o'connor best tube fx loop...in dumbles?

[swt]

HI. has anybody tried this type of circuits in dumble amps?. i wanna try the parallel side of it. thanks in advance!

[swt]

i've been doing a search and studying a little on fxs loop, and realised that the tut and the dumbleator are not so different in essence. the only thing that i don't get is the virtual ground, and if that is really necessary. taking a look at some mesa boogie loops, i think i can convert the dumbleator to parallel really easy. any opinions?

[tictac]

The loop I use in my ODS type amp is a cross between the TUT loop and the Dumbleator. The input and series part of the loop is like the Dumbleator, the rest is the TUT loop.

I really like the Parallel mode of the loop and use it 99% of the time, it's a bit fatter and louder.

TT

[swt]

did you have problems with that virtual ground?. i used it once but changed the sound a bit and also changed the gain by fliping the switch, so i didn't like it. i'm gonna try this again. did u used that virtual ground?. what else changed?. thanks a lot for the reply!

[AcePepper]

Hi All,
1st post here. I've done a couple amps w/O'Connor/TUT FX loop. They've worked great for me. I really like the series/parallel option. In series, with no FX plugged in, you can dial in some "fatness" (extra tube stages) but it doesn't really change/color the tone to speak of. Just more of what was there. Kinda cool!

I kept the "virtual earth" thing in place, never messed with it. In parallel the loop was great at keeping the tone of the amp and mixing in some digital 'verb/delay/whatever. The level switch was handy for matching/dialing in levels of different devices. It was possible to get good level/tone from a stompbox 'verb or a rackmount-type device. In all I think the TUT loop is great! I hope the D-loop works as well.

I'm also starting a D-type amp (done lots of amps, 1st Duh-mble) and am pondering a D-loop or a TUT loop. Am also pondering Glasworks "Reverb-A-Loop." Anyone tried that one? What about adding 'verb to the TUT loop?
Thanx!
Ace Pepper

[Luthierwnc]

I've done the reverb-a-loop except using a 6K6 driver instead of the 12AX7. Works great. Adds a lot to the clean channel on an HRM. The cab shown has had a few residents -- like a hermit crab.

I don't have the schematic for the parallel loop. I think it was on blueguitar for a while but I never saved it. sh

[swt]

i'm just a bit afraid of those two 1meg resistors...you know that series resistors in this type of amps are a little bit dangerous tonally speaking. i'll try it and then report what happens...

[tictac]

The way I have the loop wired with a DPDT switch, switches the virtual ground OUT of the circuit and a 22M resitor IN for negative feedback like the Dumbleator.

I actually like the tone better with the virtual ground IN [parallel mode]

And don't be afraid of those 1M resistors either, the amp sounds great in parallel mode.

The only drawback in switching to the stock Dumbleator ciruit there is a slight gain loss. I'm going to try removing the 22M and hardwiring the virtual ground to see if I can even out the gain of both modes.

[tictac]

Did some experimenting and you really need that vitual earth to keep the gain equal in both modes.

Make the input stage like the dumbletor and the rest of the loop like the O'Connor Loop and it performs well. I dont have the level switch in my loop, you can leave the level switch out and use a 220/500pf to get more of a Dumble flavor in the return path.

You could also use 250k pots with bright switches like the Dumbletor but I find the 100k pots work fine, there's plenty of gain on tap.

TT

[swt]

Well tictac...really appreciate your help. I'll try that. according to Kevin O'Connor, the input stage is design that way to get more gain, and linear output. it's supposed to be better. i'll try both, and everything you mention, and let you know my preferences. just one more question...what's the voltage to the tube, main and plate, if you remember, and also, what type of tube did u used?. 12AT7?. tut is supposed to have that one, but never knew about the dumbleator...thanks again!!
PS: is the return impedance better as a 1m or as 220k like the dumbleator??...i guess it'll perform better with a lower input impedance as the output of effects is lower...

[dogears]

I prefer the Dumbleator by a wide margin.

[tictac]

The O'Connor input stage doesn't give you anymore gain but it's supposed to be more linear. I've tried both and the Dumbleator type input stage is simpler to build and performs just as well to my ears.

I'm using a 5751 which has more gain than a 12AT7 and less than a 12AX7. The B+ node for my ELoop is between the PI and V2 nodes so it's somewhere around 230VDC.

I've tried the Stock Dumbleator ciruit too and I didn't find a "Wide Margin" of difference. My loop is a mix of the O'Connor loop and the Dumbleator. Personally I like having the parallel option, I think you have better control of the effects mix without altering the dry tone much but that's just me.

[dogears]

I did not like the top end or the bottom end due to the huge neg feedback. Mich clearer articulate tone with the Dumbleator to me. If you are not using the huge neg feedback then I agree, not by a wide margin.

[swt]

do you guys think there's a way to get a parallel fx without the neg feedback?. a usable one i mean...mesa boogies have some parallel loops, but they make racks and reverb regenerate the signal by themselfs throught the little 25k pot...maybe using a dumbleator and a bigger pot?? . thanks for the insights...

[tictac]

Scott,

I was thinking about what you said about neg. feedback in the return stage; hadn't really thought about what effect it was having on tone as there seemed to be plenty of gain. I attached what I did below.

Basically I replaced the 2nd 1Meg resistor in the virtual earth mixer with a 22Meg and .22 cap network like in the Dumbleator. Lowering the neg. Feedback does really make a big difference, more low end, and gain for sure. I had to change the PI input cap to a .01 to trim the bass. Now I see why Robben turns his bass control to zero!

I really do like the parallel option for the loop though. Im using an external tube reverb unit and in series mode loop you are stuck with the entire signal going thru the effect. Great for Dick Dale Surf music but in parallel mode I can have the reverb wet as can be then blend just a touch of it in with the dry signal.

Now to add a ground defeat switch to get rid of the ground loop...

Thanks for the observation