Parallel effects loop for Marshall style amps

franc · Post by **franc** » Sat Oct 13, 2007 9:50 am

I just finished installing the board into the small chassis and the chassis onto the main chassis.
Bummer is the fact that I still have to build the rest of the amp before I can hear it

I'll try to make it so I can first hear it without and then with the loop.

I used shielded wire on all wires except of course heaters, ground and B+ but also the wire from the plate of the extra tube, going to the PI input cap, I used normal wire. I had no clue where to connect the shield to and figured it's a small distance going from inside the small chassis, going to that cap (everyhing in the front of the amp. We'll see what happens.

The shielded wire I had on stock is whit and very inflexible

jerrydyer · Post by **jerrydyer** » Tue Oct 16, 2007 4:13 pm

If there are any doubters left you can hear larrys loop at my site. go to old first page from the buttons menu and find the VM50 walkthru video

www.surrealamplification.com

franc · Post by **franc** » Wed Oct 24, 2007 10:01 am

Just finished the amp with loop

Wow, it worked first time

Left out the loop at first, simply by not connecting the signal wires to and from the loop and then inserted it.
I could not hear any difference in 'tone'
So far so good!
Then with a short link cable from send to return and both pots dimed

A bit noisy but what a great boost!

Still some experimenting to do, to see if I can get it quieter.

Already love this loop!

novosibir · Post by **novosibir** » Wed Oct 24, 2007 12:07 pm

franc wrote:Already love this loop!

Bad Kitty · Post by **Bad Kitty** » Fri Oct 26, 2007 3:30 am

I spent a couple of days putting the Larry Loop in. After a stupid mistake with my socket wiring I managed to get some sound but it's very weak and distorted. When I jump the loop with a short cord it works fine but not without one. I checked my jacks but they seem to work like they should.
I'm sure it's another wiring glitch. I'll triple check everything again.

Mike

novosibir · Post by **novosibir** » Fri Oct 26, 2007 9:15 am

Bad Kitty wrote:I'm sure it's another wiring glitch. I'll triple check everything again.

Do it! But do it well!

Larry

Bad Kitty · Post by **Bad Kitty** » Sat Oct 27, 2007 5:14 am

I'm starting to make myself crazy. I KNOW I have the thing wired up right but I'm still just getting a weak, distorted signal without jumping the jacks. I've checked the jacks with a meter and they're working right, I've gone over my layout with the schematic dozens of times.
Anybody have any ideas?
I keep looking at Larry's sig line and I just know it's probably going to turn out to be true this time too

.

Mike

Bad Kitty · Post by **Bad Kitty** » Mon Oct 29, 2007 2:31 am

Found it. I was checking resistor values for the umpteenth time and found out that the 820K wasn't soldered in

.
Another satisfied customer here!
I think I will hook up the serial/parallel switch though so I can go between the preamp on my rack processor and the Marshall preamp.

Mike

myfoot · Post by **myfoot** » Sun Nov 04, 2007 7:01 am

Larry, sent you a pm. I may as well jump in and find out how to do this. Wonder if we could get George to sell a kit (to forum members only per your request) with all the parts included. I think I'm going to order the PPIMV from him to put in my new 50 so I'll probably be bothering all of you on that thread as well

EDIT: got your mail back Larry . Thanks for your help

Ivabiggun · Post by **Ivabiggun** » Sat Dec 01, 2007 2:00 am

Here is a link for the 820K resistor: http://www.mouser.com/search/ProductDet ... 94-820K-RC

Where is the 2M2 resistor that has been mentioned? I don't seen that anywhere on the schematic.

Ivabiggun

novosibir · Post by **novosibir** » Sat Dec 01, 2007 6:38 am

In the version w/ true bypass switch are 2 2.2M resistors to avoid the switching pop.

Larry

Ivabiggun · Post by **Ivabiggun** » Mon Dec 03, 2007 9:49 pm

Hi Larry, I just want to make sure that I have the grounding issue correct. Do all the ground points in the circuit go to one central point or not. I need to get this correct before I start building. Please forgive me for asking this as I have read through this thread and I know it has been mentioned. Just want to be sure. Thanks again for this great design.

Iva

novosibir · Post by **novosibir** » Tue Dec 04, 2007 8:25 am

Yes, all the grounds in the loop section including its filter cap should run to one point. This point ideally should be located between the V2's & PI's grounding points.

The loop section's ground contents every ground after the input coupling cap to the cathode follower (jacks, pots, voltage dividers, cathodes, filter cap) and ends with the cathode ground of the recovery stage. When you have a Master after the (plate's) coupling cap of the recovery stage, it already should be grounded to the PI's ground.

Larry

rockstah · Post by **rockstah** » Wed Dec 05, 2007 6:07 pm

for the schematic impaired and after having Larry verify and using jreinhard's chassis shots as reference i have drawn up a Layout of Larry's Parallel FX loop.

if any of you guys want a copy please send an email to mark@markabrahamian.com with "fx loop" in the subject line and i will send it to you.

i learned a lot just drawing it up and would like to thank Larry for being so generous with the schem and jreinhard for his help.

Mark

Ivabiggun · Post by **Ivabiggun** » Wed Dec 05, 2007 6:10 pm

Hi Larry, thanks for the grounding question reply. Forgive my ignorance, but does 2M2 mean 2.2uf's? What voltage do you reccomend?

Thanks,
Iva