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LM741 Bass/Treble & Volume Control

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Thayne

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A couple weeks ago, I made a simple amp circuit with a TDA1517 chip. Now, I want to add a bass/treble and volume control circuit before the amp. There are a lot of example circuits online, I have seen too many to list. That is the first issue, picking one. My second issue is everyone is always complaining about every circuit -- there are so many experts it seems; so, it is difficult, as a beginner, to know who is making mountains out of molehills, full of BS, ego, etc.

What I have are a these LM741 op amps. A pile of them and all the resistors and capacitors to build with. I read that this LM741 is an old school, go to chip for this sort of thing I want to do (sounds perfect). A lot of people were saying bad things about obsolescence and better options, etc. I don't care. I have them and it is a good chip to learn with (so I read somewhere). I know the issue of the two power supplies or using one and making the artificial reference ground. OK, no problem.

So, I found a circuit I think is OK. First, I know there are a million opinions, but is there anything obvious to a experienced person why to pick something else? Or, maybe there is an old school, go to circuit to go with the old school, go to chip that I didn't find yet?

Thank you!
 

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KlausST

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Hi,

everyone is always complaining about every circuit
Me too.
The point is: for most devices or circuits there are benefits and drawbacks.
If you want the most perfect circuit, then you should expect it to be expensive, and maybe needs long development time for doing
* finding suitable circuit
* calculating part values (R, C...)
* finding optimal amplifiers
* doing PCB layout.

But if you want to do a quick and dirty circuit... there´s not much to complain.

--> Thus you should first decide your requirements.

If it´s just for a baby-alarm, then you usually don´t care about noise and distortions and bandwidth.
But if you go for high fidelity sound then many users (including me, and I assume audioguru, too) will complain about the LM741.

It it one of the oldest, outdated Opamp. In my eyes absolutely not suitable for audio.
There are so much "audio" Opamps. Although old, the NE5532 / NE5534 are sitll Oamps with good audio quality.

Klaus

PS: Just to give you a clue ... I assume the circuit is from the late 1960ies... at least 40-50 years old.
In that time the LM741 maybe was the only one available Opamp. Thus they tried to achieve better sound with the BJT input stage. Which should be replaced now with a second OPAMP.
 

betwixt

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That has to be the incomprehensible schematic I've seen in a long time!

I think (without unraveling it) it is a standard Baxendale tone control circuit with a single stage pre-amp.
It will work but as others keep stating, the 741 will give disappointing results. For it's time it was OK as an LF amplifier but it was never intended to be used for audio and it was superseded about 45 years ago. With the cost of a modern high quality device being almost nothing, it seems silly to use such an inferior device, even if you have lots of them at hand.

+1 as a critic I'm afraid.

Brian.
 

Thayne

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Re: LM741 Bass/Treble & Volume Control

OK. I understand. I have a lot more op amps around, I will just have to sort through them all. The 741 would have been great. Look at the attached pics of the main board my wife found going to trash.

BTW, this circuit is supposed to be something simple, fun, and to learn, but also decent enough I can use it. I already have a lot of very nice stereo equipment if I want excellent quality. There is no way I can replicate anything near that -- not yet, maybe never.

Thank You!

- - - Updated - - -


edit: What about an LM358/GL358? I looked up the datasheet, seems ok, but it is just facts obviously. What are the opinions? Junk? Not suitable for audio? Haha.
 

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betwixt

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Those look to be hand made boards. The date codes on the 741s are I would guess 'YYM", last two digits of the year and a month code. That dates most of it to 1970.

The LM358 is like an 'up market' version of the 741, vastly better but still under-performing compared to more modern types. They consume only 20% of the power of a 741, work on a wider supply voltage range and have a wider output voltage range. For pre-amp use I would suggest an NE5532 or similar, they are DUAL op-amps but still in an 8-pin package and produce about 100 times less noise (background hiss) than a 741.

To give you some idea of how inappropriate the 741 is for quality audio, it was intended as a low speed voltage shifter and amplifier and originally used in the hammer driver circuits of teleprinters!

Brian.
 

frankrose

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I am not an expert, but at 20kHz the loop gain of LM358 is just ~26dB. I think it is suitable to use as an audio buffer amplifier, but to gain audio signal I would say it is not the best. And sad TI doesn't mention noise or THD in the datasheet. For example a professional audio amplifier like LM4562 has a gain bandwidth of 55Mhz, at LM358 it is ~100kHz.
 

Audioguru

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The lousy old 741 opamp has lots of noise (hiss) because it was designed 51 years ago.
The lousy old LM324 quad and LM358 dual have lots of crossover distortion that sounds awful and has lots of noise (hiss) because it was designed for low power.
Here is a fairly good bass-treble tone controls circuit:
 

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Thayne

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Those look to be hand made boards. The date codes on the 741s are I would guess 'YYM", last two digits of the year and a month code. That dates most of it to 1970.

The LM358 is like an 'up market' version of the 741, vastly better but still under-performing compared to more modern types. They consume only 20% of the power of a 741, work on a wider supply voltage range and have a wider output voltage range. For pre-amp use I would suggest an NE5532 or similar, they are DUAL op-amps but still in an 8-pin package and produce about 100 times less noise (background hiss) than a 741.

To give you some idea of how inappropriate the 741 is for quality audio, it was intended as a low speed voltage shifter and amplifier and originally used in the hammer driver circuits of teleprinters!

Brian.

First, thanks for the responses. I will download the circuit and check it out - thanks for that. edit: That circuit is exactly for me. Nice and easy and helps me understand what is going on. Thanks!

A teleprinter! Haha. That main board is out of a diagnostic audiometer for testing peoples' hearing. You got the date right for sure. The entire electronics is hand built. It was very well done, very organized and I say even beautiful piece of work. The back sides of the pots are amazing -- like four, five "decks" of components stacked together really nicely. Hundreds of resistors and variable resistors all around the stems(?), amazing. The circuit traces are all hand drawn and also beatiful. As an architect, who was educated and trained when hand drafting was the only way, I really appreciate this part especially.

I will look for a NE5532 in my growing mountain of salvaged electronics. What types of devices would this generally be in? A wide variety of audio goods? Or, very specific types?

The thing is, if I go and buy a chip (which is a very great deal of trouble where I am), I might as well go all out and get one of the better ones. If I was to do that, would an LM4562 be better than the NE5532? There is ONE store in the entire city that I just found recently that may have a chip like this. If they do, it will likely be whatever the "best", readily available, popular chip(s) is. And, it will cost about the price of an entire device you would find it in.

Thanks guys!
 

Audioguru

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The LM4562 is a dual opamp so one can be a low output impedance buffer to feed the tone controls circuit.
 

betwixt

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That circuit is exactly for me. Nice and easy and helps me understand what is going on.
I'm not sure if you noticed Thayne, but the circuit of the tone control section in post #1 is exactly the same as the one Audioguru sent you! It is just drawn in a more conventional way.

I marvel at the way people say "There is ONE store in the entire city ..." when here, the nearest city is an hours drive away and it certainly has no component shops in it. Everything here has to come by mail order.

Brian.
 

Thayne

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I'm not sure if you noticed Thayne, but the circuit of the tone control section in post #1 is exactly the same as the one Audioguru sent you! It is just drawn in a more conventional way.

I marvel at the way people say "There is ONE store in the entire city ..." when here, the nearest city is an hours drive away and it certainly has no component shops in it. Everything here has to come by mail order.

Brian.

The circuit I posted in #1? That circuit gives me a headache. I never looked close enough at it to find that part. I admit, I was hoping someone would post a better example to work off. I was having bad luck finding something simple without a ton of comments saying how bad it was.

Almost everything has to come mail order here too -- unless you get lucky and someone risks opening a store. The problem is when it does have to be ordered, it takes about six to seven months -- always. In addition to the shipping costs, which are very high, there is a tax that starts at $15 minimum and can go all the way to 500%, or more. If you don't pay it, the government sends the package back. In that case, you could lose all your money, but definitely the shipping. Oh, and if you go to the store, you risk getting robbed and maybe killed. It happens all the time here in the city of Salvador, Brazil and Brazil in general (88k murders per year).


The LM4562 is a dual opamp so one can be a low output impedance buffer to feed the tone controls circuit.

Thank you.
 

Audioguru

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I order some of my parts from Digikey or Newark that are in a neighbouring country. If I order by phone or online before 8:00PM then the shipment arrives at my door the next morning.
The low shipping cost includes a customs broker's charges and customs duty.

I can walk to a local electronic parts store but all the numerous very close RadioShack stores are gone.

Brazil is so savage that you cannot do normal shopping in stores like everybody else? Everybody in America has a gun and I went shopping there with no problems. Here in Canada there is very little crime (except from a few visitors with guns). Almost all Canadians do not have guns.
 

zlatkoMM

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Yes i have something similar ...
ahh i see i think that noninverting require 10k resistor to work ..
 

betwixt

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Yes, you need to hold the non-inverting input at about half supply voltage for it to work. Grounding it will stop it working.
As the DC level is stabilized through the bass control, it is also necessary to AC couple the input signal. Any DC offset on it will upset the output voltage.

Brian.
 

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