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Old 26th December 2005, 01:07 AM   #1
navin is offline navin  India
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Default long cable line drive

This is a offshoot from my "EL34 Schematic confusion" thread.

EL34 schematic confusion

so far we have an ECC88 based crossover and 2 x ECC88-6SN7-EL34 based power amps.

Crossover: 2 x ECC88 (Steve Bench ckt)
Line Stage: 4 x ???
Power amp: 1x ECC 88 AF, 2 x 6SN7 Phase Splitter, 4 x EL34.

octal: ECC88 (4), EL34 (8)
nonal: 6SN7 (4)

However since my power amps will be about 10m away from my preamp (no space near the pre amp) but I can hide the power amps behind the speakers (push - push).

what line drive will do. I was looking at the 6SN7 shown below

http://www.tubebuilder.com/images/sc...s/6sn7_sig.gif
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Old 26th December 2005, 01:11 AM   #2
anatech is offline anatech  Canada
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Hi navin,
You need to get the lowest impedance output with the lowest distortion possible. Balanced lines wouldn't hurt depending on how much electrical noise there is in the area.

You may be further ahead to drive a transformer coupled balanced line. Everything is a trade off. The answer depends on what your biggest problems are in your house. You may not know this until everything is built and you switch it on.

-Chris
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Old 26th December 2005, 09:44 AM   #3
navin is offline navin  India
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Quote:
Originally posted by anatech
Hi navin,
You need to get the lowest impedance output with the lowest distortion possible. Balanced lines wouldn't hurt depending on how much electrical noise there is in the area.
balanced lines seem to be a good idea. any idea of a ckt that can do this though?
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Old 26th December 2005, 11:08 AM   #4
SY is offline SY  United States
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Balanced is good, but the ability to drive capacitance is better. A properly designed cathode follower is what you seek.

Hint: 6SN7 is not a particularly great tube for this application.
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Old 26th December 2005, 01:35 PM   #5
navin is offline navin  India
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Quote:
Originally posted by SY
Balanced is good, but the ability to drive capacitance is better. A properly designed cathode follower is what you seek.

Hint: 6SN7 is not a particularly great tube for this application.
ok SY, thanks for that info. 6SN7 is out any idea what ckt i should use for this please!
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Old 26th December 2005, 01:47 PM   #6
SY is offline SY  United States
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My Heretical article (A Heretical Unity gain line stage) is a reasonable tutorial on CF design. You don't necessarily need the bells, whistles, transformers, and servos I threw in, but a high gm triode and a current source can do wonders.
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Old 26th December 2005, 01:58 PM   #7
SY is offline SY  United States
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Whoa! I take that back. I was thinking that you have 30' cables, not 30 meter. That's about 100 feet. At 100pF/meter as a typical value for shielded cable, that's 3000 pF. You'd need a much bigger, heftier cathode follower than I think is reasonable For a line that long, I'm with Chris, transformers and 600 ohm balanced line.
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Old 26th December 2005, 02:01 PM   #8
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Still under the influence of Christmas cheer SY? 10m is about 30'...
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Old 26th December 2005, 02:05 PM   #9
SY is offline SY  United States
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OK, so I was wrong when I thought I was mistaken.

Heh, heh.
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Old 26th December 2005, 02:41 PM   #10
navin is offline navin  India
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Quote:
Originally posted by SY
My Heretical article (A Heretical Unity gain line stage) is a reasonable tutorial on CF design. You don't necessarily need the bells, whistles, transformers, and servos I threw in, but a high gm triode and a current source can do wonders.
i did consider the Ecc81 and 82 but feared their reputation for stridency.

BTW I know you have answered this before but since m sources are all line level high impedance why the input transformers. OPTs in understand as tube impedances are 1000 time higher that of my speaker but the output impedance of my source is on the order of 10K and so is the input impedance of the ECC88.
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