Reduce the gain of the amplifier LM1875

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Without seeing the schematic, the easiest way is to fit an attenuator at the input. The potentiometer will generally be across the input terminals. If you measure its value you can then simply calculate an in-line resistor to act as a potential divider with it.

ie Assuming the pot is 10K, putting a 10K in series with it will give you 3dB attenuation.
 
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Original poster should also know that LM1875 is internally compensated and stable for gains of 10 or greater.

Very important. I have read that a gain of 10 leaves a rather marginal stability margin. The gain should preferably be 20-30.

Does anyone know how a resistor between the inverting and non-inverting inputs, in a non-inverting amplifier coupling, affect stability? This way the input signal is feed to both inputs in a way that should effectively reduce the gain. I have not tried in practice, yet.
 

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...Does anyone know how a resistor between the inverting and non-inverting inputs, in a non-inverting amplifier coupling, affect stability? This way the input signal is feed to both inputs in a way that should effectively reduce the gain.

I would think you would know this one.

Excess gain is wasted-off. Stability probably improves. But closed-loop gain hardly changes.

However..... in this situation, lowish chip gain and a pre-attenuator IS the proper solution for almost all cases.
 

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I notice the rough sound with the series resistance 39 k at the output of the potentiometer.
If I change the potentiometer for a 100k like this:

ALPS RK27 Potentiometre Stereo Axe Crante Haute Qualite 100 Kohm - Audiophonics


would be a better solution or the resistance in series in the output of the potentiometer does not suppose any problem with the sound and is my thing.

Greetings and thanks.
 
Does anyone know how a resistor between the inverting and non-inverting inputs, in a non-inverting amplifier coupling, affect stability? This way the input signal is feed to both inputs in a way that should effectively reduce the gain. I have not tried in practice, yet.
Negligible change in operation since the opamp is using feedback to maintain its inputs at the same voltage. No voltage across the resistor -> no current -> no effect. In reality there will be a tiny reduction in gain since the opamp has a finite amount of gain and therefore there is a tiny differential signal across the inputs, a tiny current flows in the resistor and the attenuation depends on the other resistor values in the circuit.

For an inverting amp you are better off adding a resistor divider before the input resistor. If the attenuation resistors are not significantly lower in value than the existing resistor going to the amp then you will have to do the math to work out what the current division is.
 
I have used various My_Ref amps that use the resistor and capacitor connected between the inverting and noninverting inputs to provide stability for a LM3886. The circuit is a current amplifier. The voltage gain is 1, or unity.
The amps all have been stable. I think a gain of 10 could be controlled the same way.
 
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