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Old 9th September 2012, 04:14 PM   #1
diyAudio Member
Join Date: Jul 2005
Default Broskie Unbalancer

I have been inspired to build one of these after reading a thread about this tube stage
Buffalo III DAC Tube Output Stage

Details of Unbalancer circuit
The Unbalancer

...and instruction manual here:

I see there are a few people interested in this device so thought I would start a thread for discussion and also hope some experts out there can answer a few queries.

I'm a DIY novice but have always wanted to build a valve amp. I had intended to build an SRPP preamp stage and collected many of the parts, before seeing the Unbalancer and changing tack, I have some questions about suitability of these parts for this Unbalancer:

As I have an existing power supply board I hope to use, I'd like to build this point to point. I have four 6SN7 tubes and see that 6CG7 is a recommended tube for both stages. Comparing the data sheets for both tubes, other than the pin numbers they seem very similar apart from a couple of parameters that I don't understand: 6SN7 Output 0.7uuf vs 6CG7 output 2.2uuF, the plate dissipation figures are also a bit different but suspect this isn't an issue. So could anyone confirm if it would be ok to use 6SN7 tubes for both stages of the Unbalancer, would they be a good choice or would there be any disadvantages?

The manual shows a volume control can be integrated, but it is not clear to me where this should be added in the circuit, i.e. input or on the output. I would like to use this as the output I/V stage for a BB1794 DAC and ultimately feeding a PAss F5 amp. Could anyone recommend where a stepped attenuator would best be placed for my needs please?
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Old 3rd January 2013, 04:49 AM   #2
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Join Date: Jun 2007
Appears no-one offered the OP some help - I'll start:

(1) 6SN7 will be fine, but I'd just do the PCB build if you haven't done tube projects before. I built my unbalancer using the PCB, and it was still quite hard to get everything perfect. This means you'll need to use the 6CG7 (get the ones with shields, not 6FQ7).

(2) Put the stepped attenuator after the Unbalancer. (I put mine in between, but another forum thread has some good discussions around CMRR). I doubt you'd hear a difference, though.
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Old 3rd January 2013, 08:19 PM   #3
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Join Date: Jun 2004
Location: Copenhagen
Hi Bud!
Put the volumecontrol at the input of the F5, to avoid a long cable after the potmeter.
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Old 7th January 2013, 12:03 AM   #4
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Join Date: Nov 2007
Location: Dallas
Only need a single twin triode to unbalance a DAC.

Excellent CMRR, PSRR. balanced input impedance,
Very low output impedance, and able to drive as
little as 4K7 load with good symmetry.

Why it has excellent rejections, harder to explain.

Broskie's BCF offers much the same. But this one
is *mine*, obviously figures which I would prefer...
Attached Files
File Type: asc wako2.asc (3.3 KB, 126 views)
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Old 7th January 2013, 03:57 AM   #5
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Join Date: Jun 2007
kenpeter - interested to see your design however the attachment cannot be opened
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Old 7th January 2013, 07:21 AM   #6
diyAudio Member
Join Date: Nov 2007
Location: Dallas
I found no problem to download and open the attachment at another PC.
You will of course need both LTSpice and
Linear Technology - Design Simulation and Device Models
Index of /spice/valves

You been around a while, I would assume you had all the Spicey stuff...
Not trying to open that .asc file straight out of the browser are you?

Last edited by kenpeter; 7th January 2013 at 07:27 AM.
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Old 19th January 2014, 11:40 AM   #7
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Join Date: Jan 2005
Location: a littlee town in western denmark
I am also interested in The Unbalancer,,,,but i can see the print is out of stock...does someone know when it comes back in stock ?
maybe some off you have a print for sale
hope not it is wrong to ask in this tread
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