Ampeg VT40 preamp

[fuzzo]

Hi guys,

I don't understand the wiper connexion of Midrange control in this schematic:

http://www.schematicheaven.com/ampegamps/vt40preamp.pdf

What's the component marked "8910001" ?

thanks

[anchovie]

Looks like it might be an inductor with multiple taps, connected to a switch.

[Mark Hammer]

Note this drawing:

You can see that a resonant section is based on a cap, resistor and inductor in series.  The VT40 drawing simply depicts a multi-tap inductor used in combination with assorted cap and resistor values.  Same deal.

[fuzzo]

 thank you  Mark.

So , I can esaily make a AOP circuit to do the same thing. I have just to calculate the frenquencies boosted by the Ampeg swtich and create the appropriate frequency range with the AOP circuit.

I found the frequencies boosted by the switch with inductor : 300Hz, 800Hz - 1KHz, or 2500Hz - 3000Hz . described in this manual page

[zeta55]

I have an Ampeg V2, the preamp looks just about identical. It's a very nice midrange circuit.

/Krister

[autoprod]

Comparing with my '76 VT40, the inductors read 100, 300 and 800 mH.