Blackstar Series One 45

[hovis90]

More specifically the built-in DPR power reduction part of the diagram.
Thanks

[bassetrox]

Also interested.

[teemuk]

They applied a patent for it so run a UK patent search. The application has the schematic.

[bassetrox]

I was actually just after a regular schematic, rather than the DPR specifically... But I ran a patent search anyway... link is: Espacenet - Bibliographic data

for the OP and any who are interested, HOWEVER... there seems to be a mix up, all the graphs and text relate to DPR, but the schem for the patent is their ISF circuit...

[teemuk]

for the OP and any who are interested, HOWEVER... there seems to be a mix up, all the graphs and text relate to DPR, but the schem for the patent is their ISF circuit...

There are at least two patent application documents for it; one with incorrect images, one with correct ones. Search a minute more.

In all it's glory the bare essence of the circuit is:
- Screen voltage regulator (instead of B+)
- Dual potentiometer, one half adjusting VVR voltage the other input sensitivity of the power amp so that overdrive threshold remains constant despite the voltage setting
- Bias servo monitoring the VVR output and adjusting bias accordingly