[sdiy] Varistors in tremolo circuits: worth it? Merits of various tremolo methods?

[anthony]

Whoa, so it's really like a frequency-modulating vibrato? There's so much 
confusion in the music world as to which is which. I always have a clear 
distinction in my mind: The whammy bar is a VIBRATO and the knob marked 
"Vibrato" on that Fender amp (someone else's, not mine for sure... only 
because I am a pauper...) is tremolo. And a Leslie speaker does both at the 
same time: with two mics you can make one or the other stand out more, along 
with stereo spread etc. etc. And of course I've always been partial to the 
Hammond scanner vibrato. I need more electromechanical sound-makers in my 
life! (Hmmm I have a lot of solenoids and a couple of child's 
xylophones...). Always wanted to make a sequencer that was based on a 
spinning rotor, lights/LDR's or even hall effect sensors.

But I digress...

So, how do varistors make true vibrato possible? (Perhaps I should pore over 
the schematic I have a little more carefully...)

St. Elsewhere,
Anthony


----- Original Message ----- 
From: "Bob Weigel" <sounddoctorin at imt.net>
To: "anthony" <aankrom at bluemarble.net>; "synthdiy" 
<synth-diy at dropmix.xs4all.nl>
Sent: Monday, April 28, 2008 11:26 PM
Subject: Re: [sdiy] Varistors in tremolo circuits: worth it? Merits of 
various tremolo methods?


> It's not a tremolo.  It's vibrato.  That's what made the magnatone 
> special.   It is a cool circuit for sure.  Had to troubleshoot one long 
> ago. Was a pain. -Bob
>
> anthony wrote:
>
>> I have a nice stash of many varistors that I've collected from countless 
>> old power supplies & surge protectors & such.
>>
>> I noticed that Magnatone used varistors in at least one of their amps - I 
>> think it was for the tremolo circuit. How does the sound quality compare 
>> to other tremolo circuits? Is it worth the hassle of figuring out what 
>> the specs of each of my varistors is and trying it out? I have quite a 
>> few SNR130K20's.
>>
>> This made me wonder about a comparison of all of the methods used for 
>> tremolo circuits in tube amps: how do they compare? Which is better? Or 
>> is it more of a Beethoven vs. Bach comparison?
>>
>> I notice that most amps that have tremolo are push-pull amps and the LFO 
>> modulates the bias on the power tubes.
>>
>> Single-ended amps with tremolo do it by varying the cathode bias of the 
>> last gain stage before the power tube.
>>
>> There is definitely room for a big difference in the way the tremolo 
>> could sound between these methods.
>>
>> And then there is the lamp/LDR method that seems to be a lot less common 
>> in tube amps, although many great tremolos have been made based on LDR's. 
>> I think both neon and incandescent lamps have been used. I would guess 
>> that neon would yield a nice and choppy tremolo, but wouldn't be reliable 
>> over time. Same with the incandescent lamp really.
>>
>> And THEN I started thinking about tube amps with tremolo AND reverb and 
>> how the reverb sound is modulated along with the dry signal just the 
>> same, but I would think that it would be better to have the tremolo bang 
>> on the reverb. My studies of Hammond Organ schematics have revealed their 
>> clever way of doing this: they just take the output from the main amp, 
>> use a light bulb to reduce the volume and drive the reverb tank straight 
>> from that - no reverb transformer. The reverb output goes to a separate 
>> amp and maybe even its own speaker. But it made me think you could make a 
>> groovy little(ish) 2x10 combo amp with a tremolo/dry sound in one speaker 
>> and another amp with the reverb sound, taken from the secondary output of 
>> the 1st amp's output transformer straight into the reverb tank (with 
>> attenuation of course). You could probably do it with one speaker by 
>> mixing the reverb back into the power tube.
>>
>> Lastly, I want to make a dual clone of a Gibson GA-5T Crestline (have the 
>> 6AQ5A's and the 6X4's...). I want to make the tremolo(s) work 
>> independent, in unison (just one LFO) and then panning. One thing I don't 
>> think I've seen a schematic for is a tube circuit that shifts the phase 
>> of an LFO signal 180 degrees. Pretty much the same way you'd do it with 
>> solid state parts?
>>
>> SpongeBob SquarePants,
>> Anthony
>>
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>
>