ZERO LOSS LOOP IN A MHUSS/VALVESTORM 18W TMD?

[ViperDoc]

On a break from a project, I decided to crack open a new Valvestorm 18 Watt TMD build and I noticed their chassis is pre-drilled for the Metro Zero Loss FX Loop, of which I have several. I'm using the following layout for this build:

Valvestorm 18watt_TMB_Layout.pdf

I can see how I would easily add this loop into the TMD side in between the treble output and MV input. How would you wire it to be useable on both channels? My modding history is not a sterling as I'd like. The thought occurred I could add a PPIMV, but I'm not sure I want to do that. Unless it's the only way to do it. Any suggestions would be much appreciated.

Thanks.

[pdf64]

A schematic would show that it’s not possible, as each channel uses a different LTP input.
It would need changing, eg decouple one LTP input to 0V, use mixer resistors to join the channels, and insert the loop between mixer resistor node and other LTP input.

[ViperDoc]

A schematic would show that it’s not possible, as each channel uses a different LTP input.
It would need changing, eg decouple one LTP input to 0V, use mixer resistors to join the channels, and insert the loop between mixer resistor node and other LTP input.

Thanks, pdf64, that was what I thought might be the case. I'm sucking my thumb imagining your suggestion, but it's perhaps not a good fit for this amp. I've only built one 18 watt TMB from a [not-to-be-shamed] kit and its plexi channel sounds like a banshee past 50%--made quite a bit better with a cathode-follower mod. I'm looking forward to trying this version out. If the 18 watt design relies on power tube distortion for the gain tones, then maybe a wet-dry setup would be better, or just running effects into the front. Thanks again, as always, for your help.

[ViperDoc]

On a break from a project, I decided to crack open a new Valvestorm 18 Watt TMD build and I noticed their chassis is pre-drilled for the Metro Zero Loss FX Loop, of which I have several. I'm using the following layout for this build:

Valvestorm 18watt_TMB_Layout.pdf

I can see how I would easily add this loop into the TMD side in between the treble output and MV input. How would you wire it to be useable on both channels? My modding history is not a sterling as I'd like. The thought occurred I could add a PPIMV, but I'm not sure I want to do that. Unless it's the only way to do it. Any suggestions would be much appreciated.

Thanks.

Sorry for the self quote, but in this layout, there is a 220uF/50V cap in the power supply. I looked in my kit and noticed it supplied a 500uF/50V cap instead. Is this an acceptable replacement or should I get the correct value? Thanks.

[sluckey]

Huh? There is no 220µF cap on the layout you posted. But there is a 500µF cap on the board that is connected to the cathode of the output tubes.

[ViperDoc]

Huh? There is no 220µF cap on the layout you posted. But there is a 500µF cap on the board that is connected to the cathode of the output tubes.

Right. I posted the Rev. B layout that I’ve had for a while. Turns out there’s a Rev. C as of very recently that changed the 500 uF to a 220 uF as well as made some other tweaks. I didn’t know that until this morning. Seems like quite a difference, I just don’t know what that would do or why they changed it. They also replaced the 47 uF input cap with a 50 uF, changed some resistor values, etc. I’ll post both files when I can.

[sluckey]

I’ll post both files when I can.

Not necessary. The 18W TMB is not a clone of any famous amp. It is the brainchild of several members of 18watt.com. The 18W TMB was a very popular project with lot's of builders joining in and offering ideas. During the time it was being fine tuned there was a lot of experimenting with cathode bypass cap for the output tubes. Values ranged from 50µF (the orig Marshall 1974 value) to as high as 1000µF. 500µF seems to be the most popular compromise.

So obviously the exact value of the cap is not critical, although you may have a personal preference for a particular value. Meanwhile, just use the supplied 500µF cap. You can always easily change it later.

PS... There are many slightly different layouts for the 18W TMB. Some are called 18W Plexi. Since you have a kit from Valvestorm you may want to use his layout.

[ViperDoc]

Thanks. I'll just build it with what I have, I'm sure the Rev. B build sounds good! I'm going with Orange Drop caps on this one, should be fun. I'm going to put it into a 1210 combo cab. Now I just need to make sure I detect the foil ends on those caps.

[pdf64]

Cap construction can differ from one type to another. Be prepared for no discernible shielding effect, hum is the same either way around.

[ViperDoc]

I've seen various ways of testing the foil side. They don't seem to translate very well over iPhone audio. I did see one that sounded quite obvious using a DIY device he had made, but he was finding the biggest audible difference at 20 Hz on a generator. I'm not sure if that would relevant! I would add up technically, though, right?