fed up with bosoz

[cowanrg]

Grey,

great post, thanks. in response to the thump question, yes i am using a relay to interrupt the output. its the velleman k4700 kit. i understand you completely though. but should the kit correct this problem? could i maybe wire it up to short to ground before the relay kicks in?

i will check my solder joints again. they should be fine. my hakko and the WBT solder are a match made in heaven. but ill check it all anyways.

as far as the noise issues you bring up, a few could be possibilities. not enough capacitance (aside from bad solder joints) isnt likely. oscillation is most likely the problem, although i dont know why. also, i had mentioned before that im getting significantly louder humming on the left channel than the right. im not sure why this is.

ok, i did a little checking. since i posted this thread, i have yet to hear that thump again. i think it was happening before i re-grounded the relay circuit, so that may have cured the thump.

however, the noise is still there, and its best described as just noise. its not really a hum or a buzz, but just background hiss. like on a poorly mastered cd, you heard this noise in the back. it happens with or without a source plugged in.

at full volume, it does hum, like a ground hum. its inaudible at lower volumes, but from about half to full volume it becomes apparent, and very loud. i lifted the ground on the amp, preamp, and cd player. none had earth grounds, just grounds through the interconnects. nothing changed at all, i still got the same noise and hum. so i guess its NOT a ground loop.

i did some more general messing around and found more wierd things. with a cd player plugged into the inputs, there was LESS humming. when i unplugged the jacks, the humming increased. this was whether or not the player was on or playing. even off and sitting there, having the player plugged in made it quieter. as soon as i unplugged them, the noise was much higher.

if i unplugged the cd player, but left the cables attached, there was no differene in noise. there wasnt a change in noise level when i plugged and unplugged them into various inputs. but as soon as the other ends were plugged into the cd player, plugging and unplugging them was like making music with noise...

i disconnected the velleman thingie and the noise floor was much higher and there was a MUCH more apparent hum at lower volumes than before. that is just confusing and i wont say more about that...

i think i might buy a rotel preamp from work at cost and toss the guts into the case and call it a day

[cowanrg]

i think i might spend several hours on this tomorrow. here is the list of things im going to try:

1.) remove ALL grounds and create a star ground.
2.) remove all RCA jacks and have temporary input/output jacks to correct any grounding issues
3.) temporarily get rid of all input switching and volume control (i have a cd player with volume control)
4.) recheck all solder joints
5.) recheck resistor values

anything i missed?

[Cobra2]

Picture?

You could also try twisting the trafo, 0-90º, sometimes it makes a difference! (even with toroids).

Arne K

[Stones]

Originally posted by cowanrg
Grey,

great post, thanks. in response to the thump question, yes i am using a relay to interrupt the output. its the velleman k4700 kit. i understand you completely though. but should the kit correct this problem? could i maybe wire it up to short to ground before the relay kicks in?

Consider for a moment what grey wrote re:
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.

If my understanding is correct the velleman kit is currently wired in series with the output (it disconnects the output for X amount of time) if you are going to strip the unit back to basics once you have your "other" problems solved if you still feel the need to use the velleman kit seriously consider using it to short the output to ground for x amount of time rather than disconnect the output this will not only yield the benefits that gray explained but will also mean that the velleman relay is not in the signal path.

for what its worth your strip it down to minimum requirements to assist fault finding gets my thumbs up as it removes some potential problems from the equation.

Best of luck, Mark

[cowanrg]

Originally posted by Cobra2
Picture?

You could also try twisting the trafo, 0-90º, sometimes it makes a difference! (even with toroids).

Arne K

if you follow some of the threads i posted, you can see some pics. here is a link:

http://www.diyaudio.com/forums/showt...241#post662241

[cowanrg]

Originally posted by mark stones


Consider for a moment what grey wrote re:
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.

If my understanding is correct the velleman kit is currently wired in series with the output (it disconnects the output for X amount of time) if you are going to strip the unit back to basics once you have your "other" problems solved if you still feel the need to use the velleman kit seriously consider using it to short the output to ground for x amount of time rather than disconnect the output this will not only yield the benefits that gray explained but will also mean that the velleman relay is not in the signal path.

for what its worth your strip it down to minimum requirements to assist fault finding gets my thumbs up as it removes some potential problems from the equation.

Best of luck, Mark

i think i might rewire the velleman kit... its just a preamp, so how much DC can really be on its output? so i might as well just use it as a short to ground at startup, not a full protection circuit...

BUT, i will try to bring it back down to basics as soon as i can. i had a slight "delay". i got my new toys in that ive been waiting on for 6 months. im gonna play with those all day, then i work tomorrow, then im out of town for vacation. it might have to wait. maybe that will give me some time to step back and rethink things.

(dual velodyne DD-18's in cherry)
http://www.cowanrg.mesanetworks.net/...ges/subs_2.jpg

(mmmm, pretty)
http://www.cowanrg.mesanetworks.net/...ges/subs_4.jpg

(gotta love full parametric EQ and room correction from a sub)
http://www.cowanrg.mesanetworks.net/...ges/subs_6.jpg

[SvErD]

Originally posted by cowanrg


if you follow some of the threads i posted, you can see some pics. here is a link:

http://www.diyaudio.com/forums/showt...241#post662241

Hi, first of all I would really recommend you to get rid of that enormous trafo. 800 VA in a preamp is way beyond overkill. It must put up a huge hum-field.
If you must use it you could improve a couple of things IMO:

1. Rotate the trafo 180 deg to get all AC wiring towards the front of the amp, now you have ac and dc wires close together.

2. Shield the input power leads and rout them along the left side of the amp all the way to the front and then along the front to the trafo.

3. Twist or braid your DC wires between the PSU boards and amp board.


cheers

[fcel]

Cowang,
In your other thread, I did add a big reminder to let you know that I have wired my Vellerman kit not according to what the manual says. I have mentioned that I have wired it in such a way that before turn-on and during turn-on, the output is short to ground and after a couple of seconds, the relay opens and the signal is outputed to the speakers.

[grataku]

I think it's time for you to throw this whole thing in the toilet and flush. It seems to be getting you to a place you don't wanna be.
Not to mention these incessant new threads about problems with the world most succesfully built preamp may start to get Nelson aggravated.

I have a lot of experience with the circuit. I built the boz and made it X added ccs and never-ever-ever had any problems with hums, startup thumps or blownup parts or anything (working super well as with any other circuit designed by 'The Zen Masta' ). Vellman kit is not needed here so you might as well save your money.

[cowanrg]

SvErD,

you cant really tell from some of those pics, but there is a half-round piece of steel around the transformer as well as the piece of steel that separates the PSU section from the preamp section. i guess thats not enough?

ill try temporarily re-routing cables to see if it makes a difference.

fcel,

i do remember that. you werent using the DC protect features of the circuit, just the turn on relays.

grataku,

that doesnt help me out a whole lot. as you can probably see, ive spent a LOT of time and money making this, and im not about to just abandon the project.

sorry about the multiple threads, but new problems just keep popping up. its obviously not a design flaw on nelson's part. i just cant understand how i could mess it up SO much. i mean, looking through the passdiy gallery, there seem to be a LOT of these that are just thrown in a box and wired up like somoene was on crack. maybe they dont sound very good, but ive not seen very many people have problems with theirs.

and actually, i thought that some kind of circuit was needed to stop turn on and turn off thump. i remember reading that in the article. plus, many people on this forum see to have had problems with it as well. im not the only one there.

do you have any pictures of your perfect unit? maybe some constructive advice then? im willing to give anything a try at this point. i understand the concerns with some of the wiring and transformer, but i dont see how that can make it do what its doing. maybe an incredible amount of noise could cause it to oscillate, but i didnt think that was possible.