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June 15, 2012

MC Step-Up Transformer using Altec 4722

Despite the extreme convenience of computer-based audio systems, the turntable has not lost it's place in the hearts of many audiophiles. Sometimes that extra effort can be worth it, balancing the plinth, brushing the dust off the record, cleaning the stylus, flipping the record after a few songs, the list goes on. There's just something nice about that analog warmth of that teeny tiny stylus wandering through the grooves of a well pressed record.

One of the requirements for owning a turntable is a phono pre-amp. A phono pre-amp brings the low-level signal from the record player up to a point where it can be run to a standard amplifier. Equipment like CD players and DACs don't have this requirement because their output is already at a suitable level. So, a very small gauge wire runs from the cartridge through the tone arm and goes to whatever jacks are on the turntable, generally RCAs on more modern decks. A pair of RCAs are run from these jacks to the phono pre-amp, which amplifies the signal and passes it on to the main pre-amp or integrated amp in the users system. Occasionally, the pre-amp or integrated amp will have a built in phono input, but many enthusiasts prefer a separate unit as the quality can be better. To complicate matters further, many phono pre-amps only amplify the signal of a moving magnet (MM) cartridge. There are also moving coil (MC) cartridges that have an even lower signal that the phono pre-amp simply does not have enough gain to play at a proper listening level. In order to remedy this, one can use an MC step up transformer.
A common step-up transformer, the Ortofon ST-80 SE

An MC step up transformer is completely passive, no electricity is needed to run it. The signal runs from the turntable to the MC step up transformer which amplifies the signal a small amount, then the signal runs to the phono preamp, which amplifies it further to the point where it can be run to the main-pre amp or integrated amp, where it is amplified yet again before it makes it's way to the speakers. So the flow would be Record Player > MC Step Up > Phono Pre > Pre / Integrated.

Many DIYers have taken to the fact that vintage microphone transformers can be used as an MC step-up device. As JELabs has stated: "Moving Coil cartridges behave very much like condenser microphones - low impedance and low output - requiring a voltage boost. Step-up transformers are passive devices and as long as they are wired properly, they are virtually noiseless. To me a wide bandwidth input transformer is the most elegant way of boosting MC output to MM phono level." There are a variety of units that fit the bill, from the Altec 4722 and 15095, Denon AU320, RCA MI12399A, Tamura TKS83, and Thordarson T-43606-A just to name a few. Below you will see a variety of these units in step-up devices made by JELabs.

A Variety of Step Up transformers

I'll be making use of the Altec Peerless 4722, it's one of the most popular vintage units and commands a price because of that demand, but from the way JELabs described it, it seemed that the units have a bit more of a euphoric warmth than the others, which I always appreciate. The Altecs are in the shape of a vacuum tube with eight pins at the bottom designed to fit into a vacuum tube socket. The chassis was custom-made by Keith, eBay seller po1019, and is a very fetching little unit. Holes were drilled for the RCAs, ground posts and switches and punched for the tube sockets that would be holding the Altecs.

Prepped Chassis
Cardas RCAs (GRFA) and ground posts (GRND) will be adorning the petite chassis. These were secured using a small socket wrench.

Some Cardas bling
More to come...

Need a pair of low impedance cables for your turntable? Contact Zynsonix Audio today.  

The Fine Print:
The above steps detailing the building of a MC step-up transformer are for entertainment purposes only and not to be performed under any circumstances. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted and cause physical harm to yourself, your surroundings or your property. Please keep this in mind.

1 comment:

  1. I'm interested to know how you connected all the earthing?