222.166.160.146
This circuit is probably considered as the minimalist pre-amp. I have extended this idea to become a minimalist active crossover and pre-amp.
Thanks to the number of of secondaries of the LL1660/1671 series of transformer, an RC circuit is applied to each or combination of these output coils for each channel of individual amp. Currently I am using this as a 2 channel setup where the cross over design freq is around 3K.
The high pass is having a 12db slope while the bass has a 6db slope.
Here are my application notes so far:
1. Since there are 4 output coils, coil A of the top coil is combined with coil B of the bottom coil to form an output for the high pass. The other 2 coil will form the low pass. (refer to the LL1660 spec sheet for which is coil A and B).
2. Since the amplification of the pre-amp is done before the cross over, there is no separate gain control of each pass, you have to rely on your volume of your high and low pass power amp to set the ratio of the treble and the bass.
3. Since there is no gain control of each pass, I found that a power amp that has gain similar to those of commercial amplifiers should be used. If you amp has gain less than 20, this idea may not be for you. In my case, my high pass amp (a papworth tube amp) has a gain of around 30. The low pass amp (a diy tube amp) that I use has a gain of around 20.
When I first listen to this setup, it gives me the improvement that I would have expected when listening to an active setup. At this moment I am very pleased with this, and I am looking into ways to extend this idea into a 3 ways speaker when I have enjoyed enough from my current setup.
If you have done something similar, please share your experience.
Alan
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