Audio Metrics MM pre...looks easy to build - diyAudio
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Old 16th October 2007, 07:37 PM   #1
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Default Audio Metrics MM pre...looks easy to build

Audio Metrics is (was?) a company that built stuff for broadcast consoles (aka Radio Systems Design).

This MM phono pre, with a balanced output, or unbalanced.
It uses an LM394 matched NPN before the LM318...followed by the NE5533 (is a dual NE5534) for the (differential) output stage.

It looks easy enough to tinker around with. Can you suggest some more modern opamps to try here?
...and will a MAT02 work instead of the LM394CH ??

Here is the manual w/schematic
http://www.radiosystems.com/PDF/turntablepreamp-man.pdf

thanks,
=RR=
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Old 18th October 2007, 06:34 PM   #2
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This circuit isn't going to be that easy to tinker with, although you can probably put in the MAT02 without a problem if you don't change the bias (tail) current.

The LM 394 is used in place of the first stage of the LM 318. The LM 318 input transistors are turned off by connecting their bases to the negative supply and the LM 394 is connected to the compensation pins which are connected to the load of the first stage internal transistors in the LM 318. This means that the external first stage (LM 394) has to have a specific bias current to properly bias the LM 318 second stage. You can't tinker with that bias current too much.

If you want to replace the LM 318 you need another opamp with compensation pins connected to the first stage load. I believe the NE5534 has this feature. As for the NE5532, any good unity gain stable dual op amp is a potential candidate. I have no recommendation because I haven't worked with the newest opamps.

Regards,
Ray
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