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December 12, 2019, 07:27:19 PM

Author Topic: Balanced S3X for speakers.  (Read 463 times)

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Offline Tom-s

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Balanced S3X for speakers.
« on: September 05, 2018, 03:07:39 AM »
The Single Ended eXperimentor kit i'm waiting for will be used with speakers 90% of the time.

And i'd like to use it "balanced" with headphones.

This makes for the option of just removing the headphone jack + wiring and hardwire the OT to the speaker binding posts (4Ohm). For headphone use i'm planning on a banana plug adapter cable for balanced XLR aswel as one for 6.3mm/3.5mm.

From what i figured, to be balanced i need 4 identical resistors 1W+-; ie one from each speaker binding post to ground. That replace the 0Ohm resistors.

Is there another/more easy way to hardwire the transformers to be balanced?

In the future i'll hope for a TRRS 6.3mm option. Then i can build one in the existing plate hole if needed (more headphone use).

Another question. Do i gain or lose output power/dB with this change?

Online Paul Birkeland

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Re: Balanced S3X for speakers.
« Reply #1 on: September 05, 2018, 04:43:46 AM »
The world is still kind of waiting for a 1/4" TRRS jack.  If Neutrik made one that was the same size as the current jack we use, it would very likely go in the SEX kit.

The easiest way to do what you want would be to carefully drill out the headphone jack hole to accept a 4 pin XLR for balanced headphone use.  This is not that hard to do with a stepped drill bit.

You can then wire up the amp and just connect the wires leaving the output transformers and the wires going to the binding posts to the 4 holes on the XLR jack.  It will not switch the speakers off when you plug in headphones.

At the binding post end of the amp, instead of the single jumper resistor between the black post and the chassis, use a 100-250 ohm resistor from each binding post to the chassis.  1/4W is an adequate power rating for this purpose.
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Tom-s

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Re: Balanced S3X for speakers.
« Reply #2 on: September 05, 2018, 05:04:41 AM »
That's my point in removing the headphone jack as a whole.

With the 4p XLR in place, the speakers still need to be disconnected manually.

So instead of removing just the speakers every time and drilling the chassis to get the XLR to fit. I prefer just removing the wiring and connecting the headphones in total. And using all headphones via the speaker connection.

To me, both options look about equal. For now the only "advantage" in the variant i propose is that it is completely reversible. So i can change it all back to stock when i decide to dislike it.

Ok, so 100 Ohm, 1/4w it is.

Looking forward to your point of view.

I got it from these topics:
https://bottlehead.com/smf/index.php?topic=2288.0
https://bottlehead.com/smf/index.php?topic=3750.0
https://bottlehead.com/smf/index.php?topic=10424.0

Another last option would be to be able to use both, as per mainline, as PJ suggested here:
https://bottlehead.com/smf/index.php?topic=6341.0


Online Paul Birkeland

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Re: Balanced S3X for speakers.
« Reply #3 on: September 05, 2018, 05:58:48 AM »
Both was an "or" option, not an "and" option.  We used to provide a PC board that would allow different impedance configurations and it would use the winding centertap for two of the options and a resistive center tap for the other two.  They were never connected at the same time.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Tom-s

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Re: Balanced S3X for speakers.
« Reply #4 on: September 05, 2018, 10:40:44 AM »
Thanks for the clarification! :)

If i plan to use the resistor made center tap, and find myself with a headphone not able to use 4pin XLR at some point. Would it be a problem for the amp in that configuration if i used a single ended adapter (speaker binding post to 1/4" jack)?


Edit: And would a resistor made center tap balanced setup alter the output/gain of the amp?

Edit 2: Don't blame me for being interested in this; he started it: https://bottlehead.com/smf/index.php?topic=2367.0
« Last Edit: September 05, 2018, 11:00:14 AM by Tom-s »

Online Paul Birkeland

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Re: Balanced S3X for speakers.
« Reply #5 on: September 05, 2018, 04:25:09 PM »
If i plan to use the resistor made center tap, and find myself with a headphone not able to use 4pin XLR at some point. Would it be a problem for the amp in that configuration if i used a single ended adapter (speaker binding post to 1/4" jack)?
The amp won't care if you plug in an adapter that shorts the cold output of each channel together.


Edit: And would a resistor made center tap balanced setup alter the output/gain of the amp?
I think you might lose a thousandth of a dB or so.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man