Why do none of my DIY Pedals work with my amp But work with "Some" other amps???

[Minion]

Hi, I have built maybe 8 or 10 pedals that are on this site and on tone pad and most every one of them doesn"t work with my SS amp but work with some other amps (Mostly tube amps)...The pedals actually work but as soon as I stop playing the curcuits seems to Oscilate Madly......

I think it may have to do with the fact that my amp uses a Dual Rail supply with the Input refranced to ground (0V) were most of the pedal curcuits have the Input referanced to half supply Voltage (4.5v).....If I use the Pedals on a single Rail powered amp the Pedals work fine but my Good amp uses a Dual polarity supply and none of the pedals work properly with it.....

I tested this theory by changeing a couple pedals to work off of a dual rail supply with the Input referanced to 0v and they work with my amp.....I also have a cheapo Danelectro pedal that also oscilates with my amp but doesn"t on my Garnet Tube amp.....

Is there any Validity to this theory???


Cheers

[soulsonic]

I wouldn't think that sort of thing would make a difference since everything doesn't share the same global supply. It may have something to do with the construction and layout of the pedals themselves, or possibly the amp. What kind of amp is it?

[John Lyons]

I think there must be something else going on. No reason that your effects would osciltate if your amp is run on a dual rail suppy (that I can think of) Maybe an impedance issue but oscialtion...?
What SS amp is it?

John

[Paul Perry (Frostwave)]

Earthing problem? (maybe with some amps, the wiring is such that you complete the ground connection another way).

[R.G.]

Hi, I have built maybe 8 or 10 pedals that are on this site and on tone pad and most every one of them doesn"t work with my SS amp but work with some other amps (Mostly tube amps)...The pedals actually work but as soon as I stop playing the curcuits seems to Oscilate Madly......

What leads you to believe that it's the pedals that have a problem? With that many pedals "voting" for the other amps and against your amp, I'd guess that it's the amp that has an issue, and likely the amp that is oscillating.

I'm with the "dual rail doesn't matter" camp. I think you have an issue with the input of your amp.

Is the amp direct coupled at the input? A lot of hifi amps are, and if you have a converted or self-made hifi amp, it may be as well. If it is, put a DC blocking cap and a pull-down resistor in front of it. 10uF non polar and 1M should do.

Try that and tell us what happens. It may be that it oscillates all the time with that in front of it; in that case, your amp needs some fixing on the input to be stable with a non-DC input load.

[foxfire]

were the other amps that you tried plugged into the same outlet that your good amp were plugged into? i can't crank my amp or use a distortion pedal at volume on any amp at my shop. my amps don't like the electricity at my shop. they start to scream the second i stop playing.

[John Lyons]

Time to go buy an AC outlet tester! $7 ish and it will tell you if the outlets are wired correctly. Nice thing to know when strange things happen...or before they do and you fry yourself or an amp! They are simple to use and it's a nice tool for the gig bag.

John

[Minion]

Well My Main amp is an amp I designed and Built myself from scratch....It uses a LM3886 Power amp IC and has 3 overdrive stages that can be enabled or disabled and has a Bandaxals tone stack for tone controlls....There is a 4,7Uf Film DC Blocking cap right between the Pre and Power amp stage and the amp is extremely stable even with all 3 Overdrive stages enabled (but it sounds a Little over the Top)....

I have been doing DIY electronics for a number of years so I am not a newbie and I am a fairly competant builder, I have built several Guitar and bass amps,Mic Preamps,Powered Monitors,Headphone Drivers and many other things but the Single Suply Pedals don"t seem to work with this amp.....

I have built the Jfet-Vulcan,Moferatu Overdrive ,Mig Muff, Orange squeezer, fetzer Drive ,Octive up,Chaos, Dr Boogie,Mos Face ,Metal Simplex,Pepper Mill ,Supa sustain,Sonic distortion,X-Fet,DOD-YJM,Rat, and a few others I can"t think of right now and out of all these Pedals none of them work accept for the ones I can convert to a Dual supply......

Out of the Pedals that I have designed most all of them work but I use dual supplies with them.....Last night out of frustration I designed a simple Opamp based one with a Fet buffer output stage simular to the Rat, with one Inverting opamp driveing the Next Opamp that has Clipping diodes in the Feedback Loop....It has a Single Knob that controlls the Volume and distortion at the same time (Just a pot between the Opamp stages) and no Caps in the Signal Path accept in the feedback loop......

I"ll probably try it tonight and so if I can get it working.......



Cheers

[R.G.]

OK. It's hard to tell how much experience someone has. Sorry if I shot too low. I'll give you the "experienced builder" version.

No, there is no validity to the theory that dual rail and single rail units can be a cause for oscillation as long as both units are properly constructed and connected. That "as long as" includes things like the power to all units being independent and properly wired.

A correctly constructed effect has an output signal that is an AC signal riding over a ground wire. There should be no DC on the output. That is what the final output cap is for, to remove any DC from the output signal. A correctly constructed effect will have an output impedance from very low, perhaps 100 ohms or so, up to about 125K.

A properly working amp will take in an AC signal and work fine with it. Some marginal amps will oscillate when their inputs are open. Some high gain amps, perhaps like yours with multiple overdrive stages, have so much gain that input grounding is CRITICAL and any kind of sloppy grounding can introduce noise, hum or oscillation.

The effects are not the problem, given that they work as intended with other amps. There is likely a grounding issue inside your amp that needs resolved. I suggest that you isolate the input jack from the chassis and carry the input ground wire along with the signal wire to the place where the input is fed.

What is the grounding scheme in your amp like?