DC-3 Loop Mod Schematic

[y2stevo]

Hi Guys,

Recently I bought a DC-3,
I'm having an issue when running effects in the loop. I picked up a Boss GT-100 and i've been mesing around with. When using the "4 Cable method" or going directly from the GT-100 into the effects return of the DC-3 an Oscillation occurs. It's like the sound of a helicopter.
I've read some people have had similar issues and that the cause may be the Parallel Effects loop. Does it sound like it may be part of the issue?

I haven't got a chance to try other effects units in the loop just yet but I have a Marshall JVM and it has no issues with the GT-100 when trying the same setup.

I'm finding it hard to find a schematic for the Parallel to Serial loop mod for a DC-3, Could anyone help me there?

Thanks

 

[y2stevo]

I should say that I think I have the Revision A version.
The amp has input jack and footswitch (Channel) jack on the front. It has an EQ/Reverb Stereo Jack socket on the back panel. There is a 5 way rotary knob (On, Off, Rhy, Lead, Footswitch) on the back to select the EQ's function.

 

[soundchaser59]

This may not help anything, but.....on my DC3 the loop was converted to serial, and I have to plug in backwards. I have to plug in to the loop as if the Return jack is actually the Send, and use the Send jack as the Return. It works great this way, it's odd but it works great!

When I plug in to the loop normally I get no sound.

Worth a try, maybe...... 'specially if your loop has already been modded.

 

[crguti]

^ if your loop has been modified like that, you didn't get a good job.

 

[soundchaser59]

Preliminary email contact from Mesa suggests that my fx loop reversal problem may be as simple as switching a couple of wires.

I am good with my soldering iron, but how to know which wires to switch??

 

[soundchaser59]

I'm finding it hard to find a schematic for the Parallel to Serial loop mod for a DC-3, Could anyone help me there?

Maybe.......sent you a pm....

 

[MJ Slaughter]

Hi Guys,

Recently I bought a DC-3,
I'm having an issue when running effects in the loop. I picked up a Boss GT-100 and i've been mesing around with. When using the "4 Cable method" or going directly from the GT-100 into the effects return of the DC-3 an Oscillation occurs. It's like the sound of a helicopter.
I've read some people have had similar issues and that the cause may be the Parallel Effects loop. Does it sound like it may be part of the issue?

I haven't got a chance to try other effects units in the loop just yet but I have a Marshall JVM and it has no issues with the GT-100 when trying the same setup.

I'm finding it hard to find a schematic for the Parallel to Serial loop mod for a DC-3, Could anyone help me there?

Thanks

If you PM me your email I can send it to you. Very simple hand drawn diagram. So easy to do.

 

[soundchaser59]

I got the schematic scanned and emailed.

On the serial loop mod schematic, the label is wrong. It says the Send is the orange wire, but the send is actually the white wire, and the orange wire is the Return.

I fixed my "reversed fx loop jacks" problem by switching the orange and white wires on the switching jack. (the "mix" pot is removed) There is a red wire that goes to the Return jack tip, and the orange wire should connect to the same lug as the red wire. The white wire connects to the Send jack tip.

I'm no photographer, but here are some half way decent pics, two pics show the orange and white wires reversed, two pics show the orange and white wires after I switched them for the fix. I plugged in a couple of short patch cords so I could check where the tips were wired, the alligator clip on the continuity tester is holding the tips together where there would normally be a pedal.

Wires Reversed 1
Wires Reversed 2
Wires Correct 1
Wires Correct 2

You can see on the schematic where it says "FX LOOP" and where someone hand wrote "orange" next to the "SEND" wire. The Send jack has been changed to a switching jack. In the second reversed photo you can see where the red and white wires are soldered together. Just switch the white and orange wires, put the orange with the red.

In other words, when a cord is plugged into the Send the signal from the white wire goes to tip to fx to return tip to red and back in via orange.

No cord plugged in the signal should remain normalled white to orange, bypassing the loop and the red.

Hope this makes sense. My loop works correctly now, the Send is actually the Send! 8)