A 2 or 3-channel SE 'Horn-amp'

[Cressy Snr]

Ooh look, a TOCOS pot!

[IslandPink]

I couldn't fit an LDR board in there !

[IslandPink]

Here's the updated version of the bass pre-amp which I'm going to build .
This is a small 5687-based gain stage followed by a filter. The 5687 sections are loaded by DN2540 cascode CCS's .

I spent a while trying to use a more complicated filter, like an RIAA network, to fit exactly the profile of the passive filter Troelsgraven uses for the 2515 on his OB's .
It seemed quite tricky to get it right without knowing how to optimise on LTSpice , and I started thinking about a compromise for the short-term .
All I really need is equalisation of about -5dB going from 40Hz to 100Hz , then followed by a 1st-order LP from 150Hz . In actual fact a simple 120Hz 1st-order LP gives about 5dB from 40Hz to 100Hz and then continues to roll down as the ( Fostex 208 ) comes up . So, I won't be far off with this simple filter.
If I end up with a slight hollow in the overall response, at 150 to 200Hz, I'll have to resinstate a short 'shelf' filter using another section in front of the 0.22uF cap to ground .

I'm now off to solder in the 3K3 resistors and 0.22uF caps. I'll just use small polyester metallised film caps for now & see how it sounds. They don't have to sound good at 5kHz on this unit !