Hello Dale,

It is the red wire.

Kind Regards

Marshall Support

Hello.

Thanks.  Very much appreciated.

At the risk of pushing my luck here:

If it's the wires in the red block then there are four of them.  Black I assume is common???  What do the other three carry???

I'm guessing it's obvious why I'm asking!!!  LOL!!!

I want to splice into the audio between the PRE AMP and the POWER AMP to try and create a very simple effects loop.  My "pseudo" effects loop that I created (using multiple amps. as per my other thread) does work but not as well as I thought at first i.e. there's a certain amount of latency introduced between the amps. that I've detected and it adds a lot of bass to the "slave" amps. which I cannot EQ out with the controls on the amps.  And, well, let's be honest: it's hardly an elegant solution.

I'm also not worried about buffering or levels or anything like that i.e. I just want to add a send jack and a return jack and hook an EQ pedal inbetween.  If it works: it works.  If it doesn't: too bad and I'll have to give up on this "quest".

 So any suggestions as to which of those four wires (in the red block) I should check for audio and connect to a send jack and a return jack???

My amps. are out of warranty so I'm prepared to sacrifice a CODE25 "for science" as it were (assuming I do something wrong and it all goes pearshaped) (so I won't be holding you responsible if it doesn't work I assure you).

 Regards,

Dale.

Hello Dale,

We do not carry out any modifications on our amplifiers so we are unable to comment or give advice, as what you are trying to achieve has not been tried or tested by Marshall. 

Kind Regards

Marshall Support

Hello again.

You're not helping!!!  LOL!!!  (Only joking).

I do understand.  Could you then just answer the below i.e. it's then factual info. I'm asking for and not modification advice.

Could you just tell me what those wires in the red box are carrying to the POWER AMP board individually???  There's four wires in the red box and they cannot all be carrying the exact same audio???  Maybe common, left, right, something like that (although that doesn't account for four wires)???

Regards,

Dale.

I'm guessing you're not going to be too pleased to hear this BUT:

It works!!!

Thanks for the INITIAL info.  It helped.

Regards,

Dale.

@Dale Peterson

Hi, I am actually curios if your mod actually worked out...

I would like to use a looper pedal with this amp (CODE 25). Buying an 100W amp just to get an FX loop is out of the question (wife, cats and soon babies).

I am trying to do the same mode like you and after researching quite a while, it turns out that only 3 people attempted that and reported on a forum. All stopped by saying: "I will try to splice into cables 1 and 3 and post back on the results"... No follow up. Can you please let me know if it worked and if not, what happened?

@Marshall support team

Please help me a bit on this one:

This 4 conductor cable (1 black and 3 whites) on the CODE 25, which looks like it is replaced by a 4 conductor cable (2 pairs of black white cables) on CODE 100 and 100H is supposed to carry audio signal from the sound processor to the amplifier board. Pins 2 and 4 are shorted and my guess is that those are supposed to be ground pins. Pins 1 and 3 would be the "hot" cables.

It looks like the sound from the USB and the sound from the INPUT + Effects are going through those cable pairs. Can you please tell me which one is which?

Also it would be great if you could tell me which standard of multiplex connector do you use for that particular cable.

As a side note: you might want to check either the CODE 25 wiring or the BT software. It turns out that the BT left and right channels are inversed on my amp. The line in and USB channels are correct. On the amp bar code is written, after the serial number, 01-16.

Kind regards,
Matei

diyaudio.com/community/threads/marshall-code25-effects-loop.403158/#post-7449368