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Old 11th February 2004, 02:28 AM   #1
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Default unbalanced to balanced converter

The x amp like alephx, SOZ, are indeed a very-very good amp. But mostly we have unbalanced input source (cd player, etc).

I think about having balanced zen line stage, to make a perfect unbalanced to balanced converter. but Grataku said this :

This topic has been popping up about once every four months for the past 2 years so you maybe aware of it. You shouldn't expect miracles from this circuit. The BOSOZ is not a great unbal-to-bal converter, actually a user has already posted simulations of the circuit that quite clearly show different voltage levels from the hot and the cold outputs when the cold input is unused, or grounded, in SE operation. The same guy has already posted a version with current source which performs better "instrumentally". If you want a Pass original circuit you could go for the AlephP that has a full complement of current sources
So what will be the perfect unbalanced to balanced converter will be like, in terms of x passlabs diy amps.
I'm trying not to go to opamps, to match the novelty of aleph amps. What will it be like if we wanted to use hot mosfets?
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Old 11th February 2004, 03:09 AM   #2
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Which one is perfect?
Which one is the miracle?

If the gap is acceptably narrow between imperfection and perfection, the imperfection could be considered virtually perfect. BOSOZ with the constant current sources (even without CCSs) reaches to our satisfaction technically and musically, in my opinion.

I would like to see who comes up with the perfect one with both technical and musical satisfactions.
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Old 11th February 2004, 04:24 AM   #3
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Default BZLS with CCS

Hello lumanauw,

Salam audio!

the original BZLS will have an absolute voltage difference between hot and cold output if you run it with unbalanced source. I have already simulate it.... A guy from china had also probed the real world BZLS circuit with unbalance input, and it indeed showed the voltage difference (he posted the result in this forum with the picture of his osciloscope readings).

If you want to make BZLS a (near) perfect unbal-to-bal converter (in terms of voltage diff at the outputs), i've made some simm in this thread:

BoSoZ with CCS -- need sugestion...

Probably you have to change the Q5 transistor for a higher voltage ratings. I'm still collecting parts for that circuit, and haven't had time to make the PCB at Bandung (I'm in Jakarta). Also, I'm having trouble with a low WAF.

Budak nu kasep,
The Great Saiyaman
Siapa bertelinga hendaklah ia mendengar... (Mat 13:9)
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Old 11th February 2004, 11:05 AM   #4
Faber is offline Faber  Italy
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The simplest way is to introduce a current source that replaces the two 750Ohm resistors.

This works fine for me and the mod is simple and fast to implement.

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Old 11th February 2004, 04:37 PM   #5
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Here's another thread regarding unbalanced-to-balanced converters that might be helpful.

Transformer at input of SOZ to convert unbalanced->balanced?

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Old 11th February 2004, 07:31 PM   #6
eLarson is offline eLarson  United States
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And when you use the current sources you can decrease the value of the negative rail to decrease dissipation.
Would a woodchuck bother to chuck MDF?
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Old 11th February 2004, 09:23 PM   #7
Luke is offline Luke  New Zealand
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Nelson suggests the use of pots on the outputs to trim the output voltage so as its balanced. This seems quite easy to do.
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Old 11th February 2004, 09:35 PM   #8
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That's a nice circuit, Fabrizio, and would do the job very well.
Input and output pots are a welcome addition to make certain
that it fits into all occasions, and it is my experience that a cap
across the zener will drop the noise quite a bit.

But I do think you need some Emitter resistors on the
current source transistors to stabilize the current values.

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Old 11th February 2004, 11:20 PM   #9
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Quote Faber: 'The simplest way is to introduce a current source that replaces the two 750Ohm resistors'.

The circuit below is an X design of the BOSOZ and with the CCS.

The circuit runs at 88 mA bias per rail, so watch out on the
power rating of 680 R resistors (dissipation around 5 W ).

Best regards,
Kristijan Kljucaric
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Old 11th February 2004, 11:25 PM   #10
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XCCS-BOSOZ Power Supply:

The transformer rating is for the one channel.
For stereo use 80 VA or higher.
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