Parallel effects loop, feedback amp

[Bob-I]

Structo asked about my parallel loop in the clip thread. Instead of burying it in there, here's the loop.

Instead of using a D-ulator and changing to parallel mode, which I wasn't really all that impressed with, I built it based on a feedback amp for recovery. Aiken has a good article that I used in designing this http://aikenamps.com/FeedbackAmp.htm scroll about 1/2 way down and there's a 2 input summing amp schem.

The only thing missing from this schem is that I added a 1MA pot as a master volume at the output. It helps me to adjust stage levels.

[Structo]

Thanks Bob.

I have been working on a parallel loop myself.
I used the schematic provided by Bluesman.

The problem I was having was the mixing of the wet and dry and also I seem to have less volume when my delay is on.
When I turn that off I get more volume.

Right now I have the delay and a Boss RV-5 reverb pedal in the loop.
The delay is first.

How are you able to adjust the dry/ wet mix?

How is the balance between effects on or off?

[Bob-I]

Thanks Bob.

I have been working on a parallel loop myself.
I used the schematic provided by Bluesman.

The problem I was having was the mixing of the wet and dry and also I seem to have less volume when my delay is on.
When I turn that off I get more volume.

You must have the effect device on full wet, no dry signal at all. Since the recovery amp is inverting you'll end up with phase canceling.

Right now I have the delay and a Boss RV-5 reverb pedal in the loop.
The delay is first.

One of the problems with pedals is they're not line level devices. You can get away with them if you keep the drive low.

How are you able to adjust the dry/ wet mix?

The return level, since the effect is on 100% wet the return level adjusts the mix.

How is the balance between effects on or off?

No change at all. Again effect 100% wet, otherwise the phase cancalation lowers the volume and kills the tone.

[Structo]

Well I tried several variations of the parallel loop and I ended up reverting back to the traditional serial loop.

I can see where the parallel loop could work good but with reverb and delay, the two didn't play very nice together on the parallel side of things.

My delay has a blend knob so I can adjust the wet/ dry thing there.

So when I had the delay fully wet, it made the reverb sound really bad.
And when the delay wasn't on, the reverb was too low.

It also sounds better tonally in series to me, at least with my setup.

Truth be told, I probably didn't do it correctly all the way through as I would have had to basically start over and didn't feel motivated enough to do it.
Maybe someday I'll make another one and try it.

[Bob-I]

Yea, a parallel loop doesn't work well with more than one device in the loop. I use the Quadraverb because I can add reverb and delay in the same device, the overall mix is 100% wet but the reverb and delay levels are set individually.

A serial loop is a better choice for multiple devices.

[bluesfendermanblues]

Yea, a parallel loop doesn't work well with more than one device in the loop. I use the Quadraverb because I can add reverb and delay in the same device, the overall mix is 100% wet but the reverb and delay levels are set individually.

A serial loop is a better choice for multiple devices.

Or add further effects in parallel....like in Fuchs amps and Verbrator pedal, where reverb is added in parallel to/in the effects loop.

Don't know how he does it, though

[Bob-I]

Yea, a parallel loop doesn't work well with more than one device in the loop. I use the Quadraverb because I can add reverb and delay in the same device, the overall mix is 100% wet but the reverb and delay levels are set individually.

A serial loop is a better choice for multiple devices.

Or add further effects in parallel....like in Fuchs amps and Verbrator pedal, where reverb is added in parallel to/in the effects loop.

Don't know how he does it, though

I don't see why you couldn't add a 3rd link in the chain. The CF shold be able to drive 2 devices and a dry, the recovery amp can mix more than 2 inputs but you may need to tweak it for more gain, my design is 0 gain, just a mixer.

[Structo]

Bob what is the scale of that drawing?

Even if I reduce it in my browser by 50% it is still huge!

I will have to revisit this again sometime in the future.

[Bob-I]

Bob what is the scale of that drawing?

Even if I reduce it in my browser by 50% it is still huge!

I will have to revisit this again sometime in the future.

It's bout YO big...

I export it for max resolution so you can download it and scale for young or old eyes.

[bluesfendermanblues]

I don't see why you couldn't add a 3rd link in the chain. The CF shold be able to drive 2 devices and a dry, the recovery amp can mix more than 2 inputs but you may need to tweak it for more gain, my design is 0 gain, just a mixer.

You're right, I read the Aiken article and its just a matter of adding the return of further effects to the "virtual grond" at the input grid on pin 7.

I don't want to drill holes for more jacks, so I guess one could make a cable with 2 send jacks and 2 return jacks.

[dogears]

I dicked for years with the virtual ground parallel loop that Fuchs uses in all his amps. It is a nice versatile solution. However, after hundreds of hours tweaking and recording, I came away greatly preferring the standard series design. If you want parallel, a tube or opamp mixer sounds way better for me.

My Dumbleators with the Suhr MiniMix are parallel and have none of the low end texture issues I find in virtual ground loops (due to the extreme negative feedback that sets parity gain).

You could make a stereo dumbleator and use the second gain stage as a parallel mixer. Way way better me thinks....

[bluesfendermanblues]

My Dumbleators with the Suhr MiniMix are parallel and have none of the low end texture issues I find in virtual ground loops (due to the extreme negative feedback that sets parity gain).

Ok, I read about in on Suhrs webpage, isnt he using virtual ground, only with IC in a small box?

You could make a stereo dumbleator and use the second gain stage as a parallel mixer.

How would you sum the signal?? Did you mean using the attached schematic?

[Bob-I]

My Dumbleators with the Suhr MiniMix are parallel and have none of the low end texture issues I find in virtual ground loops (due to the extreme negative feedback that sets parity gain).

Ok, I read about in on Suhrs webpage, isnt he using virtual ground, only with IC in a small box?

You could make a stereo dumbleator and use the second gain stage as a parallel mixer.

How would you sum the signal?? Did you mean using the attached schematic?

Interesting thoughts.

As for summing the signal, there's an unused triode in that schematic, you could use it just like I used the summing amp on the first schem.

[dogears]

I am not sure what John does, but the Mini Mix is not the effects loop. It only mixes the dry and wet. There is no gain. I can only say that it sounds far superior to my ears than the effect loops like the London Power design using the virtual ground.

As for the stereo Dumbleator idea, one could use the unused half 12ax7 to mix the effects and dry....

My Dumbleators with the Suhr MiniMix are parallel and have none of the low end texture issues I find in virtual ground loops (due to the extreme negative feedback that sets parity gain).

Ok, I read about in on Suhrs webpage, isnt he using virtual ground, only with IC in a small box?

You could make a stereo dumbleator and use the second gain stage as a parallel mixer.

How would you sum the signal?? Did you mean using the attached schematic?

[talbany]

FWIW..
I am working on a Dumbleator 2 Layout..Waiting on some more info..Should be out hopefully in a week or so..

Tony