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Tone controls ?

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tblo163

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The 7w stereo Amp.that I built,using the Vellerman circuit (one of my earlier threads) works o.k.Now I want to replace the twin gang volume pot with
3 pots to acheive vol,treble & bass control.I have the 47k twin gang pots,&
a good selection of caps & resistors,I've designed a circuit that I think might
be suitable. The question now is-will it WORK?.Any suggestions welcome,and
I look forward to your EXPERT oppinion.Thanks Terry::confused:
 

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audioguru

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Your tone controls are passive and therefore cause a huge signal loss. Also the input must be from a very low impedance. Your volume control is not a low impedance.

Most tone controls are active with an opamp so there is no signal loss. The first opamp in my circuit provides the tone controls with a very low source impedance.
 

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crutschow

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A quad op amp would, of course, allow you to build Uncle $crooge's tone control for two channel stereo with only one op amp package.
 

tblo163

New Member
Your circuit looks interesting, I presume I need 1 for each channel? I've had a look at the data sheet,I shouldn't have done that,it's confusing.it shows pins1&7=out,
pins 2,3,5&6=in,this seems to indicate that the 8pin chip can be used for both channels.I will keep searching for a circuit with volume,treble & bass controls,
I have an unlimited stock of LM324N ICs,could 1 of these op-amps be used?
Thanks for the help
 

tblo163

New Member
Explanation

You might think that I take your advice lightly, I assure you I appreciate all your help.I have considerable experience building circuit boards for PWMs.
EFIEs,MAF & MAP enhancers ect.,but I've only just started to make amplifiers,
so I'm still learning.The only reason that I am building amps,is that I can not
find a suitable circuit for a AVC LAN Data Interface to make my cd/changer work,and the MP3 Player offers more choice and sound quality.The stereo amp that I've built works o.k.for a 1st attempt,but there is plenty of scope
for improvement,and thanks to yourself & other members I am going in the right direction.Thanks again Terry.
 

audioguru

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Most Helpful Member
Your tone controls circuit is also missing a resistor to ground on its right side (for the bass control).

The TL072 has two opamps in it. Pins 1, 2 and 3 are for one opamp and pins 5, 6 and 7 are for the other opamp. That is why it is called a dual opamp. The TL074 has four opamps in it. It is called a quad opamp.
They are low noise, have extremely low distortion and have full output frequency response to 100kHz.
I forgot to add a volume control to the input of my circuit.

The lousy old LM324 quad opamp is very noisy (hissss), has 3% of crossover distortion and has a full output frequency response up to only about 1kHz.
 

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renekenshin

New Member
Your tone controls are passive and therefore cause a huge signal loss. Also the input must be from a very low impedance. Your volume control is not a low impedance.

Most tone controls are active with an opamp so there is no signal loss. The first opamp in my circuit provides the tone controls with a very low source impedance.
Hi, i was looking for a schematic of an active tone control and i happen to stumble into your's and it looks interesting. Can you add a loudness switch with it? I think i saw a similar circuit on google but it uses a tapped potentiometer and some additional resistor and caps connected between the tap and the switch, i'm guessing that the switch must be some sort of a bypass to disable or enable the loudness function?
 

audioguru

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A tapped volume control is very rare. You can add a bass boost switch around the first opamp.
 

crutschow

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Hi, i was looking for a schematic of an active tone control and i happen to stumble into your's and it looks interesting. Can you add a loudness switch with it? I think i saw a similar circuit on google but it uses a tapped potentiometer and some additional resistor and caps connected between the tap and the switch, i'm guessing that the switch must be some sort of a bypass to disable or enable the loudness function?
As you may know, a loudness control increases the bass and treble response of the audio signal as the volume is reduced to compensate for the change in frequency sensitivity of the ear with sound level (according to measurements made by Fletcher-Munson). Do do this with an analog volume control requires the addition of a tap on the volume control which adds some additional elements affecting the frequency response at low volume levels. Can't think of a way to to that in an analog circuit without a tapped control.

As you noted, the switch is to enable or disable the loudness function.

I remember an old vintage Eico amp that had separate loudness and volume controls connected in series. You would calibrate the amp by turning the loudness control to maximum and then turning the volume control to the maximum listening level you would ever use. After that you use the loudness control for normal control of the sound and leave the volume control untouched. That way the loudness contour would be tailored to your room listening level.
 
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