Help me to increase the BASS in TL 071 preamp

[Suraj143]

Hi I have this preamp circuit connected to my amplifier. Can somebody tell me how to increase the BASS of this preamp? What changes do I have to do?

Thanks

 

[audioguru]

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?

 

[Suraj143]

Hi audioguru thanks for viewing my circuit.

The pots are I don't know whether they are linear or not.

I'm giving inputs from another old radio.How can I measure the source impedance.?

And the load impedence you mean the power amp impedence? Can I measure that also from a DMM?

Thanks.

 

[kchriste]

I'm giving inputs from another old radio.How can I measure the source impedance.?

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.

 

[Suraj143]

Hi kchriste thanks for your input.

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 have only DMM.

 

[rupertherbert11]

hi Suraji

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

 

[Suraj143]

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.

Can I measure them with a DMM?

 

[Nigel Goodwin]

Can I measure them with a DMM?

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.

 

[audioguru]

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.

 

[Suraj143]

Ok thanks for the replies I satisfied with the current quality because I don't have special equipments to measure the impedance.I'm worry about that.

Also for my speaker wires I used very thin cheap wires.After changing that also I got a good quality.

Is there any method to give signal to this preamp other than giving from an old radio?

How do I confirm that current input signal is weak or good?

 

[audioguru]

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.

 

[Suraj143]

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.

You mean to give input via another op amp? can I use same TL071 for that also?

Does your radio or speaker have poor low frequency response that requires the bass control to boost the bass?

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.

How did you measure that?

 

[audioguru]

You mean to give input via another op amp? can I use same TL071 for that also?

Use a second opamp. A TL072 has two opamps in an 8-pins case.

I think its poor low frequency.How do I get that to know?

A high quality tuner or CD player will have good low frequency response.

How did you measure that?

Since you ask then you don't have the test equipment to measure frequency response.

 

[Suraj143]

OK thanks audioguru I'll make a preamp with TL 072 so I can give inputs from many devices.

Now when I give inputs from computer it will give some quality.
when I give inputs from a CD player it will give another quality.

So after adding the new preamp it will be all right I believe.

Thanks a lot audioguru.

 

[audioguru]

Add the second opamp like this:

 

[Suraj143]

Thank you very much audioguru for your support.I'll make it for sure.
This time I'll have plenty of bass.

Thanks

 

[mneary]

You'll have plenty of bass if your power amplifier can provide it.

 

[Suraj143]

Hi you mean by adding extra TL072 preamp as audioguru's diagram?
For sure ASAP I'm going to build that.

 

[audioguru]

You'll have plenty of bass if your power amplifier can provide it.

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.