Looking for a tremolo circuit.

[überfuzz]

I'm building an amplifier in which I like to have tremolo. I'm thinking a opto-bug tremolo that dumps signal to ground (but I'm open to suggestions). Anyone got a circuit or could anyone point out a nice tremolo circuit?

Cheer!

[tubeswell]

IAnyone got a circuit or could anyone point out a nice tremolo circuit?

Garden variety trems:

BF style with 1 x 12AX7 and LDR bug wiggling the pre-amp signal is quite smooth trem

Bias vary trem at output tubes (5G9 or 6G9B, 6G16) is more dramatic hypnotic bang for buck


Other, real-estate hungry, 'trems':

Brown harmonic trem (if you have room for 2 or 3 extra 12AX7s)

Maggie 260 "trem" with the 4 hard-to-find (and expensive) varistors in the resistance/capacitance bridge and several 12AU7s or 6CG7s

Vox AC30 'trem' with heaps of caps, resistors and a 12AX7 and a 12AU7

Hammond Organ 'trem' with a SR in a resistance/reactance bridge, and a couple of 12AU7s in addition to the LFO stage (needs the most real-estate to implement, but sounds quite spectacular)

Ampeg trem (uses photoresistors) Schematic

[Chuck H]

Bias vary trem at output tubes (5G9 or 6G9B, 6G16) is more dramatic hypnotic bang for buck

I'll start by mentioning that this is a great rundown of typical tube trem circuits. Thank you. Now...

Wouldn't the 470k cathode follower arrangement of the above mentioned amps cause a problem with most currently available preamp tubes? I'm looking at implementing a power tube bias vary trem and I've been trying to find alternative coupling examples because of the New Sensor preamp tube cathode problems. I'll be modulating EL34's so I won't need quite as much swing. I'm hoping that a 100k cathode resistor will be enough. By going with 100k cathode and elevating the filaments on a 50VDC bias I'm hoping to avoid the need to use only certain tubes for the trem circuit.

[tubeswell]

Wouldn't the 470k cathode follower arrangement of the above mentioned amps cause a problem with most currently available preamp tubes?

If 'currently available' = modern production, then sadly admittedly, yes.

In the last 3 bias-wary trem amps I've built, I've used a mosfet source follower (in place of the CF) to successfully overcome this issue.

In another amp I used a cathode-biased CF stage (with a 100k load) AC-coupled to the LFO, whereupon the cathode voltage came to 172V (with 426 HT), and it held up pretty well. (Prior to that I had a DC-coupled CF and the cathode voltage was around 220). You could possibly even go to a 56k load resistor this way and get the cathode voltage down further. You lose a bit of swing, but there's plenty of current. Another way would be level-shifting.

[überfuzz]

Thanks for the input fellas! Although it almost led to a technical overload.

At first glance the Ampeg tremolo looks kind of complicated. Then most seem to have serious tube craving. If I beg on my knees, could I see you mosfet circuit? I've tried to make one myself without any success...

I really like like the ab763 for the simplicity, but it would be fun to try something new.

[rathmann]

Remember that the oscillators of most vib/trem circuits are largely the same, and given that they're not in the audio chain can be replaced with mosfets a la R.G. Keen's "Solid State Replacement for the Fender Tremolo" available here http://www.geofex.com/Article_Folder.../sstremolo.htm. This can certainly free up a stage (or two as in the "brownface" trem) allowing the choice to go with a more complex trem not be limited by number of tube stages available. As written up here it's essentially a drop-in replacement for many of the Fender tremolos, but shouldn't require too much tweaking for any other trem circuit.

tubeswell - have you had any experience with either the AC30 or Ampeg trems? Any opinions on the sound of these? I love the "harmonic" trem I did in a SE combo but want to branch out and try a different "phasery" option.

[tubeswell]

tubeswell - have you had any experience with either the AC30 or Ampeg trems? Any opinions on the sound of these? I love the "harmonic" trem I did in a SE combo but want to branch out and try a different "phasery" option.

Nah - I just happened to come across to after I'd built the Hammond Organ vibrato unit and someone pointed out to me that Ampeg had done a similar thing with photoresistors (instead of an SR unit) , which I thought looked cool. I do like the sound of the SR unit vibrato, and I guess its possibly a bit 'smoother' than the Ampeg version, because of the reactance bridge, but the SR units are relative cheap (like US$20 on e-bay) so whether the photoresistors are much of an economic advantage for a one-off build its hard to say. But I sure would be interested to hear the Ampeg version.

[tubeswell]

Thanks for the input fellas! Although it almost led to a technical overload.

At first glance the Ampeg tremolo looks kind of complicated. Then most seem to have serious tube craving. If I beg on my knees, could I see you mosfet circuit? I've tried to make one myself without any success...

I really like like the ab763 for the simplicity, but it would be fun to try something new.

Apart from the link to R.G.'s fet circuit in rathmann's post, here is a simple version of the source follower I use with a normal LFO triode stage:

[tubegeek]

I am gathering the last few parts needed to take a junked AM/FM radio and convert it into this, a Valco/Supro/Gretsch amp on a small, Champ-like scale. This schematic is not completely as originally drawn - I photo-edited the trem section to make it easier for me to follow and to add an INTENSITY control - but none of the values are any different.

Has anyone got an opinion on/experience with this circuit?

I am planning to try embiggening the cap values in the oscillator to slow it down if needed, based on a comment I read . . . somewhere . . . .

[Rhodesplyr]

Hammond Organ 'trem' with a SR in a resistance/reactance bridge, and a couple of 12AU7s in addition to the LFO stage (needs the most real-estate to implement, but sounds quite spectacular)

Which Hammond 'trem' are you talking about here? The tonewheel organs from 1945 to 1975 need a rotating multi-pole air capacitor (the scanner) in addition to the phase delay line and a complicated multi-contact switch to vary the depth. The pre-1945 organs had a "tremulant" that was also operated by the organ's run motor.

I have heard of one or two people adapting the scanner and phase delay line as a stand-alone vibrato/chorus unit, but it's rare.

David

[tubeswell]

Which Hammond 'trem' are you talking about here?

http://music-electronics-forum.com/t27630/

In this one I used an AO-47 saturable reactor unit from a Hammond Organ vibrato. I've got another SR unit I'm saving for a combo build