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Old 4th September 2008, 04:45 PM   #1
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Default Line stage modification

Hello there.

I want to change some things in one of my amplifiers.

The CD input features a non-inverting OP-AMP with a gain on 2.9***.

I want to change the IC with:
1. A discrete preamplifier
2. A better IC
***a. OPA2132
***b. LM4562

I`ve found some discrete preamplifiers like this, but the first issue is the minimum load.

A more simple option, is to change the IC.

Both options will have a dedicated PSU. The default PSU is unregulated.

The Muting circuit is imperatively required ?

A drawing of the schematic.
http://img293.imageshack.us/img293/705/p9047599dv9.jpg
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Old 5th September 2008, 07:07 AM   #2
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Found an interesting preamplifier.
Look at page 9.

http://www.2shared.com/file/3877130/...77article.html
Attached Images
File Type: jpg zenbride_sch1.jpg (23.4 KB, 712 views)
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Old 5th September 2008, 08:03 AM   #3
AndrewT is offline AndrewT  Scotland
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Have a read of Nuuk's buffer site. Particularly Pedja's
Go back to the Pass site and find the B1 buffer.

Why do you need gain on the CD input? 0dBfs~7Vac. That is far too high for any domestic power amp.
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Old 5th September 2008, 11:58 AM   #4
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Well, as you can see in the first post, the gain is 2.9, ~ 9dB.

It is not a unity gain buffer.
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Old 7th September 2008, 02:53 PM   #5
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Some suggestions guys ?
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Old 7th September 2008, 07:45 PM   #6
AndrewT is offline AndrewT  Scotland
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you have a suggestion but you seem to be ignoring it.
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Old 8th September 2008, 12:46 PM   #7
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I aint ignoring it. I just want to improve the line stage. If this is designed with 2.9 Gain, the upgraded stage will have.... 2.9 gain.

This in fact is a OP AMP preamp, and a buffer will not suit it.
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Old 19th September 2008, 05:07 PM   #8
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I`ve studied the B1 Buffer.

Sounds pretty neat.

If I replace the pot with a fixed resistor, the input impedance will be stuck, but what about the gain .
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Old 29th October 2008, 07:00 PM   #9
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Found the AX596 line stage.

Same gain = 10db

http://dc98.2shared.com/download/418...45947-be66662e

Some thoughts ?
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Old 29th October 2008, 09:50 PM   #10
lineup is offline lineup  Sweden
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it is a good discrete opamp
dual complementary input with resistor bias, 22 kOhm

will perform with very low distortion
needs a regulated +-15 VDC supply, as can be seen in your image

I would add 220 Ohm EMITTER resistors into all 4 input transistors
to balance and get ~0.3 mA into each input transistor
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