Parallel loop - for ampgarage users only - ENGL-inspired ver

[bluesfendermanblues]

Here's an updated version of the parallel loop concept.
http://ampgarage.com/forum/viewtopic.php?t=10477

The 'old' version was an attempt at putting AIKEN design ideas into the dumblelator. Result: It worked, but had its limitations. In parallel mode it didn't have the nice compressed sound of the regular serial Dumblelator, it was a bit clinical, and the effects signal would be out of phase with the direct signal (just like Tony pointed out).

With inspiration from Merlin's new book "Designing Tube Preamps for Guitar and Bass" 2nd ed, the original, serial mode, Dumblelator can be modified with a design element from the ENGL Fireball effects loop.

All it takes is a 500k Dual gang pot (stereo pot) wired in antiphase plus a couple of 10k mix resistors. The best pot would be an anti-log pot, but a regular linear stereo 500k pot will do. Since the two 500k sections are wired in parallel. the recovery input will still "see" 250k (close to 220k like the original Dumblelator). The 10k series resistors prevent the signal sources from being directly shorted to ground at any setting. And doesnt add to or detract from the sound.

When the loop's send and return jacks are not in use, the switching jack ensures that the dry signal is applied to both potentiometers simultaneously, so the signal level reaching the recovery stage is constant regardless of the setting of the mix control.

If you want to try this mod on an outboard "two knob" dumblelator, and you dont want to drill new holes, you might consider substituting the "Send pot" for a couple of resistors and putting the mix control in the "send pot" hole on the faceplate. On my Dumblelator I always leave the send pot at 11 o'clock anyway. "The return" knob will still act as master control.

When deciding on the build-in option, you might consider the values in the schematic below, substituting the amps "Master volume" for a couple of resistors and putting the Loop's "Return" control on the faceplate instead. A lot of people on this forum have done that and I read somewhere (on this forum) that you can use other values (usually lower than 1M) for at master volume sub.

You can spice it up with an added built-in reverb (like the Aflynt design or a 1-tube or Prosonic reverb tank). With nothing connected to the send/return jacks, the mix control will add reverb in parallel. If you connect multi-effect unit, the built-in reverb will be disconnected, since both reverb and added echo can be a bit over the top for live use.

Hope you'll fun building the loop or using the ideas to modify an existing loop. It adds a completely transparent, parallel functionality and preserves the sound (additional compression of the recovery section) of the original Dumblelator loop.

Enjoy! - Let me know what you think.

[marcos]

Thanks for the contribution, Claus,
I have been thinking about something similar since reading Merlin´s book.
I will try it out on a C-lator I have ordered, I´ll let you know how it works out.
Marcos

[bluesfendermanblues]

Thanks for the contribution, Claus,
I have been thinking about something similar since reading Merlin´s book.
I will try it out on a C-lator I have ordered, I´ll let you know how it works out.
Marcos

Looking forward to hearing you results. I'm going to add a build-in loop in a #183 clone as well as modding a standalone D-loop.