Got hold of a Blackstar HT-5R Mk 2 (the one with the tone control on the clean channel) and happy with it's size, weight and clean sound. Not happy with overdrive channel. It's A, Too much distortion for an "overdrive" channel, B, Too fizzy on distortion, and C, Too much distortion for an overdrive channel ( I know I've repeated myself but I'm trying to make a point ). Anyway, I've got rid of about 80% of the fizz by replacing the 12" speaker for an old 25 watt Celestion G12M that I had lying around from the 70's. But the excess distortion seems to be most people's gripe when checking on the net. Most advice from the net is to change the 12ax7 for a 12au7 which lowers the gain. Blackstar recommend swopping it for a 12at7 which is still a lower gain tube than the 12ax7. But this is not the way! Lowering the gain of the 12ax7 tube lowers the overall volume of the amp which is not what is required. It's the gain of the distortion that needs reducing not the volume of the amp! The clean channel is fine with the 12ax7 so that is not the problem. The problem as I see it, is in the overdrive/distortion circuitry around IC 3A which is a TL 072 op-amp. I have a schematic for the previous HT-5 Mk1, but I think it's been modified on the Mk2 - the difference is a tone control on the clean channel and reverb (electronic not spring). So the circuitry must have been modified if only to accommodate these 2 additions. So what I really need is a schematic of the pre-amp of the Mk2 combo/head so I can start to modify the circuit. Was hoping to fit a switch to allow the distortion as is now and the proposed reduced distortion that I hope to achieve. This in my opinion is the logical way to go with this amp, but if anyone can offer another way of dealing with the excessive distortion problem, please let me know. Blackstar don't seem to want to hand out schematics.