Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: oguinn on August 08, 2019, 03:49:15 AM
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I initially built my SEX to power both headphones and the 8 ohm speakers I have at the house. Since then I completed my Stereomour and bought a Kaiju, so the chances I'll use the SEX for speakers again are very slim.
All this talk on the boards about impedance switching got me wondering - is it worth the time, effort, and potential broken wires to change the impedance from 8 to 4 ohms? I'm not currently experiencing any noise (unless the preamp is attenuated quite a bit, which... easy solve there), so that's not a super compelling reason. Is there any other sonic benefit I'd get from flipping the chassis and making the change?
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Nope, I would leave it where it is until you end up with a really sensitive pair of headphones, then you can consider going down to 4 ohms.
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Done. Thanks for making that easy.
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For me, most of the appeal was the fun/challenge of doing it. PJ's solution is extremely clever (for example, one switch can "throw" a wire to either an OT terminal or to a pole of the second switch, which in turn can "throw" the wire to 2 different OT terminals, providing 3 different OT terminal connections for the same wire; another combo of switch positions achieves something even more elaborate). It really is (to my mind) an ingenious use of two DPDT switches and it was quite satisfying to appreciate the cleverness of PJ's solution and then build and install boards that successfully implemented it.
Sonically speaking, I suspect the switches are at best neutral and possibly a detriment. The switches require a bunch of additional signal wiring right next to the OT and only a short distance from the PT (b/c in the SII, unlike in the Kaiju, the OT terminals face inwards toward the PT) - and even if neither has enough flux leakage to impact the signal, the additional wiring makes a larger "antenna" for possible RFI. I recall reading a statement of John Camille to the effect that all wiring is a potential antenna and accordingly wiring should be kept as short as possible. I shielded the additional wiring in copper braid (which took forever and resulted in a bizillion wires to chassis ground), but I still regard the switches with some suspicion: "Are they hurting my sound?"
But they were fun to make.
cheers, Derek
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Yeah, had I done it I would have just hard-wired for 4 ohms and not worried about the switch. I think it's really clever and cool, but it's not a realistic use case for me given that I have... checks notes... too many amps already.
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I added impedance switching to my Kaiju. I did it also for fun and for the sense of accomplishment. I was also curious about what kind of sonic differences there were between different output impedance, and having the switches allows me to experiment and effectively do a/b comparisons. For me, the effort was worth it.
I have a SEX kit on order, and I'll be adding impedance switching to it as well, using the schematic PJ posted. But instead of using two 2p2t switches per channel (for a total of four), I think I can use just a total of two 4p2t switches. I plan to mount these switches to the top plate, so having fewer switches helps.