[sdiy] Partial solution - WAS: RE: Odd transistor connection, why???

[JH.]

You're right, it's a PNP.

Funny thing is that's the first thing I thought I'd checked, but apparently google brought up a wrong reference as NPN also, and I 
didn't look further.
With a PNP it's all obvious, of course, and it's almost the same circuit EMS used for the expo converter on the VCF (not VCO), i.e. 
where precision is not so critical. (The VCO got an extra zener-biased transitor in the emitter path of the PNP.)
In fact, the transistor's BE voltage drop acts as a reference voltage here. I wonder about temperature stability.

JH.

----- Original Message ----- 
From: "karl dalen" <dalenkarl at yahoo.se>
To: "David Ingebretsen" <dingebre at 3dphysics.net>; <synth-diy at dropmix.xs4all.nl>; "JH." <jhaible at debitel.net>
Sent: Tuesday, May 18, 2010 8:54 PM
Subject: Re: [sdiy] Partial solution - WAS: RE: Odd transistor connection, why???




--- Den tis 2010-05-18 skrev JH. <jhaible at debitel.net>:

> Från: JH. <jhaible at debitel.net>
> Ämne: Re: [sdiy] Partial solution -  WAS: RE:  Odd transistor connection, why???
> Till: "David Ingebretsen" <dingebre at 3dphysics.net>, synth-diy at dropmix.xs4all.nl
> Datum: tisdag 18 maj 2010 10:51
> >The VCO core is still baffling
> me, but I'm happy to confirm the EG
> >operation. Now I can learn more about it.
>
> The expo converter looks a lot like those in the EMS VCS3
> (and the Living VCOs, for that matter).
> But where EMS have used a reverse-biased NPN in the emitter
> path of a normally connected PNP to work as reference
> voltage and servo
> amplifier, *this* circuit seems to marry the two functions
> in one transistor. Interesting! I would not have expected
> this to be
> working, but as it obviously does, it's quite brilliant as
> a low-cost solution, going one step further than EMS.
> What I don't understand: The collector of that
> zener-connected transistor should now work as an emitter, so
> contrary to what EMS did
> this works as an emitter follower (and zener diode), which
> would not provide the necessary signal inversion to feed
> back to the emitter of Q7.

I get the impression the drawn dont work because
the transistor are drawn NPN when its labeled PNP
1N5138 in which the servo should start pump balance
current into expo?

http://www.synthfool.com/store/2n5138pop.html
Now, thats wierd! :)

>The diode-connected transistor seems to be the discharge path for the >integration capacitor. Low leakage, as was mentioned before.
>Q1 and Q2 form the schmitt trigger.
>Integration cap is rather small, so they need very low leakage (thus Q5 >instead of a diode), and probably get away with a rathe
>rhigh resistance to discharge it (1k2||3k9).

I assumed it is drawn wrong too it should be charge not discharge.
Unless Steiner decided base collector diode has lesser breakdown?
Or does it have lesser leakage this way? Weird!

Regards
KD