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64/67 AC30TB bright cap value?

edo

Power User
The axe model defaults to 60, I'm not sure what specific vintage it's modeled after, and wanted to know what's the correct bright cap value for the JMI mid 60's TB.. Does anybody know?
 

pdup

Experienced
One of the differences between older AC30's and the Korg RI is the bright cap (C8..) on the Brilliant channels vol pot. On the Korg the value is 120pF, in the original circuit the value was 100pF. The cap will increase brightness on lower vol settings, but as the vol is turned up the HF boost will gradually decrease and when reaching a certain level (50-60%, I think) the cap will have no effect.
 

Andrew Male

Experienced
The axe model defaults to 60, I'm not sure what specific vintage it's modeled after, and wanted to know what's the correct bright cap value for the JMI mid 60's TB.. Does anybody know?
I think it's a Korg era TBX, don't quote me on that though.

Be nice to get a 64 copper panel in there.
 

edo

Power User
One of the differences between older AC30's and the Korg RI is the bright cap (C8..) on the Brilliant channels vol pot. On the Korg the value is 120pF, in the original circuit the value was 100pF. The cap will increase brightness on lower vol settings, but as the vol is turned up the HF boost will gradually decrease and when reaching a certain level (50-60%, I think) the cap will have no effect.
So if I wanted to model a 60's JMI grey panel AC30TB I'd have to set the bright cap at 100?
 

pdup

Experienced
The Axe is no AC30. You have to dial in by ear. And remember that any old AC30 will have caps +/-20% value, pots the same, maybe worn tubes, speakers with badly glued voice-coils to the cone. If Cliff has chosen a default of 60 pF I'm sure it's in the sweetspot of some good original AC30 - and the rest of the electronics.
 

edo

Power User
Yeah, i see your point, it was just curiosity as I find that with higher settings the amp sounds more similar to my ac30h2 which sooner or later I'd like to mod to 60's jmi specs and wanted to know the correct value for that amp, that's all!


Inviato da mio iPhone utilizzando Tapatalk
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
The bright cap value is normalized to a Drive pot of 1M. An AC30 has a 500K pot so the value will read out as half the actual value. IOW, it's displaying 60 pF which is equivalent to 120 pF.
 
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