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Old 26th April 2011, 09:36 PM   #1
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Default DIY Line preamp sugestions, 10meter cables

Hi

I need a line amp with a gain of around X10 to drive 10meter cables and 10K input impedance power amps.

I would prefer an all descrete design avoiding op amps. Maybe even an open loop design.

Any sugestions?

Thanks.
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Old 26th April 2011, 09:47 PM   #2
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I have a Erno Borbely SE headphone/Line amp ( assembled but only tested ) - capable of even driving 50 meter cable - extremely low impedance available - I had listed about a month back
let me know if you are interested
kannan
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Old 26th April 2011, 09:47 PM   #3
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You could use a diamond buffer which I give away for free.
http://www.diyaudio.com/forums/blogs...e-pcbs-me.html
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Old 26th April 2011, 10:00 PM   #4
lineup is offline lineup  Sweden
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Discrete, transistor amplifier x10 and driving 10k.
And no global feedback.
It happens I have just such a circuit.

It uses 3 small signal transistors. Like 550C or 2SC2240 or 2SC1815.
Two stages with volt amplification is followed by 1 transistor as buffer.
Circuit is tuned for lowest possible THD distortion.

Into 10kOhm:
At 1 Volt RMS out THD only 0.011%
At 2 Volt RMS out THD is 0.046%
This is, I think, all below hearing limit 0.05-1.00%

Power supply is 15V. Preferably one usual 3pin regulator.

Enjoy
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Old 26th April 2011, 10:45 PM   #5
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Hi Thanks for your very quick replies and sugestions.

Peranders your diamond buffer looks like a very nice, but as its surface mount i think i will pass on your offer, my eyes are not good, i struggle a bit even with conventional components. It does look a great design though.

Lineup, is there a way to loose the coupling cap between the 2 gain stages?
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Old 27th April 2011, 02:59 AM   #6
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Quote:
Originally Posted by lineup View Post
Discrete, transistor amplifier x10 and driving 10k.
And no global feedback.
It happens I have just such a circuit.

It uses 3 small signal transistors. Like 550C or 2SC2240 or 2SC1815.
Two stages with volt amplification is followed by 1 transistor as buffer.
Circuit is tuned for lowest possible THD distortion.

Into 10kOhm:
At 1 Volt RMS out THD only 0.011%
At 2 Volt RMS out THD is 0.046%
This is, I think, all below hearing limit 0.05-1.00%

Power supply is 15V. Preferably one usual 3pin regulator.

Enjoy
But how does it do into the capacitance of the cable?

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Old 27th April 2011, 04:45 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
you can find what current it takes to charge up the capacitance of the cable.

The faster the charge rate, the higher the current.

The highest sensible cable capacitance current is usually to assume maximum signal level @ 20kHz into the cable and any subsequent RF filter.
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