External CPU for chipamp

CJ900RR · 12th July 2009, 09:10 AM

Hello.

I'm thinking of building me a small amp based on LM1875 to have in my bedroom. I want to make it as small as possible and therefore have an external CPU for it.

How long do you think that the cables from the CPU can be? I need about 1-1.5m (3-5 feet).

Any thoughts about this? Good or bad?

DigitalJunkie · 12th July 2009, 09:31 AM

CPU = power supply?

Sure,you can do that.
A couple of tips, Use adequately sized wire between the PSU chassis,and amplifier chassis. You don't want to add too much extra resistance.
I'd also put some local filtering caps in the amp chassis,for a bit of "local" reserve,and also some small bypass caps to shunt any HF/RF noise that might get picked up by the power cable.

AndrewT · 12th July 2009, 09:47 AM

Quote:

Originally posted by DigitalJunkie
A couple of tips, Use adequately sized wire between the PSU chassis,and amplifier chassis. You don't want to add too much extra resistance.
I'd also put some local filtering caps in the amp chassis,for a bit of "local" reserve,and also some small bypass caps to shunt any HF/RF noise that might get picked up by the power cable.

do the exact opposite.
Use a small diameter cable from remote PSU to Power amplifier.
Fit first stage smoothing with the rectifiers and transformer.
This is the rC stage using the r that is the effective resistance of the transformer secondary and the PSU wiring.

Fit main smoothing right next to the amplifier PCB. Still put the recommended decoupling on the PCB.

This forms a second rCLC filtering stage.
r = resistance of the umbilical cable.
C = main smoothing capacitance
L = trace and wiring inductance
C = decoupling.

The whole PSU thus becomes
rCrCLC. This is a very good filter for reducing all the mains artefacts that need attenuating.

Beware,
The sound quality of the amp will depend totally on the middle C (main smoothing) and the last C (local decoupling).

Have a look at Carlos FM's snubbered PSU. It would be ideal for this style of remote PSU.

Zoodle · 13th July 2009, 03:32 AM

Hi Andrew,
How about putting only the transformer in a separate box?
And/or using a shielded umbilical?

Eva · 13th July 2009, 04:30 AM

How about buying a SMPS? It may be small enough to fit in the same case as the amplifier.

AndrewT · 13th July 2009, 08:36 AM

Quote:

Originally posted by Zoodle
How about putting only the transformer in a separate box?

you have seen my recomendation.

12th July 2009, 09:10 AM	#1
CJ900RR diyAudio Member Join Date: Jan 2006	External CPU for chipamp Hello. I'm thinking of building me a small amp based on LM1875 to have in my bedroom. I want to make it as small as possible and therefore have an external CPU for it. How long do you think that the cables from the CPU can be? I need about 1-1.5m (3-5 feet). Any thoughts about this? Good or bad?

13th July 2009, 04:30 AM	#5
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	How about buying a SMPS? It may be small enough to fit in the same case as the amplifier. __________________ I use to feel like the small child in The Emperor's New Clothes tale

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12th July 2009, 09:31 AM	#2
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	CPU = power supply? Sure,you can do that. A couple of tips, Use adequately sized wire between the PSU chassis,and amplifier chassis. You don't want to add too much extra resistance. I'd also put some local filtering caps in the amp chassis,for a bit of "local" reserve,and also some small bypass caps to shunt any HF/RF noise that might get picked up by the power cable.

13th July 2009, 03:32 AM	#4
Zoodle diyAudio Member Join Date: Jun 2009	Hi Andrew, How about putting only the transformer in a separate box? And/or using a shielded umbilical?

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