Explendid amplifier designed by Michael Bittner, our MikeB

[tlf9999]

Originally posted by MikeB
I do not like currentmirror in inputstage much...

I am the opposite. Current mirrors have the advantage of being independent of rail voltages so that one can run the amp under different rail voltages without any modification.

The minus side for me anyway is that it tends to oscilate, much like CCS.

Originally posted by MikeB
But i have a completely different parts-choice and feedbackcompensation.

I really doubt component choices will drastically change an amp.

Originally posted by MikeB
For this circuit you should not replace the vas-transistors, the
sb649a has very different specs than 2n5401.

are they sufficiently different so as to perform differently sonically?

[MikeB]

Hi tlf9999 !
This circuit uses a currentmirror, just not in inputstage...
This amp is quite independent of supplyvoltage, it does not
need adjustments for other voltages.

My experience is, that slight changes to an amp can dramatically
change sonics, especially when feedbackbehaviour get's altered.
And i think the sb649a is different enough to the 2n5401 to
make audible differences.
I believe that proper feedbackcompensation is one of the most
important key to a good sounding amp.

If you don't like mine, you can still buy the bi120-kit, i am sure
it's a damn good amplifier !
I did not have the feeling to having made a plagiate of the bi120...

Mike

[destroyer X]

from the chair, when someone told me to use Silver Mica for a miller capacitor.

I laugh as a hell.... in my intimate thinkings i heard my voice telling me...

"One more electronic magic...the guys knows more woddoo than electronics".

I told him:

- Are you kidding?.... what a hell, i have many years of experience.

he asked me:

- Have you tried?

I said, no!


... and them i tried...

Really, some parts produces different sonics, and high speed transistors, those 100 megahertz, or more, I do not know the reasons exactly, affect the audio quality around the top end frequencies that we can hear.

I made this question, this one you made to Michael..... and he insisted that he can guarantee the ones he used, that cannot tell nothing related the others, as he do not used all possible choices.....but that i could try....i change mine transistor into his transistor, and result was better.

Really, the best answer you will give to yourself, and i strongly suggest you to make those comparisons, as many surprises will appear.... check it and inform us when return.... will be good cooperation to us, to confirm subjective impressions or even to dennie those things.

I made changes, i used TIP3055 and TIP2955...then i used 2SC2922 and its couterpart to the output...tried BD139, tried BC639 and also tried BC546/556 for other positions.

Now using the original schematic transistors, except the differential ones, i am using BF422 or 423 (do not remember with one), and the amplifier sounded much better.

I made modification stage be stage....and listening...the biggest difference was the TIP2955/3055, with those ones, the amplifier had clear losses in high frequency level and also details, because it's speed i suppose.

Well, different than you, that asked kindly, i made things more agressive with the guy....i had to apologize with him, when i realised that my decades of experience never made me humble enougth, to check things that i perceived, and imagined, as foolishes and magics.

If you search, you will read that i wrote that transistor is just a transistor, not a magic part...that have maximum voltage, gain, working frequency, prefered used voltages, maximum current...and not more than that...respecting this all things goes rigth....negative...things are not exactly this way....i was wrong, there are better transistors to determinated positions...more adequated, with better frequency response, and lower noise too.

Well, you did not told nothing related those things i perceived.... each one of us are different...but maybe, some things that appear written in our forum, have the smell, the appearance, and looks alike a Myth....but better to check.... was better to me.

- Yes, Silvered Mica are normally better..do not know the reason.
- Some special "Golden condenser", even in the supply (that is ridiculous!, don't you think?...i do think also...ridiculous..but sounded better!!!!?.)
- Miller capacitors must be tuned, changing values...increasing 2 picofarads each time..hearing white or pink noise.....or observing high frequency slew rate.
- Drivers with "floating resistors" alike you have in Symasym, with charge caps in parallell sound better than two resistors into the output line (more used)
- Controling transistor gain, will produce better sonics...and many times, the search for lower gain will be better, except for input!
- The pc board design produces differences.., as wires travelling in parallel result in capacitances, some capacitances will work good for you, others not. (and inductances too)

And this is FOR ME ONLY:

Every intention to develop, amplifiers that was already developed, result of long time research ...is ridiculous in my point of view.... this is re-invent the whole thing.... as we will go rounding, alike a dog cathing it's own tail,...and probably, will finish deciding for the original schematic (if compared A to B).... i passed that shame with Aksa and Symasym and GEM...now...old and gray...i learned something new.

regards.

Carlos

[destroyer X]

Normally, people do not construct two amplifiers and then go to hear them to evaluate.

Because you can dislike, and the result was that you prepared two boards to go to trash, in place of only one board.... do not make sense to me, but i know there are methodic people that use this method.

To compare, to analise and judge some amplifier modifications, you need one prepared as the original schematic, and the second one to move parts... this way, A to B comparison will be imediate, as a flash...because the time you switch amplifier off, the silent when you remove some capacitor, or transistor, and sold another one in the empty place.... time to check, and switch on again, return music to the same point.... will loose reference...do not believe in good audio memory, related to details, you can just have rithm, music, song and some instruments, in special, the ones that appear bad recorded...this call our attention when judging...the bad side is easy to observe, as it "screams" to the ones are searching for defects...and evaluations can be done with those two possibilities...searching the one is better, and searching the one is worst...both aproaches are possible.

You need instantaneous switching from amplifier A to B, using same speaker in this case.... and enormous care with the volume, both amplifier must be flat and exactly the same volume, put bargraph or meter pointers, everything you have at hand to have sure that both are electrically with output more or less the same....as we cannot perceive small differences...care to be evaluate by ears too.

the preference,is to evaluate with someone helping you, as you will always prefere the one you "create" modifications...this is some nature trick very common.... we always prefer, our car, our wife, our equipment, our way to do the things... with wonderfull exceptions of course (you that is reading may be the one..i am not!)...You cannot know the amplifier is playing...if is your amplifier or the standard original amplifier.

So, to check those Myths....people have to construct 2 boards, and spend long time hearing, many king of music...and do not delay more than 1 minute each time you check...as your ear and brain will adjust...interrupt,and go ahead, switching A to B.

This way you will see that some capacitor Silvered, or some Golden Stripped electrolitics are better or not.

Related to Miller....have to tune it first...tune in value...i have 6 Aksas here.... 4 with Hugh boards and two that i construct.... anyone of them have exactly the same capacitor value, variation is around plus and minus 25 percent.

So, to be conclusive, have to start with the "intention" to change parts and compare....this way, 2 units will be done, in place of a single channel to evaluate quality.

I explained how to make A to B comparison testings, and many people in this forum already told things about... and about that i have good knowledge, despite always learning new things.

I just heard a friend, by phone, that told me that my ear is a trash box!

I asked him to explain his idea a little bit better. He asked if i apreciate MP3, i told that i think is reasonable, despite have the idea that something may be missed, obvious evaluation, because of the data size reduce ratio.

He told that MP3 produces enormous Anarquic mess ..destructing all original waves and re-constructing segments, repeating tones that are repeated in the music... some re-creation of the reality,... removing frequencies that our ears cannot listen (but perceive as brain excitation, that can be alike some DC over flow)... that MP3 cut low volumes tones in the presence of loud tone...as low volume will be "erased" by the higher sound pressure levels, and the well known losses in treble....and he told me much more, i will stop here.....
This is something to think about, i accept that sound, as reasonable to good...millions are accepting too, but it is not Hi fidelity.... as the fidelity is destruct and submited to the need to reduce data..exactly not reproducing music as it was made.... to me, this is something to think...i will do it.... as damn Paulo called me deaf....having good informs guys, please, clarify that point to us.

My suggestion is to read, all forum, at least 2 times...entire forum, to have all informs related the subject.... subjective evaluations... metering versus subjective, and many topics correlated. They will be good tools to evaluate and develop a more precise hability to compare things.

I have read all forum 4 times...and will return 6 monthes ago to read again, as those last 6 monthes i did not read all topics..only the more interesting ones.... the ones have pictures and new amplifiers shown.

Symassym4 i made one channel only.... and i started to move some parts, in special, my biggest doubt; was to use Miller in the second Vas transistor... the one to the rigth, and up the schematic, or to use RC interconnecting differential colector....i decided by RC interconnecting the colectors...but i think this was result of influences i received by respectables Graham and Michael.
Those, use to run from Miller caps more fast than the devil run away from God. My decision was keep the circuit untouched, original...but i am not completelly sure about that decision, because having not the second amplifier, to compare...i cannot decide using memory, each one was better?

Symassym calculated capacitor was 68 picofarads, as simulated by Michael...i reduced to 46 adjusting slowly here, and i think was better.... WAS IT?

Good to remember, Michael used Wave to make comparison recordings.

regards,

Carlos

[MikeB]

Hi Carlos !
This millercap on the right side of 2nd diffamp is no good...
It was 68pF, but forget it !
In symasym5 i use some kind of millercap on the left side of
2nd diffamp instead of the RC in 1st diffamp.
I prefer this version as it sounds softer...

Mike

[destroyer X]

This new version, Symasym 5, I cannot talk about it, as i did not heard it with the needed care.

But you can talk about, if you want...forum is ours.

regards,

Carlos

[tlf9999]

Originally posted by MikeB
This amp is quite independent of supplyvoltage, it does not
need adjustments for other voltages.

That, I think, is an important attribute of a good amp.

Originally posted by MikeB
My experience is, that slight changes to an amp can dramatically
change sonics, especially when feedbackbehaviour get's altered.

Sometimes, what we think we heard is quite different from what we heard. Without proper controls, it is hard to conclude if there are sonic changes from component changes.

[destroyer X]

Your think that heard that is different related what you heard.

Can you be more detailed please.

regards,

Carlos

[MikeB]

Hi tlf9999 !
I am aware of these psycho-placebo effects, i am talking of non
subtile changes to the sound. For example, in a previous amp
i replaced some bc546/556 by 2n5551/5401, and afterwards
had a completely different sounding amp ! (Way better)
No hokuspokus or mystery...

Mike

[tlf9999]

Originally posted by MikeB
had a completely different sounding amp ! (Way better)

If the differences were so obivious, think how much more difficult it would be to manufacture any piece of electronics.

Mike, I am sure you could tell them apart. It is just that without proper controls in place, it is hard to take individual experiences at face value.