Self built effect not working if plugged in after another pedal. Any ideas?

[iandy4]

Hi Guys,

I noticed a problem that some of my opamp based pedal designs suffer from.  The problem is with a few different blending circuits I have built and the problem is consistent.  In both of my pedal designs which suffer from this problem, the designs are basically a buffer to split the signal between an effects loop in parallel with the clean signal which then gets combined (all stages opamp based).  If I have everything plugged in (echo effect plugged into the effects loop and guitar and amp plugged respectively into my circuit) and then turn on the power to the echo effect first and then my blend circuit I get no sound.  However if I plug my blend circuit in first then the echo effect everything is fine.  If any one knows:

1)why this happens
2)how to solve this

I would really appreciate it.  Especially because the circuit I just built is the first one I did completely in my head before building and it worked flawlessly except for this one issue.  If necessary I can draw up a schematic and post it.  The fact that it happened in two similar designs leads me to believe that it must be a problem that I just haven't heard of yet.  

[Galego]

It would definitely help if you posted the schematic...

[iandy4]

 


If you guys see anything odd or that should be added please let me know.  I was thinking it probably should have pull down resistors but i haven't done enough research to know if adding 1M R's to ground at the in, send, return, and out was the right way to do it.  The opamps used are 072's and the power supply used is this one: http://www.generalguitargadgets.com/pdf/ggg_bipolar_ps.pdf  I think I remember R.G. mentioning that the coupling caps aren't really necessary in a design like this were I used a bipolar power supply but that it's good practice to include them anyways.

[R.G.]

How is your bipolar supply related to the power supplies of the other pedals? Do they share any connections at all except for signal and signal ground?

[iandy4]

How is your bipolar supply related to the power supplies of the other pedals? Do they share any connections at all except for signal and signal ground?

I basically built the GGG power supply from the link above as a separate unit and plug it in to power my various opamp based circuits.  I am using the same power supply for all of my opamp based projects that are still in the breadboard stage.  I didn't quite understand your question but if you are asking if this circuit shares any power connections with another circuit, then no.  The way I have it, the power supply schematic on GGG's website goes directly to the + and - pins of the opamps in this ciruit and this circuits ground.  Hope that was clear.

[iandy4]

oooh and I just remembered that the diodes I used were 1N4007's rather than 4004's as the GGG power supply circuit shows.  I also recall that the power supplies positive and negative sides were slightly unbalanced in respect to ground, something like 5.1vdc and -4.9vdc if I remember correctly.  If you think it may help I'd be glad to poke around with the multimeter.

[iandy4]

I don't know if it matters but the echo effect I am using in the fx loop of my circuit is the re-20 space echo

[ayayay!]

I don't know if it matters but the echo effect I am using in the fx loop of my circuit is the re-20 space echo

It does!  That's probably it.  How much amperage does the GGG supply provide?  100mA, 150mA, 200mA?  The RE-20 pull 75mA.  Add up all your pedals/circuits and see what it comes to. 

[R.G.]

Hmm. I thought you didn't power the other effects from the same power.

[iandy4]

No they are separate power supplies so I can't imagine how it could be a lack of power.  But that point brought up a question that I am now trying to figure out: how to measure current consumption for a circuit powered from a bipolar power supply.  Do you test the positive side and negative separately and add the amperage readings?.  The strange thing is that it seems to be working ok now   although I've had the same problem happen a few times with this one and with the other blend pedal I built so I'm sure it's lurking in there.  I'm wondering if it's not doing it because I didn't discharge the caps in the GGG power supply for my blend pedal the first time that I intentionally tried to make the problem happen.  Unfortunately I have to get ready to teach my guitar students tomorrow so I can't take a good look at it tonight but the first chance I get I'll try and make the problem happen and then take some voltage readings and report my findings.  Thanks for the help guys and I hope you stay tuned!