BOSOZ PSU voltage question - diyAudio
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Old 24th September 2005, 09:06 PM   #1
cowanrg is offline cowanrg  United States
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Default BOSOZ PSU voltage question

im once again trying to get my bosoz working.

i am suspecting its the PSU boards that are faulty now. i stripped the whole preamp back to bare components and checked and rechecked all solder points and parts. it all appears ok. however, when hooked up on my workbench as the simplest configuration and each piece at least 1-2 feet from eachother, i still get the exact same buzz. so, its originating inside the circuit. (this is without an input plugged in).

so, its either in the preamp (which has been rebuilt twice and had 3 sets of fets), or in the PSU, or a problem with transformer. since i dont have a new transformer and want to buy a new one as a last resort, im working with the PSU boards. the easiest way i can think of to troubleshoot them is to bypass them completely.

i wired up the transformer to a bridge, then to a pair of caps for a simple power supply. but, without regulation, i am getting around +-85v unloaded. is that too high, or can i run it temporarily on that? i have plenty of heat sinking. i just want to see if there is a buzz or hum without the PSU boards in the circuit. if there is still a hum, then its coming from the preamp. thanks guys.

edit:

also, i am now running the whole test setup through a furman power conditioner just to be safe to compensate for any line noise.
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Old 25th September 2005, 04:07 AM   #2
cowanrg is offline cowanrg  United States
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anyone? if it can handle 80v, ill just try it out and go on from there. but i dont want to make my problems worse if its too high of voltage for the circuit.
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Old 25th September 2005, 04:22 AM   #3
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I'm running mine at 70V with no problems, and I don't see why 80 should cause difficulties, provided that your FET's are adequately heatsinked.
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Old 25th September 2005, 05:10 AM   #4
cowanrg is offline cowanrg  United States
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great, thats exactly what i needed to know.
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Old 25th September 2005, 05:24 AM   #5
lgreen is offline lgreen  United States
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I've had 80 as well, worked fine. Be careful to make sure your PS caps don't get in excess of their rating, for me 100V; I found out that my xfo was giving me more voltage due to low load, high wall V and over-tolerances.
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Old 25th September 2005, 05:26 AM   #6
cowanrg is offline cowanrg  United States
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just to be safe, i reached into my parts bin and pulled out a pair of sprague 2,000uf 200v caps. they should work fine for the test. its almost midnight now, and i dont like to rush into things tired, so ill wait until tomorrow to give it a test. hopefully it will be quiet, then i can concentrate on fixing the PSU boards.
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Old 25th September 2005, 08:49 AM   #7
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I was looking at the power supply and wanted to ask a few questions.
Since the voltages are not symmetrical wouldnt it be a good idea to use lower voltage caps on the negative side at a higher capacitance?

whats the point of using 100V caps on the negative side when we can use something at alower voltage?
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Old 25th September 2005, 05:49 PM   #8
cowanrg is offline cowanrg  United States
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Quote:
Originally posted by promitheus
I was looking at the power supply and wanted to ask a few questions.
Since the voltages are not symmetrical wouldnt it be a good idea to use lower voltage caps on the negative side at a higher capacitance?

whats the point of using 100V caps on the negative side when we can use something at alower voltage?
hum, im not sure what you mean, it is a symmetrical supply. it is +-60v. im just using 200v caps for testing, its what i had sitting around.
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Old 25th September 2005, 06:36 PM   #9
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ups.... I posted in the wrong thread.
I meant the X-Bosoz.
Sorry for the mix up.
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Old 25th September 2005, 07:28 PM   #10
cowanrg is offline cowanrg  United States
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not a problem.

well, i tried it out, but without success. it worked, but im still getting nasty noise. it measures about 68dB if i measure an inch or so from the speaker cone. ive tried multiple amps, different interconnects, etc. there is NO source connected either, so its the circuit alone thats creating the noise. it starts loud (~80dB) then settles down to ~68dB.

so, as Magura suggested, it could be the transformer. the only two pieces that are original to the preamp are the preamp board and the transformer, everything else is a new addition. so, its one of those two.

i have 3 stereo systems in my house and none of them have noise problems at all. i even have one in the shop that is crappy, but still dead quiet. so, the presumption that my AC line is just really noisy might not be the case. its the preamp doing something funny.
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