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Old 19th June 2001, 07:05 PM   #1
gimpus is offline gimpus  Italy
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Join Date: Feb 2001
Location: North-East of Italy
Hi everybody.
Perhaps this is a silly question, but I'm a neophyte and I'm a little confused, so plz forgive me.

I've downloaded all the articles from the Pass Labs website.
In the Zen article Mr Pass puts an active current source to improve the efficiency of the circuit, but in the SoZ the Mosfets are biased by a resistor. The circuit of the latter seems a bridged version of a simplified Zen.

So the question is: what about building two Zen's (maybe the improved version with the Pi filter on the supply) and bridge them using the Balanced Zen Line Stage? (I'm not so rich, being a student....)

Would it be good? I think it would be more efficient than a SoZ.

Would it be necessary the Bride of Zen?

Thank you, Al.
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Old 19th June 2001, 09:13 PM   #2
diyAudio Member
Join Date: Feb 2001
Location: Columbia, SC
Bridged Zens will work. You will need either a balanced input, or a phase inverter. Nelson's balanced preamp would be ideal if you already have a balanced input.
Yes, it would be more efficient than a SOZ.
Go for it.

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Old 19th June 2001, 09:52 PM   #3
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Join Date: Jan 2001
Location: Germany
Of course it will work.
You have to consider a few things to make it work ok.
First as stated you need a balanced signal in the input.
With a balanced preamp you have that solved.
The output devices can work at a lower voltage because because of bridged mode. The bias current has to be higher because each part of the bridged amp will see a load half of the real one. If you have an 8 Ohm speaker each part of the amp will see 4 Ohm. Thats the way brisged will work. With a 4 Ohm speaker you have a problem. Or an idea I had was to use two parallel circuits working in bridged mode, thus 4 Zens for one amp.
Good luck.
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Old 20th June 2001, 01:35 AM   #4
diyAudio Member
Join Date: Oct 2000
Location: Michigan
I had this same notion of using a zen amp for each balanced channel a while back and emailed NP for clarification on whether this was possible or even desireable. What follows are my questions and the answers I received:

Q: When using the Balanced Bride of Zen as a single-ended preamp or conversion tool between single-ended and balanced, do you need to ground the unused inputs or outputs for proper operation as is done on some other balanced devices? Or do you simply connect up your single-ended source to one leg of the balanced input and leave the other leg open?

A: You ground the unused input, you leave the unused output unconnected.

Q: Can I use the balanced outputs to drive a pair of Zen stereo amps in a bridged mode (one channel for + and one for -)? Any dangers in doing this? Any advantages?

A: It works fine, although as you describe it, is only suitable for 16 ohm loads. You can get great performance by doing 4 channels series/parallel for driving 8 ohms to 40 watts. I have done this and it was spectacular.

Q: What exactly do you mean by 4 channels series/parallel? Does that mean 4 channels for the left audio channel and 4 channels for the right audio signal?

A: Yes.

Q: In other words, a paralleled stereo zen amp to handle the + signal and another for the negative signal of each audio channel? That would be a total of four zen amps for stereo amplification.

A: 8 Zen channels.

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Old 20th June 2001, 09:15 AM   #5
gimpus is offline gimpus  Italy
diyAudio Member
Join Date: Feb 2001
Location: North-East of Italy
Cool Clarified!

Many Thanx, guys.
Your answers were precious in clarifying a lot of doubts.

The bad thing I discovered is that "THERE'S NO FREE LUNCH",
as stated my Optimization teacher..... :-(

Best regards, Al.
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