bcarso
Well-known member
Sure you can do a Forsell op amp. One caveat: if you use the Tosh output devices you may wish to measure the P devices for breakdown voltage, as they are technically right at their limits at quiescence. Fred is aware of this and has never had a problem, but your mileage may vary. Since Tosh is probably one of those Kaizen companies and not a "goal-post-mentality" one, it's likely most of the 2SJ74's are quite a bit higher breakdown that the stated max.
I'm glad you posted this because I hadn't looked at this synth L variant in any depth, and I find that this one doesn't have a parasitic R that's in the alternative circuit. When the other circuit is used in resonator boost-cut applications, the effect of the parasitic is to come out of the dip (for example) at a lower level than you went in---it's as if the synth inductor has an R in parallel as well as one in series. This can be compensated for, or just taken into account in an overall EQ, but it's a nuisance.
If you want really high Q's a GIC type circuit is recommended, but requires two op amps---and ones with pretty decent CMRR too.
I'm glad you posted this because I hadn't looked at this synth L variant in any depth, and I find that this one doesn't have a parasitic R that's in the alternative circuit. When the other circuit is used in resonator boost-cut applications, the effect of the parasitic is to come out of the dip (for example) at a lower level than you went in---it's as if the synth inductor has an R in parallel as well as one in series. This can be compensated for, or just taken into account in an overall EQ, but it's a nuisance.
If you want really high Q's a GIC type circuit is recommended, but requires two op amps---and ones with pretty decent CMRR too.