This is a standard Baxandall tone controls circuit that has a range of boost or cut of about 20dB which is planty.
Are the pots linear?
Is the source impedance very low like from the output of another opamp?
Is the load impedance 10k or higher?
Measure the audio level with no load. Then connect a rheostat or resistor decade box across the output and adjust the resistance until the audio level drops in half. Disconnect the rheostat (or resistor decade box) and measure it's resistance with a DMM. The reading will be equal to the output impedance of the old radio.
If there is no load then how can I determine the audio level is half way mark?
I'm taking the signal from line out jacks.You mean to connect a Variable resister to this line out jack?
I think the jack you have in your old readio is for headphone, or any xtra speakers. The impedance of the normal speaker and the head phone is 8 or 16 ohm. So you can consider this as a low impedance circuit. Normally the microphone( electret) and the pickups have the higher input impedence. My advice you can consider this us a low impedance device
This is the socket I have in my old radio.I'm taking signal from it.Its printed "line out" left & right.If I change the volume level it wont change because its there as line outs.
Only thing I need to verify my source impedance & the load impedance.
Kchristie gave a solution but I have only DMM & a 100K variable resister.
No, you need a signal generator and either an AC millivoltmeter, or a scope. However, line outputs like that should be a reasonably low impedance.
Bit puzzled as to why the two resistors creating the spilt supply are different values?, you should also have a decoupling capacitor from their junction down to chassis.
The split supply voltage is slightly higher than half the total supply voltage because the TL07x opamp has an output that is a little better going high than it goes low. It doesn't make much difference but it looks more symmetrical to see it clipping on a 'scope.
The tone control circuit should be fed from the extremely low output impedance of an opamp. Then the new opamp can be fed audio from any audio source.
Does your radio or speaker have poor low frequency response that requires the bass control to boost the bass?
My home speakers are flat to 55 Hz. I made a bass boost circuit that boosts 30Hz by 10dB (10 times the power). Then they sound like a sub-woofer is with them but I don't have a sub-woofer at home, only in my car.
I think its poor low frequency.How do I get that to know?
My home speakers are flat to 55 Hz. I made a bass boost circuit that boosts 30Hz by 10dB (10 times the power). Then they sound like a sub-woofer is with them but I don't have a sub-woofer at home, only in my car.
Yes, because 20dB of boost from the tone controls with the bass control set to max requires 100 times more power from the power amplifier.
My clock radio has 20dB of bass boost at low volume, 12dB at a higher volume and is flat at max volume. Then the little amplifier never clips and the bass sounds like it comes from a big speaker. It has a 3" speaker.