Preamp noisy - 100K pot?Relays?

Tex Houston · 3rd August 2007, 01:48 AM

Hi there. I've built a pre using Rod Elliott power supplies - all good. I'm using a pcb from Ebay to switch channels - it has 4 relays and a 100K volume pot.This is powered from the aux output of the supply (which is unregulated). Problem is it's noisy at low levels and on full - fairly quiet in the middle range - where am i going wrong?

anatech · 3rd August 2007, 03:41 AM

Hi Tex,
Two things.
1. Can you post a schematic and take a picture of them to post also?
2. **** Power supply ****

Your power supply is very important from a noise standpoint. It must be quiet electrically. A "wall wart" unregulated supply is the worst thing I can imagine to run a preamp off. Maybe a bicycle generator with rectifiers might be worse.

Your grounding is important of course. Did you ground the case of the volume control (this would normally make it noisy in mid travel).

-Chris

Tex Houston · 3rd August 2007, 06:20 AM

Thanks for the reply - here is the schems for the power supplys and the pre. The switch is fairly basic with a 5V reg and relays feeding an alps 100k pot.

Tex Houston · 3rd August 2007, 06:21 AM

and the pre....

Tex Houston · 3rd August 2007, 07:51 AM

Just learning.....

Leolabs · 3rd August 2007, 08:13 AM

Grounding???Wiring???

AMV8 · 3rd August 2007, 12:55 PM

Hi

It might help to locate the source of the noise if you can describe the type of noise you are hearing. Is it hissing or low frequency background or what.

Don

Tex Houston · 4th August 2007, 02:52 AM

It's a buzzing hum at low levels, pretty quiet mid turn and kindy hissy at full volume. Preamp and power supply are connected to star ground as is the volume pot through it's connection to the front panel. Layout OK?

anatech · 4th August 2007, 04:13 AM

Hi Tex Houston,
Try lifting the transformer up while the volume is down and the amp running.

-Chris

Tex Houston · 4th August 2007, 04:46 AM

Thanks for your help. I tried lifting the transformer and it made no difference at all. Does the value of the pot make a difference? Would a 50k or 20k pot be better in this instance? It is running straight into a gainclone by the way.

3rd August 2007, 01:48 AM	#1
Tex Houston diyAudio Member Join Date: Apr 2007	Preamp noisy - 100K pot?Relays? Hi there. I've built a pre using Rod Elliott power supplies - all good. I'm using a pcb from Ebay to switch channels - it has 4 relays and a 100K volume pot.This is powered from the aux output of the supply (which is unregulated). Problem is it's noisy at low levels and on full - fairly quiet in the middle range - where am i going wrong?

3rd August 2007, 03:41 AM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Tex, Two things. 1. Can you post a schematic and take a picture of them to post also? 2. ** Power supply ** Your power supply is very important from a noise standpoint. It must be quiet electrically. A "wall wart" unregulated supply is the worst thing I can imagine to run a preamp off. Maybe a bicycle generator with rectifiers might be worse. Your grounding is important of course. Did you ground the case of the volume control (this would normally make it noisy in mid travel). -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

4th August 2007, 02:52 AM	#8
Tex Houston diyAudio Member Join Date: Apr 2007	Hum It's a buzzing hum at low levels, pretty quiet mid turn and kindy hissy at full volume. Preamp and power supply are connected to star ground as is the volume pot through it's connection to the front panel. Layout OK?

4th August 2007, 04:13 AM	#9
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Tex Houston, Try lifting the transformer up while the volume is down and the amp running. -Chris __________________ "Just because you can, doesn't mean you should" © my Wife

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3rd August 2007, 08:13 AM	#6
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	Grounding???Wiring???

3rd August 2007, 12:55 PM	#7
AMV8 diyAudio Member Join Date: Jan 2005 Location: near london	Hi It might help to locate the source of the noise if you can describe the type of noise you are hearing. Is it hissing or low frequency background or what. Don

4th August 2007, 04:46 AM	#10
Tex Houston diyAudio Member Join Date: Apr 2007	Thanks for your help. I tried lifting the transformer and it made no difference at all. Does the value of the pot make a difference? Would a 50k or 20k pot be better in this instance? It is running straight into a gainclone by the way.

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