[sdiy] The simplest synth ever (was: Russian parts and synth schematics...)

[Jaroslaw Ziembicki]

----- Original Message ----- 
From: "mikas" <mikas at turbodsl.lt>
To: "Jaroslaw Ziembicki" <aon.912230836 at aon.at>
Sent: Tuesday, August 31, 2004 11:49 PM
Subject: Re: [sdiy] Russian parts and synth schematics...


Here some thoughts how to improve the circuit:

1) As to the non-temperature-compensated lin/exp converter
    (VT9): a transistor array CA3046 should be used. Two of its
    transistors should replace VT9 and VT12. The remainder three
    transistors will be left not connected; later on they can be
    used with some external components to keep the CA3046
    chip temperature on a constant level (eg. 60 Celsius degrees).

2) The Keyboard & VCO block can be built as shown on the picture
    ru_synth_diy - 3. Replacements are: K176LA7 = CD4011,
    K176TM2 = CD4013, KT3102B = BC547B, KT3107X = 2N3096.
    I don't like the buffer circuit (VT4 ... VT7). Best replace it by
    a TLC271 or a half of TLC272.
    The external CV and GATE inputs can be easily added later!

3) If the VCF will be unstable, then you can replace gates DD8.2
    and DD8.3 by opamps (eg. TLC272).

4) I could not find replacements for DD4 and DD5. For DD4, any 4-bit
    counter can be used (eg. CD4024, note: other pinning). The DD5
    should be 5 x NOT gate without input protection diodes. I think you
    can use CD4069 and place a 47k resistor in series with each input.

5) I would recommend you to build the synth on a perfoboard and leave
    about 30% free place for some future circuits.


Regards,
Jarek