OpAmp buffer before equalizer module?

hi members

i need consultation ... do i need to include an OpAmp buffer before this equalizer module or i can directly line in it from my PCM2706 module? Now my setup is direct from PCM module to the equalizer module without the first stage OpAmp buffer.

My question is if i do not include the first Preamp stage and volume control will it causes noises to be introduced all the way into the amplifier? the module is ready made unit. As shown below. And i also noticed the module is notoriously noisy making noisy hiss if the gain is above +8dB ... is this a common problem with equalizer modules?

Opinions were well Appreciated. Thanks


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2011-04-29 8:37 pm
A buffer won't filter noises, but if you think you need a buffer go ahead and try it.
You could add a passive RC filter either before or after the buffer, if it's needed.
That won't filter noise due to the eq, though.

It's not surprising that the eq hiss goes up if its gain is increased. That will always
happen to some degree.
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A buffer won't filter noises

My concern about the buffer is about maintaining a proper input impedance for

equalizer module and also a proper output impedance loading for the PCM 2706 module because the PCM module is driving both the equalizer and the subwoofer processor ... as i know SMD devices dont really have a high current drive capability and also my RCA cables to the whole amplifier is also quite long too.

Now the equalizer module issue ... how to counter the noise problem as the gain is increased? is that something i need to live with it?

thanks for helping


2011-04-29 8:37 pm
What is the output spec on the PCM? What are the input specs on the eq and sub processor?
Odds are the PCM will drive both together well enough, since a PCM output stage is usually an op amp,
which can drive >2k easily in most cases.

There have been eqs that don't have much noise, but their output noise level will always increase with gain.
If the eq noise is too high, the eq may be poorly designed. Or you could be picking up noise from the PCM,
or other gear nearby. If you turn the PCM off, is there still noise? If so, try turning off other nearby gear.
Or inset shorting plugs into the eq inputs, is the noise still there?
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