Dumbleator in Parallel mode

[bluesfendermanblues]

I'd like to share my version of the Dumbleator, which has a switch for parallel operation. It's not rocket science, but a simple design and I'm not trying to reinvent the wheel.

Serial mode: An 'ordinary' dumbleator run the effect in serail mode and mix the relationship between direct signal an effected signal in the effects unit. This is the classic operation as used by Robben Ford, and since the TC2290 has an analog signal patch for the direct signal, you dont' degrade your signal.

Parallel mode If you don't have a fine apperatus like the 2290 and like me use simple delay pedals, you might consider parallel operation, in which case you mix the direct/effects ratio in the dumbleator instead of in the effects unit.

Difference between this design and the 'original' dumbleator:

- all I did was adding a 220k serial resistor and 'moving' the return volume from after V1b to before V1b. Hereto adding a small capacitor compensating for the lack of high end loss, from not having the direct signal travelling through feets of cable. You can off course leave that out if you want to preserve high end.

- The cathode resistor combo on V1a can be either 27K/1.8K or 10K/1.5K as per the 'official' schematic.

- I left out the bright switches - never use them.

The return pot is 'master volume', when used in serial operation and 'mix control' when used in parallel mode. If the direct signal is too hot in parallel mode, put a trimpot or ordinary pot in instead of the 220K output resister.

Hope this schemo might be usefull to DIY'ers with less than studio grade effects, who want to try parallel operation. All it takes is adding a DPDT switch (or converting one of the bright switches) plus a resistor and a pot change place in the circuit.

It's a simple modification to a fine design. Enjoy

[erwin_ve]

Hi Blues, Great thinking!
I have one question; why is the direct signal, in parallel mode, fed directly to the grid?
I think the NFB is part of the smooth factor. In parallel mode only the fx signal is affected with NFB.
What are your thoughts about this?

Happy X-mas,

Erwin

[Structo]

Glad somebody else is working on one so I can glean more information!

I do have this schematic of a series/parallel loop.

Not sure who drew it.

Bluesman, how well does yours work?
Would you make any changes now that you have it and used it with your amp?

I am also considering putting a bypass switch on mine.

[bluesfendermanblues]

Hi Blues, Great thinking!
I have one question; why is the direct signal, in parallel mode, fed directly to the grid?
I think the NFB is part of the smooth factor. In parallel mode only the fx signal is affected with NFB.
What are your thoughts about this?

Happy X-mas,

Erwin

Hi Erwin, yep I get your point.

In order to separate the signal you need a 'mixing' resistor - 220K in this case.

So I can see two possibillities:

Either:
bypass the 220k mixing resistor with a 500p capacitor, but you loose the effect of the NFB circuit on the direct signal in parallel mode.

Or:
Connect the 220K mixing resistor at the viper of the Return pot., which will dampen the direct signal somewhat, but keep the original Dumbleator in serial mode.

Any other ideas?

[bluesfendermanblues]

Glad somebody else is working on one so I can glean more information!

I do have this schematic of a series/parallel loop.

Not sure who drew it.

Bluesman, how well does yours work?
Would you make any changes now that you have it and used it with your amp?

I am also considering putting a bypass switch on mine.

Yeah!! obvious. I didnt know this schemo, but off course

Just put the LFFN after the 220k/500p combo and add a 500p to the mixing resistor and voilá, you got both.

However, I wouldn't want global loop bypass like that. I'd prefer to bypass the whole loop in order to get the amp more pure without loop. Although this is merely speculation, since I havent heard that construction.

[bluesfendermanblues]

Here's an opdated schematic

[Structo]

Cool thanks!

What would you do for a true bypass of the loop.
I like that option because sometimes when you are troubleshooting an issue it is nice to be able to take the loop out of the equation to find the problem.

[bluesfendermanblues]

Cool thanks!

What would you do for a true bypass of the loop.
I like that option because sometimes when you are troubleshooting an issue it is nice to be able to take the loop out of the equation to find the problem.

I would set up a loop bypass just like the OD relay....

[heisthl]

Cool thanks!

What would you do for a true bypass of the loop.
I like that option because sometimes when you are troubleshooting an issue it is nice to be able to take the loop out of the equation to find the problem.

See attached:

[Structo]

Thanks Henry!

[Bob-I]

Parallel mode If you don't have a fine apperatus like the 2290 and like me use simple delay pedals, you might consider parallel operation, in which case you mix the direct/effects ratio in the dumbleator instead of in the effects unit.

It's worth mentioning that with a parallel loop it's important that no dry signal goes through the effect. It's very possible that the dry signal is out of phase with the dry signal in the parallel loop. I had reall difficulty getting a decent sound from a parallel loop until I figured this out.

I took a different approach with my parallel loop, since I don't use it as a serial loop. Instead of a common cathode recovery stage, I used a feedback mixer amp. Check out http://aikenamps.com/FeedbackAmp.htm for information on this. I find it more equal in output, no increase or loss in gain.

[bluesfendermanblues]

Parallel mode If you don't have a fine apperatus like the 2290 and like me use simple delay pedals, you might consider parallel operation, in which case you mix the direct/effects ratio in the dumbleator instead of in the effects unit.

It's worth mentioning that with a parallel loop it's important that no dry signal goes through the effect. It's very possible that the dry signal is out of phase with the dry signal in the parallel loop. I had reall difficulty getting a decent sound from a parallel loop until I figured this out.

I took a different approach with my parallel loop, since I don't use it as a serial loop. Instead of a common cathode recovery stage, I used a feedback mixer amp. Check out http://aikenamps.com/FeedbackAmp.htm for information on this. I find it more equal in output, no increase or loss in gain.

Hi Bob, The Aiken loop is pretty close to Kevin O'conner loop with virtual ground, which also works like a charm. However, a bit less coulered than the Dumbleator's recovery amp.

[Structo]

Bob are you saying the output of the Dumbleator is inverted from the original signal?

I thought when you have equal amount of stages that the signal returns in phase to the original?

Since the D'Lator uses two stages wouldn't the output be in phase with the input?

I remember we talked about that before but that was before I had a D'Lator so I didn't follow it as closely as I should.

[bluesfendermanblues]

Bob are you saying the output of the Dumbleator is inverted from the original signal?

I thought when you have equal amount of stages that the signal returns in phase to the original?

Since the D'Lator uses two stages wouldn't the output be in phase with the input?

I remember we talked about that before but that was before I had a D'Lator so I didn't follow it as closely as I should.

The first stage in the Dumbleator is a Cathode driver, which is in-phase the second stage is out-of-phase. The two in sum puts the signal out of phase....which is probably a part of the reason for the '3D' sound associated with the Dumbleator.

[martin manning]

I'm not exactly sure what Bob is talking about, but since the first stage in a D'lator is a non-inverting CF the "send" out of the D'lator is the same phase (grossly) as the "send" out of the amp, i.e., the dry signal. Now, each of the individual FX in the loop may or may not invert the signal, as well as shift its phase by some amount. Then, the recovery stage of the D'lator will definitely invert whatever comes in at its return jack. With all this going on, it's hard to say where the returning wet signal will be in relation to the dry, and mixing them together might have undesirable effects (or FX, if you like). From what I understand, this is not much of an issue for time based FX, but gain based FX might suffer from feedback issues and/or phase cancellation and loss of volume.

MPM