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Lm 324 amplifier? Answered

Hello i am trying to build a Lm324 Stereo preamp to go into my 100w tube amp, and i cannot find any schematics on 324's.
My idea was to have each channel occupy its own side of the chip, and having a switch to switch between 1 and 2 amp stages.
please help thank you.


My LM324 is showing offset of 1.8 V. how to suppress it?

The 741 op-amp is supposed to be used with a dual supply. The lm324 has the advantage that it requires only a single supply voltage to power it up. I have used the lm324 as a mic-preamp to with great success using this schematic of an LM1458 that has the same pin-outs. If you are not connecting it to a condenser mic, then just omit the 4.7k resistor near the mic and omit the mic also as shown in the schematic. The LM324 has 2 other amps in it on different pins that you could wire the same and get another channel (left and right).


you have 2 capacitors in there, those are ceramic or electrolitic kind

The 0.22 uf cap would be ceramic disc and the 1.0 uf cap would be electrolytic.... but it isn't real critical. you could use whatever you have on hand, but of course observe the polarity if using an electrolytic.

You are correct,  however a dual supply is only used to avoid having
to provide a split reference for those older op-amps,
as your two 10K resistors do for the LM1458 and
as the 18K / 22K does for the 741..

The LM1458 DC gain of 10 X 10 => 100 may be too much gain for the
synth audio signal application, causing rail distortion.

I think ski4... is smart enough, to act on the hint of using the LM324
in place of the 741...



7 years ago

You didn't specify the audio source ( Mike, tape, CD,radio ). A


I am putting my synth through it into a 100w tube amp

Doesn't a synth have enough output to feed your big amp ?

Here is a pointer to a crystal pre-amp. 
The crystal is a high level signal, probably like a synth
and a 741 like Steve said is a ¼ of a LM324.


The synth allows it to play but in order for the speakers to play richly, i need a preamp. so yea.

I do understand. 
When I was young, I found this rock canyon and started build a solid state
12V  50 Watt power amp to ring my ears in that geological amphitheater.
But we moved away and I never got the chance to fry my brain right :-D

If you build any preamp, keep the circuit small, and put it in a metal box
like an altoids tin. Ground the circuit to the tin where you bring in the 12VDC.
Start very low volume ( Don't Burst Your Spkrs ).


The tricky part to building audio amplifiers, in my opinion, is that you want only want to amplify the AC part of the signal. The picture I have attached is from H+H's Art of Electronics, 2nd Ed. The circuit I drew a red box around is just one stage, using one op-amp.

This is one of my favorite op-amp circuits, and I've posted this picture here before.

Link to the full-res actually-readable version of this picture:


An LM324 is only a quad 741.