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Old 11th January 2005, 05:55 AM   #11
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>>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,
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David
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Old 11th January 2005, 09:55 PM   #12
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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
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Old 12th January 2005, 09:30 PM   #13
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anyone have any suggestions?

I read a thread about changing a 220ohm resister to a 660 or 680, what about that option?

Thanks,

Josh
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Old 12th January 2005, 09:44 PM   #14
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Quote:
Originally posted by edjosh23
I read a thread about changing a 220ohm resister to a 660 or 680, what about that option?
If many others have their PCBs working without changes to the circuit, why should this be necessary?

Have you tried disconnecting the power (V+ and V-) from each channel and checking for hum on the channels separately?

How is your chassis ground connected?
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Old 13th January 2005, 02:37 AM   #15
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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
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Old 14th January 2005, 12:03 AM   #16
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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
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Old 14th January 2005, 12:08 AM   #17
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Quote:
Originally posted by edjosh23
any more suggestions about the hum?
Yes, two cases will make it more difficult to track down. Figure out the problem before shifting it to another case.
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Old 14th January 2005, 02:24 AM   #18
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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
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Old 14th January 2005, 07:14 AM   #19
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Quote:
Originally posted by edjosh23
could my problem just be that I don't have a pot?
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?
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Old 14th January 2005, 12:07 PM   #20
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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
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