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
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
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?
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?
cowanrg said:
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
Cobra2 said:
if you follow some of the threads i posted, you can see some pics. here is a link:
http://www.diyaudio.com/forums/showthread.php?postid=662241#post662241
mark stones said:
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/ht/images/subs_2.jpg
(mmmm, pretty)
http://www.cowanrg.mesanetworks.net/ht/images/subs_4.jpg
(gotta love full parametric EQ and room correction from a sub)
http://www.cowanrg.mesanetworks.net/ht/images/subs_6.jpg
cowanrg said:
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
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.
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.
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.
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.
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.
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.
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
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
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?
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?
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?
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?
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
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
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.
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.
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.
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.
cowanrg said:
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
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/showthread.php?s=&postid=609625#post609625
It's kind of old, so you might need to check and see if it's still valid.
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