Ever heard? MTA? M ultiplied transconductance amplifier after Frank Bloehbaum ?? MTA preamp ?
Until 3 weeks ago, I was completely unfamiliar, and the name Frank Blöhbaum was (hardly) familiar to me.
This was to change quickly after I heard his tube preamp as a preline – MTA preamp – in my friends home; Bjorn’s in hamburg.
He powered an F2A amplifier, which in turn “fired” Altec 804-8G .
A fantastically spatial, musical sound that not only cast a spell over me right away.
After a long listening session with a variety of components, Björn in his workshop cellar on an audio analyzer part of the principle behind this preamp.
Arrived at home, the inet was hooked and gegooglet diligently.
At some point I stinked on the download pages, in which F. Bloehbaum introduces his now patented MTA principle several years ago and describes it in great detail.
The reader may be advised to invest the download costs of these 3 articles and then to “feed”.
For me, they were the essential foundation for me to venture into the project.
I quickly realized that this would be the preamp that could power my V69a.
Due to its low output impedance that had to fit, as confirmed Björn.
Until then, I had bitten my teeth on the preamps before the V69a and was not satisfied .
The bass remains on the track, and some of the music sounded “strained” ……
In other words, the V69a and the Altecs were not where they should be.
So it started with Björn’s support.
The specifications were as follows:
– potential-free switching on, low standby consumption
– 5 inputs, tape out
– Volume manually, remotely controllable and later via Musesboard digitally adjustable
– 2U housing
– informative front with display of sources, mute function and volume level
– he should be hum and noise free
At a technically central location, I would have failed without Björn’s help. The used MPSA92 transistor requires defined working conditions, otherwise “he says goodbye”
The tubes must be heated to start up for about 30 seconds before anode voltage is applied. Mr. Bloehbaum also describes this very well in the article mentioned.
My own topic, I would not have got it alone.
Also, the design of the RC screened power supply is something special ……
This resulted in the following assemblies:
– Power supply to provide 6V digital voltage and 2 x 15V for the Muses
– Power supply for the pure MTA modules
– Input module with control via Arduino, separate grounding, motor control board, IR receiver and modular volume group
– 2 MTA preamplifier boards
As it turned out, I made a complex project that required a lot of setup and development time.
But today the MTA preamp works great !!
Above the assemblies, circuit diagrams and board layouts I renounce for known reasons at this point and will not publish them in the future. 
The complete construction with an analogue motorpoti plugged into the modular volume control bar.
What about the result?
– already at the first definitive turn on I was missing something: hum and noise !!
– The preamp is dead silent on the V69a !!
……… a sophisticated Zentrlae mass management as a secret of success ??
But then the first hearing after a few hours:
– unruffled , the sound is authentic and honest. Bad recordings sound bad, good ones very good
– great bass, dry, fast , even at low volumes already clearly audible (my ears are a bit older)
– a great stage in all levels
– fast , accurate presentation
How is the technical handling?
Once ready to run and built to specifications, everything is bombproof .
No change in the operating points, even when changing tubes to equivalence types no changes.
The remote control is very convenient, and with the Muses volume module it will then zukünfig also visually displayed.
This fine preamp required a lot of planning and construction time (thanks to the stepcraft router much shorter!), A lot of programming work, but is now top 1 among the Prelines of the V69a.
Dortmund 13.01.2018
Swell:
https://linearaudio.net/authors/401
Thanks:
Bjoern J., HH