Salas DCG3 preamp (line & headphone)

[MagicBus]

Then it is the DMM? Could Nash measure each phase individually?

 

[Salas]

He should, with a dummy load across phase outputs, also to scope each phase output individually would be the most illuminating

 

[MagicBus]

Later in the evening I' ll check mine too.

 

[drpro]

Loaded supplies with resistors, no issues there. So.........................

 

[Salas]

And what happens if you tie their ground points while dummy loaded?

 

[drpro]

Still working..no issues

 

[Salas]

Mysterious issue to have checked everything on the main board and in the PSUs alone but having overcurrent problem when combined. Does it work if a mono PSU is shared between audio channels?

 

[Salas]

The electrolytic capacitors and all kind of diodes on the audio board are correctly oriented, yes?

 

[drpro]

yes they are. Salas would you perhaps have a copy of the complete audio schematic that shows everything as opposed to just the one channel schematic. Perhaps I am overlooking something and seeing the complete picture might make the difference.

Thanks
David

 

[Salas]

I got the Eagle double channel blueprint but don't pay attention to designations

 

[Salas]

Check with the Ohm meter for possible shorts across film caps also

 

[drpro]

Thank you sir. I will also check film caps

 

[simon2a3]

Apologies if I've missed this previously but which way round do J1/J2 (uPA68HA) go? I can't identify the manufacturer to look up their datasheet. Thanks.

 

[AIM65]

Apologies if I've missed this previously but which way round do J1/J2 (uPA68HA) go? I can't identify the manufacturer to look up their datasheet. Thanks.

See Post#25 of this thread for datasheet

 

[simon2a3]

Merci beaucoup. Mine don't look like that datasheet though, there isn't the 45 degree notch in one corner, see attached photo.

 

[AIM65]

Merci beaucoup. Mine don't look like that datasheet though, there isn't the 45 degree notch in one corner, see attached photo.

It's allright, it's the N of the old Nec Logo with the stylised N embossed on left (pin1).
Be carefull when soldering, the pcb layout is mirrored between left and right channel of the board. Upa on left has pin 1 on left and Upa on right is reversed (180° rotation), pin 1 on right (relative to top / front view of the board).
See Teabag's blog : http://www.diyaudio.com/forums/blogs/tea-bag/1340-salas-dcg-3-preamplifier-dcstb-power-supply.html

 

[simon2a3]

Ah right, thanks again. So the left pin in my photo is 1D on the PCB, just to be sure.

Thanks for the link to Tea-Bag's blog too - I looked for it yesterday but only found his Group Buy blog.

 

[AIM65]

Ah right, thanks again. So the left pin in my photo is 1D on the PCB, just to be sure.

Thanks for the link to Tea-Bag's blog too - I looked for it yesterday but only found his Group Buy blog.

1D : not sure, I do not have the pcb under my hand and photos are'nt good quality enough, but pin 1 are identified by the white marker on silkscreen.

 

[Salas]

1D= Drain one

Left hand channel's μPA faces the inputs/outputs connectors, right hand channel's μPA faces the MOSFETS. That's how they should be populating the board.

In other words: Where the pin designations on the silkscreen are, each chip's type & logo printed face should also be.

 

[simon2a3]

Got it, thanks both. I know my round a valve amplifier but SS is like dark magic to me!