High Quality Moving Coil Step Up Amplifier

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I was commissioned to build a high quality step up amplifier of moving coil cartridges and produced this little silver box. Using top quality Toshiba JFETs this step up amplifier offers silent non coloured amplification for moving coil cartridges that compares with the very expensive step up transformers. This version uses battery power (2 x 9v batteries) but it can also be supplied with a matching mains power supply.

It’s so good I now offer it as a standard product at £175    Moving Coil Step Up amplifier

 

Nelson Pass M2 Clone

This interesting amp was in the workshop for hum reduction. There is a lot of correspondence on the internet about the amp and ways to reduce hum, and in this case the hum was as much mechanical as electrical. We swapped out the input wiring for screened cable and fitted screening cans to the Edcor autoformers all with little effect on the hum levels. The next set is to try a DC blocker on the mains to see if that helps the mechanical noise from the transformer.

 

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Rose RV23 Preamp

This preamp dates from the early 90s when it had a reputation for great sound quality. It stands the passage of time well and still sounds very decent. It had had various mods and servicing over the years, including main electrolytic capacitors, valve sockets etc.Someone had also replaced the ribbon connector with some Cat cabling.It is a hybrid valve /solid state design, with transistors used for the phono stage and valves for the line stage.

My work was to upgrade the coupling capacitors, and add a choke power supply by adding a choke and additional smoothing capacitor. Once this work was complete it transpired the original main smoothing capacitor was pretty spent, so that was replaced too.That took a while to find as it broke down after around 2 hours use, but was fine up until then.

The result was very worthwhile, performance has been lifted to a very pleasing level. The pre operates with a much quieter background, displays subtleties better and is more dynamic to boot.

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Onix OA21

This iconic little amp came in to the workshop for some TLC. Not much wrong really. A blown internal fuse but bias and every other parameter measured fine. So once checked and the fuse replaced the amp works fine and sounds good. There is a noticeable thump on switch on, which is typical for an amp of this age as capacitors and transistors age. A recap and change of transistor would cure this but for an amplifier of this age, I often simply install a slow start module as a cheaper fix for switch on thump. It really depends on how much the owner likes the amp and wants to invest in its future.

Audiolab 8000a. 

The venerable 8000a can be split into pre and power amps relatively easily. Sockets are already provided, so it’s a case of removing two buffer resistors to remove the internal link between pre and power amps and adding two input caps to block any DC going to the power amps. It is also relatively easy to plumb in a relay in parallel with. The main delay circuit to add an 8sec mute to the pre out. Finding a relay that fitted the circuit board proved impossible, so I had to plumb in a larger relay. You also have to install the power for the relay from the main delay circuit.

The photos show the finished article with the white blocking caps and relay visible in the topside photo and power supply cable underneath.