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Old 20th September 2003, 11:06 PM   #11
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Quote:
Originally posted by Steve Eddy


Have you considered Nelson's Balanced Zen Preamplifier?

Look, Jam! No transformers!

I've seen it before. In visualizing this circuit, if I were to tie the +in & -in together & apply a test signal between the GND & ‘incorrectly’ tied inputs, I believe that the outs would still leak the test signal, instead of being canceled out..

Have I visualized the circuit incorrectly?
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Old 20th September 2003, 11:23 PM   #12
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Quote:
Originally posted by Brian Guralnick
I've seen it before. In visualizing this circuit, if I were to tie the +in & -in together & apply a test signal between the GND & ‘incorrectly’ tied inputs, I believe that the outs would still leak the test signal, instead of being canceled out..

Have I visualized the circuit incorrectly?
The circuit is just a classic differential input pair. It's primary function is to amplify only the difference between the two inputs and reject anything that's common to both inputs.

How much common-mode signal gets through it will depend on the particular circuit. Nelson measured its CMRR at "slightly greater than 80dB." That's using its output balanced. If you use the output unbalanced, it only does about 20dB.

I wouldn't expect to be able to do much better than that if you're planning to use just two active devices in the circuit.

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Old 20th September 2003, 11:49 PM   #13
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Quote:
Originally posted by Steve Eddy


Nelson measured its CMRR at "slightly greater than 80dB." That's using its output balanced. If you use the output unbalanced, it only does about 20dB.

se
20db...... Bingo..... I'm trying to create a set of unbalanced outputs which zero to the local ground. Since my powersupply is shared between the left & right, & I wish to feed a unbalanced stereo amp, which also shares a common L&R ground, just wireing the -out on both L&R preamp channels to the GND & +out as my new audio signal would kill the intended function of this amp.

Using this circuit's GND instead of -out will only give me that 20db CMRR.
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Old 21st September 2003, 01:34 AM   #14
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Quote:
Originally posted by Brian Guralnick
20db...... Bingo..... I'm trying to create a set of unbalanced outputs which zero to the local ground. Since my powersupply is shared between the left & right, & I wish to feed a unbalanced stereo amp, which also shares a common L&R ground, just wireing the -out on both L&R preamp channels to the GND & +out as my new audio signal would kill the intended function of this amp.

Using this circuit's GND instead of -out will only give me that 20db CMRR.
Awwww screw it. Just grab a transformer and be done with it.

Sorry, Jam. I held on for as long as I could.

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Old 21st September 2003, 01:57 AM   #15
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Steve,

Thats my boy........
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Old 21st September 2003, 02:00 AM   #16
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He wants a semi-conductor based circuit...so I dun think he is willing to indulge in a trafo...though I can't imagine why...
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Old 21st September 2003, 02:19 AM   #17
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Originally posted by li_gangyi
He wants a semoi-conductor based circuit...so I dun think he is willing to indulge in a trafo...though I can't imagine why...
Yeah, yeah, yeah. But what people want isn't always what's best for them. If it were, we wouldn't have any need for Democrats and Republicans.

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Old 21st September 2003, 02:27 AM   #18
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Ok...let's assume he's a little cash strapped right now...what would you guys give him?? A cheap0 trafo or a well-designed circuit that could possibly beat that trafo in terms of pricing and performance...I'm not saying that trafos are bad...but given the costs...I would think twice...especially for a kid like me...
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Old 21st September 2003, 02:52 AM   #19
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Well, I prety much gave up. I guess I will use a transformer.

Q1: Which companies make these high performance line matching transformers?

Q2: With a transformer, should I buffer the output?

Q3: Using a transformer would make life extra easy for integration into the Balanced Zen Pre-amp. However, I do not need the signal gain, would a simple voltage follower buffer make things any better?

Q4: Are there any worthy pre-amp output buffer stages which can drive headphones?
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Old 21st September 2003, 03:24 AM   #20
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Quote:
Originally posted by li_gangyi
Ok...let's assume he's a little cash strapped right now...what would you guys give him?? A cheap0 trafo or a well-designed circuit that could possibly beat that trafo in terms of pricing and performance...I'm not saying that trafos are bad...but given the costs...I would think twice...especially for a kid like me...
Oh ye of little faith. I knew he'd crack sooner or later.

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