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Old 3rd August 2007, 02:48 AM   #1
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Default 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?
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Old 3rd August 2007, 04:41 AM   #2
anatech is offline anatech  Canada
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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
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Old 3rd August 2007, 07:20 AM   #3
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Default Schematics

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.
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File Type: pdf p05.pdf (54.6 KB, 143 views)
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Old 3rd August 2007, 07:21 AM   #4
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Default Pre schematic

and the pre....
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File Type: pdf preamp schem.pdf (88.9 KB, 159 views)
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Old 3rd August 2007, 08:51 AM   #5
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Default Layout

Just learning.....
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Old 3rd August 2007, 09:13 AM   #6
Leolabs is offline Leolabs  Malaysia
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Grounding???Wiring???
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Old 3rd August 2007, 01:55 PM   #7
AMV8 is offline AMV8  United Kingdom
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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
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Old 4th August 2007, 03:52 AM   #8
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Default 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?
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Old 4th August 2007, 05:13 AM   #9
anatech is offline anatech  Canada
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Hi Tex Houston,
Try lifting the transformer up while the volume is down and the amp running.

-Chris
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Old 4th August 2007, 05:46 AM   #10
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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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