Pre amplifier board
I believe this was the last production Crimson pre amp board the CPR 2 it replaced the CPR 1 and used discrete transistor gain stages instead of the opamps used in the CPR 1, it also used a lot of tantalum capacitors in pursuit of improved sound quality.
The pre amp module had onboard RIAA equalization for LP playback but no provision for tone controls although you could fit a balance control if you wanted ;), essentially you had some amplification and equalization for LP's that fed into a final gain stage for further amplification before being fed to the power amp.
Power amplifier board
Like the pre amp board these type VII power amp modules were final production versions of the Crimson bipolar amp range, they had several different models with power outputs ranging from 60W to around 200W. The pair in the image above are nominally rated at 60W into 8 Ohms and 100W into 4 Ohms, the output power was dependent to a degree on the performance of the power supply especially into more difficult speaker loads so a good power supply is essential.
Power supply
The image above shows the interior of a completed power amp, ideally each channel would have a separate transformer but having a rectifier/capacitor assembly for each channel is a good compromise. This amp used 60W modules supplied by a 225VA transformer and two 10000uF capacitors per channel, as it's over 27 years old I'm going to replace the four main capacitors with new Panasonic 10000uF 63V components.
Power supplies
The image above is the power supply section for the pre amp module, the transformer is 300VA with two 15V secondaries (it's a bit of overkill but it's cheaper than buying a new one!), the capacitors will be replaced with two 10000uF 35V Panasonics fed from the rectifier. As this is a pre amp the voltages are significantly lower than a power amp (+/- 40 - 50 V DC) at +/- 15 V, the board above the rectifier/cap assembly is a regulated power supply and fed +/- 21 V from the rectifier it will output +/- 15 V DC for the pre amp.
Power supply components
Rectifiers
The above images show the rectifier from the pre amp power supply (it's used but works fine), the bridge rectifier outputs DC voltage from the transformer secondaries, however it's not smooth DC it contains ripple and too smooth this the DC lines are fed to capacitors as in the image below.
When connecting capacitors to the rectifier output polarity is very important, get it wrong and you'll need new caps (at least) and a mess to clear up, electrolytic capacitors have + and - terminals and these must be attached to the +/- on the rectifier.
Capacitor and rectifier assembly
This is the amplifier from earlier I've replaced the original capacitors with the new Panasonic ones, they're quite a bit shorter so I had to reverse the mounting plate to get them close enough to the rectifiers, the amp now sounds a lot smoother with better bass a good upgrade for £20!
The image above shows the transformer secondary connections, as most transistor amps use dual rail power supplies a transformer with two secondaries is required one end of each winding is earthed (yellow and blue wires) and the grey and red go to the AC input on the rectifier (the ~ symbol in the rectifier images earlier).
Pre Amplifier upgrades
The Crimson pre amp had a number of component issues namely the two selector switches and the balance pot all three have been replaced and some new wiring is being installed (only on the Disc and CD inputs and power amp outputs)
