bass preamp

[Gus]

A sim of a older solid state bass amp preamp section.


A graph with the controls as set in the sim



Something a little different, note the volume control.  Needed to add R21 to bias Q2 as a 2N5088, schematic had only R6 the base to + power bias.  Also changed Q1 to a 2N2222.

R15 and V1 at 37VDC is from voltages marked on the schematic.

I like looking at older solid state schematics.   Some like the Vox that R.G. writes about are interesting there are other interesting Sears and Harmony and Wards and Kay and other old solid state amps that with more modern parts might be fun to build and play.

[PRR]

> Needed to add R21 to bias Q2 as a 2N5088, schematic had only R6 the base to + power bias

? ? ? Should work with just R6 to R5. If these are in the ratio of hFE, the emitter will sit just a hair below half the supply voltage. 2.2Meg/5.6K = 393, a perfectly reasonable hFE for small hi-gain transistors. hFE of 100 or 1,000 will also work, setting emitter near 0.2 or 0.7 of supply, 4V or 14V. Any of these variations will allow well over 1V peak signal.

[Gus]

In the sim the resistor from base to + supply value to bias the 2N5088 was large(schematic in the book has a 2.2 meg), so I added R21.  I was using stock download LT spice transistor models and transistors that people might have.  The schematic did not have the transistor numbers listed.

The schematic had some of the transistor voltages.  I kept the schematic resistor values.
Q1 22VDC collector, 3.3VDC emitter
Q2 6.9VDC emitter 
The voltages in blue in the screen shot are what the sim shows at the nodes

I am wondering what the volume/gain control might wired like it is?  Was it to reduce the number of transistors used?
It does go to 0 volume wiper at the 'top" of R11 shorts the signal to ground
At increasing gain it "folds" R14 and C2 and a part of the volume resistance across R4 for more gain as the wiper moves "down" and has less of a load on the collector of Q1

Tone section is simple
R10,R9 is a 1meg RA control varies across C6
R7,R10 is a 100K A control and C5 are a simple treble reducing control.

[Gus]

please remove double post