[sdiy] Another CV breakthrough question

[Colin Fraser]

> -----Original Message-----
> From: owner-synth-diy at node12b53.a2000.nl
> [mailto:owner-synth-diy at node12b53.a2000.nl]On Behalf Of jh.
> Sent: 19 May 2001 11:41
> To: Tony Allgood; Synth DIY
> Subject: Re: [sdiy] Another CV breakthrough question
>
> I never thought about it - but now that you mention it: yes,
> mismatch of any
> diode drop voltage will cause this problem. It's basically
> two stacks of
> diodes which give a certain level shift upwards, and if there
> is a mismatch
> this will result in a differential signal as the ladder
> current changes.

The transistors in my TB303 ladder are 2SC1815, but the service manual and
schematics don't mention this.
Now I'm wondering if these 1815s are matched, or maybe Roland found these
had more consistent Vbe than the normal NPNs they were using in the rest of
the circuit, so didn't need to be selected ?
Or maybe they didn't care about cv breakthru in such a cheap box...

Colin f