I've been toying with the idea of building one 1176 with switchable topologies in certain parts of the circuit (I/P = Xformer vs. IC, O/P = Class A vs. Class AB, and maybe even Zener vs. 7824 for 30V regulation). Maybe this has been done before, but I wasn't able to find anything on the board here.
I'm trying to think of a possibility to use _one_ I/P control for both topolgies (Xformer / IC). The problem obviously is that the values for the respective pots are quite different (and probably the tapers as well): 600R double pot used in a T config. before the Xformer, as opposed to a single 10K shunt after the IC stage. Which would mean that you would have to have two I/P controls, one for each topology... would look a bit odd, you couldn't use the standard frontpanel layout etc. etc.
Now if I took that 3-deck I/P pot as offered by Hairball (500R/500R/1K), used the two 500R decks for the T attenuator in the Xformer stage and used the 3rd deck (1K) as the shunt after the IC input stage, would that work?
- The original shunt behind the IC's is a 10K pot, forming a pad with 27K in series with the following FET that performs the gain reduction. I figue that 5532 wouldn't have a problem driving just 1K, but maybe it would affect the characteristic of the gain reduction? On the other hand, in the original Xformer I/P, the secondary is terminated with just 270R, and then the 27K and FET in series...
- What about the tapers of that triple pot? Would the two 500R-decks (linear) match the taper of the original T600 attenuator if used in the same configuration (incl. 2 fixed resistors, forming a bridget T)?
- and would the remaining 1K deck ("CW modified log taper") be right at all? If the "CW" indication that the changes in value get less rapid as the pot is turned clockwise, I would be in the ballpark... but if it's just the other way round, it wouldn't really be usable as I/P control...
While I'm at it, here's another question regarding sonics of the different original/replica Xformer models that may be used for each topology:
- in what way do the Magnetika O-12 and Cinemag 3837-1 differ from the original UTC O-12, regarding construction (core material etc.) and resulting sonics?
- and what about the versions of the 5002 O/P Xformer by UA, Ed Anderson and Cinemag? Also, for the Class AB-Stage (B11148 Xformer), are there different properties with different manufacturers?
Thanks a bunch, my appreciation in advance for any comments!
Cheers.
I'm trying to think of a possibility to use _one_ I/P control for both topolgies (Xformer / IC). The problem obviously is that the values for the respective pots are quite different (and probably the tapers as well): 600R double pot used in a T config. before the Xformer, as opposed to a single 10K shunt after the IC stage. Which would mean that you would have to have two I/P controls, one for each topology... would look a bit odd, you couldn't use the standard frontpanel layout etc. etc.
Now if I took that 3-deck I/P pot as offered by Hairball (500R/500R/1K), used the two 500R decks for the T attenuator in the Xformer stage and used the 3rd deck (1K) as the shunt after the IC input stage, would that work?
- The original shunt behind the IC's is a 10K pot, forming a pad with 27K in series with the following FET that performs the gain reduction. I figue that 5532 wouldn't have a problem driving just 1K, but maybe it would affect the characteristic of the gain reduction? On the other hand, in the original Xformer I/P, the secondary is terminated with just 270R, and then the 27K and FET in series...
- What about the tapers of that triple pot? Would the two 500R-decks (linear) match the taper of the original T600 attenuator if used in the same configuration (incl. 2 fixed resistors, forming a bridget T)?
- and would the remaining 1K deck ("CW modified log taper") be right at all? If the "CW" indication that the changes in value get less rapid as the pot is turned clockwise, I would be in the ballpark... but if it's just the other way round, it wouldn't really be usable as I/P control...
While I'm at it, here's another question regarding sonics of the different original/replica Xformer models that may be used for each topology:
- in what way do the Magnetika O-12 and Cinemag 3837-1 differ from the original UTC O-12, regarding construction (core material etc.) and resulting sonics?
- and what about the versions of the 5002 O/P Xformer by UA, Ed Anderson and Cinemag? Also, for the Class AB-Stage (B11148 Xformer), are there different properties with different manufacturers?
Thanks a bunch, my appreciation in advance for any comments!
Cheers.