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BOSOZ, what is purpose of bottom CCS?
BOSOZ, what is purpose of bottom CCS?
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Old 6th August 2017, 03:25 AM   #1
OllBoll is offline OllBoll  Sweden
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Default BOSOZ, what is purpose of bottom CCS?

Hello there,

I'm planning to build a BOSOZ-ish preamp but want to optimize it for my usage. I have a balanced source, want a balanced output signal and my goal is 10V semi clean output. My power supply is a single rail 48V so I'm thinking of how I can optimize it as it looks to be on the low end.

Primarily I wonder about the purpose of the bottom CCS is and more specifically if one could optimize it to consume less voltage headroom.

My primary questions are:
  1. What happens if I omit the bottom CCS completely and just bias the transistors + adding source resistors to ground as if I have two separate amps?
  2. Reduce the impedance to say 750 at each side instead of 1500.

I assume also that I could swap it with an active CCS as in the F1 which is probably the best with regards to performance but that sounds more complicated =)
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Old 6th August 2017, 08:51 AM   #2
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BOSOZ, what is purpose of bottom CCS?
1. think LTP

for rest look in JFet BOSOZ threads
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Old 6th August 2017, 10:23 AM   #3
AndrewT is offline AndrewT  Scotland
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When you state "bottom CCS", are you referring to R4 & R6?
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Old 6th August 2017, 12:09 PM   #4
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by AndrewT View Post
When you state "bottom CCS", are you referring to R4 & R6?
Yes
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Old 6th August 2017, 06:02 PM   #5
AndrewT is offline AndrewT  Scotland
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I would not call the resistors in the bottom as CCS.
They determine the current (Id) flowing down through the two sides.
The top resistors then determine the voltage drop to feed the outputs.
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Old 13th August 2017, 01:05 AM   #6
PRR is offline PRR  United States
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> single rail 48V

It is drawn for dual-rail (+/-60V). It sure could be re-drawn for single supply. Have you done this?

> Reduce the impedance to say 750 at each side instead of 1500.

It is "1500" because the P3 P4 gain-pots are on the outputs. Taking 5K pot, 221r stopper, 750r drain resistor, and neglecting internal drain resistance, *worst-case* is 5971/4, and 1493 is exact equal to 1500 on my abacus.

Zout=1500 is generally acceptable in small benign rooms (hi-fi dens).

If you need less, you don't put the gain-pots on the outputs. Make R9 R10 say 47r and take it from there.

Are you actually *driving* like 750r?? Or the load likes to see 750r?

With 48V supply, gates biased at semi-arbitrary 24V, each Drain can swing 20V p-p or say 7V RMS. Do you need "10V" one side or both sides? If you mean 5V each side, it "works". How high the THD may be, can probably be estimated from the paper. A point: the output from one side will show high 2nd THD (say 1.5% @ 5Vrms), but if you take both sides proper differentially this will cancel into the sub-0.1% zone.
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