Inside the The ART Digital MPA II

The ART Digital MPA II – Solid state and tube preamplifier

This was my first microphone preamplifier and admittedly it was a grudge purchase. I was looking for the Behringer 2 channel 12AX7 preamplifier to do some mods, higher voltage plate and RIAA preamplifier.  At the price it’s a steal, then just over R1200.00 for Mic200 and about R1900 for the Ultragain Pro.

ART Digital MPA II
ART Digital MPA II

Unfortunately none of the agents in South Africa had stock (what’s with Behringer in South Africa, first first class monitors then the preamplifiers). In any event  Pieter Smuts Music in Parow had the ART Digital which I purchased knowing I would never modify it, let alone open it.  The pricing was very good as is most of this music shop’s pricing.

Then I had the good fortune of having a colleague, Brian, a part-time musician confess to me that he has never played on tube equipment, not even the main stream stuff. So after about a two month loan period he staggered in one day saying that it was absolutely brilliant.  Well there has been a lot of snobbery going on those days, not much changes of course, and one such device which took a fair bit of hammering was the previous ART Pro MPA II, non digital. So I did eventually decide to crack the hood and have a look inside.

12AX7 Preamplifier
12AX7 Preamplifier
ART MPA II Tube Preamplifier 12AX7
Tube Preamplifier 12AX7

First of all the build quality is exceptional, the two large meters make this series extremely attractive but what does it really sound like?  I can say that at least three people I know have tried it and they recommend it, highly.  The tube voltages can be varied from +48V (phantom supply most probably) and the more conventional >+200V.  There is variable input impedance and yes, I did try it with a turntable pre-amplifier expecting some ghastly results. Definitely worth a listen.

There’s quite a few websites which offer modifications to improve performance (Bless them!) and they are listed below:

Audioproz

Revive Audio

Moddefecation

The tubes inside these microphone preamplifiers were not added as a gimmick measure neither for pure market value – I used this in conjunction with a Focusrite Scarlett 18i20 through optical and it was great to draw a comparison between the two although one shouldn’t, they are two completely different types of preamp but with both with great reviews.

Inside the ART Digital MPA II
Inside the ART Digital MPA II

Getting right down to the nuts and bolts we now have the chief rival of many high performance chips and the nemesis of the famous 4558, the 5532.

Showing PCB build quality and one of the op-amps.

NE5532P Preamplifier used in MPA ii
NE5532P Preamplifier used in MPA ii

There will be an outcry amongst the op-amp extremists because the 5532 chip is now also considered a bit dated. We apologise upfront of course, unfortunately we had no part in the design of these lovely preamplifiers. Modifications sheet includes changing these from 5532 to OPA2132, OPA2134, OPA2107, LT1358, or LME49860NA.

The main interest in modifying these preamplifiers is making them “sound better with less noise” and having read as much as possible about these modifications one wonders what we are really looking for here.  Whilst in search for the holy grail I have no doubt in my mind that the final result will be better because we have paid more I always think more positive results can be obtained by adding more features but not at the cost of noise or quality. balancing transformers may be a good start but as the inputs are variable impedance this will take some doing unless it’s for long output feeds. The other thing is having headphones output – this is sadly lacked. This would be a switched stereo/mono type.

Pros:

I think the only con I could find on this preamplifier was a lack of headphones output. The pros are plenty, one being the variable impedance.  So the preamplifier does have a tube stage and although some of us complain about the hybrid setup the advantage of tubes in the preamplifying stages are not missed, especially in over-driving a signal.

What is better than the quality of this professional series preamplifier is no doubt the cosmetic finish. I love the fact that the designers used VU meters (along with LED peak). The front panel is thick alauminium, CND machined.

From the manufacturers:

Two Ch. Mic Pre w/ A/D Conversion

The all new ART Digital MPA-II delivers all of the same great features of the ProMPA with the added versatility of digital output. Like the ProMPA-II, each input circuit has 48v phantom power and features variable input impedance which can radically vary the overall performance of any high quality dynamic or ribbon microphone. The Digital MPA-II can be configured for dual mono or stereo operation with selectable mid/side mic support, summing the adjacent channel, to decode left/right signals.

The input section of the Digital MPA-II operates at either a low or high plate voltage applied to the two integrated hand-selected 12AX7 tubes for wider variation of preamp tone and performance. Large back-lit analog VU output meters display output levels while multi-colored LED arrays, with average or peak hold, show tube gain and digital output levels.

In addition to XLR and 1/4″ analog outputs, the Digital MPA-II features a high quality A to D converter which offers digital connectivity on S/PDIF, ADAT, or AES/EBU outputs. A rotary control on the front panel allows selection of format and sample rates from 44.1 to 192 KHz and 16 bit dithering. There is also a push button for, and two wordclock jacks, allowing loop-through.

The Digital MPA-II comes in a standard 2u space rack-mountable steel chassis, with CNC routed black anodized aluminum face panel.

 

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1

Awesome write up! I just got one of these two days ago. I powered it up and it was working nicely, but when I went to swap the tubes I noticed a burnt capacitor (C128). I so badly want to use it but don't want to damage the unit.

I can't find a schematic for this anywhere and haven't gotten any response from ART yet. Do you by any chance know the value of that capacitor? It's on the left hand side, just above the 12ax7 to the left. You can see it in your photo: https://analogian.co.za/wp-content/uploads/2017/03/Tube-Preamplifier_2_1068-768x576.png

If you had that info I would be SO GRATEFUL. Either way, keep up the good work here!

Author2

Hi Sean and welcome to the site. I must apologise for not seeing your comments here, was caught up with other matters. I hope ART managed to assist you but if not I'll have a look see today or tomorrow to get the value. Bursting caps shouldn't be commonplace for a fairly new release like this so you may have to see that the polarity is correct before replacing with new. Also this cap may be duplicated on the other channel. A high voltage leak which would be from the anode supply feeding this cap could also be the cause. I'll get back to you soonest, good luck!

Ian