interesting idea about tremolo/vibrato

[phsyconoodler]

I was monkeying around last night and was playing while a friend rapidly moved the tone control on the amp up and down.
  The effect was very much like a univibe. It was pretty uncanny.
 What if there was a way to make the treble cap oscillate it's capacitance? Already done?

Varying the volume on the guitar sounds like an optoisolator on/off effect,but the tone control on the amp and guitar make it sound cool.
  Yeah I know,maybe I'm 50 years late but my brain is active right now and it wants to be fed.

Magnatone 'varistor' doing this?

[plexi50]

Cool idea! What about an oscillating PI? Just an off the wall thought
Im doing something different here by building a Fender AB864 using octal 6SN7 & 6SL7 preamp tubes

[phsyconoodler]

I made my V-Verb's vibrato sound very much like a univibe but the treble thing sounds very interesting indeed.Nothing is oscillating,just the treble is being varied.Maybe make a wah pedal that taps into the treble control on the amp. Now I'm getting giddy!

[HotBluePlates]

This seems like the basic plan of the Fender vibrato circuit (using 3 or 3-1/2 tubes).

You have a typical oscillator. The oscillator signal is fed to a split load inverter, whose output then passes through a low-pass and a high-pass filter (different filter on each leg). You now have a trebly signal and a bassy signal, 180 degrees out of phase. The guitar signal is mixed in at this point, and there is a differential stage which passes either the trebly or bassy signal on to the rest of the amp's circuit.

Fender 6G12-A Concert

Totally different method, maybe more in line with what you're wanting to try:

The is a component which is a voltage-controlled variable capacitor, which is called a varactor. I don't know the range of capacitance available, or the voltage ratings available. It would normally be seen in RF tuning circuits in solid state radio circuits. Maybe there is a varactor with a large enough capacitance and/or large enough voltage rating for your use.

[Iannone]

Perhaps you could use a vactrol in conjunction with a variable voltage DC power supply in place of the tone pot?  I'd have to think about how to get a meaning voltage range and how to control the speed of the voltage changes, but my first impression is that it might be a promising approach.

[kagliostro]

 http://it.rs-online.com/web/c/?sra=oss&searchTerm=varicap&x=0&y=0

here may be there is something of interesting about led and rectifier diodes use

http://www.hanssummers.com/varicap.html

Kagliostro

[Shrapnel]

Perhaps you could use a vactrol in conjunction with a variable voltage DC power supply in place of the tone pot?  I'd have to think about how to get a meaning voltage range and how to control the speed of the voltage changes, but my first impression is that it might be a promising approach.

Sounds like the thought I was having. Using a "roach" or a modern similar functioning version mimic a series resistor (or more precisely, a potentiometer). AS the trem oscillator does its thing, it then varies the resistance in series with a bypass or bright cap, which in turn, as we well know, changes the bleed-off from the cap.

http://it.rs-online.com/web/c/?sra=oss&searchTerm=varicap&x=0&y=0

here may be there is something of interesting about led and rectifier diodes use

http://www.hanssummers.com/varicap.html

Kagliostro

That first link looks like it is all surface mount chips.  The second link I can't say much about, as I couldn't access the site.

[tubeswell]

I like the saturable-reactor-based vibrato that Steve Lucky did a while back. I have acquired a couple of these SRs thanks to Brad (Willabe) and am going to integrate one into my next combo.  Merlin Blencowe's vibratron also intrigues me (as a simpler circuit) http://www.freewebs.com/valvewizard1/Vibe.mp3

[kagliostro]

That first link looks like it is all surface mount chips.  The second link I can't say much about, as I couldn't access the sit

the first link was only to have an idea of which capacitance and voltage rating has the varicap that are easy to find

the second link, .................... you must read, sorry you can't

Kagliostro

[Shrapnel]

That first link looks like it is all surface mount chips.  The second link I can't say much about, as I couldn't access the sit

the first link was only to have an idea of which capacitance and voltage rating has the varicap that are easy to find

the second link, .................... you must read, sorry you can't

Kagliostro

Tonight I was able to access the second link, and READ it now.  So I assume the internet, or my ISP had some hiccups.

[Willabe]

Kagliostro

Tonight I was able to access the second link, and READ it now. 

And ?


                Brad     

[Shrapnel]

Tonight I was able to access the second link, and READ it now. 

And ?


                Brad     

It's all about Varicap diodes (varactors).. or with parts, using LEDs and regular rectifier or zener type diodes as substitutions... as they don't go obsolete and disappear every few years. It's mostly on the RF side of Amateur HAM radio though, so I dunno how well it would work, as I've never experimented even with the diodes tagged and bagged  with the label. Forward and reverse biased diodes (LED & Recto) He seemed to get variable capacitance from them. I'm not sure if its just at RF frequencies that this would be useful, not to mention the series resistors involved usually don't give it much room to conduct. With our signal voltages, we can't even think of forward baised diodes for a varicap, so that leaves reverse bias only, and mileage may vary in the exact pF values you get.


This page here, http://www.zl2pd.com/Varicaps.html, is provided by Hans Summers and looks to be more organized as to the status of the variable capacitance diodes. Again, it seems to be geared at RF applications.

[Merlin]

This all sounds awfully complicated for an auto-tone pot. A tone pot is just a variable resistor in series with a cap to ground, so if you replaced the resistor with an LDR, that's it. (And an oscillator to drive an LED of course..)

[phsyconoodler]

Indeed.Simple works for me! I'm going to try using an oscillator to an LDR.I really like the sound of varying the tone control,just need a way to control it. Oscillator-LDR-speed control-treble pot. And a switch to turn off the oscillator and bypass the LDR.

 Maybe a solid state oscillator circuit would be nice and compact and the entire circuit could be dropped onto a PC board.Connect a couple of wires and pop it into your favorite amp.

Or.....simply tie the tone control into the optoisolator photo resistor and oscillate the resistance of the treble control rather than the PI.
I might try it out on a Fender amp just for fun.