A look at the LERA

[chokeyou]

I've got a space echo that is just dying to be fiddled with.

Anyways, Id love to modify the space echo and bypass the existing repeat speed pot (by replacing a switchable jack in one of the unused jacks on the front panel), run a cable to my pedalboard where I've got myself a little fast/slow box setup.

now on with the lera question:

http://geofex.com/Article_Folders/lera/lera.htm (for reference)

where does one hook up the physical slow speed and fast speed pots? I obviously see where the one hooks up, on the far right side of the schem, but where's the other setting control? the 10k pot used to set up the minimum resistence (highest speed) leads me to believe there is no "low speed" control in this circuit, where would one put that?

[R.G.]

Most effects have a slowest and highest speed that they'll go. Those are usuallly defined by the end of travel on one speed pot. When it's fully up, the speed is as fast as it will go, and when it's fully down, it's as slow as it will go.

Usually "fastest" corresponds to the lowest resistance setting, and "slowest" corresponds to the highest resistance setting. That's one reason that reverse audio pots are generally better for speed controls on a lot of LFOs.

So to make a fastest speed, we just let the LDR go to as low a resistance as it will. To set a slowest speed, we want to limit how big the resistance can get. To do that, we can put a parallel resistor across the LDR. That way the LDR/resistor combo can't get any bigger in resistance than the resistor. So if you want a variable slow speed, you can put a high value pot set up as a variable resistor in parallel with the LDR.

To limit the fastest speed, we limit how low the LDR can go in resistance by putting a resistor in series with it.

Of course, if your Space Echo uses a different setup on speed, you may have to reverse that advice; if it uses lowest resistance for slowest speed and highest resistance for highest speed, that it. If it uses the pot as an actual voltage divider, you'll have to hook the LDR in series with a fixed resistor and take the control voltage from the junction of the resistor/LDR. You can still put limits on the divider action with parallel and series resistors.

It may take some tinkering to get the right values, of course.