Drive pedal hiss

[sliberty]

Are there any rules of thumb to minimize the hiss generated by overdrives/boosts? For example are there certain key locations in a circuit that should have metal film rather than carbon film resistors, or any other ideas like that? I am not looking to redesign the pedals, just make them as quiet as they can be given their circuit design.

[GGBB]

Considering what metal film resistors cost, use them for everything. Everything before gain at least.

[sliberty]

Resistors are cheap, but shipping is expensive

Will that actually help? Is there anything else worth doing?

[Rob Strand]

The simplest answer is don't use large valued resistors.
A slightly better answer is not to put high-impedances (directy or indirectly) in series with the signal lines.
High impedance in parallel with a low impedance source, eg the input resistors to ground, aren't a problem.

Don't put a lot of high frequency boost if the signal source has no spectral components there.

Beyond that you need to understand specifically where the noise originates in the circuit and what design aspect causes it.   That's more difficult.  It requires a lot of reading and analysis.

[sliberty]

Thanks for the reply, but you kinda missed the point. I've built several drive related pedals which are copies of commercial products. So the values of the resistors are the values that must be used, or it won't be that pedal anymore. I was looking for advise on how to quiet the hiss in my copies of these pedals.

[Rob Strand]

I was looking for advise on how to quiet the hiss in my copies of these pedals.

Unless you somehow have faulty parts there's not much you can do.  If you freeze every aspect of a design it is what it is.   You can only improve by changing *something*.    If you aren't over-driving (ie. clipping) opamps then sometimes you can replace the opamps with lower noise versions.  That assumes the noise is coming from the opamp, sometimes it doesn't.   If you are overdriving the opamps then changing to lower noise opamps can affect the sound.

If you have built exact replicas and yours are somehow noisier than the real ones then that's a different story.  You have to weed through all the parts which might be the cause until you find the problem.   That would involve changing out parts.   Active components like opamps are are good place to start.  In some cases (new) semiconductors have been subject to damage by static electricity.  This can make them noisy.   I've seen cases where poor handling on the production line has resulted in many failures in the finish product.  If you bought them from dodgy suppliers you could have bought parts which don't meet spec ie. they are noisy.

[samhay]

^it's not just parts that give rise to noise. Circuit layout, wiring etc starts to become (more) important for high gain pedals.
Are you building with a PCB, vero, perf, point-to-point, ...?
Is your wiring tidy and as short as possible?
Do you have shielding - circuit in a box, shielded input/output wires if long, etc...?

[GibsonGM]

^it's not just parts that give rise to noise. Circuit layout, wiring etc starts to become (more) important for high gain pedals.
Are you building with a PCB, vero, perf, point-to-point, ...?
Is your wiring tidy and as short as possible?
Do you have shielding - circuit in a box, shielded input/output wires if long, etc...?

..well-filtered power supply if not battery-powered, power wires routed away from signal wires, or at right angles if they must cross...component leads short....?

Other than that, some hiss is entirely normal as you are multiplying whatever noise is present at the input many times with a "drive" pedal (booster).  Any source of noise appearing at the input will be amplified...this includes anything coming in from your guitar - noise picked up due to AC wiring in the vicinity/lights...RF interference....etc etc.

[sliberty]

Recent builds have been PCB, some with board mounted pots. Other builds with "verified" very layouts. Wires are short. Boards are in enclosures and jacks are grounded. Power is battery.

I agree that some hiss is to be expected. Just want to minimize I'd BECAUSE of the multiplying factor.

[samhay]

I may have mis-read this.
Have you compared your build to any of the original effects - i.e. do you know that your circuit is noisier than the original? (I assumed you had, but now are having second doubts.)

If you haven't compared them, then you may well have an effect that is already 'as quiet as they can be given their circuit design.'  It's the nature of the beast, particularly if you play guitar(s) with single coils.

[Hatredman]

Singles coils pick up hum, I think he's talking about hiss, só the guitar is not imporant.

.

[anotherjim]

Are you able to compare your clones side by side with the originals and with the same powering?

Metal film resistors? Any over 10k might be a safe rule of thumb if you don't want to figure it out. We'd have to see the circuit to tell you which are most critical although as already said, that's certainly all the ones in series with the signal.

In my experience, various hiss & fizz noise can be due to the guitar, it isn't all hum (humbucking won't cure it, it isn't induction in the coils). Mostly, it's due to incomplete or badly designed screening in the guitar. Despite all the noise sources you can have in your environment, people still build guitars like Leo originally did. Baffles me that so many pickups are still made with separate black & white wires instead of twisted pair inside screen for example.

To prove that a pedal itself actually is noisy, get a 1/4" jack plug and short tip to shell contacts (don't skip this, it will rule out noise signal entering the pedal). Plug it in the pedal input and have a listen. If it makes an objectionable amount of noise when working off nothing at all, it is a noisy circuit.

[amptramp]

The guitar is going to have volume and usually tone controls on it and these are not low noise components.  They may be OK at full volume and minimum treble cut but once you stray from that, you are adding some series resistance from the coil to the output that is certainly not of metal film quietness.  Similarly, the tone control may have some effect too.  If noise is a primary concern, build a buffer into the guitar.  You could add the gate resistor, source resistor and FET of a Tillman in the guitar and keep the drain resistor, coupling cap and output resistor to ground in the first box the cable goes to and the impedance of this line will be dominated by the drain resistor.

Some people have added this Tillman booster to the cable so they don't have to butcher the guitar.  The nominal gain of about 3 and the reduced impedance tends to eliminate noise at the source.  Also, check the wiring in the guitar.  One old Cort that I had was very noisy.  The ground was taken to aluminum foil and the ground connections of the controls were soldered to the back shield of the pots, which were grounded by contact with the shield.  After a bit of corrosion, of course it was noisy.  So I took a wire and ran the ground properly, disconnecting it from the backshells of the pots.  The result?  A guitar that a professional musician declared to be a great blues guitar.  (And I got it and an old noisy Univox amp for the combined price of $20 at a garage sale.)

[sliberty]

Thanks for the replies. Some of the pedals I've built that have what I consider to be excessive hiss are the Emerson EM Drive and the KOT. I don't have access to originals to test side by side. They sound fine alone, but stacked, as you would imagine, the hiss is multiplied. The next time I order parts, I may order a stock of metal film resistors and try replacing all resistors in the EM Drive (its a small simple circuit) as a test bed.