True bypass tone suck and leak?

[Ben79]

The Rangemaster I built into a sweet tin that's in the finished projects thread -http://ilovefuzz.com/viewtopic.php?f=151&t=3277&start=4245 I realised it was sucking tone when bypassed. I also noticed that the volume pot added noise when it should be bypassed.

I thought perhaps the footswitch lugs were touching something so I tried it with the lid off - same problem.

So I took the battery out to see if it was some kind of power interference (I don't know much about electronics). The added noise got better but the tone suck was still there.

It's normal DPDT true bypass and I've looked over the circuit and can't find anything wrong.

Any ideas?

[KaosCill8r]

I don't really think any switch gives you true bypass. I have some true bypass pedals that leak oscillation through my chain when bypassed.

[Dr Satan]

I don't really think any switch gives you true bypass. I have some true bypass pedals that leak oscillation through my chain when bypassed.

It's more likely that the true bypass wiring on those particular pedals doesn't ground the input and/or output when bypassed. There is more than one way to wire something to be true bypass, and some ways are better than others.

Which begs the question of what method of true bypass wiring did Ben79 use? One of my first builds was a Fuzz Face and Muff Fuzz circuit slapped together and it produces some high gain fuzz, so much so that the bypass method I originally used was not good enough to keep oscillation noise from coming through on bypass. A simple rewiring of the switch to have input grounding solved the problem for me.

[Ben79]

Thanks Doc. I used this, as I always have without issue. That would explain the noise but I still don't understand how it could suck tone.

[Dr Satan]

Yeah the tone suckage is a hard one to pin down sometimes. Could be a cold solder joint or maybe the switch itself. Maybe even a bad cable. I've had that happen more than once. Build or mod a pedal and then something acts wonky so I pull the pedal and scour it with a fine tooth comb only to find out that it's a patch cord further up or down the chain that shit the bed. I don't know if some sort of parasitic loss could occur from not grounding the input on bypass or not. I wouldn't think so, but I really don't know.

[Ben79]

I'll reflow all the joints passed through on bypass and see what happens.

Thanks again.

[facelessfx]

Try rewiring your switch like this:



Like Dr Satan said, it could be caused by the circuit input not being grounded when bypassed. The above switching will fix that.

[Ben79]

OK, 3 years later, I've built another one of these and had exactly the same problem! Bad tonesuck when bypassed using the simple true bypass DPDT method.

I remembered this thread so I rewired the DPDT à la above from FacelessFX and....the pedal now doesn't work properly. Passes signal in both bypass and engaged but now in both it is muffled and if turned up when engaged it starts to oscillate.

Checked it many many times and I'm sure the footswitch is wired correctly as above.

What's really odd is there's always continuity between pedal input and output when I measure with the DMM but I can't see why.

Could it be something to do with the circuit design itself.....?



I mocked the circuit up on breadboard before soldering it together using all the same components and it sounded great so I know they're good. It also sounded fine when the footswitch was wired up originally so I'm sure my circuit build is good.

I'm perplexed.

[crochambeau]

Are you using a battery of a power jack?

DC resistance should not show a low impedance from signal in to signal out when the pedal is engaged.

[BetterOffShred]

You're doing this positive ground right? Not sure if you have something somewhere "grounded" to 0v instead of 9v... ? Just wondering.

[Ben79]

Yeah positive ground and I checked the continuity of 'pedal in' to 'out' with the battery out and no cables plugged in. Battery is wired in with - to circuit, + to ground (when input plugged in).

Both my electros are + to ground and there's just one ground connection on the circuit which tests good.

Only mods I've made are a spst to switch in a bigger input cap in parallel with the 0.005 for full range boost and I didn't have a 10ka so I used a 20ka with a 10k across it (should be a 20k to get 10k I know but it works fine).

I'm wondering if it's the footswitch.

[Ben79]

....it was the footswitch.



Thanks anyway guys.

[BetterOffShred]