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Old 15th August 2013, 05:12 PM   #1
jblmar is offline jblmar  United States
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Default DIY AB Switch for ST1701A

Hello,
I decided to build an AB Selector switch for testing the Left & Right channel output of the DUT when using my ST 1701A. Better than manually reconnecting every time either channel is selected for testing. Can someone post or direct me towards a schematic? I would like to include a high degree of switching isolation in the switch box out to the 1701A to maintain the channel being tested.

Thanks
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Old 16th August 2013, 02:06 AM   #2
jblmar is offline jblmar  United States
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Moderator,
If I posted in the wrong forum, please move this thread to the correct forum.
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Old 17th August 2013, 10:59 PM   #3
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Quote:
Originally Posted by jblmar View Post
Hello,
I decided to build an AB Selector switch for testing the Left & Right channel output of the DUT when using my ST 1701A. Better than manually reconnecting every time either channel is selected for testing. Can someone post or direct me towards a schematic? I would like to include a high degree of switching isolation in the switch box out to the 1701A to maintain the channel being tested.

Thanks
How you doing ? I would use a four section rf switch isolate the ground and hot of each and switch with a break before make 4pole 4 section switch and use position 1 and 3 or 1 and 4 . silver coin contact ,
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Old 18th August 2013, 12:40 AM   #4
jblmar is offline jblmar  United States
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Originally Posted by Triodethom View Post
How you doing ? I would use a four section rf switch isolate the ground and hot of each and switch with a break before make 4pole 4 section switch and use position 1 and 3 or 1 and 4 . silver coin contact ,
Thanks for responding.
I have a few simple A/B toggle switches rated @ 3A 125VAC DPDT. Center contact is common, to A or B. To be used as + and - per channel.
You don't think that will work? Silver contacts are a good suggestion for this application.
I'll look into your suggestion, but I'd rather use what I have since I have so many of these switches.

Last edited by jblmar; 18th August 2013 at 12:45 AM.
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Old 18th August 2013, 01:46 AM   #5
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I use a simple DPDT switch. Outside teminals connected to the + and - of the two channels and the center terminals connected to the output +/-.
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Old 18th August 2013, 02:00 AM   #6
jblmar is offline jblmar  United States
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I plan to use the first end contacts of the DPDT switch as the +/- of the left speaker terminals of the DUT and the other end contacts as the +/- of the right channel speaker terminals. The center (common terminals) will be the +/- OUT of the selected channel to the input of the 1701A.
Common (GND) - terminals connected (3 terminals across)
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Old 18th August 2013, 03:27 AM   #7
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Originally Posted by jblmar View Post
Common (GND) - terminals connected (3 terminals across)
Can't say for sure but I would think that this could increase the chance of crosstalk (or worse) on some DUT's.
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Old 18th August 2013, 04:11 AM   #8
jblmar is offline jblmar  United States
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Originally Posted by ronaldw441 View Post
Can't say for sure but I would think that this could increase the chance of crosstalk (or worse) on some DUT's.
I mean to say the (-) speaker terminals from the left and right channels of the DUT connected to the (-)common terminal that goes out to the balanced input of the 1701A. Switching channels would switch their respective + terminals to common then out to the 1701A. This is the same as connecting a channel manually. Positive & negative to the 1701A.
Would you suggest not to connect the negative from A&B to the Common terminal?

On second thought;
I see your point and it's a good one. Some amplifiers have the - speaker terminal connected to chassis ground, and others don't. The 1701A manual states to connect a 3 wire cable to the DUT. PLUS & MINUS to the speaker terminals then to the balanced inputs of the 1701A, but to connect a third wire(Ground) to the DUT only not to the 1701A Ground terminal.
Having the switch - contacts connected can introduce noise from the unused (open) side of the switch. Better to follow the switch design the same as that stated in the Manual. Have the switch do as would be done manually.
I could be wrong. I 'll have to try this both ways and take noise measurements. I guess it's not as easy as wiring up a switch and forgetting about it.

Last edited by jblmar; 18th August 2013 at 04:36 AM.
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Old 18th August 2013, 03:46 PM   #9
jblmar is offline jblmar  United States
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I misspoke. The common (-) connected between A & B. Not to (-) Common as this is the output of the switch and the switch will connect it from either A or B.
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Old 20th August 2013, 01:06 PM   #10
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Here a link to an example . Have not dealt with that sellerCeramic Rotary Switch 4 Pole 5 Positions Selector RF | eBay
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