fed up with bosoz

[jh6you]

I think things are mixed up here.

I understand there are two problems: hum and turn-on-off thump noise. In my opinion, solution to the turn-on-off thump noise is considered “nice-to-have.” Probably, it might be a kind of aesthetic desire. Meanwhile, solution to the hum and buzz is considered “necessary.” Therefore, I would put the first effort on the solution to the hum and buzz. After that, if I have any good opportunity, I would try to fix the turn-on-off thump matter.

I think, before we complain any circuit name or its designer, we need to ask a question to ourselves first—ie whether I understand the basic grounding principle or not. As far as I understand, the most hum and buzz happens mainly because we ignore the basic grounding principle. There could be other reasons, but in general at very low probability level or at minor magnitude.

I would do the followings: Make one star ground where located away from the PSU. From the star ground, send pair of any AWG wires having the same length separately to the center of input RCA complex, separately to the output RCA, separately to the volume unit, separately to the circuit grounds, and separately to the PSU. And re-check whether such wire arrangement is forming symmetry about the star ground to the left and right channel.

This method might result in an ugly look wiring. But, it doesn’t matter as long as there is no hum and buzz. It doesn’t matter as long as safety hazard free is still valid, and it doesn’t matter because the amp top cover hides it. Now, there is no hum and buzz. But, if the ugly look wiring is somewhat concern, then we could go back, rearrange and minimize number of wires, carefully monitoring any potential hum or buzz.

If we are focusing too much on the neat and beautiful wire arrangement from the beginning, we easily overlook the basic grounding principle. I know this based on my poor experience.


Drinking a cup of coffee . . .
And, hoping this info will help . . .


Good luck!

Regards
jH

[grataku]

Cowangr,
obviously it must be something that you are so blinded by the months and the times you've looked at the pcb that you can't see.
Other sending me the boards for inspection I don't know what to suggest besides starting over.

I am espacially concerned about your grounding. In your description of the path to ground I haven't heard the word 'thermistor' anywhere. You should have a second look at some of the recent schematics that nelson published, he is being consistently showing the same gnd scheme.
I agree with one of the earlier posts about the trafo. Try moving that 3ft away during testing.

Someone with a fresh pair of eyes should have a look. Don't you have a friend with the same hobby that can help?

[cowanrg]

ok. so i was on vacation for awhile, school just started back up, i started my own business (now self employed) and a few other things have delayed me even going down into my shop for awhile.

jh6you,

thanks for the words of encouragement. i have taken your advice (although not original to you alone)

grataku,

thank you as well. the grounding was adequate, but maybe not the best. the thermistors are built into the PSU boards im using. i have one for each channel for each ground.

here is what i have done recently. i took the entire thing apart, into pieces. i wired up just what was necessary to run the preamp. i completely cleared my workbench and hooked up the most basic version of the circuit. i had a power inlet to transformer, out to a single power supply board, to the preamp. the preamp has NO input RCA's, just a single mono RCA output (just doing one channel for now). ground of rca is connected to star ground, as well as earth ground from inlet, ground from psu board and ground from preamp board.

i arranged it on my workbench so that the transformer is about 2 feet from the preamp board, the psu board is 1.5 feet from both the preamp and transformer. and, the conclusion? i still get a hum/buzz. its more like the hissing i was describing before. its just not very quiet at all. 1-2 feet away from the speakers you can definately hear them. its a hissing kinda like a background noise that is relatively common, but its much louder, and there is a buzz in the background too. this is with NO input at all, and nothing else connected other that what i described above. so, its definately a problem with the circuit.

i hope this helps some people to get some ideas as to what is really going wrong. i checked all my solder joints on the preamp and PSU boards. i even swapped to the other PSU board with same exact results. all solder joints look great. it might be a tad quieter than when it was all crammed inside the case, but its marginal (and its been a month since i heard it last). and it still buzzes pretty loud as soon as it comes on and slowly quietes down, but never goes away.

bad zeners, bad fets, bad builder?

[Tom2]

cowanrg,

I looked at your bosoz web page and you seem to sharing the secondaries with both power supplies using Kirstijans boards.

I think that would lead to weird ground and power supply problems.

I would think you need four seperate secondary windings or two separate power transformers each with two separate secondaries.

I know someone asked this before but, is the common heatsink for four mosfets of the gain stage electrically isolated? In other words are the drains not shorting out?

Just trying to help. I've been there also.

Tom

[Magura]

This could be a bad transformer as well, I have seen that before. In your case I would go and get 2 <120VA trafos and see what happens, such small trafos are cheap after all.

Magura

[butler853]

cowanrg,

I was wondering if you are making sure to bleed the power supply caps every time before connecting/unconnecting the power supply board to the preamp board. I am building an aleph P1.7 using Kristijan's boards. After testing it the first time, I disconnected the power supply without draining the caps, and fried the 3.3 ohm resistor at V+ on the preamp. Maybe the 6.8 ohm resistors at V+ and V- got fried on your preamp boards? I dont know if that would cause the problems you are having with it though. The only other thing I might suggest is try to disconnect the earth ground from star ground and see if that reduces the hum.

[grataku]

Hi,
if all you have stated is true then the only thing that comes to mind is badly routed grounds on the PCB maybe the ground of the bypass caps runs together with the signal ground inducing the buzz or hiss.
I used Nelson's PCB and never heard hissing.

[cowanrg]

Tom2,

i am sharing secondaries with both left and right channel boards. however, when i did the test, i was only testing one channel, so the entire setup was acting like a mono configuration. and it still had the hum/buzz/hiss to it.

The heatsinks is electrically isolated. im using some mica pad thing, and even nylon screws just in case.

Magura,

i got your email as well, thanks. i checked on that transformer, and it was like $40 when bought in the US. it was only like $9 in the UK, but their US distributor is much higher. ill have to look elsewhere.

butler853,

ill have to check those resistors to see. usually i DO let it bleed before i disconnect and reconnect things, but ive been messing with this so much that it could have slipped.

i have tried lifting the earth ground and it gets worse if i rememeber. but i havent tried it with the "minimal" configuration.

grataku,

i have heard of MANY people building this preamp with kristijan's boards with much success. he has built it as well, and everyone seems to think it was dead quiet.

so, i guess it has come down to the transformer. Magura had a good explaination of how the larger transformer could have been inducing the noise im hearing. it seems valid enough. at this point, im willing to try anything.

i cant seem to fine a cheap transformer suitable for this project. nelson suggests 2 avel lindbergs per channel, the 30VA 30+30 ones, but i would have to call avel to get a price. they seem to be around $25 each though, which is $100 for all 4. i would hate to spend that money just to "test" a theory.

would a 55+55 work for one channel? avel makes a 80VA thats 55+55 that might work.

[Magura]

Originally posted by cowanrg

would a 55+55 work for one channel? avel makes a 80VA thats 55+55 that might work.

Yes, that is what most of us have used as far as I know, myself included (I used a 120VA 2*55V). I had my version of the BOSOZ out for a test spin a couple of days ago, the trafo's I gave you the number of are the ones I'm using. The test was performed with a birdsnest and bad grounding tech. and it still was dead quiet. I even ran it off a 75VDC unregulated supply. I am now contemplating if I should make the supply regulated, but I guess I will.

Magura

[Raoul]

would a 55+55 work for one channel?

I built my BOSOZ with a couple of Apex Jr. Avel surplus transformers. The secondaries are 28.4V + 28.4V, 150VA. I adjusted the zener stack in the P/S to compensate for the lower voltage. They cost $22.00 a piece, but I think Steve posted a special offer for diyAudio members somewhere on the forum.

http://apexjr.com/miscellaneous.html


edit: Found the link to Apex Steve's special offer

http://www.diyaudio.com/forums/showt...625#post609625

It's kind of old, so you might need to check and see if it's still valid.