Need diagram for a Nagra BM2 portable mixer. Anyone ?

[Rob Flinn]

As it says in the title

 

[mig27]

There you go mate!

 

[Dave Peacock]

Thanks - I was looking for this!
Do you know if changing R22 to 600ohm would change the input impedance from 100K to 600 ohm?
Also the output is producing a very low level buzz, it doesn’t change with any differences in grounding etc. So I’m thinking possible power supply filtering - do you think testing C8 & C9 would be good start with this.
Forgive the questions, I’m new to investigating things like this. Thanks!

 

[radardoug]

Yes it will but why would you? It does not need to be 600 ohms. The buzz will not be affected by C8/9, they are in the output circuit. What power supply are you using on it? That would be where the buzz will come from.

 

[k brown]

There you go mate!

View attachment 104349

Wow - not much to it, was there? Not even ring of three.

 

[gyraf]

Unclear what you're asking: Are you inputting through P4, or through what could be interpreted as banana jacks (the two dual-concenteic-circles above P4)?

At P4 impedance is around 1K2 to 2K5, and if R22 is meant for attenuating an external signal, then it takes out some 35dB of signal level while providing an input impedance of 101K. Yes, change to 600R or the like to get less attenuation at lower input impedance IF you are using "(the two dual-concenteic-circles above P4)" as input

..note: plus on gnd/chassis (!!) - and this one need batteries or a very clean power supply.. For noise test, try it off a 9V battery

/Jakob E.

 

[fazer]

Germanium PNP. Interesting thanks.

 

[Dave Peacock]

Unclear what you're asking: Are you inputting through P4, or through what could be interpreted as banana jacks (the two dual-concenteic-circles above P4)?

At P4 impedance is around 1K2 to 2K5, and if R22 is meant for attenuating an external signal, then it takes out some 35dB of signal level while providing an input impedance of 101K. Yes, change to 600R or the like to get less attenuation at lower input impedance IF you are using "(the two dual-concenteic-circles above P4)" as input

..note: plus on gnd/chassis (!!) - and this one need batteries or a very clean power supply.. For noise test, try it off a 9V battery

/Jakob E.

Thanks Jakob, this answers exactly what I needed to know. - It was regarding lowering the input impedance of the banana inputs at P4.

Re the noise I'll test it on a 4.2 with a Nagra supply and see if it's still present. I only have a third party supply for the Nagra III I was using it with before.

 

[Dave Peacock]

Wow - not much to it, was there? Not even ring of three.

They are a very simple layout inside.....

 

[cyrano]

That's beautiful...