Parallel effects loop for Marshall style amps

[novosibir]

I like it a lot so far, but I've noticed a couple of things. The loop send control "thumps" when I turn it all the way down. Does this mean I have some DC across the pot?

I don't have any clue, what you mean with the 'thump'! Hum? Buzz? Crackling? Static Noise? Hiss? Motorboating?

Also, I noticed the "dry" path's tone is quite a bit brighter than the "wet" paths tone, even with nothing in the loop. I think I may try a different value of bypass cap across the 220k, or remove it all together. Any suggestions?

The dry path is 'brightened up' with the 220p, to correct the unavoidable high loss through this additional circuit.
The wet path is not corrected - on purpose - because many of the effects devices are brightening up the sound, so through the wet path the amp is 'duller' than w/o effects loop.

Shure, you can tweak the sound with other cap values, but the amp with loop through the dry path does (should) have exactly the same brightness than before w/o loop.

Larry

[erigm]

I like it a lot so far, but I've noticed a couple of things. The loop send control "thumps" when I turn it all the way down. Does this mean I have some DC across the pot?

I don't have any clue, what you mean with the 'thump'! Hum? Buzz? Crackling? Static Noise? Hiss? Motorboating?

Also, I noticed the "dry" path's tone is quite a bit brighter than the "wet" paths tone, even with nothing in the loop. I think I may try a different value of bypass cap across the 220k, or remove it all together. Any suggestions?

The dry path is 'brightened up' with the 220p, to correct the unavoidable high loss through this additional circuit.
The wet path is not corrected - on purpose - because many of the effects devices are brightening up the sound, so through the wet path the amp is 'duller' than w/o effects loop.

Shure, you can tweak the sound with other cap values, but the amp with loop through the dry path does (should) have exactly the same brightness than before w/o loop.

Larry

Larry, thanks for the help. The "thump" only occurs when turning the pot to zero, and it happens as you turn it. Once the pot is stationary, there is no more noise. Turning the pot anywhere higher than just the very bottom of its rotation is free from any sound as well. There is no motorboating, crackling, sqealing, or hissing ... just a "thump".

I never tried the amp before without the effects loop. It's not a strict marshall design, but a channel switching design of my own creation. I sent you a schematic a while back. I think I'll just remove the bright cap because I like the tone right now going through the wet path.

Thanks for the help and a great design!

Eric

[josewails]

Larry, I sent a p.m. to you. Could I get a copy of f/x loop? Much appreciated. -Jose-

[rip]

Larry, the schematic for the loop shows the last cap being a .022uf which is the .022uf that's at the beginning of the PI, and yet has a lead connected to the 100k in the loop. My question is when using an eternal board for the loop where is connection made to join the .022uf that's already on the main board and the 100k resistor that's on the loop board? Do I just run a lead from the .022uf from the main board to the 100k resistor on the loop board?

Ricky and Larry perhaps this was solved or a modification to the loop circuit for a master volume but in Ricky's pics I don't see the 1K5 to ground. Hate to bring this up considering the original problem seems to be solved but Ricky you may still want to add it if it was forgotten.

Rip

[Ricky Lee]

Larry, the schematic for the loop shows the last cap being a .022uf which is the .022uf that's at the beginning of the PI, and yet has a lead connected to the 100k in the loop. My question is when using an eternal board for the loop where is connection made to join the .022uf that's already on the main board and the 100k resistor that's on the loop board? Do I just run a lead from the .022uf from the main board to the 100k resistor on the loop board?

Ricky and Larry perhaps this was solved or a modification to the loop circuit for a master volume but in Ricky's pics I don't see the 1K5 to ground. Hate to bring this up considering the original problem seems to be solved but Ricky you may still want to add it if it was forgotten.

Rip

The 1k5 resistor is under the 22u cap, hard to see in photo. http://s623.photobucket.com/albums/tt31 ... hoto46.jpg" onclick="window.open(this.href);return false;

[rip]

Awesome. Sorry about that.

[Kitarist]

Can someone tell me which loop should i put in my 1987.

I'll only use a little delay and reverb!!

Thanks!!!

[Kitarist]

Larry was good enough and sent me the schematics but i need to know..

Does anyone know if larrys loops needs additional tube or not ?

[paulster]

For me the clue was the two triodes V3a and V3b that have been added between the treble pot and the phase inverter (labelled V4a/b on the schematic).

Yes, it needs an additional tube.

[Kitarist]

so it needs another 12ax7 or ecc83 right

[erigm]

so it needs another 12ax7 or ecc83 right

You can use any kind of 12A_7 tube, but the values that Larry put in there are optimized for the 12AX7/ECC83. So, yes ... it needs another 12AX7/ECC83 (same tube).

[Kitarist]

My friend just installed the larrys loop so i have questions now.

I have huge volume loss when both pots return and send are at zero. is that normal ? The amp gets loud as it was when i pust both pots at max or so...

he also installed a switch but when i turn it off there is also a volume drop (probably he didnt wire it right)

So is that normal?

Thanks!!!

Davor

[novosibir]

Davor, when the loop is correctly installed, then there's absolutely no differences in volumes, no matter where the Send & Return level pots are set to! So your tech did something wrong by installing the loop in your amp! But there are so many possibilities, what he might have done wrong, that only some higher resolution pics of inside the amp could help!

Larry

[erigm]

My friend just installed the larrys loop so i have questions now.

I have huge volume loss when both pots return and send are at zero. is that normal ? The amp gets loud as it was when i pust both pots at max or so...

he also installed a switch but when i turn it off there is also a volume drop (probably he didnt wire it right)

So is that normal?

Thanks!!!

Davor

Sounds like he didn't get the dry path wired right.

[Kitarist]

Here are the pictures:







I called and he said i might try cutting out the green wire that is wired from dry to wet path. Anyway master Larry will tell me whats really wrong

What i think the problem is:

Well i think the green wire is really the problem because he actually wanted to do a "bypass" but when i flip the switch off the effects loop acts like there is a cable put directly from wet to try so it acts like a boost and thats why pots react to the volume.