MXR 136 PWM Limiter - Readable schematic?

[tonedude]

Is there a fully readable schematic of the MXR 136 PWM Limiter?

 

[tonedude]

... or if someone could help me with the correct values for the 4069 cmos oscillator?

So far I think I have
2x 20k
120k
47k
36k or 56k?
and
3x 20pf

I'm asking because the oscillator in the Fostex 3070 comp uses the same design, but with different values. The 3070 has a oscillator clock running at 200khz, and the MXR136 has a clock at 250khz. The other difference is that the MXR136 uses one clock for both channels, and the 3070 uses one clock for each channel. I't seems to be a good idea to use the same clock for both channels and also use the faster clock in the 3070, so I will try to implement the oscillator from the 136 in the 3070.

 

[mjrippe]

Unfortunately, MXR schematics always look like third generation photocopies.

 

[Khron]

Might something like this be of any help at all?

https://www.theremin.us/Circuit_Library/Astable Multivibrator Calculator/CMOS_Calculator.html
And/or mess with some values in LTspice, or your simulator of choice.

 

[tonedude]

Thanx for helping me out!

I'll try different values and see what happens. I think I know that the cap circled in red is the one that determines the frequency of the oscillator (its 33pf on the 3070), but I guess the other values maters to, so I'll mess with the circuit and report back here if someone else want to try modifying their 3070.

 

[tonedude]

I found gutshots of the M136 and figured out the resistor values in the oscillator. I then changed C15 to 22pF, R48 to 36k and R49 to 120k in my Fostex 3070, that gave me an oscillator clock running at 350khz in the fostex, but the function of the 3070 wasn't stable at that clock speed. I then reverted back to 33pf for C15, but kept the changes for R48-49, that gave me a 270khz oscillator in the Fostex with all the functions of the compressor/limiter and gate being stable. I will use it some more days, then make the same modification to the other channel. But as it is right now the modified channel works and sounds just fine.

 

[mjrippe]

Nice work! I have wanted to check out one of the ART Dual Limiters currently available to see how close they are to the MXR.