Tone Control Pre Amp Modifications

I made the attached transistor pre amp & its working ok. But I made some couple of changes in some values.The BASS is ok, but the voice it too low.
Any improvements?

Suraj143 said:

the voice it too low.

Click to expand...

What does this mean?

Also, why did you make the changes? What was wrong with the original design?

ak

You have changed the blend ratio from the bass & treble circuits, so bass is far stronger.

Change the components back to what they should be and add an extra gain stage if the output is too low at that.

Also remember the tone controls have minimal effect on mid-range frequencies so the bass and treble must be adjusted to match the mid range.

You could make it into a 3 band tone control and have more control on the mids, and therefore voices.

rjenkinsgb said:

You have changed the blend ratio from the bass & treble circuits, so bass is far stronger.

Change the components back to what they should be and add an extra gain stage if the output is too low at that.

Also remember the tone controls have minimal effect on mid-range frequencies so the bass and treble must be adjusted to match the mid range.

Click to expand...

You are correct.The BASS is too much.I set position to half way mark on my BASS knob.BC109 transistors aren't common.So I used C945.

*Is there any noticable difference between BC109 & C945?

*I didn't mentioned on the diagram, For BASS I used a 100K pot.

*I guess the input cap 10uF is far bigger I guess...!!!

I think I will put all the parts as in the original & give a test run.

The BC109 would likely be somewhat higher gain - the data sheet says a minimum of 240 & maximum 900 vs. 90 - 600 for the C945

There is a good range of overlap, so probably not a massive difference in practice.

The input cap should not have a great effect, a little larger than the circuit says is fine, it will just take slightly longer to settle when power is turned on.


For info, the ZTX851 is a good moderate-gain transistor for audio (min. gain 100, typical 200). It's also one of the lowest noise transistors you can easily get, and they are cheap! The ZTX951 is the PNP complement of that.

Tone controls circuits have their parts values calculated, not guessed and not random.
Here is one using a modern opamp but the RC values are about the same as the original circuit you found.
A BC109 is a very old low noise audio transistor. A 2SC945 is noisy (rumble and hiss) and is used for switching circuits.