fed up with bosoz

[vdi_nenna]

could it be a bad/leaky zener in the power supply??

[cowanrg]

i dont know, could it be?

there are 32 zeners between the two power supplies...

how would i test this? im getting the right voltage out of the power supples (within like 1%). so, can they be bad and still give me the right voltage?

[vdi_nenna]

Seems daunting, doesn't it? An expert could answer that for sure, but this is what I found.

http://www.ecircuitcenter.com/Circui...p_limiter1.htm

[cowanrg]

is that site in english?

it appears as though its explaining how to correct a circuit that has a problem with leaky diodes. however, this circuit has been built hundreds of times. is a leaky diode a bad diode, or just a problem with a circuit design?

[Magura]

Originally posted by cowanrg
is that site in english?

I just gave it a go with babelfish, it seems a leaky zener is a bad zener.

What brand of zeners are you using?

Personally I am very critical when it comes to zeners. Zeners from Vishay and Onsemi have never let me down so far.

Magura

[Magura]

I use these for just about anything, they are a few cents more a piece than the standard zeners, but they seem to be of very uniform quality.

http://www.google.dk/url?sa=t&ct=res...rvYIbLmRZuXqFg

Magura

[cowanrg]

to tell you the truth, i have had bad zeners before and they have caused me MAJOR headaches (remember the aleph3?). i had a few bad ones in this power supply circuit as well. maybe i should just get all new ones. hell, ive replaced every OTHER part in this thing so far.

from mouser's catalog it seems that the vishay zeners are only about $0.07 each for the 9.1V 1W type.

is this something i should try? id rather not go and buy more parts and waste money is its not a valid problem, or if there is some way to test for it. can i just make an unregulated supply with a bridge and some caps to see if thats the problem?

[Magura]

I usually go for the 3W version, can't tell you why, maybe because they can be used anywhere, I simply bought a good stock of the 9.1V 3W zeners.

I would replace those zeners ASAP, simply to exclude them from the equation.

You can't just make an unregulated supply, as your trafos will give you more than 80V unregulated.

Magura

[GRollins]

I scanned the thread quickly and may have missed where someone tackled the thump problem.
Is it safe to assume that you are using the turn-on relay to interrupt the output?
If so, that is likely the problem.
When the circuit is turned on, the outputs jump to a positive DC voltage. What happens when you put a pulse (an AC signal) into a cap? It causes a charge to appear on the other side of the cap. This is normal. This is good. This is what you want a cap to do. If it didn't work this way, then the music wouldn't get through the cap and all would be for naught.
But that's also the problem. Now you've got a charge on the output side of the DC blocking cap. Two things can happen. One--it can sit there until doomsday or until the real-world imperfections of the cap allow it to leak away. Or--Two--it can discharge to ground.
Fair enough. There's a resistor at the output that will allow this DC charge to dissipate. (You did install that resistor, didn't you?)
Now, here's the deal...you can either allow that resistor (100k?) enough time to discharge the DC blocking cap down to ground--or--you can kinda help those electrons find their way home by shorting the output to ground (not open) for those first few seconds while the preamp is powering up. This will do an excellent job of removing that thump-inducing DC charge. Once it's gone, it will not come back.
"But, Grey, won't that blow up the preamp? After all, you're shorting the output to ground. My buddy George did that with his amp and it..."
The short (ahem) answer is no. It won't hurt anything.
The somewhat longer answer is that the MOSFETs are not going to exceed their ratings and that the DC component isn't going anywhere anyway because it's being held back by the salf-same cap that's causing you annoyance in the first place. The AC part of the signal can take care of itself. The preamp will be fine.
The noise(s) could be any number of things. Bad solder joint. Wiring harness in the wrong place. Wrong value resistor in the wrong place. Etc. etc. etc. Right off the top of my head, I find it unlikely that it's anything to do with the power supply. One, the audio portion of the circuit is a differential. Differentials have, to greater or lesser degrees, something called Common Mode Rejection Ratio (CMRR). This means that a signal that appears on both sides of a differential is ignored. Yes, this applies to noise on the rail, too. Now, the BOSOZ doesn't exactly have the greatest CMRR in the world, but it tends to weigh against rail noise. Another argument is that hiss, per se, is just not something that you see coming off of your rail. Why? Because hiss, in the sense that most people mean, is a higher frequency sound. By definition, high frequencies are shunted to ground by the power supply caps. Hum, yes. Hiss, no.
Hiss, in this context, suggests oscillation. Check your Gate stopper resistors (those 221 ohm resistors that Nelson puts in front of the MOSFET Gates).
Buzzes and hums can be caused by scads of different things. Not enough capacitance in the power supply. This includes caps that you think are there, but aren't really, meaning bad solder joints or screws that aren't tightened properly. Ground problems. Ground loops...if you're using a three-prong AC plug, use a "cheater" plug to lift ground, not only for the preamp, but also try the amp, source, and anything else in your system. If the hum stops, you've got a ground loop. Curing ground loops can be annoying and frequently involves large quantities of alcohol and cursing. Persistence is the key.
Good luck.

Grey

[cowanrg]

oh yeah, forgot i would get +-80v.

ok, ill replace the zeners. i was hoping to get this done today (well, months ago actually), because im visiting my partents this week, so i could bring it with me if it was fixed and working. i guess ill just have to wait.