Note this is running with reduced voltages initially - I will order some new resistors to increase the voltages and that will give it some additional bite. I will also add the V2 mod and that will also provide bite (although at near unity gain).
So initial impressions:
So initial impressions:
- Can sound bluesy
- Can bark
- Chuffing loud (97dB/W and 2W)
- Does have some bass but it's not a bass amp.
I’ve managed to nail most of the hum, only two issues at max volume:
I will try the normal techniques:
- wide band hiss increasing the noise floor (not so much of an issue)
- a small amount of 50/100Hz hum, almost gone
- a spike at 20kHz that seems to be coming through the elevated heaters, so I think this may be some oscilation:
I will try the normal techniques:
- dc bench heater
- reverse the heater wires to give 180 from the B+ phase
- adjust the artificial tap resistances
- use a quieter B+ source for the reference.
Much better sound now - after a few mods and switching from attempting to use the 8R tape as the NFB to using the 16R tap for the speaker and the NFB.
Clear, clean (for a marshall) and probably over doing the NFB, but still sounding good:
I think now it's a case of ordering the parts to:
(b) two extra triode stages and attenuators for unit gain but shaping of the sound
(c) cold clipper changes
If the V2 mod turns out to be a loss, I may just double up the V1 and move the cold clip to the V2mod. That parallel doubling up should then reduce the noise floor of the highest sensitivity triode stage.
Clear, clean (for a marshall) and probably over doing the NFB, but still sounding good:
I think now it's a case of ordering the parts to:
- get the B+ voltages up
- to fix the 20kHz annoyance
- various mods for the sound
(b) two extra triode stages and attenuators for unit gain but shaping of the sound
(c) cold clipper changes
- improve shielding.
- FX loop
- 10% volume attenuator so I can crank up the amp to max and keep the neighbours happy.
If the V2 mod turns out to be a loss, I may just double up the V1 and move the cold clip to the V2mod. That parallel doubling up should then reduce the noise floor of the highest sensitivity triode stage.