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?
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?
hacknet said:
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
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. You´d 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 you´d 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.
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. You´d 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 you´d 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.
just to make sure, is this how it is supposed to look like?
An externally hosted image should be here but it was not working when we last tested it.
If you use Till´s schematic with the regulator in you´ll lose about 4V so that you´ll have about 70-71V at the source of Q3 (I meant the source pin in my last post as well as I thought you won´t use the regulator).
So if you still use R2=800Ohms and your buffer draws 50mA you´ll get about 30-31V at C5.
Q2 (IRF9610) won´t have a problem with too high voltage anyway but if you use the BS250 you´d have to get voltage down somehow.
So if you still use R2=800Ohms and your buffer draws 50mA you´ll get about 30-31V at C5.
Q2 (IRF9610) won´t have a problem with too high voltage anyway but if you use the BS250 you´d have to get voltage down somehow.
http://www.vishay.com/docs/70209/70209.pdf
datasheet tells max. power 0.83W for BS250 so you need less than 50mA. But you can try out different resistors for different current, and also larger FETs for more mA. Try IRF9610 and ZVP3310 if you can find one.
datasheet tells max. power 0.83W for BS250 so you need less than 50mA. But you can try out different resistors for different current, and also larger FETs for more mA. Try IRF9610 and ZVP3310 if you can find one.
i actually started with the intentions of finding a ZVP3310. but could not find them, i thought of farnell but i din`t want to trouble them over a couple of transistors. so i`m left with the BS250. thats i`m using now.
one question, is there a certain formula i can use to determine the amount of current it will draw, i know how it works for tubes but can`t seem to find the equivilant graph for a fet. i`ll be gratefull for the help... thanks in advance!
one question, is there a certain formula i can use to determine the amount of current it will draw, i know how it works for tubes but can`t seem to find the equivilant graph for a fet. i`ll be gratefull for the help... thanks in advance!
sorry for bring this up again. but i would like to ask another question.
with reference to the above schematics, could i increase R3 to 47k and have R4 with a value of something like 470k? in this case, hopefully ommiting P1.
An externally hosted image should be here but it was not working when we last tested it.
with reference to the above schematics, could i increase R3 to 47k and have R4 with a value of something like 470k? in this case, hopefully ommiting P1.
The buffer stage http://www.diyaudio.com/forums/showthread.php?postid=277343#post277343
has the purpose to enable you to use 47k input resistor. Without the buffer transistor you need the lower value.
In case you don´t want P1, choose R3 and R4 in a way that they are like the pot divided somewere and added thze halfs to the resistors.
has the purpose to enable you to use 47k input resistor. Without the buffer transistor you need the lower value.
In case you don´t want P1, choose R3 and R4 in a way that they are like the pot divided somewere and added thze halfs to the resistors.
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