Question regarding BYOC pedals

[Suhnton]

Hi everybody, I'm fairly new here, this is a great site with lots of info.
I was hoping someone could offer some advice/solution to a problem I'm having with a couple of clone pedals I built recently. In the past few months I've built:

1 Tube Screamer with Keeley and Jack Orman mods
2 Tremulus Lune tremolo
3 Red Llama
4 Green Ringer
5 Big Muff (Triangle Version)

I installed a 9V adapter plug in all all them, as in keeping with my miserly nature, I didn't want to keep forking out for replacement batteries. However, therein lies the problem. The Screamer, Red Llama and Tremulus all work fine on an adapter, however, the Green Ringer and Big Muff are very noisy when an adapter is used. I checked the pedals numerous times nothing has been left ungrounded. I'm wondering if the fact that the Ringer and Muff use discrete components rather than opamps (as the other 3 do) has anything to do with it.

I was hoping to hear from anyone who has experienced this problem, and if so, what steps were taken to resolve it. Thanks in advance.

[Mark Hammer]

First, I think you need to specify what sort of noise we are talking about: hiss/hash or hum? makes a difference when it comes to troubleshooting.

The Ringer and the Muff should not be any noisier using an adaptor than any of the others noted. Are they noisy with a battery only? If the noise in question only results when using an adaptor, then that would point to insufficient regulation on either the circuit board, the adaptor itself, or both.

The Screamer and the Llama both provide a fair amount of gain, so you would expect some hiss to be audible, though these two pedals seem to be pretty good when it comes to hiss-type noise. It,s not a question of chip vs discrete. The Muff and Ringer simply do not take such great pains to tame any hiss. So, perhaps that's the issue.

But again, you need to be more specific about what sort of noise it is.

[Suhnton]

First of all, thanks Mark for your response. I seem to recall seeing your name over at the Tonepad site, which is where I got the schematics for the FX I built.

The noise I'm referring to appears to be power supply hum, as it's only present when an adapter is used. On battery, they don't produce any hum. I have tried two adapters with the same result.

I built all of the FX point-to-point on perfboard. I did my own layouts, except for the Muff, which I copied the layout on the Tonepad site. I used the same component values as those specified, so was thinking that if there was insufficient regulation on the board, other builders would have mentioned it. I read some of the build comments, but couldn't see anything related to my problem. If I can, I'll take a photo of the internals of the Muff and post it up later.

Once again, thanks for your time.

[Mark Hammer]

Fortunately, that is the easiest sort of noise to overcome.

Think of hum as being a kind of hiss, albeit the sort of hiss that only seismologists would consider noisy. How do you get rid of hiss? You turn down the treble. How do you get rid of ultra-low frequency "hiss" in the power? You apply a treble-cut filter to the power source.

Most well-designed effects will have a medium-to-large (10uf-220uf) capacitor from the point where the power hits the board, to ground. While the tone control cap on your guitar is a considerably smaller value (.02uf, typically), it works in exactly the same way. That is, it bleeds frequencies higher than some value to ground so they no longer form part of the output.

Normally, that is accomplished by the adaptor, though they vary widely in how well they take care of it. Some do a remarkable job, and some do a slapdash job, and assume there'll be some additional caps on the circuits you power with the adaptor that will finish the job. It would seem your adaptor is somewhere between the excellent and ho-hum zones.

This leaves several possibilities for improving the situation. One is to attack it at the level of the effects themselves. A second is to address it at the adaptor. Of course, the third option remains to address it at both levels since you might find yourself using a different adaptor at some point in the future.

Both the Green Ringer and Big Muff show a 100uf cap to ground from the +9v supply. Increase that cap to 220uf and it should go a long way towards reducing the audible hum. It will have no audible effect on the quality of the effect, largely because it is an extension of the power supply, in many respects, rather than a component of the effect. Think of it like the adaptor's "ambassador".

The reason why the effects do not produce the hum when using batteries is because batteries do not convert AC into DC, so there is no 60hz component at any point. A high quality adaptor will remove the 60hz component enough that it behaves like a battery.

To make the adaptor itself more capable of delivering hum-free performance from other pedals you might make that have insufficient power filtering, you can simply get yourself a little plastic box and install a couple of jacks in it. One is to plug the adaptor into, and the others are for running power cables to your pedals. They can all be wired in parallel. This is no different than using a daisy-chain cable. The difference is that inside the little box, you're going to stick a 1000uf cap between V+ and ground, so that the extra filtering is applied to everything. I find it is also a good idea to wire up an LED and a 3k3 fixed resistor, exactly as you would wire up a status LED on a pedal, so that you can see that the power is actually on.

[Suhnton]

The power filter unit sounds like an excellent idea. I'll definitely make one of those. The other thing is that the Muff schematic I got from Tonepad doesn't show the 100uF filter cap (the GGG schem does), so I didn't install one. That's probably a major contributing factor right there. I'll do as you suggest and increase the cap values to 220uF. Once again, thanks for taking the time to answer my questions, I really appreciate all of your help.

[Mark Hammer]

You're welcome. I suspect that anyone listening to you play that Muff at 100db will probably appreciate it too!