Jcm 2000 Tsl 60x Serial Loop Mod

[The Creator]

Hi all Marshall users, this thread is about adding a serial loop to the JCM 2000 TSL serie. It might be applicable to others also...

As we all know the stock loop on this amp is in parallell, and not so good.
I have studied the wiring and have 2 options for adding a serial loop.
Help me out if I'm wrong.

1. Cut wire after connector 13 (Upper right corner on schematic page 1), before junction to connector 4. This will let You have all sound and volume sent to Amp and XLR. See picture :
2. By adding a switch for choosing serial or parallell. This require some more work.
The switch will be inserted at the same place, and you have to cut 2 more places. See picture below.
Can someone that has super knowledge to this amp confirm this will work.
That would be very helpful. THANKS

 

[tbonesullivan]

Does any amp actually have a GOOD parallel effects loop? It seems that many companies love the parallel loops, but there are also a ton of mods to turn them into series loops.

 

[JohnH]

I have a parralel loop on my DSL401, and actually I like it. Its all I knew for 10 years. I miss it on my more recent and otherwise better VM.

The 401 loop was a bit weak. ie even at max effect on the pedal, I might want a bit more effect once the amp had mixed in the dry. So I fixed that by slightly boosting the max loop level, but still a parralel loop. I did a similar tweak to the reverb.

I like having an FX mix knob on the amp.

 

[The Creator]

Anyone else that confirm this mod would work?

 

[The Creator]

As no-one come up with a confirmation I just took the chance...
Here is the modification in pictures.
First let the amp stay a few days without power.
Remove the back cover, and speaker cable.
Disconnect the reverb at bottom. Note where the wires go.
Next remove the 2 big tubes, to get the amp out of the combo.
This is the schematic:



Then remove the fx card:


for drilling the hole to the switch, this is a 3 pole on-on


Put a napkin/paper to prevent spoon in amp. Cover also the hole for xlr connector.




Center of hole is 194mm from left edge, and 10mm from top edge.
This is how I reused the connectors.



On the fx-card, The R37 is located 15mm from left edge in center.
Here is the wires installed.


Mod completed with all wires connected:

Amp tested and working

Happy modding guys for those who want serial fx loop.

 

[José Pedro Baggans]

Hi, did you tested the option #1? Because I tried just disconecting the wire that goes to R1 and the amp doesn't sound at all

 

[Thiago Sforcin]

Hi, did you tested the option #1? Because I tried just disconecting the wire that goes to R1 and the amp doesn't sound at all

José Pedro you also need to check the ground connection between both jacks (in bold black) and the wiring between the jack switching (tip to tip - grey wire on the schematic #1). Worked fine on my amp !!

Thanks The Creator for sharing it !! Works great !!

Updating: for any reason this mod defeats the OD tone stack and global reverb. I'll try a new configuration and reply here soon !!

 

[cbhuss75]

I’m so glad someone finally documented this. Did this mod cause your reverb and time stack to not function?

 

[The Creator]

My amp did not change in tone or function, only got a serial loop

 

[Ctysin]

Tried option #1, doesn't work, you need the switch to complete the circuit, so option #2 seems to be the only one

 

[RicplaysMarshall]

Hi.

I am getting my tech to mod my TSL601 for this. Can you guys confirm this mod works and there were no other side effects? Hank’s

 

[RicplaysMarshall]

My amp did not change in tone or function, only got a serial loop

Hi

I know this is an old thread. I can’t find anything else anywhere on this. I am trying to get my amp tech to do this mod on my TSL601. Do you have any more info on other people achieving it successfully?

 

[jrbrtsn]

Ok, I just did this mod on my TSL602, which was built in 2004. Good news and bad:

Good: For the clean channel, this works as advertised by The Creator.

Bad: When switched for serial FX routing, the output of the main amp is *always* the clean channel, regardless of which channel is currently selected on the amp.

Verified: When switched to the parallel FX routing, all channels work as they did from the factory.

Note: When switched for serial FX routing with nothing connected to the FX loop, no sound comes out of the main amp.

 

[jrbrtsn]

Hi

I know this is an old thread. I can’t find anything else anywhere on this. I am trying to get my amp tech to do this mod on my TSL601. Do you have any more info on other people achieving it successfully?

I tried this on my TSL602, which was built in 2004. For the clean channel, this mod works perfectly. However, when switched for serial FX routing, only the (FX modified) clean channel sounds through the main amp, regardless of which channel is currently selected.

 

[jrbrtsn]

After using my amp with the mod installed for a few weeks, I will share observations which may help you get the sound you want:

1) In parallel (factory) mode, if you route the output from your effects through a preamp placed in front of the TSL's FX return (to increase that signal), you can get more of the effect sound coming through the TSL. I have done this with a G-system in my FX loop, and the results are quite satisfactory. NOTE: this usually requires some tweaking of the G-system's various module parameters to increase the intensity of the effect.

2) I was slightly mistaken regarding the (modded) serial FX loop's send signal; it appear this is merely a line level version of whatever is plugged into the TSL's input jack. Therefore, the gain and EQ controls of the TSL's clean channel are *not* applied to the FX send signal in serial mode.

Hope this helps somebody!