[sdiy] Ultrarough draft of my hot-rodding of the Music Easel ring mod

[Aaron Lanterman]

On Nov 27, 2008, at 4:42 PM, Grant Richter wrote:

> Actually, I looked at it again and you have a simple typo for the  
> non inverting buffers.
>
> Take IC6a, pin 1 and 2 are connect together only, and the junction  
> of the 1K and 100K goes to pin 3. Pin 3 can not be grounded as it is  
> the input.
>
> The same with IC4B. Simple mis-draw.
>
> I believe pins 5 & 6 are switched on IC6B, it is currently wired as  
> a comparator with hysteresis.

Thanks! You have a sharp eye.

> It would also be a real good idea to change R112 and all the others  
> to 1K resistors. An LM837 will source 40ma into a 600 ohm load at 25  
> volt p-p. That is quite a bit of power. Buchla control voltages are  
> all unipolar from 0 to 10 or 15 volts. Don put the 220 ohm resistors  
> INSIDE the feedback loop of the op-amp and was partially relying on  
> the current limiting internal to the 741s to keep things under  
> control. The LM837s can drive a mile of 600 ohm twisted pair wire  
> and will happily blow things up if allowed to. Definitely raise the  
> current limiting resistors to the now standard 1K.

I may set it up so that there are couple different options - if people  
want to wire up with 4558s, they could use 220 in the feedback loop,  
but if they want to use something like the LM837, they could use 1K  
output.

Or, huh, you know maybe I should just flat out nix the whole idea of  
using 4558s; how much of the "vintage Easel sound" is the 4136  
responsible for anyway?

It would also be nice to be able to use some quad op amps, and there's  
no quad equivalent of the 4558 around anyway.

- Aaron