Double Flush

[Guybrush]

Hi all

I'm looking to put together a Madbean Double Flush tremolo and have a question.

Can anyone tell me what the Intensity knob does? The build doc says it increases the intensity of the tremolo but I'm not really sure how that translates into sound. Does it change the trem from smooth to choppy or is it something else?

Thanks in advance

[selfdestroyer]

This may help:

Edit:
There is actually a few demos of this:
https://www.youtube.com/results?search_query=Double+Flush+tremolo

Cody

[Guybrush]

Thanks Cody

I apprecite your help. I did watch a few demos but I'm still finding it difficult to put my finger on precicely how the intennsity knob affects the sound.

I've just noticed that there isn't a depth contorl on the Double Flush and as it's based on Tremulator (which does have a depth control) I'm gusseing it may be this. I'll just have to build it and have a fiddle!

Thanks again.

[midwayfair]

The intensity control is a variable series resistor to restrict the current flow from the op amp output through to the LED that drives the LDR on the audio side.

At minimum resistance (when the knob is all the way up), the resistance between the op amp output and the LED is only 470R, which will drive the LED pretty hard and allow it to light up very brightly as the LFO op amp output swings positive. At maximum resistance, the current flow will be pretty low, and the LED won't be able to light up much.

The balance pot is a different type of depth control, which you might also see in a handful of amps using optical tremolos; the signal is either an all-pass with the voltage divider being ~1.8K (R5) || the full 100K (from the balance pot) PLUS the LDR's resistance || R6 (100K). Regardless of how much the LDR swings in that situation, it won't affect the volume much at all. When the balance pot is turned all the way up, the voltage divider now becomes the 1.8K PLUS the 100K || the LDR's resistance || R6 (100K). Now the 100K of the Balance pot is dividing against the LDR, so when the LDR's resistance goes low (when there's lots of light on it), it can attenuate the signal a bunch.

Since the intensity control is partly responsible for how low the LDR can go, it will determine the maximum possible depth as the balance control is turned up.

There are some advantages. Mainly that it's fairly simple and gives you some fine control over the LFO's total depth. It allows you to make some adjustments to handle variation in the LDRs used, too.

There are disadvantages, though.

It's an extra potentiometer for a fairly minimal effect. The LFO already involves THREE op amp stages. As a trimpot? Sure. But as designed, essentially you're putting two inferior depth controls on the outside of the enclosure instead of simply constructing a single full-range depth control.

Total output also drops as the balance pot is turned up, because it puts a bunch more resistance in series and that divides against the 470K (R7) at the next op amp input all the time, hence the need for some make-up gain.

[Guybrush]

Thanks Jon

Incredibly informative and interesting as always. I think I might still be on the look out for my perfect tremolo!

The Cardinal is next on my list! 

Thanks again