Recycling a phono preamp section from an old stereo amp
I have had an old Sony TA-AX22 lying around. It was a nice enough little Sanken amp with input selectors, power sockets for other units etc. There was even a schematic to be found. I haven't had a use for it, so I decided to take it apart. One part I wanted to keep was the phono preamp section, because I could use that. I'm intending to build a new one one of these days, but here's a working one if I can set it up.
There might be room inside my turntable for the amp, turning its output into a real line out.
Extracting the preamp section
It was easy enough to cut out with a rotary tool and a cutoff disc. It does expect bipolar power supplies, though.
The circuit contains a single TI TL4558P ("4558") opamp and some filter/correction passives. The amplifier output would normally be shorted(!) to ground by the source selector switches when not selected.
Original RCA inputs would have been quite fine, but were a part of a larger cluster, so I cut them apart and will replace them.
Plans for power
Nominally, the rails are supposed to be +- 16 V filtered DC. Three options come to mind for getting there.
One is using an AC and/or tapped power brick. I might have a couple.
Another is taking a floating DC brick and splitting it. That should also be interesting. The load should be quite minimal.
Third option involves using the power supply of the turntable. If I remember correctly, it should be suitable for this.
Connections and casing
The cut board section is 36 x 112 mm. Depending on what other circuitry goes in, I probably hope to pick some suitable slim box for this.
Testing
Listen, maybe measure sweep. I don't remember if I've used this amp with a turntable, but it should be better than nothing and I can pit it against another amp if I get one.