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What causes noise/hiss in a circuit?

Started by skiraly017, May 17, 2006, 03:16:04 PM

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skiraly017

May 17, 2006, 03:16:04 PM
What component(s) can be responsible for noise in a circuit? For example, in a Small Clone build I have there's hiss/white noise/background noise...whatever you want to call it. No more noise than any other analog chorus pedal, but it's still there. I've tried using metal film resistors instead of carbon film but that resulted in no appreciable difference. So what's causing the noise? Is it because it's analog and not digital? What about installing a noise filter like they do in car audio? This isn't so much an issue as it is curiousity.
"Why do things that happen to stupid people keep happening to me?" - Homer Simpson

R.G.

#1
May 17, 2006, 04:27:15 PM
Noise comes from many things. In pure analog circuits, it comes from the thermal agitation of electrons (thermal noise in resistors, transistors, diodes...) from inconsistent conduction ( flicker or 1/F noise in transistors) or excess noise in resistors. In RF work, it comes from all of the infinitely many RF noise sources in the universe all transmitting at the same time.

In either digital or sampled circuits (like the analog delay) it can come from sampling noise or quantization noise. Any sampling delay, analog or digital, with have noise which is caused by the sampled nature of the signal. When the samples are reconstructed into a continuous time signal, the little ambiguities about exactly how accurate each sample was is reconstructed into noise.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

DuncanM

#2
May 17, 2006, 04:52:59 PM
Bucket Brigade devices like the one used in the Small Clone are also inherently noisy - companding helps - but the BBD will produce more noise than anything else in the circuit.

Hence everyone went digital for chorus...

skiraly017

#3
May 17, 2006, 05:07:16 PM
Quote from: DuncanM on May 17, 2006, 04:52:59 PM
Bucket Brigade devices like the one used in the Small Clone are also inherently noisy - companding helps - but the BBD will produce more noise than anything else in the circuit.

Hence everyone went digital for chorus...

Is there a quieter op-amp that can be substituted for the BBD in the Small Clone?
"Why do things that happen to stupid people keep happening to me?" - Homer Simpson

skiraly017

#5
May 17, 2006, 05:14:21 PM
"Why do things that happen to stupid people keep happening to me?" - Homer Simpson

Connoisseur of Distortion

#6
May 17, 2006, 05:42:20 PM
Quote from: skiraly017 on May 17, 2006, 05:07:16 PM
Quote from: DuncanM on May 17, 2006, 04:52:59 PM
Bucket Brigade devices like the one used in the Small Clone are also inherently noisy - companding helps - but the BBD will produce more noise than anything else in the circuit.

Hence everyone went digital for chorus...

Is there a quieter op-amp that can be substituted for the BBD in the Small Clone?

whew. if only it were so simple...  8)

DuncanM

#7
May 17, 2006, 05:57:00 PM
QuoteIs there a quieter op-amp that can be substituted for the BBD in the Small Clone?

Unfortunately the BBD is not an op-amp, it's a delay chip that (basically) has a number of 'buckets' that shift a sampled input voltage along the line to the output - each clock pulse shifts the signal one bucket along - like a fire fighting line in the days before pumped hoses....

IIRC the MN3007 chip in the Small Clone has 1024 'buckets' so at a sample rate of 40kHz for full bandwidth you can get a delay of 25mS.

However, the Dynamic Range and Signal to Noise performance are not great - we are talking about 30+ year old technology though.
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