Built in reverb pedal in parallel loop with phase switch

[elno]

I am building an amp for a local guitarist who wants to have a Reverb Pedal as his on board Reverb, so he can change pedals if he desires.
He wants to have a Reverb Knob on the control panel, like a conventional amp.

I have come up with an idea (schematic attached), using a combination of a couple of circuits from Merlin that I think may work.
I want to be able to invert the phase of the Dry path, to accommodate pedals that invert the signal and also those that don't.
I haven't included values for all the resistors and caps, because that may take some experimentation; suggestions welcome.

I would appreciate your comments and suggestions, on this cct., or if there is a better way.

Cheers, Noel.

 

[Bill Coltrane]

You don't need a phase switch at all, if the reverb pedal can be set 100% wet. All reverb pedals I have encountered can do this.

Just a parallel signal path and a volume knob is enough.

 

[PRR]

Reverb has no phase. (The time delay is a spread around values much longer than the period of most audio.) Your polarity switch may "do something", but this isn't like no-delay mixes which can null-out completely.

"Usually" the dry signal is fixed level and the reverb adds to that. Another plan is the reverb lightly loads the dry signal so dry drops a few dB when wet is at max.

 

[elno]

Thanks Bill and PRR for your interest and input.
You are both quite correct, obviously.
Reverb has no phase as such.

That said; I had another client with a reverb pedal that sounded better with the phase inverted, when in a parallel loop (he used a stand alone SS phase inverter, placed after the Reverb pedal). Maybe there were other issues with that pedal ??

I should have mentioned that the phase inverter switch was not particularly for the Reverb. He asked if he could have a selectable inverter, to cater for possible phase problems with any other effects that he may want to put in the loop.

This is not something I have done before, because I prefer a series effects loop, so incorporating phase inversion, in a loop, is foreign to me.

In your opinion; Is this cct. suitable for the purpose?

Noel

 

[jjman]

If/when a reverb pedal is switched off, it may pass dry signal. My boss delay passes dry thru the wet-only out when switched off. A pedal that flips the phase should come with a giant warning sticker on it.

 

[elno]

Further investigation of phase flip

After the replies to my loop query; I decided to check reverb pedals, before committing to the parallel loop in this build, to see whether there was any phase inversion (in any of the ones I gathered from a few blokes) and whether or not, it caused any issues.
I wired up a parallel loop on the bench and fed a 400Hz sine through it and scoped the output. Three pedals showed variations in output when rotating the Loop Mix control, but nothing to consider a problem.
Yesterday I checked the pedal that I mentioned in post #4; a Biyang "Tri Reverb", which is a nice sounding Reverb and is favoured by a few guitarists I know.
This pedal has a serious phase inversion problem and when the Parallel Loop Mix is around the mid position, the signal sums to very little (almost zero).
Inverting the output, or the input of the pedal restores normal behaviour.
I expect, there are other pedals, apart from reverb that may cause the same parallel loop problems.
This is why I wanted to have a built-in phase inverter cct., in the Loop.

Regardless of which brand, or type of pedal is used in the parallel loop; do any of you clever blokes have any comments about this loop cct. and whether it will do the job OK. Any suggestions on component values are very welcome also.

Noel.

 

[thoglette]

Regardless of which brand, or type of pedal is used in the parallel loop; do any of you clever blokes have any comments about this loop cct. and whether it will do the job OK. Any suggestions on component values are very welcome also.

You're going to have to add some gain to the return of the reverb leg.

The wet/dry mix is a bit unusual. It's more normal to use use a gridstopper as a mixer being fed from a pot on the reverb output.

Is your customer allergic to transistors/opamps? If not there's easier ways to skin this cat than using a whole valve (and heater) to invert, drive and recover the reverb.

Have a look at Ampeg G15, Fender Champ 12, Marshall AVT20 and any other number of vintage/modern reverb feed/regen circuits.

The simple way to do polarity inversion on low-level signals is a 10k:10k transformer. In fact, if you return the reverb into a transformer (CT earthed) and put your mix pot across the output you'd get mix and inversion all in the one pot.