Micro V Voltage Divider Beginner Question

[Phend]

Hello:
Here is a GGG circuit of the Musitronics Micro V.
I need a class in Schematic Reading 101.
Obvious that all +9v "boxes" are connected together with invisible lines.
Same with the Vref.
Vref = 4.5v
Question is where is the 9 volts divided to get 4.5 ?
Between R2 and R18 ?
Thanks for any insight you might give.

[antonis]

R8/R9 Q2 bias configuration..
9 x 33k/(22k+33k) - V_BE = Vref

[GibsonGM]

It's just a fancy way of obtaining the Vref...usually we'd find a simple 2-resistor + cap to ground at the junction providing it...this one is top shelf. 

[ElectricDruid]

It's certainly unusual. I wonder why they felt it necessary to add the extra transistor, and I wonder if it's still necessary in the "modernised version" we're looking at. What OTA did the original use? CA3080?

There's a lot that's pretty unusual about that circuit, actually. That's not your standard OTA filter circuit either.

[PRR]

PNP Q3 may suck great chunks of peak current from Vref. A resistor divider would just sag. Same with a big cap would sag slower. The NPN Q2 provides a relatively stable source.

[Phend]

Ok, how would those familiar with this circuit rate it. Good, don't bother, difficult to get to work, eats batteries ect... ?

[Phend]

Finally started putting this effect together.
Question:
In the lower right of the circuit resides R16a and R16b in parallel.
Both values are 1M.
How sensitive is this 500K equivalent to some +/-  ?
Any idea why the designer of this circuit put two 1M resistors in parallel ?
Will 470 and 15 in series measured at 501.68 work ?
Thanks in advance, will show when complete and working !

[iainpunk]

i doubt it makes much of a difference, but i'd replace the parallel resistors with a 1M trimmer with a 100k stopper resistor in series to ''tune'' it to the best sound (and to test if it really makes a difference for future reference)

cheers

[Phend]

Thanks Iain, since I have no 1M trim, will use the following combo:
220 + 220 + 0-100 Trim = 440 to 540
Since I am the "Hard Telling Not Knowing" student thanks for the advice, will try that combo.
Hum HTNK