Reducing noise In a Pedal !

[Izzy]

Ignore my stupididty but whats coupling?

[Sir H C]

Coupling is when a signal at one part of the circuit shows up elsewhere where it is not desired.  Usually either capacitive or supply related.  Often if the supply is not super good, it wiggles a bit with the signal.  If you have enough gain and not enough power supply rejection, that wiggle can be seen back on the input or elsewhere and get amplified up again.

If you look at a lot of amplifier circuits, you will see that there are filter capacitors and resistors all along the power supply rail keeping the local supply for different parts of the circuit separate.

Capacitive coupling often happens from two wires running next to each other with signals (this can also be inductive coupling).

[Izzy]

Thanks.
One question

I saw this on the net:



Isnt this too much wire?

[Sir H C]

I would be suspect of that much wire.  Start to get coupling you don't want.

[RedHouse]

Vertical -vs- Horizontal mounted resistors isn't an issue in audio spectrum circuits which are mounted inside shielded containers as we do. If you're picking up radio stations you need some better decoupling (like a 47-100pF cap at your input).

Horizontal mounting is used in higher frequency circuits (like radio and microwave applications) because it keeps the signal path at or near what is known as a ground plane which helps controll the circuit behavior within the box. Again these issues are not a factor in audio circuits, but the closeness of components and wires (as was mentioned before) is the thing to be concerned about.

[Izzy]

I would be suspect of that much wire.  Start to get coupling you don't want.

Thanks.

That was not my build actually. I found that one the net. It was build by some pro builder I guess who had tons of self build effect pedal.
WHen I saw that I was kinda surprised to see a pro using that much of wire.

[ubersam]

Thanks.
One question

I saw this on the net:

http://www.beavisaudio.com/images/prototype.jpg

Isnt this too much wire?

If you think that is bad... check mine out..



Surprisingly, it is pretty quite considering that it has a max. gain figure of 341 (1+(500Kpot+10K)/1.5K), compared to the 118 max gain figure of the stock TS. Another factor that causes noise is the guitar itself: noisy pick-ups, bad wiring/shielding, etc. Even bad cables can pick up and introduce noise into the chain.

[Izzy]

Damn, and you said you dont get noise?

hmm thats strange! What magic did you do?

[Gilles C]

It must be the Twisted Wires magic...

And the flat cables maybe???

Gilles

[Izzy]

ahaha nice! Then I will try to do the same.

[Izzy]

One question. Since people here said that exposing resistors lead doesnot reallt matter if we have good sheilding enclosure, - I want to make a circuit with all resistors in vertical position to save space and make my pedal more compact. Am I taking a bad move here?

[Izzy]

And does putting a metal tape inside a TIN enclosure will help to shield better than a Tin without the metal tape?

[Barcode80]

IMHO, if the enclosure is already metal, adding the tape won't make much difference. i honestly have never heard any noise difference between raised resistors and others. the only thing i would warn against is that raised resistors have a higher risk of ground out since there is more lead available that might touch the enclosure if you aren't careful.

[Izzy]

thanks. I think I should try that way to save some space then.

[Izzy]

Before I change my previous layout completely and make circuit as compact as possible by placing resistor vertically, I want to make sure  that I am not taking wrong step.
I dont want to get noise, as I am trying to build this DS-1 as quiet as possible.
Help me out here.

[Izzy]

So If I substitue Carbom film resistor by all Metal film resister, by how much % will the noise decrease? Any rough estimate?

[Meanderthal]

 You won't hear a difference between Carbon Film and Metal film as far as noise goes, but the Metal film tend to  be within 1% tolerance and Carbon film 5%.
It's Carbon Composite resistors(the old brown ones) that can get niosy, and for that matter many of those are only within 10 or even 20% tolerance... not a good thing for biasing or anything like that...