Tuesday, May 12, 2015

AMC CVT1030MKII Pre-Amplifier


It was quite nice to get some haute equipment in the last few weeks, Id like to highlight a AMC CVT1030 Pre-Amplifier with the MKII addition. 

The AMC 1030 is a hybrid topography, utilizing class A arranged FE-transistors and high/lo gain 12au/AX7 valve variants. The FET's are incorporated into the solid state regulated power supply/filter stages, which is ideal considering we can clean up AC taps not required in  valve rectification with a little more reliability.Their are some neat features including  a direct/normal phase that bypasses tonal controls and includes a upgraded balanced output module (MKII.)

Power Supply PCB 90-1261-1
Because we are dealing with a valve topography and filter were looking at high voltage 250Vdc electrolytic here. I preferred the Panasonic EE series, these are phenomenal in the power supply, the EE is known for extreme reliability especially under duress; rated at over 10,000hours with very little capacitance change (20=-%) at +105C under load. For lower voltage lytics Panasonic FC/FR high temp long life capacitors were utilized.

Phono PCB MD90-1261
The phono stage is a modular PCB designed for only moving magnet cartridge bodies. All the lytics here were replaced with Nichicon low impedance and audio grade Elnas.

Headphone PCB MD90-1262
The headphone has a nice switching mechanism so you can cut out the outputs, it also is incorporating into the "phones/normal/direct" feature allowing tone controls still. Again the lytics like the phono were replaced with a low impedance Nichicon capacitors which are perfect for audio applications along with the audio grade Elna's. 

Pre-Amp Block (main) PCB MD90-1261
The original design had some decent proprietary films, we opted to go with the WIMA polypropylene 2.2uf 250V films, talk about BIG and expensive but the results are worth every penny. Some re-routing of grid resistors had to be performed, its important to note when rerouting valve resistors were talking some pretty decent radiant heating escaping, make sure you give plenty of room for them to vent so as not to heat up the foil side of the PCB or soldering mask. My favorite Panasonic ECW polypropylene were utilized where the WIMA's would not fit. All the electroytic capacitors on the main block were replaced with Elna and low impedance PWs.
I should note that the tracing on the socket side had been utterly destroyed by a prior "repair" centre, all new tracing had to be laid and new gold contact 9-oin PCB sockets installed.  The original ECC valves were replaced with all matched Electro harmonix 12AU/12AX7 lo/hi valves. Im a huge fan of EH, I use them in my push-pull amplifier and highly recommend them as a modern replacement source. 

All in all, I am very impressed with this pre-amplifier, it has some killer looks, very solid seated controls/knobs. Very simple straight forward audio signal topography with no bloated frills other than the IR receiver . 

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