elfa said:
I hate to admit it but so far, I'm failing. No response out of the speaker.
The circuit I used is at the link below....midway down the page is the Baxandall
circuit described as 'Passive Baxandall Tone Stack Schematic'. Apparently it is
designed for a Fender guitar.
The problem with this circuit is that it dampens the signal very much,
and you cannot afford that when your signal output from the radio is
so low as it is.
But you may also have made a mistake in the wiring.
Most of the circuits on this web page are designed for high impedance
sources and will not work well for you.
(maybe your amp has a low inpedance input)
A little further down on this web page you find a link to "Duncan
Amps' Tone Stack Calculator". Use that and download the Tonestack
Calculator program, it is this link:
http://duncanamps.com/tsc/index.html
In that program you can compare different tone controls and see what
output curves you get.
You can see that the circuit you are trying to use now, called James,
gives very low output level.
You have a limited voltage coming out of the radio so the
tone control may not dampen the signal very much, so you may have to
choose a tone control circuit accordingly.
It depends on how strong signal your amp needs on the input.
If you look at the curves in the tonestack program you see how much
different types dampen the signal, see how low in the diagram the
curve is positioned. The James type ("passive Baxandall") is one of
the worst alternatives for you because it dampens the signal with 20dB
in neutral position.
The "Bench" type can be adapted for low dampening.
Radio amateurs often use a filter to hear weak signals through noise.
A common filter is a series connection of 1Henry 100nF and 1kOhm.
It gives a strong presence filter, cutting away bass and treble and
enhancing the frequencies between 500-3000Hz.
This type of filter does not dampen the signal very much.
You probably have difficulties finding an inductor with 1Henry, but
you can try different transformers, try different connections on the
transformers. Leave all other connections open.
You can see the results of such a series link in the tonestack program
if you choose the Bench type, lower the source impedance to 1k or
lower, because you radio has low impedance output.
Click on the signal source and other components to change values.
Turn down the bass and treble pots to zero, and make them bigger, to
1M pots. That minimizes their influence.
Now you can use the mid link to try different values and settings, use
1Henry and 100nF for example, and set the mid pot to slightly less
than maximum.
See how the curve shows a high point at about 2kHz.
Bass and treble are cut away.
That is often a good filter for people who have problems with hearing,
and gives the clearest sound when listening to speech.
The reason why we need a little resistance in series with the
capacitor and the inductor is that such a circuit can self-oscillate
if there is no resistance, it will cause ringing and create a bad
sound. With a little resistance in the circuit this problem is
removed. You can see this problem yourself in the tonestack calculator
program. If you set the mid control pot in the maximum position in the
example above you will see how the curve shoots up above the zero
line, it amplifies the sound, but that will sound bad. The circuit is
ringing. Put the pot just a little lower and you will get a nice
curve.
You can try other alternatives in the tonestack program, but remember
that you need a curve which is as high as possible, close to the zero
damping line, zero decibel.
If you dampen the signal from your radio with 20 dB as you are doing
now, you will not hear much output.
Look at the James circuit with the controls in neutral position, the
straight line curve is down at minus 20 dB, that is what you are doing
now, that is probably why you hear nothing.
You also use very high resistance components, which dampens the sound
even more, I guess.
It would help if you could tell us what tone curve you like when you
listen to speech on a radio or a stero with good tone controls.
Do you lower the bass and treble and raise the volume to hear better?
That is what people in general need to hear speech better.
You may have some special problem with your hearing and it is
difficult to give advice without knowing more about what frequencies
you need to amplify.