Tremolo LFO connections??

[trad3mark]

Hey all,

I'm working on a VERY ambitious tremolo project at the moment. So far, I've my gain stage chosen and breadboarded, I'm just working on the actual LFO type stage. I'm actually working off one that i've come across in another schematic. My question is, in a lot of the tremolo schematics, the LFO seems to be connected to the gain control. Does it matter where the LFO is connected, as long as it's part of the signal path? Like what if, for example, before the volume pot, the LFO was connected in there? would that work?

I'm not too familiar with how LFO's work, or how they work in tremolos, but i'm remaining optimistic that this will work. It would be the first really successful build i've done in a while.

Cheers,
N

[Hides-His-Eyes]

I think what you're asking is about the VACTROL, not the LFO signal, right?

It can be done (see: Tiny Tremolo project) but the 'lune' method is ubiquitous for a reason; clean, simple, adjustable operation without the need for additional buffering.

[smallbearelec]

Once you have decided on which LFO circuit you will use, you need to decide just How you will marry it to the gain stage. There are numerous ways to do this. Some trems use the LFO signal to drive a lamp or LED that then varies the resistance of a photocell in the signal path. Others apply the signal to the controlling element of a transistor/FET/tube/VCA IC. You will probably want to breadboard in order to try out both a variety of LFOs and coupling arrangements.

[PRR]

> my gain stage chosen

Tremolo needs a VARIABLE-GAIN stage.

Obviously any gain stage can be made "variable". Put a pot before, in the middle, or after it.

And you can tremolo with a pot. Standard-trick to jiggle your guitar knob with your pinkie finger. And you could automate that with a motor, crank, rack, and other standard mechanical tricks.

Size and wear may be problems.

Can you control an amplifier with an electric signal? Obviously.

What is good, cheap, and simple?

Hides and Smallbear ran down the most popular choices.

Photoresistor is hard to beat for audio purity. cost is reasonable, but it does need some drive power (not so much now we have LEDs).

JFET is cheaper and insignificant drive power, but max undistorted signal level is small, leading to noise problems. Can be done excellently, but needs insight.

The 3080 and kin chips have gain proportional to a current (which can be derived from a voltage wave with a resistor). Again the max input is limited, S/N may be good but rarely great, and it is a pain to compute the optimum values.

There are precision voltage-controlled amplifiers/attenuators with better S/N at higher prices. The THAT Corp VCAs are marvelous tools, but need a lot of interfacing.

There is the funky way. At normal bias, an amplifier has gain. If thrown off-bias, gain changes, and gain always falls to zero at zero current. Since the signal port and bias port are often the same (grid-catode, base-emitter, gate-source), it "works" to just add the LFO voltage to the signal and bias voltage at the device. Many tube-amps do it this way. In simple amplifiers, this bias-swing causes large bias-shift at the output, large "thumping", suggesting heavy low-cut filtering before the next stage. Also the max clean input signal tends to reduce at low gains.

> in a lot of the tremolo schematics, the LFO seems to be connected to the gain control.

"Gain control" is potentiometer? The LFO isn't affecting the pot (unless there is a motor etc involved). Ask what ELSE happens at that point. Is it tossing a bias around?