Line stage preamp, based on SY's "Heretical Unity gain line stage" - diyAudio
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Old 18th June 2005, 11:13 AM   #1
Danko is offline Danko  Hungary
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Default Line stage preamp, based on SY's "Heretical Unity gain line stage"

For thoose, who don't know the antecedents:
It all started in SY's "A Heretical Unity gain line stage" thread, here:
A Heretical Unity gain line stage

SY drew a line stage preamplifier, almos exactly what I was looking for.
I modified the schematic to what I exactly needed, and moamps advised, I should start a new thread, becouse of the modifications.

Quote:
Originally posted by moamps
Hi,
The drawing is better but maybe I should highlight a couple of things regarding SY's original schematic (not any variation thereof):

I have attached my "version" of the schematic.

Quote:

1) pin5 can't be connected to the ground,
Regarding to my schematic, is that still wring?
(i will use a separate powersupply for the heating)

Quote:

2) CCS can't be connected to the ground but to -12V PS,
Why? I was always wondering about that ...
Isn't it enough, if I just feed with +24V DC the CCS ?

Quote:

3) +B supplies should be separated.
How do you mean that? Each one has a dedicated decoupling-capacitor?

Quote:
P.S. It is a common view that routing tracks under the right angle should be avoided.
Why?
I read about it in a paper, but that (the paper) was about switching mode powersupplies. That paper said, that the 90degree broke tracks act as a small antenna, and it is better using rounded trancks.
Is this (what you said) is about the same thing?
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Old 18th June 2005, 11:14 AM   #2
Danko is offline Danko  Hungary
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Default the PCB

Here's the PCB, what we are talking about
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Old 18th June 2005, 11:16 AM   #3
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Rounded/angled tracks are only required at very high frequencies. For audio use they are not a problem.

Could you put component names on the pcb? it makes tracing your work a lot easier!
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Old 18th June 2005, 11:35 AM   #4
Danko is offline Danko  Hungary
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i wrote the values to the schematic....
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Old 18th June 2005, 11:36 AM   #5
Danko is offline Danko  Hungary
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... and the pcb
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Old 18th June 2005, 11:36 AM   #6
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Thats fine, but where is, for instance, R52 on the pcb?

:edit: you beat me to it!

Interesting colour scheme, it could almost be one of those new disruptive camouflage patterns!
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Old 18th June 2005, 11:51 AM   #7
Danko is offline Danko  Hungary
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i use this strange solour scheme only for presentation.
It's easyer to read the values and in the same time the tracks are well visible.
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Old 18th June 2005, 12:30 PM   #8
moamps is offline moamps  Croatia
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Default Re: Line stage preamp, based on SY's "Heretical Unity gain line stage"

Quote:
Originally posted by Danko
Regarding to my schematic, is that still wring?
(i will use a separate powersupply for the heating)
It's OK.
Quote:
Why? I was always wondering about that ...
Isn't it enough, if I just feed with +24V DC the CCS ?
If Va=100V and Ia=10mA, then Vgc=around -2V.
The CCS can't work correctly with only 2V on it.

Quote:
How do you mean that? Each one has a dedicated decoupling-capacitor?
Each one has a dedicated RC network.
Quote:
That paper said, that the 90degree broke tracks act as a small antenna, and it is better using rounded trancks.
Is this (what you said) is about the same thing?
Yes. It isn't the main issue here, though (that's why the remark is in P.S.).
But, if you don't have to use right angles, then don't.
Especially not in a "heretical" unity gain stage.

Regards,
Milan
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Old 18th June 2005, 12:40 PM   #9
Danko is offline Danko  Hungary
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Hi moamps!

What happens if I don't separate the B+ supplies of the tube? The crosstalk will increase?
What R and C values do you recommend?
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Old 18th June 2005, 01:11 PM   #10
moamps is offline moamps  Croatia
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Quote:
Originally posted by Danko
What happens if I don't separate the B+ supplies of the tube? The crosstalk will increase?
What R and C values do you recommend?
Hi,
You're right, the crosstalk will increase.
See SY's schematic for R and C values.

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Milan
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