OBEL option

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OBEL option

Postby WildEye » Sun Jun 17, 2012 6:24 pm

I'm not sure if it's really possible (read reasonable) to use a pot to blend the FX loop with the clean signal. It seems like you could get some really interesting tones. It's just something that's been rattling in the back of my head for sometime now. I think it would be cool to have that as a knob on the guitar or as a modded volumed pedal. Has anyone done this?
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Re: OBEL option

Postby ScottWalkerGuitars » Mon Jun 18, 2012 7:20 am

Hey, this is what I do on some guitars with the FX loop Blend pot. Its pretty cool, and allows for some really dynamic settings. Starting the song with just a hair of effect (wet signal), kind of a ghost tone, and as the song develops increase the mix. Its pretty cool. I think the keys are having a buffer and a linear pot.
Ignore the rest of the drawing, but you can see what going on with the blend pot.
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Re: OBEL option

Postby tigerstrat » Mon Jun 18, 2012 9:33 am

Thanks for posting that, Scott- I've been thinking of rewiring both of my stage axes for some time now, and the blend option is interesting. July is a great month for it, since we tend to take it for our summer break.
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Re: OBEL option

Postby ScottWalkerGuitars » Mon Jun 18, 2012 10:18 am

Cool! Here is a more stripped down version of it, with the bypass switch. Also a link the the Guitar Modder site, where you can access this diagram and change it for your own.
http://guitarmodder.com/beta/diagrams/new-mod-87#

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Re: OBEL option

Postby WildEye » Mon Jun 18, 2012 8:08 pm

Thanks a lot Scott (dig your guitars BTW). It's good to hear it's a thing and the diagrams will be really helpful. Now I just gotta decide wether to repurpose a tone pot or add another....the tough decisions in life... :-)

If anyone else here has done this I'd like to hear the results - I've done it digitally with some interesting results but would like to hear the real thing.
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Re: OBEL option

Postby al.hurst » Sun Jul 22, 2012 11:56 pm

I am thinking about doing this as well, Did you ever get around to putting it in?
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Re: OBEL option

Postby milobender » Sun Sep 30, 2012 10:33 am

Has anyone actually tried this schematic? I'm having problems with it right now... It works marginally at the ends of the blend pot rotation, but the entire middle drops volume so low it is unusable. I contacted Scott and he suggested it was a phase problem, which I can see, but his suggestion of switching the pot wiring around (which I've tried some to no avail) doesn't make sense to me... if one part of the signal goes directly to the effects, and another splits back thru the pot to the return side of the switch, isn't a 'phase issue' inevitable? Anyway, any thoughts would be appreciated... I may just be blind here...

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Re: OBEL option

Postby tapestry » Sun Sep 30, 2012 4:44 pm

I use the fbr jr effects blend pedal. works great and fits in the rack.
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Re: OBEL option

Postby WildEye » Sun Sep 30, 2012 6:47 pm

Do you know a link with more info on that? My google-fu is lacking on this one...
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Re: OBEL option

Postby tapestry » Sun Sep 30, 2012 7:55 pm

Here it is :) I had spelled it wrong, sorry!

http://www.bargeconcepts.com/vbjr.html
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Re: OBEL option

Postby WildEye » Mon Oct 01, 2012 7:31 am

Cool, thanks. I notice there are a couple different versions (add an input for an expression pedal and a phase switch). It works great for you and I was just curious if you have the phase switch on yours and if you have run into any phase issues when using it?
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Re: OBEL option

Postby tapestry » Mon Oct 01, 2012 8:07 am

I just have the basic one, no phase switch. It works great and I dont think I would ever want to go without it.
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Re: OBEL option

Postby drewfx » Mon Oct 01, 2012 9:03 am

milobender wrote:Has anyone actually tried this schematic? I'm having problems with it right now... It works marginally at the ends of the blend pot rotation, but the entire middle drops volume so low it is unusable. I contacted Scott and he suggested it was a phase problem, which I can see, but his suggestion of switching the pot wiring around (which I've tried some to no avail) doesn't make sense to me... if one part of the signal goes directly to the effects, and another splits back thru the pot to the return side of the switch, isn't a 'phase issue' inevitable? Anyway, any thoughts would be appreciated... I may just be blind here...

Brian


EDIT: sorry, the circuit diagram wasn't appearing before and I didn't see that the circuit was using a "normal" 500k linear pot instead of a dual-ganged blend pot. Ignore the part at the bottom.


It may be that 500k is too much resistance. Try putting a 50K-100K (or something like that) resistor across the outside lugs of the blend pot and see if it improves.



EDIT: Ignore everything below this!

You may have the blend pot wired backwards.

A blend pot is like 2 pots that each work for 1/2 of the pot's travel:
Center = both pots at full volume (100%).
CCW = 1st pot at 100%, the 2nd at 0%.
CW = 1st pot at 0%, the 2nd at 100%.
Anything in between = 1 pot at 100%, the other between 0-100%

IOW a blend pot is properly wired so that it only reduces one (or the other) of the 2 signals for 1/2 of the pots travel, and the other signal is at 100%.

If you wire it backwards (meaning the 2 sets of outer lugs are reversed), you will get 0% in the middle and only get full output of one signal at fully CW or CCW.
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Re: OBEL option

Postby milobender » Mon Oct 01, 2012 9:20 am

I was typing this on the other thread as you posted I guess "o)

After spending quite some time thinking about this I've concluded that it is not a phase problem... rather a basic design problem. At the middle of the rotation there is basically 250K volume reduction, for both sides, like two volume controls... it can't help but be very quiet in the center. As the pot rotates, it gets louder for whichever side until the end of the rotation where it's the original signal. In that vein, thinking of the situation as just using two volume controls and combining the outputs, and trying to minimize the volume reduction, I used two 25K audio taper pots, one for the dry signal split off the OBEL send, and one for the wet/return. Turning both pots at the same time (to mimic a dual/ganged pot) it worked much better, but still not up to quality standards in my opinion. The dry signal is quite alot hotter than the return and in the 50/50 blend position the volume is still considerably lower than the dry signal, and of course, the by-pass mode, making a big master volume adjustment necessary... which means you'd have to have the master volume no higher than 75% at any given time, to save the compensation headroom. (I also tried one of the specialized blend pots from Stew Mac, and that didn't work at all in this application... it was either all dry, or all wet)

I'd be happy to find out I'm wrong here, as I like the idea of an onboard blend option, but it's not working for me, and I don't see how it can in this configuration. Since there seems to be a good blend pedal option available, that seems to be the way to go.
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Re: OBEL option

Postby drewfx » Mon Oct 01, 2012 10:02 am

Just to be clear - a typical dual gang blend pot isn't the same as turning 2 pots at the same time; it's like starting with both at 100% and turning only one of them down at a time.

But I would think a dual ganged blend pot of the appropriate resistance would work better than using a "normal" pot. You can try it with either just series resistance or with the grounds connected as well. You need just enough resistance to quiet one signal to your satisfaction.
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