[el_matt0]

yea i have done that! i may have missed something of course, but like i said, none of the components were changed so i doubt its a cold-solder on one of the boards. and i was pretty anal with the wiring this time around! ive narrowed down the symptoms of the problem a bit. so again, like i said earlier, once the problems kick up, if i turn it off, wait a few minutes, then power up, the biasing was a bit off across R34, so i adjusted it as close as i could get em all to 75mV. plug my headphones back in and start listening, sounds GOOD, everything sounds like its working, no obvious problems at all, and i can listen indefinitely at these lower volumes. the measurement across R34 wobbles around a bit ranging from 60-90 mV or so (dont know if thats normal or not). and when i plug in a pair of S.E. headphones to one of the single ended jacks powered by the L+ and L- (for L and R respectively) , the R34 value on my L+ and L- boards jumps up to around 120 mV or so. it returns back to 75ish once the S.E headphones are removed, so i assume this is normal!

so basically, when i increase the volume to higher listening levels on my balanced cans, i hear buzzing start at some point and then the left channel basically cuts in and out even once the volume is reduced (and it OBVIOUSLY doesnt sound good). problems gone upon power down, and quick re-bias. explanations / solutions?

 

[el_matt0]

im no electronics whiz by any means, so im kind of wondering - is something with symptoms like this possibly related to a biasing problem? my basic intuition would tell me it couldnt be a wiring or solder problem (cold joint, short, etc) because the problem clearly only happens at higher volume levels, could i be wrong though? and to clarify, the issue definitely only occurs past a certain volume, its not just that its only noticeable at the higher levels. "SOMETHING" clearly starts going wrong at aobut 3/4 turn on my pot. :S

 

[el_matt0]

is 75mV supposed to be the reading across R34 without a load connected? because it definitely changes once a headphone load is connected and volume is applied - is that expected (goes up above 75)?

 

[amb]

Quote:

Originally Posted by el_matt0 /img/forum/go_quote.gif is 75mV supposed to be the reading across R34 without a load connected? because it definitely changes once a headphone load is connected and volume is applied - is that expected (goes up above 75)?

The initial setup for quiescent current should be done without a load, and the input shorted (or volume turned all the way down). That said, if the DC offset is 0, and the amp isn't oscillating, then a load shouldn't affect the readings. Measuring the quiescent current with the volume up and playing music is meaningless -- the amp is no longer "quiescent".

 

[el_matt0]

ok...so what course of action should i take for trying to figure out what is wrong? it doesnt sound like something "major" is wrong necessarily, but compared to how it sounded before, id say something definitely IS wrong. like i said, it seems fine listening for extended durations at low levels, but upon increasing the volume, after awhile, something kind of goes audibly awry, and upon powering it down, unplugging load, and powering back up, all of my biasing is quite significantly off. (not having moved my trimpots from when they were all roughly 75mV across R34, my L+ and L- boards read roughly 125mV or so and my R+ and R- boards read around 50-60mV until I re-adjust them.

totally bewildered as to where exactly i should begin trying to fix this....

 

[amb]

I suggest checking the voltages at various points in the circuit against the operating points PDF diagram at the β22 website (in the Initial Setup section, under "Troubleshooting").

 

[el_matt0]

so i should be doing all this testing with no load connected right (volume at zero, etc)?

 

[amb]

Yes. Those are all bias point voltages, which assume quiescent conditions.

 

[utilisateur]

Could anyone please

confirm i'm not going to get a significant difference between using
Avel Lindberg Transformers and Feickert R-Cores or O-Cores assuming they have the same rating !?

I was planning to go with Feickert Transformers but as i cant seem to reach them
i thought i should just go with Avel Lindberg as they'll most probably be cheaper ...

 

[amb]

There won't be a sound quality difference, if that's what you mean. Whatever you use, keep the transformer mounted far away from the amp boards, preferably in a separate chassis.

 

[utilisateur]

Thanks =)

I was quite persuaded the magnetic field emission wouldn't have that much of an impact if put the PS in a different chassis anyway

Time to fill that definite order than

 

[el_matt0]

hey guys, still having a bit of instability problems with my b22. as aforementioned, i didnt change any of the components on the boards since it was last setup and working succesfully, all i did was re-do my input/output and PSU wiring, as well as adding in the speaker binding posts and single ended outputs. i have yet to add the zobel networks across the speaker outputs, but since i am not using speakers yet, this should not affect the headphone out usage right! can any of you experts see anything obviously wrong with my wiring etc that might be causing me the troubles? incase the pics are unclear, basically the outputs of the boards are running to the speaker binding posts, then from there to the balanced XLR outputs. from those balanced xlr outputs basically the 2 pin is a L and the 3 pin is an R, the left XLR feeding S.E. output 1, and the right XLR feeding s.e. output 2, with the ground running to one of the empty G terminals on my psu. other than that i cant really see anything ive done wrong, no obvious shorts or anything, all my boards are cleaned, everything is heatshrunk etc to a decent degree i think. again just to reiterate the problems that ive been having are that i seem to hear a little fuzz etc in my left channel after listening at louder volumes, and once the buzz becomes apparent, the biasing is all out of whack, despite that it was all in check just minutes before! anyway, heres pics, sorry for the long post but any help will be greatly appreciated! im yet to check with the operating voltages against AMBs chart but ill try to get on that.

 

[akione]

Hi el_matto,

I'm not sure I can be of much help, but if it happened to me, I'd start by wiring the L & R channels as a single-ended amp and see if it still happens. That way you'd know if it was the amp module or the wiring.

edit: Another thing you might try is swapping the ground channels to see if it changes to the other side.

 

[el_matt0]

mmm, well heres the thing, after biasing the amp properly, it maintains stability and does in fact sound decent listening at low volumes (ie. its not blatantly obvious theres anything awry). usually only after increasing the volume significantly, i begin to hear a faint buzz in the left year, and the sound just loses its quality, not painfully obvious perse, but noticeable without a doubt! the odd thing is, it seems like the buzzing is audible in the left channel of even single ended headphones (out of either output), as well as on the balanced ones, which is why im not inclined to think its a problem with my L+orL- boards, since one of the S.E outputs is driven entirely by the R+ and R- boards, yet stll the problem persists. must be something with my input wiring or pot? but why would it cause this instabliity in this fashion....hmmmm. still seeking advice

 

[akione]

Hi,

..... yeah, I see what you mean. I should've checked the wiring plan first.

...... if it's happening when the volume increases, maybe the pot's not tracking properly ?
or an input stage is going unstable ? overheating maybe ?