neve type 1272 clone clipping ugly!

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rafafredd

Well-known member
Joined
Jun 3, 2004
Messages
2,409
Location
Rio, Brazil
Hi. I did a neve 1272 type micpre many many moons ago. It has input, gain, and output controls. The input pot comes after the transformer, and the output pot between the input stage and the output stage. It is a 2-stage only, like the 1272 mic pre mods. The gain switch varies both stages gain, and has only three positions: low, mid and high.

The thing is... When I cranck the gain and input up and the output down to get distortion, it doesn't sound right. Even with tiny amounts, it sound plain bad. So, I scoped it and it is clipping very assymetricaly. Now the strange part is that it is not the output stage. If I inject a signal in the output stage alone, it clips nice and symetrically. So, the output trimpots are set right. Iit is the input stages that clips assymetrically.

So, does anyone have a checkplot schematic with voltages for the neve 283 input stage?

I remember just one difference from the original. I used BC184L instead of  BC184C. The BC184L has different pinouts and also lower gain. Could that be the problem? I remember selecting parts that had over 320 hFE (beta). Wouldn't that be enough for this circuit? Do I need higher beta on the input stage? I know the original BC184C goes up to 600-700 hFE gain...

Please, help!

Thanks.
 
Nice. Thanks for this. I'll check voltages.

But in  the meantime, I have found the original thread. Reading it, it seems that going down to 300-350 hFE like I did would not cause these symptons I am getting.  ???

Here it is:

http://www.groupdiy.com/index.php?topic=1698.0
 

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