Advice on Neumann PV46sd

[Tropicalista]

Hello all,

After some time reading and researching this brilliant resource I’m posting my first post and looking for some advice.

I am working on a 1968 Neumann Recording Console that has a number of PV46sd line cards.
I have replaced the Electrolytic capacitors.

When on the bench they test good and have around 40 to 45db of gain. However I have two questions:

1. What does R27 do? It is a 5K trimmer. When I adjust it, the THD/Noise rises from 0.05% to 4% and it adjusts the volume by around 1db

2. All of the cards have 300 Ohm resistors at R11 & R12, but they all have slightly different output levels, ranging from 40db to 45db. Is this normal or is there
a possible component failure? Resistors test good with a multi meter. Trimmers test good.

Any help or suggestions would be greatly appreciated.

Thanks!
Will

 

[Evertide]

1. R27 + R25 => R26 ( Component Tolerance.. )

2. Pin 8 , 9 , 15 and 3 in use ?

 

[Tropicalista]

Thanks.

1. OK, so the idea here is to match the resistance?

2. On my jig I have two resistors across these points as illustrated on the schemo.

 

[Evertide]

1. Yes , minimum THD...

2. Tabel => Highest Gain...

 

[Tropicalista]

OK got it, One of the trimmers is faulty and no longer works.

1. Are these german 5k trimmers still avaialble somewhere or would you suggest I replace with a modern trimmer?

2. Any reason I might have different gains from different cards? component failure/tolerance? transformer changes over time?

 

[Evertide]

1. Hard to find. Look at the footprint ( mm ) for the new one...

2. Component changing over time or the place maters ( adjusted ad the consul )