Dynaco SCA-35 phono stage. Don't understand it.

Someone in Audioasylum mentioned that the phono stage of Dynaco SCA-35 is very good. I found the schematics on Kaufman's site. However, I cannot decipher it into meaningful schemactics.

I cannot see the typical two RC sereies in the feedback loop.
Can someone help me? Can you also explain why there are so many feedback connected to the cathod of the first tube?



diyAudio Moderator Emeritus
2002-10-24 10:19 pm
If by "very good" you mean "poor adherance to RIAA, high distortion, noisy, and high output impedance," then the SCA35's phono stage is very good.

What might be confusing in the schematic is the use of a positive feedback network between the cathodes to get the open-loop gain up high enough to equalize and the switching done in the EQ network to accommodate low level sources that were not RIAA. Tracing stuff through those switch diagrams can be a real challenge.