Commercial Gainclone kit- building instructions

[LucasAdamson]

Hi Peter, Brainiacs

I have a problem. I'm sorry to ask, but if anybody can help me, it's surely you kind fellows.

My Audiosector Gainclone LM3875 has stared to oscillate recently, meaning that there is a throbbing noise through my speakers (at roughly 3x throbs per second) of earth-hum type noise. Do you have any idea what could have caused this? It's all wired up properly and this has happened fairly recently, to both channels. Could it be changes I have made to my speakers? I have tried another, unmodified set, and the issue is still there. A point of note is that the throbbing vanishes if I place my hand near but not touching the caps/chip area, OR actually touching the caps (which incidentally are naked metal since somebody recommended this - I foolhardily peeled them, but of course this is a case of the emperor's clothes - not a real world improvement in sound. They are, of course, not touching anything but their pin holes) So, I guess something is transmitting and receiving current of some kind, that my body is kindly earthing, if I stand around with my hand nearby.

Any ideas?

Many thanks for your time and brainpower
Lucas

[Peter Daniel]

Is the Gainclone in a grounded chassis?

[AndrewT]

are the chips running hot?

[nipper575]

Originally Posted by udailey

When you want it to sound even better the boutique components will make a difference. After the input caps your best improvement in my opinion is an obscene power supply. I like the one from chipamp.com that is meant for the miniA amplifier. 9 dollars for the board and then probably 40 more to populate it. Use a decent 160VA transformer up to about 300VA. Toroid transformers are preferred and are cheap from Antek, Inc. He is super reasonable on shipping as he uses flat rate USPS and will put as many as fit in one box for only one shipping charge.
Uriah

PS so where's the pics!

Cheers for the advice.

Here are the pics, feel free to criticise. I'd love to hear what I've done wrong or what I can improve upon.

I'll just point out from now that these pics were taken before the amp was 100% completed, the heatsinks are now grounded. I still need to secure them properly also. The volume shaft is also temporary, matter of fact, the whole case is temporary as I have made it far too small for my liking. I will have to last until my summer break. When I was designing my case using Google SketchUp, I didn't realise how cramped the case was going to be after wiring up the amp. I still managed in the end.

[AndrewT]

I see nothing wrong with the way you have used the space available to you.
It works and you have room to check and/or maintain the innards.

One Safety question.
Are all the exposed conductive parts connected to Safety Earth?

No metal chassis makes this more difficult in that separate grounding wires must be run to every exposed conductive component. I think I count 9.

[nipper575]

Hi Andrew, good to know that it generally looks ok.

I would say yes, anything that is conductive that is accessible from the outside of the case is grounded to the safety earth (including the heatsinks as the picture does not show). I read many informative posts (many of them yours, haha) about grounding safely and not including items such as 10R resistors in the audio ground path.

[LucasAdamson]

Originally Posted by Peter Daniel

Is the Gainclone in a grounded chassis?

It's in a wooden chassis. There's no metal in there but the sinks and the circuit. The heatsinks are earthed with wires, but it makes no difference to the noise if they're earthed or not.

Should the metal exposed caps be earthed???? Sounds hazardous.

I am feeling the caps are what's pumping noise out, and certainly if I touch them, the throbbing noise is reduced to almost nothing (95% reduced), but as I said, even approaching the amp circuit area reduces noise mostly. The CG is connected directly to the earth pin at the socket connector, as is the heatsink, but that's all.

Thanks

[LucasAdamson]

Originally Posted by AndrewT

are the chips running hot?

I don't think so.

Thanks

[Peter Daniel]

Originally Posted by LucasAdamson

It's in a wooden chassis. There's no metal in there but the sinks and the circuit. The heatsinks are earthed with wires, but it makes no difference to the noise if they're earthed or not.

Should the metal exposed caps be earthed???? Sounds hazardous.

I am feeling the caps are what's pumping noise out, and certainly if I touch them, the throbbing noise is reduced to almost nothing (95% reduced), but as I said, even approaching the amp circuit area reduces noise mostly. The CG is connected directly to the earth pin at the socket connector, as is the heatsink, but that's all.

You may try adding small cap as described here: Commercial Gainclone kit- building instructions

If that won't help, try adding Zobel (Rz 2.7R and Cz 0.1uF on amp board).

If noting helps, you may be forced to add some shielding to amp circuit.

I have some amp running without any enclosure and in my listening environment it's not a problem, but with other setups it may be different.

[Harolda]

One build. Another to go.

http://www.diyaudio.com/forums/attac...1&d=1279486621
http://www.diyaudio.com/forums/attac...1&d=1279486621
http://www.diyaudio.com/forums/attac...1&d=1279486621