ASM-1 VCO using a 3130

[Isac Georg Jensen]

Hello,

I just wanted to let you know that I have just finished a VCO based on
the ASM-1 VCO.

Instead of using a 3140 in the relaxation oscillator, I used a 3130 as
originally proposed in Electronotes (ENS-76, VCO option 1). The 3130
operates on a 0 (pin 4) and +15 V (pin 7) supply. It goes from some mHz
to around 110 kHz with 30 pF as the discharging cap and slightly higher
with a 22 pF cap.

For the FET I've used a 2N4391 and the exponential pair is formed by a
pair of matched 2N3904.

The VCO has Saw and Square outputs as in the ASM-1. For the Triangle I
have used the overdriven transistor configuration. The Sine output is
made with another FET as suggested in the original Electronotes article.

I am now trying to make the linear detuning that Jürgen proposed for the
SEM VCO clone, but I am not quite sure how to implement this in the
ASM-1 (EN) VCO.

As far as I understand the linear detuning is done by introducing a
small constant current _after_ the exponential converter, right? Could
someone please tell me if the follwing circuit (extracted from Jürgens
schematic) will do the linear detuning:

  +15V
    |
    +----------+--+---------+
    |          |  |         |
    <          |  - 150nF   |
    < 1k       |  -         |
    |       | /   |         |
    +-------|v    |         |
    |       |\    |         |
    <         \   |         <
    < 4.7k    +---+--vvv--->< 47k
    |         |     10M     <
              v             |

   gnd   to neg.input      gnd
         of 3130

transistor is BC560C.

Thanks for all the feedback regarding the 3130.

Nothing beats plugging in a new circuit and realizing it works!

-Isac
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