Fender Vibrato Circuit: Twin or Princeton?

[Colossal]

7ender aficionados!

...any preferences towards one vibrato circuit over another?

Princeton Reverb: bias oscillator
Twin/Vibroverb/Deluxe: optoisolator

[Milkmansound]

If you have room for a whole tube tremolo - vibro champ! It's the deepest chopping tremolo fender made. Otherwise I'd say Princeton - its much more subtle and lush than the opto trem

[Teleguy61]

Ditto what mms said.
The Princeton bias vary trem is a great sounding effect.

[Firestorm]

Definitely the Princeton or Vibrochamp versus the LDR. Personally, I like modulating the output tube bias instead of doing it to a preamp, because it is so smooth sounding, but tastes vary.

If you modulate the output tube bias, you have to set the absolute bias of the tubes fairly cold, or the trem won't be as deep.

[Colossal]

If you have room for a whole tube tremolo - vibro champ! It's the deepest chopping tremolo fender made. Otherwise I'd say Princeton - its much more subtle and lush than the opto trem

Ditto what mms said.
The Princeton bias vary trem is a great sounding effect.

I have a Princeton Reverb clone but with a 6L6 power section on the bench at the moment. I personally love the sound of the bias tremolo. I just haven't compared it directly to the circuit in the Twin but have read accounts of those who also said they felt the LDR circuit was not as good.

Definitely the Princeton or Vibrochamp versus the LDR. Personally, I like modulating the output tube bias instead of doing it to a preamp, because it is so smooth sounding, but tastes vary.

If you modulate the output tube bias, you have to set the absolute bias of the tubes fairly cold, or the trem won't be as deep.

I completely agree with your assessment! It does sound very lush indeed. The amp I've got here is Princeton Reverb circuit (modded cathodyne with 100k instead of 56k stock) operating with 2x6L6s on a Vibrolux PT. 405V on the plates (GZ34 rectified) and bias voltage is right around -43.5V at the grid leaks. Cathode current is pretty low at 22.5mA. I need to tweak the bias resistor to get a little more range out.

Thanks for the comments guys, much appreciated. I kind of figured the answer would be in favor of the Princeton/Vibrochamp circuit over the Twin/Vibroverb but it's good to see that backed up 3-0!

[Phil_S]

What Milkman said...bias wiggle! No LDR/roach which doesn't sound as good and is subject to emitting a clicking noise under certain circumstances.

[rp]

Never really paid careful attention to the different Fender types, but I thought the 2x10 brown Vibroverb had a lovely vibrato - better than the later opto-bug ones. Uses a whole tube if I read it right. Didn't Cliff build one of these?

[jjman]

I have opto, bias, and VC types. All can have quirks. VC affects the gain if you adjust the intensity, even when switched off. This because that control affects the dc bias of a preamp stage, as well as the ac trem signal to it. Opto can have the tick-tick problem. Output bias type affects all channels but that's not a problem for me.

I think they are all cool but the output bias type avoids the gain-change and tick-tick risks. It needs to be capable of a strong effect since I like the machine-gun option. Not sure if the single triode Princeton type is that strong. Using 2 triodes allows for the output off a cathode which should have more stamina. Mine is on an old 2xel84 Harmony and uses a small pentode 6au6 for trem.

[Tyrannocaster]

I am not a fan of roach trems in general, but note this info, which I got over on Doug Hoffman's site. The ticking goes away if you substitute an incandescant bulb or LED for the neon roach:


1. Cut open the trem bug.
2. Remove the neon lamp.
3. Replace the neon lamp with a red LED. (See notes.)
4. Tape up the modified trem bug.

Note 1: The LED is polar, so it'll only work one way. Before you tape up the trem bug, warm up the amp and see whether the LED blinks. If it doesn't, reverse its leads.

Note 2: You should pick an LED that's about the same size as the photocell(s) and frosted so it diffuses the light to cover the cell(s). I spec'd red because the red LEDs seemed to be brighter than the yellow and green LEDs that came in the same blister pack I bought from Radio Shack.

This fix works because the LED is a current-sensitive device and the trem circuit contains a 100K resistor to limit the current to an appropriate value for the LED. The ticking is gone because there's no sudden large voltage change across the LED (as there was across the neon lamp) to get coupled through the photocells into the sensitive audio circuitry.

[Cliff Schecht]

Yeah I built a Vibroverb and love the trem on it. The only caveat with this trem circuit (as built stock) is if you bias your amp at 70% then the trem sounds a little weak. Biasing close to 60-65% gives a much stronger trem effect but you lose some magic reducing the output stage bias current. I left it stock but it's an easy fix to increase the intensity if desired.

[rp]

...The ticking goes away if you substitute an incandescant bulb or LED for the neon roach...

Awesome little tip, wish I still had a BF to try it on. Wish I still had my Vibroverb, wish...

[Colossal]

Yeah I built a Vibroverb and love the trem on it. The only caveat with this trem circuit (as built stock) is if you bias your amp at 70% then the trem sounds a little weak. Biasing close to 60-65% gives a much stronger trem effect but you lose some magic reducing the output stage bias current. I left it stock but it's an easy fix to increase the intensity if desired.

Cliff, where did you set your grid bias voltage to and where did your output current end up?

Thanks,
Dave

[tubeswell]

I prefer the 5G9 (with 6V6s) or the 6G9B (with 6L6s) trem

[Bear]

Hmm. Might have to think more about VC preamp bias based options. No issues with post-PI driver stages, ala SSS. Harder chop is good with me, too.

[C Moore]

http://www.el34world.com/charts/Schemat ... _AA764.pdf
Can I butt in without causing trouble.....
Is there an explanation to how this circuit works.?
I thought Merlin explained it, maybe I need to look again. This is not phase shift is it.?
Thank You