Sony home theatre – Reworking the surround amplifier for stereo use – Part 2

The preamplifiers

First of all, the build so far:

Sony KM7 rear surround amplifier used as stereo 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 rear surround amplifier used as stereo amplifier - showing cooling fan
Sony KM7 rear surround amplifier used as stereo amplifier – showing cooling fan

Most readers will agree that the heatsink is inadequate hence the fan and unwanted noise.  Who cares, we’ll fine tune later.

Kemo Nr.B110 pre-amplifier
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.

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.

Modified Surround amplifier - the preamplifier
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.

Next:  Putting it all together.

Sony home theatre – Reworking the surround amplifier for stereo use

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