Explendid amplifier designed by Michael Bittner, our MikeB

[PMA]

Originally posted by 12 Cents
Now I wired up a better PSU -> ah, better.

Q: What happens if I leave out C14 completely? Cause that's just what I did.

Unfortunately it might not be that simple to disconnect that feedback capacitor. Few days ago I added Bode plot stability explanation to my "evaluation page"

http://web.telecom.cz/macura/symasym.html

Please read it carefully and look at the Bode plot image. Disconnecting the feedback cap may lead to very low phase margin (blue phase curve, close to non-stability point, danger of oscillations). I would always connect a small value of the feedback cap for the Symasym circuit, say 3.3pF - 6.8pF.

Regards,
Pavel

[PMA]

P.S. Yes, my amp did not oscillate without the C14 feedback capacitor. But step response started ringing, which confirms lesser stability margin, exactly as shown by Bode plots.

[12 Cents]

Well, I did not mean to do so. In the end I specially bought my MJL3281A and MJL1302A from ebay dot com. I just left the choice of feedback cap until I forgot completely... d'oh.

Anyway, two channels are up and playing and I'm fine for the moment...

Now I have to look for a bigger transformer, think about housing etc.

[12 Cents]

Thinking about using these black beauties to the right for this amplifier...

[12 Cents]

Now, folks, go all build this amp...

[destroyer X]

Ahahahahaha!...you will be excomungated..... they will turn shocked with you.

Enormous and delicious bass reproduction with those 10000 zier gut enormous can in the supply, when they use, sometimes 1500 each rail, saying that is nice..ahahahaha!.... and you have no snubber, no filter...nothing!...some of them there, i hope only few guys, may believe that this enormous capacitor, those enormous electrolític condenser will suck, will drain, all audio quality....ahahahaha!

Also using Aligator, Crocodile styled clips, don't you fear that the sound can be reptil....reptilian sonics?

The sonic image could turn dark...as condensers are black.... "a dark sound stage"...hehe....i love our forum, there are things that are very funny that often appear to us...of course no"reptilian sonics and no dark sound stage"...all this is a joke i am doing, because things i had read those last days...cannot say the place i read.

Do not show this to Chip amplifiers forum guys.... as some of them, maybe 10 or twelve will hat you to spend enormous money to "kill your amplifier quality".....ahahahaha, of course i do not think alike those 10 or twelve.

You will be comdemned to go inside a rocket to Jupiter, one way ticket only...ahahahaha!.

I will construct a very huge transformer to my amplifiers.... will have more than 40 pounds...this way, maybe, i will have a "heavy bass!"

Also i am thinking to put a lens...optical lens....in front of my speaker coil..... to have sound difracted, dispersed, better distributed...ahahahaha!

The adjustments you are doing, with experienced Pavel, will produce a better sound, and more precise amplifier, and this is nothing related my jokes....Pavel is doing a serious scientifical work...the jokes are nothing related to him or his work.

Life is beautifull, and funny too.

Very pretty 12 cents, i can see that you expended 100 Euros more 12 cents to produce that beautifull amplifier...i am sure that it is sounding great!

Lovely your son!....you hairs are good too, as we cannot see you in the avatar...but your son is great.

regards,

Carlos

[12 Cents]

Thanks Carlos!

Well, the alligator clips will have to leave of course. They are not up to the current these caps are able to deliver (if that is ever needed, maybe on a party some day... I play not full throttle usually). These very nice caps - I have a small stock of them, got them relatively cheap, will not tell you how much, was lucky ...no thanks, no wimpy 1500µ black gate stuff for me, also not bypassed by anything, be it silver, pp, cryoed carbon or whatever. Impedance fits me well and the energy these cans can store makes for a nice and stiff supply.

I think I will comment a bit on the sound when it's time, no rushing in here maybe...

What I found fascinating is what the amp picks up with the input just left open, quite some hum and noise, but then the wiring of the psu etc. will contribute to that. So, with the input shorted, I hear only some "soft" sounding noise when I put my ear into the speaker like with those seashells, I could not exactly say if it's maybe this seashell effect... So a shielded input cable with low impedance termination at the preamp side would be desirable. Pavels method of input wiring will be of great help here.

Regards,
Lukas

[PMA]

Originally posted by 12 Cents


What I found fascinating is what the amp picks up with the input just left open, quite some hum and noise, but then the wiring of the psu etc. will contribute to that. So, with the input shorted, I hear only some "soft" sounding noise when I put my ear into the speaker like with those seashells, I could not exactly say if it's maybe this seashell effect... So a shielded input cable with low impedance termination at the preamp side would be desirable. Pavels method of input wiring will be of great help here.

Regards,
Lukas

Well, symasym is the quitest amp I ever built (hum, buzz, noise). This is true when properly built and wired. 50 Hz artefact of some -105dB in my measurement is an arrangement problem, not the amp's. The amp's residuals are well below -110dB. Again, improper built may this degrade to some -70 dB.

I have been listening to symasym for several weeks until now and have made some comparison tests. I can honestly say that from my experience this is one of the best amps I've heard.

Regards,
Pavel

[12 Cents]

Up to now, I only heard with this... thing...

[PMA]

Lukas,

oh, I see. Did you have a chance to compare with another amp, or is this your 1st one?

Regards,
Pavel

P.S. A little bit off topic - your Christian name (Lukas) - am I right?