Tonepad Ross Compressor - problem with noise from One Spot - help !

[glweid]

Hi,

I'm new to the forum and just built the Ross Compressor from TonePad with the Hamer mods. It sounds great with a battery, no noise at all but when I plug in a One Spot I get noise so I'm wondering if there is any way to get rid of it and I get no noise from my other pedals. Any possibilites an a simple mod to the +9v supply on the board that may get rid of it ? The One Spot is a switching supply so maybe this circuit needs a transformer supply.

Any help is appreciated !

[Mark Hammer]

There is a 10uf cap, shown at the far right of the Tonepad schematic, and shown in the upper right hand corner of the Tonepad layout.  This is intended to smooth out power fluctuations.  If you have room, try replacing it with a 100uf unit.  That might help out.

Keep in mind that the earliest MXR pedals had no external power jacks, and that switching wallwarts are a fairly recent invention.  Consequently, I would not expect the basic Dynacomp/Ross design to fully anticipate the quirks that might occur with contemporary switching supplies.

Certainly let us know if the problem is reduced or eliminated by a bigger supply cap.  I imagine thatmore and more folks are converting to the more efficient and convenient switching-type wallwart, especially as pedalboards get more and more cluttered.

Incidentally, I also managed to get line noise when powering more than one Tone Core pedal from the same switching adaptor the other day (disappears if I power each pedal separately).  Seems to depend on the location, though.

[glweid]

Mark,

Thanks much for the input, I will try a 100 uf instead of the 10uf and post the results within a few days.

Your mods really helped  - it sounds awesome ! Now if I can just get it to fit in the box !!

Thx
Gary Weideman

[Mark Hammer]

As far as I know, I've only "contributed" one mod to that unit, and that was simply transplanting what Boss and Nobels and Pearl had already done on their very similar units, but doing it with a toggle instead of a pot.  Everything else came from other people.  Glad it helps to make the unit more usable, though.

[A.S.P.]

sometimes, with switching power supplies, smaller caps are more helpful... (ESR)
often a series-resistor adds to the helpfulness.

[Mark Hammer]

Thanks.  Useful info.

[bwanasonic]

If the noise you are getting is hiss, try a series resistor, as illustrated here.

Kerry M

[R.G.]

It's also worth trying putting a resistor in parallel with the pedal - about 100 ohms.

[A.S.P.]

"dummy-load"?

[R.G.]

Yep. Switchers get funny about almost-zero load, so that's a good way to test the hypothesis.

[Processaurus]

sometimes, with switching power supplies, smaller caps are more helpful... (ESR)
often a series-resistor adds to the helpfulness.

I've seen a small >.1uF film cap in parallel with the main big electrolytic filtering cap in some power supplies in app notes, where there is a possibility of high frequency stuff in the power lines, like digital circuits.  Apparently electrolytics don't catch the really high frequencies.

[glweid]

Well I tried a 100 uf instead of the 10 uf, it didn't seem make any difference so went to a 1uf but that seemed to make it al little worse. Thus I went back to the 10uf.

I added the series 100 ohm resistor on the +9v power line and that helped a bit.

I did not try a resistor in parallel but at this point it sounds pretty good. If I get more time to play with and find that the parallel resistor helps I'll post it to the board.

Thanks for all of the input !