Impedance switch for SII?

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Deke609

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Reply #15 on: October 16, 2018, 02:01:43 PM
Minimum current rating for the DPDTs?



Offline Paul Birkeland

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Reply #16 on: October 16, 2018, 02:11:44 PM
Ohm's Law can tell you this:

The amp makes 3.5W into 8 Ohms.  Solve for current, then add some safety margin.

(Repeat as necessary for other impedance taps, all of which will make 3.5W but into a different load)

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Deke609

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Reply #17 on: October 16, 2018, 02:23:31 PM
Hah!  Thanks PB. That was dumb!



Deke609

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Reply #18 on: October 19, 2018, 11:04:30 AM
I'm going to build the impedance switches this wknd and have a few questions:

(1) If I were to leave out the bal/unbal part of the circuit and only build for impedance switching, I can leave out the resistors, right?  Their only purpose is to provide hot and cold references to ground in balanced mode?
 
(2) Is there any performance advantage (sound, health of the amp, etc) in implementing balanced at the OTs rather than at the speakers? If there is an advantage to balancing at the OTs, what value of resistor should be used? Anything in the same 50-100 Ohm range that applies when balancing at the speaker outs?

Many thanks,

Derek



Offline Paul Birkeland

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Reply #19 on: October 19, 2018, 12:50:18 PM
(1) If I were to leave out the bal/unbal part of the circuit and only build for impedance switching, I can leave out the resistors, right? 
In the schematic PJ posted, a resistive center tap is provided for two of the balanced impedance settings, while the other two use the junction of the two secondary windings as the center tap.   

(2) Is there any performance advantage (sound, health of the amp, etc) in implementing balanced at the OTs rather than at the speakers? If there is an advantage to balancing at the OTs, what value of resistor should be used? Anything in the same 50-100 Ohm range that applies when balancing at the speaker outs?
You're talking about putting resistors that handle very little current on one side or the other of a few inches of wire. 

Paul "PB" Birkeland

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Deke609

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Reply #20 on: October 19, 2018, 01:39:45 PM
Thanks PB.

I'll stick with balancing at the speaker outs and build two 2 DPDT boards (sans resistors) for impedance switching.



Deke609

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Reply #21 on: October 20, 2018, 06:23:51 PM
I built and installed the impedance switching boards today and they work! Very cool.

My only issue is that flux found its way to the contact pads of the DPDT slide switches. I was able to get most of the flux off the throws, but the poles at the center are inaccessible without opening up the switch. Does anyone know a trick for cleaning the center poles of slide switches?

cheers and thanks,

Derek



Deke609

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Reply #22 on: October 21, 2018, 03:21:06 AM
And here is how I implemented PJ's ingenious 2-DPDT solution for impedance switching, in case anyone is interested. I dealt with balancing separately.

I believe my implementation is correct, but can't vouch that it is. But it sounds good, other than 16 Ohms which is too quiet and distorted on my LCD4s - I think the current is too low to drive them. 



Offline Paul Birkeland

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Reply #23 on: October 21, 2018, 07:24:04 AM
But it sounds good, other than 16 Ohms which is too quiet and distorted on my LCD4s - I think the current is too low to drive them.
No, this is likely a wiring issue with the proto board.  16 ohms should be noticeably louder than the lower impedance settings. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Deke609

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Reply #24 on: October 21, 2018, 07:46:39 AM
Thanks PB. Hmm. Weird that 2, 4 and 8 sound great.  I'll re-evaluate the 16 Ohm config. I must have goofed something specific to the 16 Ohm wiring.



Deke609

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Reply #25 on: October 21, 2018, 07:58:41 AM
Update: checked my wiring, and couldn't find a problem in my implementation, so I tried switching to 16 Ohms again ... and lo and behold it sounds great and louder than at 8 Ohms.  Not sure what was going on last night when I tested it. Last night it sounded horrible. Maybe the flux on the switch pads prevented good contact?  16 Ohms was the first config I tried last night.  Maybe subsequent switching cleaned the switches?  Dunno. But it's working now.

« Last Edit: October 21, 2018, 09:12:58 AM by Deke609 »



Offline denti alligator

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Reply #26 on: July 10, 2021, 09:47:09 AM
I would still love to get my hands on one of these. Any chance they would be sold as a kit?

- Sam

Rega P3-24 (w/AT 150MLX) w/Groovetracer upgrades / Eros II / FLAC >J.River >DSD256 >Gustard X20 / Moreplay > Stereomour II / Klipsch Forte II w/Crites upgrades / C4S S.E.X. 2.0 +Nickel MQ Iron / Speedball Crack / Sennheiser HD600 w/Cardas cable


Offline Paul Birkeland

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Reply #27 on: July 10, 2021, 10:26:36 AM
We have no plans to put that kit back out.  It was unusually hard for our suppliers to keep the little switches in stock, and explaining how to properly use the kit was something we had to do over, and over, and over again.  This is a big part of why the new SEX amp says to wire for 4 ohms for headphones or 8 ohms for speakers.  This has eliminated a lot of "I wired my amp for 16 ohms to use with Grados and it's too sensitive and I hear some noise" kind of threads. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man


Offline oguinn

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Reply #28 on: July 10, 2021, 01:04:50 PM
Unrelated: Anyone heard from Derek? Hope he’s ok.
« Last Edit: July 10, 2021, 01:08:44 PM by oguinn »

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Offline Paul Birkeland

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Reply #29 on: July 10, 2021, 01:17:34 PM
Unrelated: What happened to Derek?
Derek and I had a disagreement over a post he wrote here.  I suggested that content would be better posted in a different forum and I believe I offended him in doing so and he left.  There was never any intention for him to stop participating here, but this is not the first time that this exact chain of events has happened, nor will it be the last time. 

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man