Apparently all the negative voices have been silenced! Then we can start building soon - starting with the centerpiece. Or are there still objections to this very elegant circuit that can be resolved?
Dear Morten,
I received the circuit boards today. Many thanks for your efforts and the fantastic quality - and for this wonderful surprise
😎.
I'll get to work in the next months and report here on the progress, measurements and listening impressions ..!
Greetings from Lower Saxony,
HBt.
Psst
Hopefully Heinz Lichtenegger, the CEO of Musical Fidelity, is reading this and will get in touch with us. A reboot of the legendary MF-A1 without inherent sound, with the utopian THD ... but cozy warmth.
I received the circuit boards today. Many thanks for your efforts and the fantastic quality - and for this wonderful surprise
😎.
I'll get to work in the next months and report here on the progress, measurements and listening impressions ..!
Greetings from Lower Saxony,
HBt.
Psst
Hopefully Heinz Lichtenegger, the CEO of Musical Fidelity, is reading this and will get in touch with us. A reboot of the legendary MF-A1 without inherent sound, with the utopian THD ... but cozy warmth.
Attachments
Very quick and short answer:
They are totally different,
but 3/4 + 3/4 is much more better than Babelfish's MF A1 reboot.
HBt.
They are totally different,
but 3/4 + 3/4 is much more better than Babelfish's MF A1 reboot.
HBt.
I can explain the technical differences, but we have to decide for ourself which version is subjectively better (also in terms of sound).
Later (this year) I will report on our project, at the moment other tasks are tying up my energy - but I am already looking forward to the first assembly and the first sounds of this unusual class A push-pull amplifier ..!
#
At the moment I have the venerable NAD 3020i (restored) working in my living room again. The mains transformer of the current original A1 model gets too hot for me, that's quite clear --> its insignificantly larger 100VA core is too small for stereo-operation!
The 3/4+3/4 amp. is best set up as a mono block, with its own 100VA toroidal mains transformer.
HBt.
Hello StevieK,
we probably won't need an additional ohmic resistor (base to Vcc) in the current mirror. Only the test setup will give us absolute clarity on this point. Should it become necessary, I will also solder a suitable value to the PCB solder side. If someone wants to do without the symmetrical current mirror or make other changes, all this is possible with Morten's fantastic layout, with this PCB some modifications or small changes (in the assembly) are very elegantly possible (up to a completely different idea) ...
The ultimate current mirror (truly balanced, without the otherwise obligatory resistors in the emitter electrode circuit ...) is an absolute must if we are looking for THD values better than 0.003%. At the same time, the original (the A1) can't be called the yellow of the egg technically; it presents us with quite a few challenges ... this is primarily the frequency response compensation, but also the DC offset control loop (which many fans think is Tim de Paravicini's ingenious class A Iq throw, the way the Iq comes about). 3/4+3/4 differs significantly from the MF-A1 original, perhaps you would like to start some simulations on my suggestions, which are nothing more than preliminary designs - then you can see for yourself whether it is a good idea to reduce the 220µF (min 100µF) capacitors to 2µ2 MKS. also with the 1R5 resistors.
You can also play with the 1R5Ohm resistors - remember, two DC voltage regulators (the offset issue, i.e. the quiescent current) work against each other here (R27 & R28 represent their load). Both amplifiers (the 3/4) have a defined DC voltage offset.
Now to the stability criterion -> in what way do you want to control the (rather unpredictable) oscillation tendency of this concept (original and all attempts to improve the original)? We are working with a power transistor whose ft is <3MHz - fellow Zen-Mod (on the other side of the garden fence) gets around this by using a beautiful Toshiba TTAxxxx & TTCxxxx.
Our compensation only works in conjunction with the complex input impedance of the 3/4+3/4 amp, i.e. it must also be driven by an ideal source with 0Ohm +/-j0Ohm. Take a close look at the input of the complete amplifier.
#
Since every story confuses more than it unravels, my advice is to try: build up & experiment or wait until I use Morten's great PCB to realize my own setup ... unfortunately I don't know when I'll get around to it this year.
I have the Supra2004-EQ in front of me and this equalizer wants to be put through its paces.
kindly,
HBt.
This was the goal to be scored: the utopian THD
Even if MC12 might have misled us here, and 3/4+3/4 would perform 100 times worse than shown here in the graph, it is still 10 times better than the competitor product on the other side of the fence - or 100 times better than the original MF-A1. Roughly speaking, so it's easier to visualize.
hbt.audio
Even if MC12 might have misled us here, and 3/4+3/4 would perform 100 times worse than shown here in the graph, it is still 10 times better than the competitor product on the other side of the fence - or 100 times better than the original MF-A1. Roughly speaking, so it's easier to visualize.
hbt.audio
If we want to achieve the goal (inspired by Bernhard) without using an EF2 output stage, then we need it - there is no way around it.
A mental comparison of both implementations of a possible reboot
... either we build up both incarnations and make metrological and auditory comparisons - or read the initial thread up to my posting #37.
Do you believe that the other side (over the garden fence) is as altruistic as you are?
Dear @m0rten,
10 euros per board plus postage and packaging is still a friendly deal.
Please get in touch with me if you ever visit my area, I owe you more than just a pint of beer and a good meal.
greetings,
HBt.