AR SP8 mk2 high output volume

Here is another alternative, leave the A30’s volume up full, or again better still take it and the input selector out, and replace it with a 100kohm resistor to ground.

And then get full 6db shaved off the AR preamp’s gain, by a tech to do this.
Parallel R39 (another 39kohm) resistor across R29 (also a 39kohm) resistor, this makes it 19.5kohm, more feedback less gain is the result could sound a bit cleaner also.

AR output stage circuit diagram. https://ibb.co/Chrcx4t

AR output stage circuit diagram. https://ibb.co/Chrcx4t

OMG- while you are at it, jumper out R-30, C25 and C26. This will allow the feedback to include everything that occurs at the output of the preamp. I would also consider eliminating the C24 bypass cap and replacing C10 with a good quality part of the specified value (bypass caps tend to smear the signal when bypassing a larger coupling cap). D18 really doesn't protect the tube during warmup, but it does affect the sound so removing it is a pretty good idea. ARC left a lot of performance on the table in this design...

BTW this preamp is old enough that the power supply filter capacitors should be replaced if you want it to be reliable. If not replaced, the preamp could develop a hum, but could also suffer a power transformer failure and that is an expensive part to replace if you can even find it (ARC does not stock it anymore- they purged older parts like this years ago).

Yep, let’s go full circle and get dizzy again, just ditch the AR and use the A30 the way it was meant to be used. And if you don’t like what the source is giving then, change it instead.