fed up with bosoz

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after many many problems:




im finally at the point to where its almost done. it plays music seemingly fine, but its NOISY and there is still turn-on thump. i built and installed a velleman K4700 circuit, but it still thumps on turn on. after the 6 second delay, the light on the kit goes off (as it should), the relays click, and THUMP. i thought that was the whole point, it was supposed to get rid of that. maybe i need a longer delay, but i doubt it.

also, one channel is getting a nice loud hum now (didnt happen before) and the other channel has a quieter hum. both are unacceptable, you can hear it from a few feet away. and when no input is connected, it is very loud.

it sounds like a grounding issue, but i cant seem to track it down. does the velleman kit need special grounding (i just connected it as it said, with the ground connected to the RCA output grounds). thanks guys.
i dont really have a star ground.

here is how ground is connected...

it comes in from the IEC connector, then it goes straight to a euro-style connecting block, where it connects to chassis ground and out to both of the power supply boards (maybe that is a star ground point). a ground wire goes from here to each power supply board, goes out each board to the main preamp board (along with + and - power).

on the inputs, ground goes from the input jacks to the volume control, then to the main board. on the outputs of the main board, it goes out to the output RCA's.

thats pretty much it... should the input and output RCA's be connected to that star ground as well? i would think that would create a ground loop.

thanks. so, all RCA input jacks and output jacks straight to a common star ground? so on my board, instead of connecting + and GND, i would just connect the +, and connect the RCA jack's ground to the star ground instead?

i want to make REALLY sure of that because thats like 6 hours of re-wiring...


i tried measuring DC on the output and just got like 3-7mv. i watched the meter when it turned on, and it went from 0.1mv or so to about 3mv when the relay clicked on. it wasnt like it shot up really quickly and backed down, it just slowly went up. my meter has a little bar graph thing at the bottom that shows spikes and stuff, and it didnt move.

so, now i just realized that the turn-on thump is random :whazzat: . i went in the shop really quick to see again if i could measure it, and i didnt get it this time. which is REALLY strange. i tried it 3 times. nothing. i made sure the amp was on first and everything. but im still getting a nice buzz which changed volume with the volume knob.
i brought one of my rotel 2-ch amps down to test it out with. its much quieter, but still has the same problems really. still no turn on thump, maybe thats fixed?

the humming/buzzing in one channel is now more of a hissing (like when you turn your volume knob all the way up and it just has that hissing background noise). its still much louder on one channel than the other.
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?
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 :)
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.

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