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Old 15th February 2004, 02:27 AM   #1
hacknet is offline hacknet  Singapore
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Default Zen Lite Buffer Stage

Hi i`ve just finnished by Zen Lite. it sound wonderful.


i`ve heard about implimenting a buffer stage to raise the low input impedence. i saw someone who used a BS250 mosfet as a buffer, problem being his suppy rail is 35volts while mine is 75volts.

does anyone has the schematics for a simple buffer stage i can impliment for my zen lite?
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Old 15th February 2004, 05:36 AM   #2
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Default Re: Zen Lite Buffer Stage

Quote:
Originally posted by hacknet
Hi i`ve just finnished by Zen Lite. it sound wonderful.


i`ve heard about implimenting a buffer stage to raise the low input impedence. i saw someone who used a BS250 mosfet as a buffer, problem being his suppy rail is 35volts while mine is 75volts.

does anyone has the schematics for a simple buffer stage i can impliment for my zen lite?
Do you really need to increase the input impedance? You said it sounds wonderful so what's the "problem" that you're trying to solve?

se
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Old 15th February 2004, 05:45 AM   #3
hacknet is offline hacknet  Singapore
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well, i`m running it off a tube preamp with a output capacitor. with the low impedence of the zen lite, the bass rolls off at 60hz.

i`m not suffering now as my below 100hz bass is augmented with a sub. i`m just looking for a way to raise it so i can sleep at night..
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Old 15th February 2004, 05:53 AM   #4
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Quote:
Originally posted by hacknet
well, i`m running it off a tube preamp with a output capacitor. with the low impedence of the zen lite, the bass rolls off at 60hz.

i`m not suffering now as my below 100hz bass is augmented with a sub. i`m just looking for a way to raise it so i can sleep at night..
Ah...

How much excess gain do you have in your system? If you have about 12dB to spare, one simple (and passive) solution would be a 1:4 stepdown transformer.

Not only would your preamp see a higher load impedance (about 40k if you use something like the Jensen JT-10KB-D or DPC) but your Zen would see a much lower source impedance (rougly about 16 times lower).

So, if you've got some gain to spare, might as well put it to good use.

se
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Old 15th February 2004, 07:13 AM   #5
hacknet is offline hacknet  Singapore
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well, my tubes are in a cathode follower fashion. and its about right now. i think i can get 12dB more gain.

from my memory, step-down transformers arn`t too cheap rite...?
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Old 15th February 2004, 09:29 AM   #6
joensd is offline joensd  Germany
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Hi hacknet,
have a look at this thread.
The last post shows a schematic with a buffer.
The only difference would be that you have much higher voltage rails. YouŽd have to scale R2 so that you get the appropriate voltage for your buffer.
Just think you have 75V drain at the regulator Q3 and your buffer draws 50mA for example youŽd need R2 to be 800Ohms to lose 40V. The resistor then would have to dissipate about 2W so you want to use a 3W resistor at least for that purpose.

Cheers
Jens

PS.: The buffer is described quite well in ZenV4 on the passdiy-site.
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Old 15th February 2004, 10:57 AM   #7
hacknet is offline hacknet  Singapore
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thanks!
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Old 15th February 2004, 12:20 PM   #8
hacknet is offline hacknet  Singapore
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just to make sure, is this how it is supposed to look like?


Click the image to open in full size.
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Old 15th February 2004, 05:24 PM   #9
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Quote:
Originally posted by hacknet
well, my tubes are in a cathode follower fashion. and its about right now. i think i can get 12dB more gain.

from my memory, step-down transformers arn`t too cheap rite...?
No, they aren't exactly cheap. The Jensen model I mentioned previously run about $70 each. Though you could probably find something less expensive from Sowter or Lundhal.

se
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Old 16th February 2004, 09:27 AM   #10
hacknet is offline hacknet  Singapore
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nah, not my cup of tea. i`m not a fan of iron too.

well, i`ll try the buffer and see how it goes.
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