Altering Schaller tremolo input impedance?

[Dingleberry Electronics]

Hi!

First of all, thaks to all of you fellow forumers. I've got so much helpful information from this forum during past two years I've been reading and writing here.


I just recently built me a schaller tremolo workalike. Works fine, sound is good. I used BC107 trannies for the oscillator section and BC109 for the signal transistor.
No hiss or other unpleasant pulsating noise while not playing. Overall warm mellow sound. I made the speed switch footswitchable and put a bi-colour led to indicate the speed settings. I made also little tweaking on the depth pot. I increased it to 100K and put a 12K resisror in series. Now the overall controll is much more usable and covers the whole pot range.

One thing that came up in my head was the input impedance. The input signal comes first trough 47K resistor and then there is 47K to ground. Then 4,7uf input cap to the BC109's base. If I have got that right, the input impedance is determined with those two 47K resistors. In this case it will be below 100K (47K+47K). That's quite low if I'm right.
That low input impedance will be a part of the warm sound I quess?
What if I put a SPDT-switch after the first 47K resistor so I would be able to switch between two different resistors to ground. (for example 47K and 1M).
Would the higher impedance setting sound "not so warm" and the signal level would probably increase too at least a bit.

So maybe the switch would act sort of "Vintage/Modern"-switch? The higher impedance will probably add more clarity to the sound.

Maybe a 1M pot  in series with the 47K resistor to ground. Then I would be able to alter the sound between those two extremes.

Does this make any sense? Would there be an audible difference in sound, or is this just one of these: "the idea is nice but actually it won't work that way..." topics?
Has anymeone experienced with this before? (pretty sure someone has...) Any info welcome as always.

-Dingleberry
 

       

[R.G.]

As I remember it, the Schaller relies on those two resistors to cut the signal level down.

The simplest thing to do is to put a buffer in front of it. The buffer can range from a single transistor or MOSFET follower up to an opamp buffer. Anything which presents a higher input impedance would work, as you suspect. Your vintage/modern switch would bypass the buffer.