I want to build a tremolo inspired by the Colorsound trem (phase shift oscillator driving a tranny as the variable resistor). I've done research and learned how phase shift oscillators work...
now I've seen a Twin T oscillator on R.G. Keen's site (quick and dirty test oscillator). I've tinkered with twin-T filters in the past and now I have some questions.
1) Would a twin-T style oscillator work well in a tremolo circuit?
2) What frequency should I choose for a tremolo (to determine the size of the R's and C's)? Something like 5 Hz?
3) I would then vary the frequency by making the 0.5 R leg of the twin-T variable (speed pot)... this way, would the range of the speed pot be big enough? Or should I put a pot in series with the 0.5 R resistor? Or rather a dual pot in place of the two R's?
Basically, I want opinions on using a twin-T oscillator for a tremolo... instead of the "normal" RC network oscillator (three RC's to make the 180 degree shift).
Has anybody tried this?
Quote from: sunder1) Would a twin-T style oscillator work well in a tremolo circuit?
I've mainly seen twin-T style networks used in conjunction with an op-amp, but also came across one recently for bi-polar in a mag.
Quote2) What frequency should I choose for a tremolo (to determine the size of the R's and C's)? Something like 5 Hz?
1-12 Hz is a good range
Quote3) I would then vary the frequency by making the 0.5 R leg of the twin-T variable (speed pot)... this way, would the range of the speed pot be big enough? Or should I put a pot in series with the 0.5 R resistor? Or rather a dual pot in place of the two R's?
The schematics I've seen just use one.
The amplitude won't be consistent across the range of the pot's travel (unless you go for some form of auto-gain control), but that's not a problem provided the gain isn't too high (adjust depth control to compensate).
QuoteHas anybody tried this?
Not what you're talking about no, but schematics exist. I've messed around with plenty of tremolos though and 1-12 Hz is a good range.
Example here (well, bridged T):
http://members.chello.at/anubics/html/schematics/Anubics_TremoloOne.gif
Has anybody tried this?
Check out
http://www.geocities.com/transmogrifox/DUEL-212.PDF
page 4 upper right hand corner. Peavey uses this Twin T LFO in their Duel 212 amp tremolo. I have a 212 and the only gripe I have about the tremolo is that it significantly reduces the overall volume when it's on. If you build a stompbox of it, you can compensate with some amplification and a volume knob.
I just tried to follow that link to see if it would work...
You need to copy and paste it into a browser. I don't know why geocities does that, but that is a legitimate link.
If you have trouble and want the schematic, then email and I'll send it to you.
It's protection against people remote-linking and using geocities as storage space ;)
So it seems to work.
That Peavey schem is cool; but it's not very sharp in Ghostview. I have some trouble reading the values; as I read them,
2M2 (twice)
1K (should be 1M no?)
and the speed pot is ? 50K?
and the caps:
0.22 (twice)
0.1 (should be 0.47, no?)
is that right? can anyone read them properly?
hm, that looks like a mis-tuned twin-T... normally, it's two R's, one half R, two C's and one double C. Why should it be mis-tuned?
I'm dumbbb... I didn't look carefully enough. The Kay tremolo and the "controllable tremolo circuit" (links on schematics page) use twin-T oscillators, too.
Using bridged T will of course get the parts count down... a good thing IMO.