[sdiy] Working with the ASM1 VCO.. weird MAT-02 behaviour...

[Jean-Pierre Desrochers]

>Maybe you loose current through the protection diodes the MAT-02 and 

>LM394 has between emitter and base. (Base of output transistor?)

>Thats one of the differences to the 2n3904s.

 

Yes.. VERY possible..

I will stick with my 2N3904 matched pair for very low frequencies..

Unless I find something else.. 

Thanks !

 

-----Message d'origine-----
De : Synth-diy [mailto:synth-diy-bounces at synth-diy.org] De la part de René Schmitz
Envoyé : 16 janvier 2020 15:56
À : synth-diy at synth-diy.org
Objet : Re: [sdiy] Working with the ASM1 VCO.. weird MAT-02 behaviour...

 

 

Hi Jean-Pierre,

 

Maybe you loose current through the protection diodes the MAT-02 and 

LM394 has between emitter and base. (Base of output transistor?)

Thats one of the differences to the 2n3904s.

 

Best,

  René

 

On 16.01.2020 17:48, Jean-Pierre Desrochers wrote:

> Hi list,

> 

> I'm working on the Elby-Design ASM-1 VCO

> 

> https://www.elby-designs.com/webtek/asm-1/vco/vco-asm1-cct.pdf

> 

> Im want to use it as a 1v/oct LFO (.05hz to 20hz)

> 

> I first mounted the circuit on my protoboard with success.

> 

> at first I used a matched pair of 2N3904 for Q1A & Q1B

> 

> instead of the MAT02 shown in the schematic.

> 

> I could reach very low frequencies (as low as .04hz).

> 

> But to do so I needed to replace R9(56k) for a 33k temporarily. Fine.

> 

> This morning I replaced both 2N3904 with a genuine MAT-02

> 

> and started the same frequency measurements as yesterday.

> 

> I bumped into something weird..

> 

> Here are the actual measurements I first did using 2x2N3904:

> 

> mVolt at 1k TEMPCO resistor vs Sawtooth period

> 

> 158.0mV => 0.050sec

> 

> 176.0mV => 0.100sec

> 

> 193.8mV => 0.200sec

> 

> 212.0mV => 0.400sec

> 

> 229.8mV => 0.800sec

> 

> 247.5mV => 1.6sec

> 

> 265.5mV => 3.2sec

> 

> 283.2mV => 6.4sec

> 

> 301.7mV => 12.8sec

> 

> 319.7mV => 25.6sec

> 

> (18mV steps, nice exponential response!)

> 

> Now here are the actual measurements with a MAT-02:

> 

> mVolt at 1k TEMPCO resistor vs Sawtooth period

> 

> 157.0mV => 0.050sec

> 

> 175.0mV => 0.100sec

> 

> 193.0mV => 0.200sec

> 

> 211.0mV => 0.400sec

> 

> 229.0mV => 0.800sec

> 

> 247.0mV => 1.6sec

> 

> 271.0mV => 3.2sec

> 

> **** Now trying to go further increasing the TEMPCO mVolts*

> 

> **** the oscillator starts backing up and re-increase its frequencies !!!*

> 

> **** I could not go further lowering the frequency. *

> 

> I tried 3 different MAT-02's and even LM394's

> 

> and they all behave the same.

> 

> Using different matched pairs of 2N3904 worked perfectly..

> 

> I suspect  MAT-02’s minimum base to emitter current reached (???)

> 

> What am-I missing here ??

> 

> By the way, all the IC's I'm using here are genuine one's

> 

> (TL082, MAT-02, CA3140, LM311).

> 

> JP

> 

> 

> _______________________________________________

> Synth-diy mailing list

> Synth-diy at synth-diy.org

> http://synth-diy.org/mailman/listinfo/synth-diy

> 

 

 

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