JHS wrote:Some further infos I got from a well known British FX-builder/-modder from the early '60th.
The 1st trannie had been addded to the circuit because OC81D didn't had enough hfe to work well in the old TB Mk1.5/2 circuit.
You can archieve the sound of the early TB Mk2pro with OC81D if you built a F-Face with OC44, 5uF I-cap, 47n O-cap and a 100k pot for vol. Adjust the voltage between C and ground on Q2 to app. 5,5V.
Maybe the R on the collector of the 1st trannie must be altered a bit too to set a perfect working point for Q1.
You can trim the highend futhermore by adding few pf to the output and/or the trannies.
BTW:
If you want the original Jimmy page sound from a VOX TB MK2pro or clone (his secret fuzz box, modded by RM), use OC81D and swap the 1k on the collector of Q2 for a 1,8-2,2k.
JHS
JHS wrote:In the Mk1.5/Mk2pro are 2 R (1k/8,2k) connected in series to the collector of the 2nd transistor, though some units have 470E instead of the 1K.
The 47k is connected to the collector of the 1st trannie and I recommend to subs the R with a 50k trimpot for biasing Q1.
If you set the value of the trimpot lower than 33k you have to decrease the FB-resister too or Q2 will be misbiased.
JHS
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