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July 04, 2020, 11:22:47 AM

Author Topic: Impedance board for sex 3.0?  (Read 406 times)

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Offline sharktopus

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Impedance board for sex 3.0?
« on: August 07, 2019, 05:35:10 PM »
I see a number of places here that there is (was?) and impedance switching kit for the sex.  Is this still available?  If not, I've seen pictures of the mainline amp where it has a physical toggle switch on the front that does the same function.  Would you be able to wire such a switch into the sex?
Drew Sanford

Offline Paul Birkeland

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Re: Impedance board for sex 3.0?
« Reply #1 on: August 07, 2019, 05:57:37 PM »
The Impedance Switch Kit is no longer available.  While it was a great idea, we have many different versions of the SEX amp and two different versions of the Stereomour amp, and the complications of making a manual to work with four or five different kits got to be too much (especially considering how many of these we were selling).  The small PCB toggle switches also frequently went out of stock.  There isn't a whole lot of use for the 16 and 32 ohm settings, and we found ourselves explaining over and over again that 32 ohm Grado headphones absolutely should not be used with the 32 ohm tap.  This is why you see the recommendation to use the amp on the 4 ohm setting if you aren't sure, or the 8 ohm setting for speakers.

That is the short version of why you don't see this kit available anymore.  The Mainline circuit is a bit different and uses a different transformer. You could very likely wire up a rotary switch on the SEX amp to go from 4 to 8 ohms, but that's not the kind of project where we can give you three simple steps to get the job done!
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Deke609

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Re: Impedance board for sex 3.0?
« Reply #2 on: August 08, 2019, 03:32:58 AM »
If the S.E.X. 3.0 uses the same OT-2 output transformers used in the Stereomour II, as I believe it does, you can build your own impedance switches using PJ's schematic for a 2-switch solution (or 3 switches, if you want to be able to switch from balanced to unbalanced). [/size]You'll find it in the following thread:

I built and installed the impedance switches on my SII-2A3 amp and they work great.[/font]

If you decide to build them, make sure you get low profile switches. I failed to check dimensions on the datasheet before ordering and wound up with very tall switches.[/font]

cheers, Derek[/font]

Roon Intel NUC ->  Yggdrasil DAC -> BeePre (w/ BeeQuiet and EML 300B)  -> Kaiju (w/ DCFil and EML 300B) or Stereomour II (2A3 [EML Mesh] and 45 Conversion [EML 45B])  -> Audeze LCD4

Offline sharktopus

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Re: Impedance board for sex 3.0?
« Reply #3 on: September 29, 2019, 05:48:06 PM »
So from what I can tell, if I am only interested in switching between 4 or 8 Ohms then I can get away with only one 4PDT On/On switch.  This would choose between the two stock wiring setups.  Only terminals 1, 3, 6, and 8 of the output transformer would be switched between.  Terminals 2 and 7 would be hardwired together and out for either impedance setting (unchanged from the stock instructions).  The wiring schematic is attached.

And I would wire it like so:
Switch     FunctionImpedance
6Left OT terminal 6
3Left OT terminal 3
12Right OT terminal 6
9Right OT terminal 3
4Left OT terminal 8
1Left OT terminal 1
10Right OT terminal 8
7Right OT terminal 1
2Left Out (Green Striped)Common
5Bridge to switch 2Common
8Bridge to switch 11Common
11Right Out (Brown Striped)Common

For each channel the two outgoing terminals on the switch would be wired to each other (eg 2 to 5 and 8 to 11)

Do any of you see any issues with wiring it like that?
Drew Sanford