Well after I ruined the lm3875s on the last boards I built a new set of boards, with Brian's suggestions and half of an old box of his. I shorted the last pot on accident (I'm waiting for the group buy) some my rca placement is not final, and neither is the back pannel (I cut a piece of alumium for the back, but have to cut holds for the AC and everything). But the wires are so much shorter and is well shielded, but I still get a loud hum. In this picture you can see that this afternoon after school I added some aluminium foil to a few wires to see if it would cut down on the hum, not at all. I've moved lots of wires all around the box but it doesn't seem to help what can be the problem. I also have checked with the aluminium top on the amp, but it doesn't help either. Here is a picture (cant get it working right now)
Thanks,
Josh
Thanks,
Josh
I got the picture working.
I've tried moving everywire, but I just can't seem to make it any better.
Thanks,
Josh
I've tried moving everywire, but I just can't seem to make it any better.
An externally hosted image should be here but it was not working when we last tested it.
Thanks,
Josh
Maybe you have a cold solder joint on one of the boards somewhere? If you aren't an experienced solderer, have a look at one of the guides on the net. (Easily found with google.)
Is the circuit grounded to the chassis at more than one point? Like at the input jacks or speaker terminals?
Loud hum is usually from a poor ground or a ground loop.
Is the circuit grounded to the chassis at more than one point? Like at the input jacks or speaker terminals?
Loud hum is usually from a poor ground or a ground loop.
xformer
Did you know that the metal dealie on top of your transformer is upside down, causing your bolt to stick too far up? If your transformer bolt is hitting the cover of your case this will cause a loud hum. Its called shorted turn phenomina. Do a search here for that. Happened to me too. Couldn't figure out which side was up if you know what I mean. Anyway, should not happen with cover off, so maybe that's not it.
I know these problems are very aggravating, you check and recheck and nothing seems wrong. Keep at it!
I would check all component values, use a DMM or check the labels.
Did you know that the metal dealie on top of your transformer is upside down, causing your bolt to stick too far up? If your transformer bolt is hitting the cover of your case this will cause a loud hum. Its called shorted turn phenomina. Do a search here for that. Happened to me too. Couldn't figure out which side was up if you know what I mean. Anyway, should not happen with cover off, so maybe that's not it.
I know these problems are very aggravating, you check and recheck and nothing seems wrong. Keep at it!
I would check all component values, use a DMM or check the labels.
thanks for the quick responces.
Since I shorted the pot, I'm not using my computer as a source and the volume control on the computer works really well, while the output on my home theater amplifier is either loud, or louder. The hum is coming through the speakers, but its definately the hum of the transformer. I can put my ear up to the torroid and hear nothing except when it is first turned on.
The bolt on the transformer is actaully quite short, only about 4 threads are poking out after the nut, about 1/2" from where the top of the amp sits.
The box is BrianGT's and he helped me with grounding, and disconnecting it does nothing, only make it worse actually.
The boards themselves, all the joints are well soldered (I was never tought to solder and my first boards had too little solder) Brian showed me a few tricks and the amp boards are well soldered, but the rectifier is a different story. I never added solder to those joints, can this cause the hum?
Because of this hum, I cannot properly compare my Denon to the Gainclone, as of now, the Denon sounds a whole lot better, even after about 15 hours of hot burn in which I burned 2 holes in my capet with the dummy loads getting too hot. Since I dont have a pot and I dont like playing music on my computer I tend not to use the amp I built very often.
Before entering the project I did a lot of research, but after I finished my first amp, and then ruined a cap and later had my LM3875s smoke and ruin, I started from scratch and this amp is much better constructed and my knowledge has trippled on the topic, I've read about the phenomina with transformers, but I hadden't heard anything bad about undersoldering.
After the rest of my homework, I'm going to add solder and hopefull come back with good news.
Right now I feel like I'm listening to KLH amplifier, or something cheap. Obviously the amp shouldn't sound like this, what can I add or change?
Also OT, but what about a tube rectifier for Gainclones? Would it work well? Would it give a "tubier" sound to the amp?
Thanks,
Josh
Since I shorted the pot, I'm not using my computer as a source and the volume control on the computer works really well, while the output on my home theater amplifier is either loud, or louder. The hum is coming through the speakers, but its definately the hum of the transformer. I can put my ear up to the torroid and hear nothing except when it is first turned on.
The bolt on the transformer is actaully quite short, only about 4 threads are poking out after the nut, about 1/2" from where the top of the amp sits.
The box is BrianGT's and he helped me with grounding, and disconnecting it does nothing, only make it worse actually.
The boards themselves, all the joints are well soldered (I was never tought to solder and my first boards had too little solder) Brian showed me a few tricks and the amp boards are well soldered, but the rectifier is a different story. I never added solder to those joints, can this cause the hum?
Because of this hum, I cannot properly compare my Denon to the Gainclone, as of now, the Denon sounds a whole lot better, even after about 15 hours of hot burn in which I burned 2 holes in my capet with the dummy loads getting too hot. Since I dont have a pot and I dont like playing music on my computer I tend not to use the amp I built very often.
Before entering the project I did a lot of research, but after I finished my first amp, and then ruined a cap and later had my LM3875s smoke and ruin, I started from scratch and this amp is much better constructed and my knowledge has trippled on the topic, I've read about the phenomina with transformers, but I hadden't heard anything bad about undersoldering.
After the rest of my homework, I'm going to add solder and hopefull come back with good news.
Right now I feel like I'm listening to KLH amplifier, or something cheap. Obviously the amp shouldn't sound like this, what can I add or change?
Also OT, but what about a tube rectifier for Gainclones? Would it work well? Would it give a "tubier" sound to the amp?
Thanks,
Josh
edjosh23 said:
I'm still thinking it's a ground issue.
The amount of solder isn't directly the issue. Sure, you can have too little solder, but usually novices err on the side of too much. In the end though it's the electrical quality of the joint that counts. Have you had a look at soldering guides on the net? There are some that show you what good and bad joints look like.
Guessing isn't much good.
A DMM is a digital multi-meter.
I just looked at a few soldering guides the ones that came up on google. I use flux, along with a wet sponge, and all my joints look like mini volcanoes. I used a 45w iron and lead free silver solder. I feel like nothing was done wrong, and everything was up to Brian's standards.
One thing that I think could be a potential problem is AC. The AC live goes across the entire enclosure to the on off switch and over all the DC wires but the cross perpendicular and the wires are about 1" above the DC wires. When I cut the final back plate The AC outlet will be higher in the enclosure, and more towards the center, along with the fuse. All sources that I have are my DVD player, my dads DVD player, his tape player, and his reciever.
I have sound blaster extigy and I'm using it to run the amp. I can use front speaker out or headphone. Both have the same ammount of hum.
The computer works fine though the Denon.
I can also use a discman, in which hum is maybe a little bit less loud, but I also cannot completely turn down the music, with the ear up close you can still hear the music faintly. But the hum is there none the less.
I just don't think its a grounding problem, because everyone says that the way Brian recomends on his website works with his PCB, and this is the way that he did for me when I was with him. This is also a copy of the box used in the user guide for his PCB.
All voltages have been checked with my multimeter.
I thought I should mention, with no input there is still a loud hum.
Thanks,
Josh
One thing that I think could be a potential problem is AC. The AC live goes across the entire enclosure to the on off switch and over all the DC wires but the cross perpendicular and the wires are about 1" above the DC wires. When I cut the final back plate The AC outlet will be higher in the enclosure, and more towards the center, along with the fuse. All sources that I have are my DVD player, my dads DVD player, his tape player, and his reciever.
I have sound blaster extigy and I'm using it to run the amp. I can use front speaker out or headphone. Both have the same ammount of hum.
The computer works fine though the Denon.
I can also use a discman, in which hum is maybe a little bit less loud, but I also cannot completely turn down the music, with the ear up close you can still hear the music faintly. But the hum is there none the less.
I just don't think its a grounding problem, because everyone says that the way Brian recomends on his website works with his PCB, and this is the way that he did for me when I was with him. This is also a copy of the box used in the user guide for his PCB.
All voltages have been checked with my multimeter.
I thought I should mention, with no input there is still a loud hum.
Thanks,
Josh
>>I use flux, along with a wet sponge, and all my joints look like mini volcanoes. I used a 45w iron and lead free silver solder.
try this... rub lightly the joint with a dry cloth... could you see it shine like a mirror?
if it does not, then might be you have a problem with the solder joint.
If you are not an experienced with solder, please do not use lead free silver solder... they are very difficult to work with...
try something like wonder wire or cardas... (check at percyaudio.com)... they flow and easy to work with... (low melting temperature)
and.. unless you solder on a very difficult surface like stell or big surface brass, please do not use flux... in my experience they tend to ruin the solder joint rather than make a good contact...
Regards,
---
David
try this... rub lightly the joint with a dry cloth... could you see it shine like a mirror?
if it does not, then might be you have a problem with the solder joint.
If you are not an experienced with solder, please do not use lead free silver solder... they are very difficult to work with...
try something like wonder wire or cardas... (check at percyaudio.com)... they flow and easy to work with... (low melting temperature)
and.. unless you solder on a very difficult surface like stell or big surface brass, please do not use flux... in my experience they tend to ruin the solder joint rather than make a good contact...
Regards,
---
David
My joints shine, I also don't use much flux, but I do use it if I know that I'm going to have my iron hot for atleast an hour.
I really don't think its my joints just because Brian, who designed the boards helped me solder.
The lead free silver solder is not that hard to work with, yes the 45w was a step up from only needing 15w, but that doesnt bother me.
This afternoon I did change my chasis ground. My star ground is under a standoff on the rectifier. The wire coming from the AC ground was in between the two boards and was not giving the chasis a sufficient ground, 2mv. I put the AC ground on the bottom, chasis ground is back to 0mv but the hum has not changed. What I knowticed last night and today was my DC offset. Its a little high, but from what I'v read its still ok. Its -80mv
I talked to Brian last night, and he recomended either waiting for the pot to come, or use one channel of the shorted pot (one channel still works) and use a normal source like a cd player/ in my case a dvd player and see if their is still a hum from that.
I've read a ton of dc offset threads, but I'm not sure what I should do, and one or two is over my head.
Thanks,
Josh
I really don't think its my joints just because Brian, who designed the boards helped me solder.
The lead free silver solder is not that hard to work with, yes the 45w was a step up from only needing 15w, but that doesnt bother me.
This afternoon I did change my chasis ground. My star ground is under a standoff on the rectifier. The wire coming from the AC ground was in between the two boards and was not giving the chasis a sufficient ground, 2mv. I put the AC ground on the bottom, chasis ground is back to 0mv but the hum has not changed. What I knowticed last night and today was my DC offset. Its a little high, but from what I'v read its still ok. Its -80mv
I talked to Brian last night, and he recomended either waiting for the pot to come, or use one channel of the shorted pot (one channel still works) and use a normal source like a cd player/ in my case a dvd player and see if their is still a hum from that.
I've read a ton of dc offset threads, but I'm not sure what I should do, and one or two is over my head.
Thanks,
Josh
the hum seems to be coming from both speakers equally
The grounding:
From AC ground to a star grund
both amp board's CHG go to this ground
it is underneith the rectifier, a bolt is under the chassis, goes though a hole, goes through all 3 ring terminals (the star groung) and into the standoff
well, someone else ran into a similar problem, but also no one, except BrianGT has worked in a similar bow, and he wired his differently.
I'm going to try putting on the pot soon, but I'm just too busy with school.
Thanks,
Josh
The grounding:
From AC ground to a star grund
both amp board's CHG go to this ground
it is underneith the rectifier, a bolt is under the chassis, goes though a hole, goes through all 3 ring terminals (the star groung) and into the standoff
well, someone else ran into a similar problem, but also no one, except BrianGT has worked in a similar bow, and he wired his differently.
I'm going to try putting on the pot soon, but I'm just too busy with school.
Thanks,
Josh
I'm thinking about maybe making the gainclone into 2 cases. I'll use the current chassis as a PSU case, and have a really small chassis for the amps themselves. Since I don't want to waiste this nice case, I was thinking maybe filling the rest of the space with the carlosfm snubber.
Should the snubber be in the same chassis as the PSU?
I'm hoping maybe after the case change and the snubber I won't have as big of a hum issue.
I understnad the snubber ends with a single v+, v-, and a ground. Should I send this though the umbilical as 3 wires or should I seperate to 8 wires before the umbilical or after (in the amp chassis).
What about using coaxial cable as umbilical, and split the ground into 2, so each coaxial is grounded.
any more suggestions about the hum?
Thanks,
Josh
Should the snubber be in the same chassis as the PSU?
I'm hoping maybe after the case change and the snubber I won't have as big of a hum issue.
I understnad the snubber ends with a single v+, v-, and a ground. Should I send this though the umbilical as 3 wires or should I seperate to 8 wires before the umbilical or after (in the amp chassis).
What about using coaxial cable as umbilical, and split the ground into 2, so each coaxial is grounded.
any more suggestions about the hum?
Thanks,
Josh
could my problem just be that I don't have a pot?
This weekend I'll take everything apart and re solder anything that I find that might not have enough solder.
I'll also put a real back pannel on it and shorten any more wires I can.
I just can't think of anything that it could be
I've read more threads, but there is only the one that looks like they might have had a similar problem, and that was changing out the 220ohm reistor.
After this weekend I'll come back with some info,
I don't quite understand disconnecting an amp. If I have the hum coming from both speaker, imput or not, ground or not, what will disconnecting an amp do?
sorry I'm incompetent
Thanks,
Josh
This weekend I'll take everything apart and re solder anything that I find that might not have enough solder.
I'll also put a real back pannel on it and shorten any more wires I can.
I just can't think of anything that it could be
I've read more threads, but there is only the one that looks like they might have had a similar problem, and that was changing out the 220ohm reistor.
After this weekend I'll come back with some info,
I don't quite understand disconnecting an amp. If I have the hum coming from both speaker, imput or not, ground or not, what will disconnecting an amp do?
sorry I'm incompetent
Thanks,
Josh
edjosh23 said:
I don't think so, I don't have pot on my BrianGT NIGC.
I didn't connect CHG to star earth because I tried it as an experiment (when I was chasing a hum issue) and everything worked so I left it off. I can't see a safety issue doing this.
FYI, BrianGT PCB has the signal and power earth connected on the PCB so you can create a ground loop if you don't follow Brian's wiring scheme properly. I learnt this from experience trying to implement a "normal" star earth scheme.
BTW, How come your amp looks very similar to the amp in BrianGT's instruction manual.
Can you post a larger, clearer picture?
Brian gave me this case. After building my first gainclone I moved my pot and there was an arc on the rectifier, both speakers blew, and then a cap burst, and the chips smoked. 
Brian helped me out, and I got the case from him along with lots of tips on design, soldering, and wire use.
the 2 big differences are, my on off switch is up front probably creating a little more hum, and he had an lcd telling the volume, I'm still in high school and would have no clue how to do that.
I've disconnected the CHG, and the hum is the same, maybe even worse.
Brian also came up with my ground scheme.
my dc offset is also -80mv
Thanks,
Josh
Brian helped me out, and I got the case from him along with lots of tips on design, soldering, and wire use.
the 2 big differences are, my on off switch is up front probably creating a little more hum, and he had an lcd telling the volume, I'm still in high school and would have no clue how to do that.
I've disconnected the CHG, and the hum is the same, maybe even worse.
Brian also came up with my ground scheme.
my dc offset is also -80mv
Thanks,
Josh
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