Ok, now it is working fine with the AU35 after I fixed the sellers output cable wiring was missing a pin connection so I only was getting half the signal, Thanks for the help and sorry for jumping the gun without checking for a most basic cause first.
Only question now I have for Jokeramik besides my last question about if the V781 output choke would be better left in or taken out now that am using AU35, is how to best terminate the secondary of the Au35. Usually a 600 ohm is used, or a zobel network. But I saw in a different RFZ schematic they used a 300 ohm resistor across output trans. I put the usual 600 ohm and it sounded much better than unterminated, as before there was too much thin high end. Sounds much better terminated, evened out the highs. Maybe 300 ohm would be better correct RFZ way?
Hello groupdiyguy,
no problem
). All OK.
)
Have a nice time with your V781
)) with AÜ 35 !!!
I´m happy that your V781 is ok!!
)
This choke prevents RF interference from entering. This was very important in these years.
The MV 810 is a complete different design. It was made by VEB Funkwerk Kölleda for the L-800-System and not by the RFZ (Rundfunk- und Fernsehtechnisches Zentralamt der DDR). This System was used for installing public adress tasks like in schools, factory, hotels, clubs, ships and so on.
Also the VEB Deutsche Schallplatten (Eterna, Amiga and so on) used these preamps for recording before they developed "VK 290" and "Mischeinrichtung 82" in the 80s.
There are two versions of this preamp:
1. MV 810: This a complete germanium transistor design in class-a single ended technology. There is a special feature to accomplish the required frequency response: a parallel resonant circuit because the transistors in these days have a low transit-frequency. Reference-level on output is 1 Volt.
2. MV 810/2: This a complete new design based on silicon semiconductors. The output class-a-push-pull stage is complete adjustable in the workingpoints. Reference-level on output ist 1 Volt.
Both versions use the same in- and outputtransformers.
The advantage to the V781, V741 and so on is, that all units from Kölleda are balanced at in-
and output. So you don´t need a choke at the output like the V781. The outputtransformer blocks all high-frequency energy. And so you have a real floating connection.
The output is usually designed in such a way that you can connect a lot of devices (some say 10).
With load you change their electrical characteristics. If it sound good in this special case then it is ok. You can´t damage anything.
The outputcaps ar important, because we have only a unipolar powersupply.
Some times the elektrolyticcaps are on their lifeend. If they aren´t change please change this. I saw some example with manufacturing date 1977 or earlier.
If you want to know more, send me an email or an PM.
)
Sorry for my english, but I´m not a native english speaker.
Best regards!
jokeramik
