Grateful Dead Music Forum

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Chat about Equipment Info
 #119291  by milobender
 Mon Oct 01, 2012 10:29 am
Yes, I understand... I wired each pot reversed from the other so that turning them in the same direction would lower one, and raise the other... I did try the actual blend pot, with and without grounds connected and it really wasn't good... It does get better with lower resistance values but it's just not up to snuff for me. The OBEL used in the typical way, with the UGB really sounds good, so why settle for less? The blend is definately a good idea, but I think it needs active mixing to keep from detracting from the circuit.

I think the problem with this idea is splitting the send this way, without some sort of compensating/dedicated amp to balance the signals.
 #119304  by TI4-1009
 Mon Oct 01, 2012 4:48 pm
I think you have it figured right. I was thinking about using a blend pot for my 250/500 tone pot on my Tiger, but once I thought it through I realized it would do exactly a you describe- as one goes up the other goes down- in the center both are around 50% (if linear).
 #119313  by WildEye
 Mon Oct 01, 2012 9:54 pm
Just to clarify, when you used the blend pot - what wasn't up to snuff? I figure it sucked the tone but was is it volume too? As I've stated before I'm no expert but I'm learning... I can see where if the blend is on the guitar then you might run into some phase issues (signal traveling farther on one channel before meeting up with the other and creating a slight shift). But is that difference is too small to make a noticeable change in tone? The pedal seems to work and has to deal with the same thing (albeit with less of a run). The pedal seems like a great solution but if you want control over the mix while you're playing you need the expression pedal - so the upgrades for the blend pedal plus the expression pedal add up$. Maybe that's the only way to go...

Waldo? Any experience with this?

And I'll do a "bump" to my first question "Has anyone here done this"?
 #119329  by milobender
 Tue Oct 02, 2012 9:07 am
Sorry for being too obscure here... it was mainly a volume issue and lack of acual 'blending... when I used the MN type blend pot (per Stew Mac) it was either all dry, or all wet pretty much. There wasn't really any 'blend'. There is a middle indent, and if you look at the data sheet, you'll see that the pot's resistance raises/lowers from full turn to indent, then it's flat at full resistance for the other half of the turn. I believe the problem is with the way the dry/send signal is both too the dry side of the pot, and to the loop, eventually to the wet/return side... the 'blend' pot is designed for two distinct/seperate sound sources... I don't know really, I tried it, it didn't work, I moved on. I'll double check my wiring and try it again today if I get a chance.

I believe, if we are talking about the pedal mentioned above, that it has opamps in it to compensate for this issue. It seems the pedal may well be the way to go.

Yesterday I tried lowering the resistance value of the pot further with a 10K linear I found in my old stuff pile... it worked better yet, but still had a noticable volume drop as it went to the mid and wet side. I plan to order a 1K, and perhaps a 100 too, and try them to see if it still works, and/or improves the situation.
 #119428  by WildEye
 Thu Oct 04, 2012 8:28 pm
Thanks, keep me posted on the progress - I'd love to have that control without having to bend over and tweak a pedal (and the upgrade + expression pedal gets steep)....
 #119519  by ScottWalkerGuitars
 Sun Oct 07, 2012 9:23 am
This is what I posted in the other thread about my experience with this circuit - dont mean to be redundant.

Hey! Sorry it didnt work out for you. Like I said, I have done this probably 10 times and each time had to tweek it until it was right. It is still not perfect though, but it works. Sometimes I have had to invert the polarity of the guitars pickups to solve the problem you have described. Barry Sless had me put it in his guitars and he loves it, very dynamic and expressive. He gigs with them all the time and uses the loop exclusively.
A couple years ago, John Cutler, Peter Miller and myself designed and built a Pedal Version of this idea, a box with expression pedal. The box allows either a FX loop type guitar or regular guitar to be plugged in, as well as the FX. And expression pedal used to mix the wet and dry. It works great . Very amazing! Barry has one we built for him, but he prefers the Blend in the guitar, over the pedal. We ended up abandoning the project, figuring for us to build this the right way it would be to high of a retail price. At that same time this company (xotic effects) came out with the same product. Although theirs doesn't have the Expression Pedal.

(edit) To cure the problem your talking about, we added the Phase switch on the network box, because certain FX will invert the signals phase. The symptom is that in the middle of the rotation there is significant volume loss. SO mattering on which buffer im using, which FX are being used, and which pickups, I sometimes end up inverting the phase at the pickups (swapping the leads).

Heres a couple pics of our prototype -



Cheers and sorry again for the troubles, i wish I had a straight forward answer for you, other than swapping the phase of the guitar at the pickups. Or, try inverting the phase at the buffer, like using a different buffer. I find that stuff like this really needs tweeking until it works, thats all I can say!!
 #119534  by milobender
 Sun Oct 07, 2012 2:12 pm
Yep, this is the direction I've been trying the past few days... but based on FETs instead of opamps... I've got the FETs here to try "o)

I concluded early on, that the passive use of one pot wasn't going to work for me, for one thing, it defeats the idea of the OBEL (which is to send the full signal to the effects consistantly) by putting a 'volume control' in series with the signal...

I'm ordering parts today for a bit more experimentation... I'm planning to include ordering some opamps and compare them with the FET designs.

 #120304  by milobender
 Tue Oct 30, 2012 10:20 am
Sorry for the delay... After trying many variations with both FETs and the Opamps, I came to the conclusion that the full blown opamp design sounded/performed the best, although I would replace the 25K blend pot with a 10K... which minimized the volume dip in the center of the rotation. However, I ended up using a very simple 2 FET circuit instead (it sounded nearly as good as the opamp design) because of space limitations. I simply couldn't make the opamp circuit small enough to fit into the cavity along with the already present UGB and Stratoblaster boards, and battery/clip... the cavity is PACKED!