grounding problem

[midgardtoneworks]

I built 2 guitar synth boards to run parallel, but have noticed sound leaking over the ground. The chain goes as such: guitar->splitter->synth1->amp1 and guitar->splitter->synth2-amp2 and amp2 picks up sound from synth1. Also amp1 picks up sound from synth2. I figured that it was traveling through the daisy chains ground, so I added a 100ohm resistor to the vcc and a 220uf cap from the circuit side of the resistor to ground. This is actually having a filtering effect on the output somehow, which really sounds terrible. Is there a way to deal with this phenomenon without drastically changing the sound of the pedals that I really like at this point? If needed I can post a picture of the schematic, but it is mostly a john Hollis crash sync with a few changes and a flip flop octave down circuit.

[crochambeau]

Have you tried separate power supplies for the synths?

[eatyourguitar]

It is usually a bad idea to run two amps without ground being isolated by a transformer on one of the amps. Lehle has a solid splitter but I would suspect you cross talk is coupled to your power supply first and formost.

[midgardtoneworks]

Have you tried separate power supplies for the synths?

I was trying to not go that route, but I think I may have to build an isolated power supply for these guys. I tried all kinds of mass decoupling with capacitors today and all I have to show for it now are a bunch soldering iron burns and a few less strands of hair. I'm going to try two dedicated power supplies for now until I get around to putting together a full time solution. What a headache.

It is usually a bad idea to run two amps without ground being isolated by a transformer on one of the amps. Lehle has a solid splitter but I would suspect you cross talk is coupled to your power supply first and formost.

I am pretty sure I traced the problem to one of the feedback loops I added(though turning it off with a switch only partially solves the problem), which as a noise guy I also view as necessary.

[crochambeau]

I almost PM'd you elsewhere on it, but public resolution on a bb is more beneficial. WELCOME, by the way, nice to see you here.

If it is a floating common or ground loop issue, I don't know if different power supplies will resolve it. If it is crosstalk through the voltage rails, obviously different rails will kill that bridge. The fact that your audio quality suffers when you employ a simple low pass filter (stop holding the iron in your teeth while soldering, BTW ) sounds like your signal path is getting a little cozy with the rails on a high impedance output, being able to chew on a schematic might be very helpful at this point.

If you can grab a transformer and lift one leg (as eatyourguitar suggests) I would think that will either resolve it or rule out ground loop as the problem. It doesn't smell like a ground loop from here, but someone has been eating hard boiled eggs, so I'm not 100% sure about my sniffer at this point.

[eatyourguitar]

this is why balanced signals kick ass. no common mode noise. no ground loops. you can just detach the ground and shield on one end of a balanced cable. adding bypass caps to your power is pointless without the resistor to make a real RC low pass

[midgardtoneworks]

So, I've actually made some progress here using the daisy chained power supply. I have isolated some of the crosstalk to my aby splitter, but some of it still appears to be crosstalk over the power supply. For testing purposes I started running each of the pedals into a mixer now, then out to the same amp. With the built in feedback loop engaged I get a lot of crosstalk, if I place a 10uf electrolytic filter cap in the feedback loop, much of the crosstalk is killed(not all), but as would be expected, this drastically changes the character of the sound(just wanted to experiment with that idea). Removing the feedback loop eliminates this crosstalk when plugged into the amps, but now some is still present when each is going into the mixer(I tested by muting the channel for the pedal that was on, turned the other off, but still got sound corresponding to to the muted channel). I will try to get a readable and fully accurate schematic up this weekend as I think that may be helpful at this point. Also of note, I removed the 220uf caps and 100Ohm resistors configured as a low pass filter from the power supplies for each pedal now as it just wasn't getting me the sound I want. I think adding another stomp switch for the feedback loop and accepting some crosstalk when it is engaged could be satisfactory for me, but I'd prefer a more elegant solution. Thanks for all the ideas guys.

[eatyourguitar]

you need a charge pump on each pedal then it would be fine to use the feedback mode since there will not be crosstalk through the power even on a daisy chain. you don't need to RC low pass if you charge pump. you can also use shielded cable in the enclosure and wire the footswitch for grounded input AND grounded output during bypass. that way the bypass is dead silent always, no matter if the pedal is a high gain triple rectifier clone.

[midgardtoneworks]

Right now, input and output are grounded, but I didn't shield any cabling. I'll take a look at the lead dress and see if I can track down a culprit that would require shielding, but I've been over that aspect a few times now. By charge pump, do you mean a string of diode, capacitor networks, do you know of a pedal with a readily available schematic that I can reference for implementation?

[eatyourguitar]

here is an example of a schematic it takes 0v/+9v and converts it to 0v/-9v. what you are looking for is a bit different. you want 0v/+9v converted to 0v/+9v. I know this sounds like nothing is converted but what is actually happening is that you are creating a local isolated supply.

http://www.guitarpcb.com/pdf%20files/pu ... 20face.pdf

here is an all purpose charge pump PCB from madbean this might be closer to what you are looking for.

http://www.madbeanpedals.com/projects/R ... e_2015.pdf

EDIT: still not exactly it. look around for a DC to DC converter. I don't have time to sort the details. mouser has them. find one you like and build the schematic on the datasheet. you need +9v to +9v isolated.

[eatyourguitar]

I found something but it is expensive

http://www.mouser.com/ProductDetail/REC ... /RN-0909S/

you might have better luck with a 555 NOT low power 555

[crochambeau]

I found something but it is expensive

http://www.mouser.com/ProductDetail/REC ... /RN-0909S/

you might have better luck with a 555 NOT low power 555

That looks like a cool module, no external components.

They have some slightly cheaper ones that step up to 9 volts, could stick a voltage divider on the input maybe?

[multi_s]

if you really want the supply to be isolated you could do it with a 555, a power transistor, a small transformer, and a linear regulator, all parts you may already have?

DC-DC converters can be made thinking of them as DC-AC-DC converters, use teh 555 to create an AC wave, drive it through a transformer to step it up a bit, take the AC off the secondary and rectify it, filter it, then regulate it. the grounds are isolated between the 2 circuits now and you can get whatever voltage you want by getting the appropriate transformer winding ratio, all from 9v dc in...

alternatively if you want to play with inexpensive smps style converters MC34063 is sort of the "classic" ic, they are less than 1 dollar each and you can find component calculators online, it is so famous like that. the grounds may not be isolated though, similar to the projects eyg posted, i don;t know if i would call them isolated. But you could step up, then re regulate, it's not technically isolated imho but it will make the output less susceptible to noisy supply.

[crochambeau]

Last I heard from Midgard, he was traversing Donner Pass...



...at least it's the right time of year for it.

I've always reached for decoupling on the power rail when it seems like circuits are tugging on each other, given a solid and unified ground. Re-rectifying a rail is about as fool-proof a method as I can imagine, but that's coming from someone with a peanut for a brain (me, in case anyone is hell bent on mis-reading my wording, it IS an election year) so YMMV.