Trouble Shooting A Noisy Boost Pedal? ...

[kurdt]

Hello!

I've got this simple, one knob, clean boost pedal which I like a lot. The only problem is, it's very noisy.
I've tried other boost pedals, with the same guitar and amp that I always use, and I've been able to turn them all the way up, with very little noise being generated (not that I'd ever want to actually use them like that).

With this boost pedal however, I can't even go past about 3 on the dial (10 o'clock), as it just gets too noisy.

The noise is a hissing sound that gets worse the more you turn it up. It's kinda like when the gain on an overdrive / distortion pedal is up way too high.

I don't use any other pedals, it's just guitar, into the boost, into the amp, and I've tried powering it with a battery instead of my PSU, and that has made no difference, so I'm guessing it's something in the pedal itself.

I've replaced the pot with a brand new one, and that's made no difference either.

So, what next?
I've wired up lots of guitars over the years, but I've never done anything with pedals, or circuit boards, so I don't really know where to even start with this.

Any help would be much appreciated!

Cheers.

Here's a pic of the circuit ...

[thetragichero]

is it noisy only on a power supply or also running off of a 9v? other fx daisy chained off same supply? signal wire(s) running next to power wires? one of the pot lugs grounded and shouldn't be, or not grounded and should be? looks like mostly metal film resistors so I wouldn't imagine it's resistor hiss

got a schematic?

[thetragichero]

other dumb stuff to check: orientation of of polar parts (electro caps, etc), make sure you've got transistor wired correctly, gently reflow solder joints (including on all off board components)

[thetragichero]

another dumb question: is it still noisy when it's placed inside a metal enclosure?

[thetragichero]

I keep checking back to see if any of these helped him or if it's more complicated

[kurdt]

Hi,

Sorry for the late reply, I've been busy with work and not had a chance to get back here.

So to answer your quetions (as best I can) ...

Yep, it's noisy when powered by a psu, or a battery. I've tried both and there's no noticable difference between the two.
I don't use any other effects, so when I do power it with a psu, it's the only thing the psu is supplying power to.

Sorry, I'm not exactly sure what you mean by "signal wire(s) running next to power wires?", signal wire as in the guitar lead? If so, then no, they don't run next to each other, I keep all the power leads behind the amp, and the guitar lead is in the front.

I haven't checked any of the soldering on the board (not entirely sure how to), but just looking at it, I can't see any obvious signs of anything that might be a problem.
When I replaced the pot with a new one, I didn't touch any of the connections on the board, so I guess there could possibly be a grounding problem there.

No, I haven't got a schematic for it. I know you can probably find schematics for popular pedals online, but this was made by a quite small company, so I doubt there'll be one anywhere.

With regard to checking the orientation of polar parts ... I mean, I get what you're saying, some parts have to go in the circuit board the right way around, yeah? Do all of them?

Oh and yeah, it is still noisy when it's in its metal enclosure. Actually I haven't tried using it when its been out of it, maybe I should do that.

I keep meaning to have a look around online for basic info on pedal parts, like a beginners tutorial or something, but it's just finding the time to do it that's the problem.

[pj]

If this is a single transistor boost as it looks (such as ehx lpb1, various treble boosts) im afraid they are noisy little beasts. Aside from the issues of the transistor component itself, theres high output impedance (usually a large part of which is the noisy carbon pot track) and a fair deal of noise from the top resistor in the bias divider on the input getting amplified by the transistor. Plus they're usually running full tilt and the boost pot is just attenuating the output which doesn't help on the noise floor front of all of the above

On the other hand the tonal effect of these boosts is loved for good reason, they soften our peaks by virtue of lowish input impedance, roll off highs and often add pleasing even order harmonics as theyre generally class A arrangements that are clipping away softly and happily all the time.

If your other boosts have been micro amp alike types with opamps and negative feedback gain control it would explain why this comes across the ugly duckling. The question is... Is it worth the tonal benefits?

[reTrEaD]

Nov 20, 2018 14:48:04 GMT -5 kurdt said:

Here's a pic of the circuit ...

Hello kurdt

A pic is sometimes a nice thing to add but without a schematic, it's impossible to diagnose potential problems, except in the most general way.

Nov 30, 2018 17:41:30 GMT -5 pj said:

If this is a single transistor boost as it looks (such as ehx lpb1, various treble boosts) im afraid they are noisy little beasts. Aside from the issues of the transistor component itself, theres high output impedance (usually a large part of which is the noisy carbon pot track) and a fair deal of noise from the top resistor in the bias divider on the input getting amplified by the transistor. Plus they're usually running full tilt and the boost pot is just attenuating the output which doesn't help on the noise floor front of all of the above

On the other hand the tonal effect of these boosts is loved for good reason, they soften our peaks by virtue of lowish input impedance, roll off highs and often add pleasing even order harmonics as theyre generally class A arrangements that are clipping away softly and happily all the time.

If your other boosts have been micro amp alike types with opamps and negative feedback gain control it would explain why this comes across the ugly duckling. The question is... Is it worth the tonal benefits?

Lots of good points in your post, pj

Impossible to say for certain because we don't have a schematic, but IF there is DC across any pot in the signal chain, that tends to be a likely place for noise to occur.  Poor wiper to element contact adds a bit of noise to an AC signal referenced to ground.  It creates a huge amount of noise if there's DC across the element.

[newey]

Kurdt-

Do you know the make/model of this item? A schematic may exist a'web, but you've only described it generally.