Switchable harmonic/amplitude tremolo

[cdemike]

I'm planning out an upcoming Marshall style build and have been kicking around the idea of adding tremolo. I really like the Brown Fender harmonic tremolo sound, and I also think the regular amplitude style would nice to have available, so I've been trying to design a simple circuit that can be switched to do both or to be completely bypassed. I think Sluckey's Trem-o-nator is really elegant in being so straightforward using a single triode, so my thought was to try to adapt its LFO to drive a harmonic trem circuit with positive amplitude provided by rectifying an unused 5v tube rectifier tap (the build will most likely use a JTM45-style PT, but I'm going with solid state rectification). The circuit would fit after the volume control in a plexi-style preamp before it feeds V2.

I've attached a draft schematic. I feel reasonably confident that the amplitude trem would work since it's been well-tested, but I'm not sure about the harmonic trem. The overall design is starting to get complicated with some modifications to the preamp, so I'm aiming for simplicity with a reasonable approximation of the Brown Fender harmonic tremolo sound. Does this look like it'd work?

[maxkracht]

I don't understand what the 7v is for. Here's a well documented harmonic tremolo from sluckeys website if that helps. https://sluckeyamps.com/revibe/revibe.htm You could build that exact circuit and wiggle a preamp tube like a vibrochamp for your regular tremolo.

[maxkracht]

Or an 18w marshall. Forgot the vibrochamp uses another tube...

[cdemike]

Thank you so much! The 7V is so that the cathodyne sees both positive and negative signal amplitude rather than just different magnitudes of resistance to ground as with the regular opto trem. I'm totally good with any design as long as it's at least somewhat simpler than the regular Brown 5-triode circuit due to space constraints in the chassis. I should have mentioned that I'm not completely sold on working it into the build, so I'm mostly exploring to see if there's a way to work it into the build without the build becoming unmanageably crowded while I wait for transformers, shipping, etc.

So really there are 3 options: build the "vanilla" amp and a separate revibe (Sluckey's would be toward the top of the list since it's well-documented), build the amp with an amplitude-only vibrato to keep things simple, or figure out a circuit that lets me build the amp with both kinds of tremolo. My threshold for overly complicated/crowded lies at using more than 2 additional tubes and associated components (also because I have a thing about unused triodes). The design as it stands now (bottom of https://ampgarage.com/forum/viewtopic.php?f=6&t=36339) doesn't have any unused triodes, so it'd be a process of adding an even number of triodes.

I completely forgot about the Vibrochamp trem -- definitely a good contender which also would let me avoid an unused triode. Seems like V2A would be a good candidate (unless it messes with the DCCF -- seems fine?).

[maxkracht]

You could easily implement a transistorized LFO. I have seen several lnd150 and irf820 versions, might help your search terms. Here's a slightly more complicated one from R.G. Keen, but plenty of options out there. http://www.geofex.com/Article_Folders/s ... remolo.htm. You don't need a tube to start the wiggle to get the sound of a wiggling tube.

[cdemike]

You could easily implement a transistorized LFO. I have seen several lnd150 and irf820 versions, might help your search terms. Here's a slightly more complicated one from R.G. Keen, but plenty of options out there. http://www.geofex.com/Article_Folders/s ... remolo.htm. You don't need a tube to start the wiggle to get the sound of a wiggling tube.

Good idea. I ran with the solid state LFO and tried to see if I could make it work with the switchable approach as well. I wanted to see if I could make the VTL5C1 work in lieu of the typical Fender opto-resistor, since I like the smoother edges, so I used a solid state adaptation of the Trem-o-nator (also from Sluckey's site: https://sluckeyamps.com/trem/Leevi_rt.pdf). I realized I probably don't need to go that far out of my way to switch from variable positive signal like in the stock Trem-o-nator circuit if I use a ground-referenced coupling cap of a fairly high value. So I used that as a starting point using two oppositely-oriented optocouplers. The rotary switch's settings would be:
1. Bypassed
2. Amplitude tremolo
3. Harmonic tremolo

How does this look?

[maxkracht]

No idea If it would work, I am an idiot, but seems reasonable at first glance. If you want to add to the complexity, you can switch on and off either side of the harmonic tremolo. Haven't tried it, but might be cool.