Hi i would like to reduce the gain to this amplifier what could i do?
Nobsound LM1875/LM3886 estereo HiFi amplificador de potencia Transistor en Amplificador de Electronica en AliExpress.com | Alibaba Group
Greetings and thanks in advance
Nobsound LM1875/LM3886 estereo HiFi amplificador de potencia Transistor en Amplificador de Electronica en AliExpress.com | Alibaba Group
Greetings and thanks in advance
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.
ie Assuming the pot is 10K, putting a 10K in series with it will give you 3dB attenuation.
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Increase the negative feedback is what I would do.
There is a resistor between pins 4 & 2. Reduce the value to half and that will decrease the gain by about the same.
Original poster should also know that LM1875 is internally compensated and stable for gains of 10 or greater.
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.
Increasing NFB to reduce gain is specifically not recommended.
Datasheet example suggests 20X gain or higher to play it safe ; so if amp is too sensitive it´s better to attenuate input signal as much as needed.
Same for the TDA7294 !
...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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Nigel, did you try increasing the resistor to ground instead? I reduced gain on my Maplin mosfet and to ~1 by removing it altogether and it didn't oscillate
No, the capacitor worked so I just left it there.
It might be an interesting experiment. Have you read this? https://linearaudio.net/sites/linearaudio.net/files/volume1bp.pdf
On pages 14-15 he suggests that more feedback is better, more than at the point the amplifier becomes unstable.
On pages 14-15 he suggests that more feedback is better, more than at the point the amplifier becomes unstable.
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.
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.
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.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.
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.
The amps all have been stable. I think a gain of 10 could be controlled the same way.
I put a series resistance of 39 k to the output of the potentiometer and reduced the noise and the gain is correct this?
put the resistance in series with the input of the potentiometer.
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