Tremolo - design challenge

[rathmann]

I've decided to build a standalone preamp for my next project. I'm planning on a two channel switcher but would also like to incorporate a brownface-type "harmonic tremolo". I've done the trem before in a small combo with some really nice results. It's basically the stock front end of any of the "6gXX-a" amps of the era, so while the amp will overdrive very nicely (paralleled SE EL84 output) it's clearly a combination of preamp and poweramp clipping.

In the combo, the tremolo effect essentially goes away when everything is wide open and the signal's well overdriven. The circuit does add a pretty cool almost "autowah" effect to the attack, but still the tremolo is barely noticeable until things quiet down a bit. In the channel switcher preamp I can't decide if the tremolo effect would be best pre or post distortion.

I'm inclined to put it first. Not totally sure why, but it seems like keeping the signal to the trem fairly manageable would make the effect more pronounced. OTOH I already use a Dunlop Rotovibe for some swirl before the preamp. Maybe the footpedal would find it's way into the effects loop - post distortion. Hmm.

Regardless of the location, with a DP4T switch I can have the trem affect the clean channel or the dirty channel, both, or remove the trem circuit entirely. But I'm not sure the location in the topology is really all that flexible once designed and built.

Any thoughts would be appreciated.

steve

[Enzo]

My first thought is this. If the trem comes before the overdrive, then you could have the situation where the trem is moving the signal into and out of the distortion area with each pulse. Might be desirable as a special effect, but not for everyday trem.

I look at it like ordering effects. For example I would much rather have a reverberated distortion than a distorted reverberation. In other words I want my amp to sound like it is overdriven in a reverberant room, instead of a reverberating amp recorded through distortion.

Just me, though.

This may be a two channel preamp, but are you going to make it so both channels play at once? If the thing will switch from one to the other, why bother to switch the trem from channel to channel? If it trems the unused channel, who would hear it?

Or do you want to switch from one channel with to the other without? If it is preassigned to a channel then channel switching would include it where wanted. If you have two channels, and add the trem after the point they mix together, then no selection is required, just on/off.

[rathmann]

Thanks for the comments Enzo.

I guess the reason for wanting to have the trem assignment switchable is to provide the option for true bypass of the trem circuit. Remember that the brownface trem splits the signal into hi/lo frequency components and oscillates them out of phase. Even when when the effect is "off" the mixer is still in the circuit. Maybe the effect of that would be negligible, maybe it would be really cool, or maybe it'd suck. I guess I won't really know unless I experiment with it.

Functionally, it might be nice to have the trem only on the clean channel and be able to switch to the lead channel without having to stomp a second switch to turn the trem off. The assignment switch would allow the flexibility of all combinations. But that's not really the issue.

I like the idea that the trem may affect distortion characteristics, and I agree that reverb and long delay effects sound best after distortion stages, but I still tend to put my short analog delay, wah, and swirly effects before everything.

I still think I'm going to put it first in the chain, but maybe when I get to designing the layout I'll keep in mind that this might need to change.

Actually, at one point I considered building the trem as kind of a third channel in the preamp that would have it's own input and output jacks. I could then use patch cables to connect it pre or post the switchable channels.

What this is really telling me is I need to setup a good breadboarding system so I can more easily prototype this stuff and listen to and play through it instead of speculating...

[rathmann]

Alright. Enzo, I think your your initial hunch is likely the way to go.

When conjecture and speculation don't resolve things, go empirical!

I busted out the ole hotplate and used the combo amp with the trem and my channel switcher head to try out and get a feel for the differences. And while it will likely sound a bit different combined in a single unit, bottom line was it sounded much better with the trem first in the chain. The effect you described was certainly there when I backed off the guitar volume -just a touch of distortion that came and went modulated by the LFO. At full distorted lead the trem effect was attenuated (most likely due to the compression of the high gain channel) the the cool tonal sag was there. It might not be an effect for everyone but I kind of liked it. It added a new dimension to the dynamic response.

When the trem was after the distortion it was way too pronounced and quickly became rather irritating. It didn't have any dynamics and was too extreme even with the depth set fairly low.

I'll finish up the design and report back when I have something up and running.