Reworking the Sony KM rear amplifier for dedicated stereo use
The preamplifiers
First of all, the build so far:
Sony KM7 Power amplifier with fan and housing – this is the rear surround amplifier
Sony KM7 rear surround amplifier used as stereo amplifier
The Sony KM7 surround amplifier has two pieces of heatsink mounted back to back. The silver plate facing the reader is the fan mounting plate which comes off the Sony.
Sony KM7 Power amplifier with fan and housing
Most readers will agree that the heatsink is inadequate hence the fan and unwanted noise. Who cares, we’ll fine tune later.
KEMO KM NR B110 stereo preamplifier kit
Kemo Nr.B110 pre-amplifier
The Kemo Nr. B100 – nice build, took about ten minutes but the paperwork can be improved. I also don’t like the fact that no technical spec is given. A mate of mine built one a while back and said the performance was quite good considering.
VELLEMAN K2573 preamp kit for Moving coil pickups – to be switched before KEMP 110 preamplifier
Kemo Nr. B110 and Velleman K2573 pre-amplifiers. The K2573 is an RIAA equalisation amplifier. Some in-house mods needed. We are looking at equipping the pre-amplifier with turntable input, aux, tape in and out (I have an open reel deck) -> deck to deck (Otari <-> Akai), DAC module and headphones out. The headphones will be fed from a class-A amplifier and pre-driver.
Power supply will be standard (non-split rail) 12V DC stabilised.
Intended layout of modified preamplifier to drive the Sony amplifiers
Modified Surround amplifier – the preamplifier
The pre-amplifier is going to be a mix of different parts – for one thing the RIAA preamplifier output is unknown, except a gain of 35dB is registered. The Kemo has no specs whatsoever and having a single transistor in the Baxandall tone control does not bode well. We will need extra amplification and we need to drive a professional series amplifier through XLR sockets.
BKM.B110 – pdf file
usermanual_k2573 – pdf file
Next: Putting it all together.
https://analogian.co.za/2017/05/27/sony-home-theatre-reworking-the-surround-amplifier-for-stereo-use/