Parallel effects loop for Marshall style amps

jerrydyer · Post by **jerrydyer** » Sun Sep 09, 2007 1:22 am

what about dry ?

Tuco · Post by **Tuco** » Sun Sep 09, 2007 1:40 am

Okay, let's see if I can post these correctly.

Please keep in mind that I am hooking the loop this way just to be sure that I have it working before I commit to a final arrangement inside the project box. In other words, it looks like a mess right now with extra long runs of wire everywhere.

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Tuco · Post by **Tuco** » Sun Sep 09, 2007 1:48 am

Jerry, the amp dry is working fine.

franc · Post by **franc** » Sun Sep 09, 2007 7:06 am

I feel stupid for bringing this up after so many pages, but...

Is there an extra 22u/450V cap in the B+ now that's not there originally?

Can't understand how I missed that after staring at the schematic for so long now

novosibir · Post by **novosibir** » Sun Sep 09, 2007 7:51 am

franc wrote:Is there an extra 22u/450V cap in the B+ now that's not there originally?

Yes, it's a 'must have' for an independent voltage supply node for the loop's tube only!

Larry

novosibir · Post by **novosibir** » Sun Sep 09, 2007 7:55 am

Tuco - you still have to remove the ORIGINAL cable from the Treble's wiper to the PI's input cap, otherwise your loop section is completely shunted and can't work at all!

Have a nice Sunday - wherever you are

Larry

franc · Post by **franc** » Sun Sep 09, 2007 9:56 am

novosibir wrote:
franc wrote:Is there an extra 22u/450V cap in the B+ now that's not there originally?
Yes, it's a 'must have' for an independent voltage supply node for the loop's tube only!

Larry

Is there a reason why it's not on the board? I had a turret board made, but never thought about this cap. Should I use a can and put it on top of the chassis?

novosibir · Post by **novosibir** » Sun Sep 09, 2007 10:17 am

franc wrote:Is there a reason why it's not on the board?

Sometimes in a JTM45 a 16

Tuco · Post by **Tuco** » Sun Sep 09, 2007 1:28 pm

novosibir wrote:Tuco - you still have to remove the ORIGINAL cable from the Treble's wiper to the PI's input cap, otherwise your loop section is completely shunted and can't work at all!

Have a nice Sunday - wherever you are

Larry

Larry, thanks for the post. I did as you said, and things are now different, but not good.

Now, when I take the amp out of standby, the guitar sounds thin and buzzy. The volume is not anywhere near where it should be, and after a few seconds it fades to almost nothing. The result is the same whether the effect box is in the loop or not. And the effect is not being heard.

Any ideas? TIA.

franc · Post by **franc** » Sun Sep 09, 2007 4:35 pm

820k resistors at .5W seem hard to come by.
Should I go up or down in value or create 820k with serial/parallel combinations?

jerrydyer · Post by **jerrydyer** » Sun Sep 09, 2007 8:02 pm

even with the long wires the ayout looks great.

does it matter where he grabs b+? I grab it closer to my preamp.

novosibir · Post by **novosibir** » Sun Sep 09, 2007 10:31 pm

jerrydyer wrote:does it matter where he grabs b+? I grab it closer to my preamp.

To avoid supply rail based intermodulationes you should 'grab' it from the PI node and not from any other spot - except you like to have some funny extra notes.

Larry

Tuco · Post by **Tuco** » Mon Sep 10, 2007 12:05 am

Larry, based on what I described in my post from earlier today (four posts up ^^), do you have any suggestions on what might be the problem, or what I might try next? TIA.

novosibir · Post by **novosibir** » Mon Sep 10, 2007 12:25 am

The brown wire back from your loop box to the PI's input cap is running close across the input jacks. That's the worst area at all, where it may run back to the amp !!! Supposing your box wiring is ok now, like above you'd have huge crosstalk into the inputs, what - 180

Tuco · Post by **Tuco** » Mon Sep 10, 2007 2:09 am

Larry, thank you again for all of your help. You are very generous with your time.

I'll figure a way to shorten this wire so that I can test the tag board and wiring.