[sdiy] ARP VCO drift - update

[Steve Carter]

Glad the BC847 worked out OK. It's odd that the nomenclature here is  
confusing. A BC847 is a single NPN transistor but the BC847BPN is a  
complementary NPN/PNP pair - I ordered some and got the singles until  
it twigged. Even more confusing is that the BC847BS is a dual NPN  
package although that would be interesting to see if it performed as  
well as an SSM2210. At £0.05 each when you buy five from Farnells they  
have to be great value!
Steve

On 17 Aug 2008, at 21:26, rob wrote:

> Hi list,
> Quick update on progress.....I fitted a BC847BPN dual NPN/PNP  
> transistor to
> the Tempco using heat paste and wrapped the 2 together using  
> insulation
> tape, even though this is remote from the main PCB. The BC847 was  
> fun to
> wire up....its super glued to a tiny piece of veroboard with thin  
> wires to
> the SMD transistor and larger wires to the PCB.
>
> VCO frequency drift has now reduced to a similar level as a Dual
> SSM2210/Tempco based VCO (Oakley or E-mu Systems). I test with a  
> frequency
> counter, but the real test is to listen to the 2 VCO's at the same  
> pitch and
> hear the tones beating. They are now nicely beating against each  
> other with
> a 5 - 10 second phase rather than quickly going away in pitch.
>
> The transistors and tempco will now be put on the main PCB and I'll  
> carry
> out the next set of tests. 1v/octave Tracking....maybe I'll pot the  
> whole
> circuit....
>
> Thanks - Rob
> www.emulatorarchive.com