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07-22-2020, 01:40 PM
Hi Guys
For the voltage reduction required, think in terms of "a lot"
Bassmaster has Va and Vs of 560V, with the splitter around 500V and the preamp in the 400s. The 22k to the preamp fan-out node would change to 100k or 150k to get the desired result... 220k or more if necessary since there are only four triodes. This gets the preamp down to 200V or less. As voltage is reduced, the current reduces and the change of R required for further change increases.
What you should do is build it as stock to know what the foundation tone is, then change that dropping resistor while the chassis is open on the bench and keep playing. Bass guitars have pretty high output so you might find it does not take too extreme of a voltage drop. Power 'off' for the resistor changes.
If you find that there is a compression point that works for your son and his bass and playing technique, but you also want to have the cleaner headroom at times, you could put the voltage drop on a switch, or for infinite control, Power Scale the preamp over a limited sweep.
To me the Dual-Volime preamp is a waste of tubes. Linking the inputs does not increase the signal strength that much and the cathode follower is a tone killer, as we know from TUT6. So, there is a whole bottle being used in a nonbeneficial way. Of course, you could use that bottle for a half-wave rectifier and gain to implement a compression side-chain although I would still go with extra gain stages instead.
Have fun
For the voltage reduction required, think in terms of "a lot"
Bassmaster has Va and Vs of 560V, with the splitter around 500V and the preamp in the 400s. The 22k to the preamp fan-out node would change to 100k or 150k to get the desired result... 220k or more if necessary since there are only four triodes. This gets the preamp down to 200V or less. As voltage is reduced, the current reduces and the change of R required for further change increases.
What you should do is build it as stock to know what the foundation tone is, then change that dropping resistor while the chassis is open on the bench and keep playing. Bass guitars have pretty high output so you might find it does not take too extreme of a voltage drop. Power 'off' for the resistor changes.
If you find that there is a compression point that works for your son and his bass and playing technique, but you also want to have the cleaner headroom at times, you could put the voltage drop on a switch, or for infinite control, Power Scale the preamp over a limited sweep.
To me the Dual-Volime preamp is a waste of tubes. Linking the inputs does not increase the signal strength that much and the cathode follower is a tone killer, as we know from TUT6. So, there is a whole bottle being used in a nonbeneficial way. Of course, you could use that bottle for a half-wave rectifier and gain to implement a compression side-chain although I would still go with extra gain stages instead.
Have fun
