Gainclone w/ preamp

[Nate805]

So I recently purchased a tube / mosfet preamp for my lm3886 pa-150 based amplifier. Both my preamp and pa-150 boards have a gain of 20db. Both my amp and preamp have potentiometers. What is the optimal setting between these two for low distortion. If i turn the preamp up high and the amp low for normal volumes, the music sounds really distorted, this is obviously not optimal, any ideas why / what would be the best setting between the two amps?

[noSmoking]

Originally Posted by Nate805

So I recently purchased a tube / mosfet preamp for my lm3886 pa-150 based amplifier. Both my preamp and pa-150 boards have a gain of 20db. Both my amp and preamp have potentiometers. What is the optimal setting between these two for low distortion. If i turn the preamp up high and the amp low for normal volumes, the music sounds really distorted, this is obviously not optimal, any ideas why / what would be the best setting between the two amps?

hi,
I built a system very similar you have to adjust each stage to prevent clipping,if you have a scope you can view it happening no scope use your ears,but basically,I would turn the preamp up until it distorts and back off enough to make sure it's not clipping or distorting,and move to the next stage and do the same ,when it's all sounding good you're there !!!!!
GOOD Luck!

[Redshift187]

Depending on the circuit the LM3886 is in, it is not stable at low gains. The datasheet says it is not stable below a gain of 20dB, and it also says it's better to set it at 26dB or higher. You are likely getting oscillations when you set it lower than that.

I have a feeling though that when you say potentiometer, you are referring to an attenuator between the pre-amp and your power amp. In that case, you are likely clipping the power amp with the high signal from the pre-amp. If your power rails for your LM3886 are up between +/- 35V DC and 40V DC, your power amp will clip with around 2.8V RMS input. That's just above the typical output level of a cd player. Going through a pre-amp with a gain of 20dB, you could be feeding your power amp a signal up to about 20V RMS!

[AndrewT]

don't know if this will work, but worth trying.
Turn Pre-amp to minimum volume.
Turn Power-amp to maximum volume.
Adjust Pre-amp volume to the loudest you are ever likely to use and still come through unclipped.
Mark the Pre-amp pot at this setting.
Now return to the Power-amp and reduce the volume to a level that you want to listen.
Continue to use the Power-amp pot as your volume control.


If the Pre-amp volume control is turned down more than -6dB then remove your pre-amp and keep it for another use, not for this combination of source and receiver.