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Old 16th July 2003, 04:04 PM   #1
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Default Zen-V with followers

I'm thinking about building something like this:
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Old 16th July 2003, 05:31 PM   #2
joensd is offline joensd  Germany
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Really like the idea of the circuit.
As the power dissipation of the ZenV5 is really quite high (obviously I´m not fearless enough) I thought about modifications as well.

What do you think you will gain from your circuit in comparison to the original?
No need for a preamp obviously...
And...

Did you simulate the circuit?

Jens
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Old 16th July 2003, 05:42 PM   #3
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I think there are a few benefits to the circuit:

1.- use smaller fets for the front end- less capacitance- better bandwidth.

2. controllable bias on the output stage- run it AB if you want! adjust to your heatsinks.

3. follower p/p will drive into lower impedance loads and go to AB mode past 2X the bias current.

4. you can use a seperate front end highly regulated lower current supply, and use an unregulated supply on the output stage.

I did simulate it, and it seems to work well. Here is the latest. I am using 4X output devices biased at a little over 900mA each. It seems to do about 32 watts into 8 ohms. 90 watts of heat total on the output stage. I have included a passive attenuator at the input. I may be wrong, but it seems to vary the amount of feedback too- less at lower volumes, which in my opinion would be beneficial. I'm thinking of building this into an integrated dual mono.
Any ideas for improvements?
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Old 16th July 2003, 05:46 PM   #4
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Oops...
please note that the output pairs should be connected at the speaker output... I accidentally omitted the connection.
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Old 16th July 2003, 06:01 PM   #5
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I corrected it, and adjusted the current through the front end (10K resistors changed to 7.5K).
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Old 16th July 2003, 07:10 PM   #6
joensd is offline joensd  Germany
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I like point 3 as it would reduce dissipation to your needs.
That would have actually been my guess for the ZenV5:
Quote:
Quote from original Zen article:
In addition, there are ways in which a Single-Ended Class A amplifier can
be operated as a push-pull device beyond its bias point, the assumption
being that push-pull performance is preferable to clipping. Pass Labs
has received one patent and has an application for another reflecting
new developments in this area.
That´ll be probably ZenV12 or something.

Regarding improvements: Do you think you could adjust the gain of the BOZ to feed the voltage follower without having too much drawbacks. But then again there´s no more ZenV5.

Jens
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Old 16th July 2003, 07:20 PM   #7
grataku is offline grataku  United States
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Hi,
from last night I have been building something very similar to your drawing for a headphone amp.
I have it down with cascoded q1 and q2 for even better bandwidth and low dist., the plan was to get the 0 DC is achieved by changing the bias point with an adjustable voltage source in place of r11 12 so I was planning to leave the r1 and 20 alone.
I am waiting for the voltage regulators at this moment. The output stage is done.
for q1 and 2 I have some zvp3306 and I am buying some zvn3306. For the output I used 610/9610.
I am thinking that there may be the need to adjust the bias of the output separately from the front end because even if the bias is perfect on the output of the first stage the mosfet on the second stage may still be rather different.
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Old 16th July 2003, 07:33 PM   #8
B.L. is offline B.L.  Poland
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joensd

ZenV12?
No!
It's Aleph!
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Old 16th July 2003, 07:47 PM   #9
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Quote:
Originally posted by grataku
Hi,
from last night I have been building something very similar to your drawing for a headphone amp.
sounds interesting... can you post the schematic?
Quote:
I have it down with cascoded q1 and q2 for even better bandwidth and low dist., the plan was to get the 0 DC is achieved by changing the bias point with an adjustable voltage source in place of r11 12 so I was planning to leave the r1 and 20 alone.
I would like to see how you did the cascoding...
Quote:

I am thinking that there may be the need to adjust the bias of the output separately from the front end because even if the bias is perfect on the output of the first stage the mosfet on the second stage may still be rather different.
I am able to do that with the circuit I have...
the pot labeled "bias" adjusts the amount of bias in the output stage, using the typical VGS multiplier transistor Q3.
The front end bias can be controlled by adjusting the value of R11 and R12 to some extent. I have the front end biased at about 50mA in the last schematic I posted. This gives about a 1.5W dissipation in Q1 and Q2, and Q3 is at about .38 watts.

Definitely let us know how it sounds when you're done! post a schematic, if you want. I'd really like to see it.
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Old 16th July 2003, 08:03 PM   #10
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Quote:
Originally posted by joensd
I like point 3 as it would reduce dissipation to your needs.
That would have actually been my guess for the ZenV5:

That´ll be probably ZenV12 or something.

Regarding improvements: Do you think you could adjust the gain of the BOZ to feed the voltage follower without having too much drawbacks. But then again there´s no more ZenV5.

Jens
I could be wrong, but I think that quote from the zen article was refering to the Aleph current source.
I'm not sure what you mean about the BOZ...
If you're talking about using it as a front end with the followers, I think you would have to find a way to bias the output stage.
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