chip-amp outboard power supply

Hi all,

I'm building a gainclone (my first attempt) and am using 2 toroidal transformers (1 for each channel), and am putting the power supply module in a seperate case, so that the main amp will fit in a nice small aluminium enclosure I already have.

My question is how exactly should I seperate this? Some people say that to keep EMI to a minimum I should place all AC components seperate (toroidals, main filter capacitors, rectifiers...) from the main amplifier components.
However, this would mean a long(ish) run of cable form the psu to the amp carrying DC which i believe is more susceptible to interference etc.. ALSO can't oscillation become a problem when chip-amps are quite a distance from the main power caps? or is this just with very high bandwidth buffer opamps?
With my limited knowledge I would have thought that putting the toroidals on their own would be the best bet with a small amount of AC components in the amp case so that the mains power caps are close to the chip-amp, but then what do i know Smile

Many thanks in advance
Andy

 

Screen the dc supply cable ......!

thats they way I'd go.

 

Hi.

My personal preference would be to put about 1/3rd of the PSU caps and the rectifier in with the toroids, and the rest of the caps in the amp enclosure. For good measure add a ferrite bead de-coupled with 0.1uF on the outputs of the PSU box.

Chris

 

I thought that the whole point of the chip amp was that it is very good at rejecting noise. If you are paranoid then Zanash's screening suggestion is the way to go.

BTW Chris in the original gainclone there is hardly any PSU capacitance, so your suggestion wouldn't apply.

 

Hi Lee.

Even small cpacitances can be divided up The idea is to keep the bulk of the capacitance near the amp for stability, whilst reducing the AC fields radiated by the interconnection cable. But as i said this is just my personal preference.

Chris

 

Hi again,

thanks very much for the advice, i've taken it on board and am drawing up some designs/schematics which i'll no doubt post and bug you lot about

Cheers,
Andy

 

Chris

On the original it is recommended to solder the caps directly onto the chip. That's what I did and you can't get muc closer than that!



Won't win any awards for neatness though

 

Hi Lee.

It's DIY you don't need to be neat. I would recomend a little mechanical support for those caps though, a small block underneath with a little RTV will make th joints more reliable in the long term

Chris

 

However, the inductance of big electrolytics like that means that they have very little effect at high frequencies. Try bypassing with an 0805 COG or X7R ceramic (100nF 50v are widely used). Do NOT use Y5V ceramics. Ever.

 

Mine is pretty true to the original 47Labs ethos of lowest number of components.

However, yes you are right Issac, I am just too lazy to do it at the moment. On DIYAudio, some recommend putting series 0.1R + 3.3nF to ground just before as well to help with ringing apparently. Can't be bothered to read the entire thread as it is >600 posts long.