Has anyone pedalized the Preimier amp tremolo?

[midwayfair]

A discussion came up on The Gear Page today, so I looked at the schematic, expecting to see a typical bias-modulated tremolo circuit like in Fenders, and got lost somewhere on the third tube. 

Because the world can never have too much tremolo ... is anyone aware of a pedalization of this one?

[teemuk]

Which premier amp? What discussion?

Care to share a bit more information about these references?

No, I'm not aware of anyone making a pedal out of tremolo circuits of Premier amps.

[midwayfair]

Here's a schematic for one of the amps that has it -- all the 50s Premier amps seem to have had the same tremolo.

http://www.harpamps.com/premier/Premier76.pdf

A link to the discussion is not, it just came up because someone was asking about the tremolo on "Rumble." It's a pretty complicated way to get tremolo (2.5 tubes and an inductor), so I'm not sure there's any reasonable call for making it a pedal, but it also has some vibe/phasing characteristics. I've been surprised by some of the things people have already turned into pedals, so I just thought I'd check if anyone was aware of a pedalization.

[teemuk]

I agree, it's an unneccessarily complex circuit for what it is.

The LFO is practically a pretty standard phase shift oscillator and such circuit can also be built without the inductor - as it is done usually, including in most Premier's other amps. Inductor is really not needed to make identically operating circuit.

One of the tube stages is also nothing but a mere buffer for the LFO's output. Basically it's there to control the grid bias with low impedance source. Yes, by its operating principle this circuit is still nothing but a bias shift tremolo, though the bias shift modulating stage is a pretty weird and complex one. Again in many other Premier amps the circuit is simplified not to include the buffer stage. It is not neccessary.

Effectively pretty much identical circuit could be built with only three tube stages, plus one stage for the LF Oscillator. The latter circuit might even be solid-state-based because one only needs a low frequency oscillator circuit that has a sinusoidal output in proper amplitude range.

Yep, bias shift oscillators tend to have some interesting characteristics, some might even call them flaws or drawbacks. The signal rides atop LF component that is much higher in amplitude than the actual signal. The LF component gradually shifts "DC" bias, therefore altering gain of the stage. There's a great chance to overdrive the gain modulating stage, in which case the output signal usually distorts in some pretty weird ways. Also, the LF component must be removed effectively post modulation or it will introduce strange "side noises" to the signal, or again proceed to overdrive stages with some pretty weird ways. These caharacteristics were annoying enough to causee designers spend great efforts in developing push-pull DC bias modulators or to employ variable resistive elements like photocells, FETs and et cetera.

All in all, IMO, the simple bias modulation (and the drawbacks introduced by such scheme) is the most important part in the signature tone of such tremolos, not so much the overall architecture of the circuitry. Simple bias shift tremolos with similar characteristics therefore do exist, probably a great deal of such designs in pedal format too. They likely do not employ identical circuitry but their main principle of operation and tone resulting from it likely does not differ drastically. However, I do feel that many people actually share the agreement that such tremolo circuits have severe drawbacks tone-wise and actually prefer other modulation methods, making tremolo designs employing such methods far more popular in comparison.

[midwayfair]

Thanks so much for the breakdown! I'm horrible at analyzing tube circuits, so this was a big help.

[teemuk]

I suggest you take a look at some other Premier amp schematics as they display the circuit in much simpler format.