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.

The Bottlehead Seduction Phono Pre Amp

After a rather enjoyable Bottlehead Crack build, I decided to press forward with another of Bottlehead's relatively inexpensive kits, the Bottlehead Seduction. The Seduction is a phono pre amp. For those of you who aren't familiar with record players, a phono preamp is necessary to bring the output of a moving magnet or moving coil cartridge up to a standard line level input using RIAA based equalization. The accuracy of this equalization is important, so when building a phono pre-amp, the parts values should be as close as possible (in other words, aim for the +/- 1% resistors and capacitors when possible).

The Seduction has been offered by Bottlehead for quite some time, 10 years I believe and was designed by Paul Joppa. This phono pre is two stages, and makes use of a pair of 6922 / 6DJ8 tubes, which are very commonly used for audio. This makes purchasing good vintage ones a rather expensive task, but there are plenty of good quality new-production and JAN (Joint-Army-Navy) tubes available for reasonable prices. 

As typical with Bottlehead builds, there is a Constant Current Source Upgrade. This adds $75 to the $369 price (as of Feb 2011), but, as always, is worth the small investment. From the Bottlehead site: Now the benefits of increased dynamics, more quiet background, better bass control and added gain found can be had for the Seduction phono preamp. Four Camille Cascode Constant Current Sources replace the stock plate load resistors, dramatically increasing the load impedance for greater Power Supply Ripple Rejection (PSRR) and the extraction of the full gain available from the tubes (up from about 36dB in the stock form to about 40dB). 

I made a number of part changes to the build in the interest of having the best possible performance:

• C4S Upgrade Board
• Gold Obbligato Caps (0.47uf and 0.1uf)
• Russian Teflon bypass caps
• Vintage Pilot Light
• Cardas Rhodium input and output RCAs
• Slightly nicer than stock Pany and Nichicon caps in the power supply
• Cardas, Kimber and Neotech Teflon wiring.
• Teflon Noval Sockets and PCBs
• Takman Carbon Film Resistors
• Ear Feet

I also used one of the Orange Drop caps in the kit to bypass one of the power supply caps, you can see it wedged on the left in the photo below. The top plate was given a copper colored powder coat, and the wood was treated with a variety of MinWax products to give it that nice reddish brown color. Please click to enlarge any of the photos below.

Note the C4S board on the upper left above the ground plane

The transformer sits on nylon standoffs for noise reduction

Vintage pilot light sits behinds the tubes

Russian Teflon Bypass Caps added

The Finished Product

The Obbligatos are very nice caps for very little money but probably aren't the last word in detail. I opted to add the teflon bypass caps try and extract a little bit more. The Russian teflon bypass caps are old war caps, you can snag them on ebay for a song, just keep an eye on shipping as it tends to cost more than the caps. You'll also find that they are quite large compared to other similarly rated caps, so keep this in mind when you try to fit them in a build. I ended up with miniature 2200pF (pico-farad) caps to compliment the 1uF (micro-farad), equivalvent to 1,000,000pF Obbligatos. The rule of thumb is that a bypass should be 1% or less of the cap it is bypassing, so this little guy is 0.22%.

I'm currently using a very special custom 10-3 right angle power cord with this kit (my own recipe). Take a look at the details here.

UPDATE (5/30/2011): A pair of Hammond 155J chokes were added to the power supply in place of the two 1K resistors. On paper, they are 1026 ohms +/- 15%. In practice, they measured about 900 ohms each, which should be close enough for this purpose. Chokes allows better filtering in the power supply (less hum in the output of the amp and less voltage drop) which should translate to better sound. There's a nice quick lesson on the purpose of chokes here. Since the stock Bottlehead design lifts the transformer with a pair of standoffs for noise reduction, I decided to use a pair of standoffs for the chokes to physically move them away from the tubes. As typical with Bottlehead kits, once you start dropping in some fancy parts, the real estate tends to go pretty quickly. The most accommodating place to mount them in my case was right next to the C4S constant current upgrade board.

Pair of Hammond 155J Chokes next to the C4S

The upgrade required about a half hour of time to mount the chokes and solder them in place, along with about $30 plus shipping for the chokes themselves. I also opted to add a little bit of Dynamat Xtreme to the tops of the chokes and the main transformer to help dampen a little bit of vibration. I'm listening away to the new Radiohead The King of Limbs vinyl as I write this, the sound is warm and smooth, just as a record should sound. 

The Fine Print:

Please remember that building circuits and performing circuit modifications can be dangerous to you and/or your surroundings and should only be performed by a certified technician. The owner of this blog and all associated parties can not / will not be held responsible if you attempt a modification posted below and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and mods, if performed improperly, can be a fire hazard. Please keep this in mind.