Adding an effects loop to a Super Lead?

[justonwo]

I'm thinking about adding an effects loop to my Metro 100 Watt. Any idea how this is done?

[justonwo]

Anyone?

[John Phillips]

It's not that useful.

You can't really get the loop after the bulk of the distortion, since that occurs in the PI, which has to be after the loop. The best you can really do is use it to operate the FX at a higher signal level, if that's useful (for rack FX, it can be).

If you do want to do it, you need to break the signal path, almost certainly after the tone stack, and insert a driver (level cut, low-impedance send) and recovery (level boost, high-impedance return) circuit, which could be done with a tube (you'll need an extra 12AX7 socket on the chassis, and a few other parts), or solid-state - Marshall use a little solid-state module on the RI 1987X and 2203, which is on a separate circuit board and should be very easy to fit... I'm pretty sure it's available as an aftermarket spare from Marshall. It has both a level setting switch and a full hard-bypass switch, and mounts to the back panel via the two jacks, so it's as easy to fit as anything like this could be. It doesn't even need a special power supply as it draws it from the bias supply circuit.

[ChickenLover]

John,
It was my belief that the effects loops that have been added to the 1987x and SLP reissue (I think early ones didn't have it but later ones do?) wouldn't really work that well for stuff like delay/etc. for reason you say...it's still before the PI and thus still before much of the distortion. I've never actually tried those amps though. But I've had people (internet unknowns) swear that it works well with delay and a cranked amp. Have you actually tried delay in the effects loop of one of these reissues? I trust your opinion/experience and like I said...all the others were internet unknowns (so I have to take any claims with a grain of salt).

BTW - I'm specifically referring to 1987 and Superlead-type reissues...not the 2203 reissue (which I assume can have a useable effects loop as long as you use mainly preamp distortion).

[da-boogieman]

I have not done this to my Metro nor do I intend to. But I seem to recall a fairly detailed schematic in 1 of Kevin O'Conner's books. I'm not really motivated to go look to figure out which one, so you might drop him an email. Perhaps he even sells a kit for it. Electrically it is pretty simple as described in an earlier post. To do a good job involves the usual combination of conscientious layout, lead dress and ground selection in order not to introduce undesirable artifacts.

enjoy