18 watt TMB with effects loop.

[geezbill]

Looking to take the plunge on one of these. I'll probably go without a kit, since there's tons of layouts and BOM's here. The tmb seems just what i'm looking for, but i need it to have an effects loop for my time based effects. Is there a layout for that? Can't seem to find it in the forums, a link would be appreciated.

[bevins]

I think some guys have done it.....but most do not because the loop sounds best after the distortion and in the case of the 18watter, most of the distortion is from the output section. This would mean after the power section, which you would have to line out into your effects and into another amp.

or

plug guitar into normal channel, use other normal channel jack and use that as your send, through your pedals, then into the TMB channel jack.

I hope this makes sense....

Bob

[Graydon]

I have built a few tube buffered effects loop devices, similar to the Dumblelator for some of my other amps. They work great. So, a while back, I tried one in the 18W between the preamp section and the phase invertor and tha tworked great as well. I actually built a combo chassis once with a pared down version of the tube buffered effects loop built-in to the amp. I made it possible to bypass it and it worked very nicely. I would highly recommend you try it if you need a loop. I punched an extra tube socket outboard of the existing tube sockets for the preamp. I made a little panel that faces out the back on a combo, sorta like a Vox AC30 Top boost control panel.

I don't have any photos online, but I may be able to scare up a photo when I get home if anyone is interested.

[tw001_tw]

.... if anyone is interested.

I'm WAY interested - the more details the better!
Please keep in mind that not all of us can (yet) design thier own modifications

Best regards
-tw

[Simon-Hans]

Hello y'all,
I finished my 18W TMB, with normal and TMB channel. In fact I made it switchable and added a post phase MV. Now I am considering adding an effects loop, but that seems not straightforward.
The point is: the effects loop should work for Normal AND TMB channels. But I can't find any comments on that!
Does anyone has an idea to create an effects loop that works for both channels? See my schematic attached.

regards, Simon-Hans

[Bieworm]

It’s easy peazy. But you’ll have to put both channels on the same input of the PI. The other input should be grounded like on the single channel 18 watt schematics.
At the output of both channels you should continue with a mixing resistor (220 or 470k each). After the mixing resistors you can add an FX loop. After the FX loop you go to the PI input.

[Simon-Hans]

Thanks! I'll make a drawing and get back to you to check whether that is what you mean!

[Bieworm]

here's something you can try..

[Simon-Hans]

Wow, thanks!!!!
By the way: the channelswitching is not done like it is represented in the schamatic. While one channel is connected to the input jack, the other channel is connected to ground. And vise versa.

[Simon-Hans]

One question: what do I have to do with pin 2 of V2A? Connect to ground (and 470k resistor) or leave it only connected to the 470k resistor?

[Bieworm]

No need to change things at V2A.
If you want channel switching you should never do this a the input. Do it at the output of the channels. That way when you switch the DPDT (toggle or relays) one channel will always be grounded.

[Simon-Hans]

Thanks for your advice!

[Graydon]

I built an 18W a few years ago with an effects loop. I am sorry but I don't remember exactly where I tapped into the circuit. I _think_ it was at the input to the phase invertor. Anyway, I then inserted a Dumblelator. It worked great. The Dumblelator also added extra gain if needed/wanted. It was alot of stuff to pack into that chassis and I had to add an extra 12AX7 also.