Onboard bass boost

[emosms]

Hi, i want to build onboard bass booster for a bass guitar.
Smth like this:



I will set the desired bass boost with a trimpot, and leave it.

The onboard EQ cannot manage well - need to keep the bass knobs, both in the onboard preamp and the bass amp all the way up. Position 12 o'clock is like fully attenuated.
Going down is completely useless.

This is due to the pickups I put.  Tried them directly into the amp. They are bright, mid intensive, handle playing dynamics very well (alnico).
I like them. Good for slapping and for mid intense finger play (the bridge pickup bites a lot), but they sound a bit thin.

I am trying to do it with two transistors (if possible only one) and power consumption less than 1 mA.

[emosms]

1. First attempt - taking the base circuit of the Quad amplifier:
tilt control, and substitute opamps with transistors:





It is not working in simulator. I guess the feedback loop around Q2 is not applied correctly - I don't know electronics much.
The pot just turns the gain up (mid position) and down (either directions), no change in frequency response.

[emosms]

2. Second attempt - using the Big Muff tone stack. Seems it is working in simulator.
Keeping the collector resistors 22k, for less current consumption.
But I need to have very assymetric bias at Q1 base - 1M, 100k, in order to obtain the gain required.
If it works at all, I guess it will clip the input signal

[emosms]

Could someone advice on these attempts above:
1. Quad tilt, not working
2. Big muff - not sure if working

Or propose a completely different approach?

Note:
If u suggest using opamps, I would like to beat TL072 consumption - probably 2 mA for a dual opamp
And NO SMD packages, Please

[Elijah]

Hi mate. I'm also not a pro in electronics but can give you this.

Enjoy

[emosms]

Good, adding second bass freq (around the existnig) would hump the bass region.

But the onboard EQ is sealed. Only wires going out. Black box 

[PRR]

[iainpunk]

i was going to say almost the same thing:



this is the schematic for a stand alone pedal i build, the bass boost o matic..
it boosts up to 16dB at 50Hz center freq.

cheers, Iain

cheers

[emosms]

 Could it be done with one transistor?
Trying to avoid opamps

[emosms]

This solution seems to work



The whole circuit, including two jfet buffers (installed), with a very high source resistor (33k) and output impedance



Works ok now (the mix pot, the vol pot - R20, 50k) - it is installed on the guitar without the bass boost part.

The only thing I would like to improve is the current consumption.

The jfet buffers draw 0.2-0.3 mA.
The bjt bass booster draws 0.8-1 mA.

Is it possible to improve? Putting transistors in different mode, substituting with jfets?

[antonis]

Improve what..??

Buffers offer power (current) gain..
Boosters offer power (voltage + current) gain...
By reducing current, you reduce power for both cases..

[emosms]

I have a jfet buffer installed, drawing ~0.13 mA current (33k source resistor).

It does work with a 50k load (volume pot).
The simulation also does not show clipping or treble loss.

Here it is the whole thing, with resistor values for lower consumption.
The gain stage (Q6) starts to clip when loaded (either 50k or 100k).
But the signal from the jfet buffer is ok (the yellow line).

I guess I have to add output buffer to the bass booster as well.
Now wondering, if the simulator is wrong and wether the BJT transistors (Q5, Q6 operate correctly)
Consuming 0.2-0.3 mA total .