Question about Effects loop stompbax with blend

[wsgarner]

I've made my effects loop box and it works, but the blend creates a feedback loop in the effects loop circuit. Basically the circuit is a true bypass with a switch and a pot between the send/return. This would work fine if I could isolate the dry signal from the wet. Basically just block the wet signal from passing through the blend pot (this is where the feedback loop is). Can this be done with a cap or diodes or something. I'd like to stay away from the op-amp thing if I can. I want this as simple as possible. And it does have 9vdc power for a LED indicator. So if power is required, its already in the box.

I would add an image of the circuit, but I can't do that from behind my work firewall.
Thanks,
Scott

[Hambo]

I did something like this recently from A B.Booster circuit by Sean Maclennan

http://www.diystompboxes.com/smfforum/index.php?topic=54809.0

he also has a minimal blender on there which is a very simple circuit and should do exactly what you want

http://seanm.ca/stomp/minblend.html

[wsgarner]

Hambo,
Looks easy enough.
I'm new at this again (20 yrs sense I did any building), so bare with me. I have some old components that I've pulled from outdated equipment that I would like to use. I've got the 1Mohm and the 10uF cap for sure. But to identify a 0.1uf cap, I did some digging on the net and am I correct in stating that a ceramic cap marked "101" would be a 0.1uF cap???
I also have what I think is an old dual opamp (for the life of me I can't remember the numbers on it; maybe 4860D or something like that). Would that sound like a correct number; 4680D?

Any way, I would like to just place this in line with the pot (from send to switch to pot to 0.1uF to opamp to 10uF to return: of course with the loop back from opamp out to Inverted in). This way I can just blend the dry to wet (wet would always be at max or what ever is coming back to return). Sound correct??

Scott

[Hambo]

Ah, 0.1 Would be marked 104 somewhere.

I cant find anything on a 4860D, not sure on that at all?
in terms of placing the components, the opamp/circuit itself will need power too.
What will you be building on?

[wsgarner]

Hambo,
I've got a small perf brd to build on.
Power is in the box for the LED already. So, powering the opamp is no problem.
I've got about 20 caps with 101 on them. A few with 471(I think). I'll have to lookup the datasheet on the chip that I have. I've also got about 20 c3198 transisters too. And maybe 3 or 4 C2240 transistors.

Scott

[wsgarner]

Hambo,
The opamp I have is a 4560D by JRC!

Scott

[wsgarner]

OK, last question on this. I'm going to put it in the box tonight.

What op-amp should I use. Will a LM741 be fine?
Scott

[wsgarner]

Here's the Layout I have:

[Hambo]

Hang on,

If you put that on/off switch in there, won't it completly cut the signal on off? I don't see the need for it, you may as well just use the stompswitch
I think the pinout is right for the LM741, and it says amost any opamp will do, but I don't know what leaving out the voltage divider section of the circuit will do? opamps are generally rated for much higher than 9v though.. so er.. may well work eh(shrug)

You into the iron game eh Scott?

[wsgarner]

Hambo,
The switch is to totally eliminate the blend (which I guess I could have done with just the pot, wasn't thinking). The send/return will still work just fine.

I picked up a 741 last night and put this mini-blind together (with the regulated voltage like it shows in the B-Blender schematic). It works, but I was expecting more blend control. I don't get any blend until about 3/4 of the pot and 100% of the pot kills the send/return. My reason for building this was the noise gate in my effects chain. I put the noise gate in due to the hiss I get from the distortion (I actually have 2|Boss MD-2 and DOD Supra Dist) I wanted the dist and the gate in the effects loop because the gate trails off the sustain too quickly when I have the dist. off (clean). So, the dist. and the gate in a loop lets me eliminate (turnoff) the dist and gate at the same time. OK, so why the bend? I thought it would produce some net tones and allow the sustain to trail off more evenly (dist. trails of to 0 vol but clean keeps going).

Blending in the clean (a very touchy pot tweak) gives me the tone I was looking for, so it works. I just wish that when the blend was at 100% the send/return would also be at 100%.

And, by the way, I left off the 1Mohm resister on the diagram (the one that goes from opamp -in to Vr), but I did put it in when I built it last night. I need to update the diagram and put it back out there on my web space.

Into the iron. Yep! The pic is from the SC 2005 state NPC championships. I got my but kicked, but it was fun. I was going to compete again this year (I put on some more mass sense 2005), but I broke my freaken' leg the first of Oct. and am just now getting back to my cardio work. Maybe next year. (Petty good for an old man if I say so myself)

[Hambo]

Maybe thats the down side of only using the mimimal blender, I must say the one I built works spot on .
It is a linear pot ur using? Could affect the blend properties if u put a log one in.. would account for that sort of behaviour.
The blend control is literally between the 2 signals so on a linear pot right in the middle would be 100% for both. I don't think it can be wired otherwise :/

Much respect, I'm into weights myself, only for the last year and a half roundabout. Don't have it in me to try competitivly, I don't even use supps let alone the other stuff, and dont like bulking - makes me feel fat and sluggish. I love a good workout tho, and its given me a much stronger sense of self respect

[wsgarner]

MAJOR Descover on this project (well, for me any way)!

I just couldn't get this opamp to work. It would be fine for about 4 seconds and then the opamp would seem to overload and the dry signal would go to nothing!! I tried everthing I could think of to fix it, but I'm no engineer! So I gave up and pulled the opamp circuit out all together! AND WHAT DO YOU KNOW!!! IT WORKS LIKE A CHARM! I had already changed to a DPDT switch and redid the way the POT was wired.

I was going to post the drawing, but my FTP server wont let me in right now. I'll post it as soon as I can.

Scott

[wsgarner]

OK, here's the drawing: