Sony stereophonic amp (60's tube)

cancon

Member
2011-03-06 2:58 am
Here's a new one for my bench - a small stereo amp made by Sony (model SRA-3). Service manual (with schematic).

The most pressing issues are that the monitor outputs have some hum happening, regardless of what's connected to any input. The record head outputs are quieter, but they must have some ultra low (or high) frequency content going on. I can't hear it, but my compressor goes crazy when fed from those outputs.

Going in through the mic inputs on the front, I couldn't get a signal until I used a cheap low Z XLR to high Z TS adapter, then the signal became too hot to use for anything other than the quietest sources. Using the aux input the signal was pretty clean even with the input gain cranked (this is contradictory of this amp's reputation, as I hear lots of praise for its distortion characteristics).

So my first guess that I need to replace the 20uf (x3) filter section and possibly coupling capacitors. The VUs don't work, I haven't poked my head inside yet, but the schematic offers little insight. I want to add a 1/4" or XLR output - but how do I choose which output to tap? I assume some are better than others based on their designed impedance, but I'm not too familiar with tape deck hookups.

Any help or advice is appreciated. Thanks!
 
What you actually have is the record electronics for a tape recorder as stated at the top of page 3. It's normal for high end boost in record amplifiers. The mag phono input equalization is not very impressive and certainly doesn't follow RIAA too closely. The meter can be adjusted all the way to 0 and can be overridden to 0 depending on the setting of S2.

This will not be a satisfactory preamp for general use until the bias and EQ networks are disabled and then has no power output to drive speakers.

 

kevinkr

Administrator
Paid Member
What you have is totally unsuitable for your intended purpose, and further there are people actually looking for these units. (They're fairly rare) I had one and was able to find it a new home with remarkably little difficulty, many tape aficionados like these units. (With a minty ReVox G36 MKIII I really had no need for one of these units)