signal is then fed via USB to the DAC. For USB cable purposes, I alternated between a L A T USB-2 cable and my regular cable, the Entreq Konstantin (hooked up to the MinimUs ground conditioner)

Sound quality

Initial listening experience with the Plus was disappointing. After a good 20 minute warm up for the tube stage, the Plus was clearly not as resolving as the Calyx, with a slightly vague and hazy presentation. Somehow, the ESS Sabre micro-detail magic was missing. Who let the pixie dust out of my system ?

Switching to the solid state output stage was a wholly different matter. The characteristic ESS Sabre sound was back. Being a dyed-in-the-wool tube person, this was somewhat disappointing. The sand based output was clear, incisive, with both more 3-dimensionability and authority. Arguably, the only advantages offered by the tube output stage was a slightly thicker tonal density, more mid-bass bloom and smoothness.

Most of my listening was eventually done on the solid state output stage with upgraded op-amps, which is covered in greater detail below.

The Plus would be best described as a smooth operator, with a slightly warm and laidback tonal balance. It would never be accused as being bright, but cleverly avoids sounding overly warm and woolly. Consistently even handed throughout the frequency range, the Plus does not overemphasize any part of the frequency specturm.

Bass is tuneful and would be considered as class average in terms of impact and extension. Drums and double bass have suitable impact and depth respectively.

Midrange is smooth and detailed and the human voice is quite engaging. I noticed though that the voicing on the midrange is warmer and sweeter than usual. Listening to Eva Cassidy's album, "Live at the Blues Alley", Eva's characteristic clear and sometimes piercing voice was thicker and sweeter than usual. The usual sibilance problems with her voice also seemed to be greatly reduced.

High frequencies are detailed and extended, with equal emphasis between the leading edge and reverbation from crash cymbals. In comparison, the Calyx has less snap on the leading edge, with greater emphasis on reverbation.

Soundstaging wise, the Plus has a more intimate presentation compared to the Calyx 24/192, with the impression of being seated at least a few rows closer to the performance.

Image sizes are slightly larger compared to the Calyx, but with less definition overall. If you like your voice and instruments to have more body and density, you will like the Plus.

In terms of resolving power, and separation, the Calyx is clearly superior to the Plus. The Calyx keeps its composure under the heaviest of mixes, and has excellent micro detail retrieval, especially at low volumes.

Op-amp tweaking

A quick search on the internet will reveal a fair amount of discussion on op-amp rolling. I tried some quick substitutions just to see the magnitude of improvement offered. The stock I/V op-amps, a pair of dual channel NE5332 op-amps were substituted with a pair of National Seminconductor LME49720 op-amps. The solid state output stage, a pair of single channel NE5334 op-amps were substituted with Burr Brown OPA627BP op-amps as well as National Semiconductor's LME49710.

After about 10 hours of burn-in, some listening tests were done. Significant gains in most areas, including bass authority, clarity and soundstaging were observed. This makes op-amp rolling a no-brainer.

As a matter of taste, the OPA627 had a fuller balance, almost sounding tube like in its bloom and liquiity. The LME49710 had more focus and speed. I preferred the much cheaper LME49710 in my system.

For the ham fisted, it would be best to get a more technically proficient friend to help. For the uninitiated who insist on DIY or death, please observe the following,

1. Dual channel op-amps must be substituted with dual channel  op-amps, and the like for single channel op-amps.

2. Ensure voltage compatibility. The Plus has a dual voltage rail of +/- 15VDC.

3. Observe strict anti-static precautions, op-amps are easily fried.

4. Be very careful when removing or inserting op-amps, the legs can be quite fragile. Invest in an op-amp puller.

Tube tweaking and rolling

Any hope for the tube output stage ? Users are advised to try removing the tube shield. I prefer the tube stage without the shield – the sound is noticeable clearer and has more “air”. I generally do not like tube damping of any form, as I find that it can easily make the sound too dark and dead.

The stock 12AU7 tube supplied is brand labeled as “Eastern Electric”. Internal construction looks very similar to Shuguang, and is presumably OEM sourced from them.

I tried substituting the stock tube with a National 12AU7 black plate (likely to be a relabeled RCA). This was much better than the stock tube, but at the end of the day, I still preferred the solid state output stage.
If you prefer the solid state output stage, the Plus sounds better with the tube removed totally - presumably this eases demands on the power supply.

Phase Inversion 

Although some discs sounded better with phase inversion, I left the button alone. It became a bit of a chore having to remember which discs sounded better with inversion. Nevertheless, this may be a useful feature to some.

Conclusion

Locally, the Calyx is almost double the price of the Plus. However, the Plus is an absolute bargain in context of its asking price.

In order not to be misconstrued as a lack of affection for the Plus, I personally feel that listeners on a tight budget should plump for the Plus. So should listeners that have a variety of sources, or would be listening primarily through the co-axial or optical input. The Calyx shines best through its USB input

The ability to tweak the unit through op-amp and tube rolling is to me, one of the strongest points of the Plus. Such tweaking is helpful to fine tune the unit to suit the end result that the user is trying to achieve.

The Plus is a competent performer at a competitive price. Well specified, and offering a choice of both solid state and tube output stages, it is likely to appeal to the masses, although I ultimately preferred the solid state output stage.

On the downside, the Plus is no giant slayer nor class leader in the ESS 9018 product class. The Calyx 24/192 ultimately has its edge over the Plus in terms of confidence, resolution and natural effortlessness.