Welcome to Bob's Devices
I build custom step-up transformers for moving coil (MC) cartridges.
Some are built from Vintage microphone transformers and some from totally new CineMag Moving Coil Transformers.
Click HERE to see the CineMag Transformer (MC) Step-Up Device.
Email me with your moving coil cartridge and phono preamp make/model and I will provide you, with no obligation, information on what would be the proper step-up for your system. If you are interested in me building you a step up transformer (SUT), I will provide you with a quote for doing so.
What do these do? These transformers are used for connecting a moving coil cartridge (on a turntable) to a phono preamplifier, phono input of a receiver, or your systems preamp.
My experience: I have built more than 100 moving coil step-up transformers and tested more than a dozen of the most popular step up transformers and several step-up pre-amps (head amps) used to match moving coil (MC) Cartridges to phono stage preamps.
Why you should have me build it: Since there are many different types of Moving Coil Cartridge, one size does not fit all. Wiring transformers for moving coil cartridges is a tricky process and my designs use tried and true techniques to eliminate hum and ground loops. I also use very sensitive test equipment to properly evaluate and test each device. Even with properly built devices, careful placement and proper interconnect cables and techniques are needed, but I have taken the guesswork out of wiring these devices yourself. There is more to this than just wiring the inputs and outputs of a transformer to the RCA jacks in a box.
My products are constantly evolving, incorporating suggestions and feedback I received from my customers. Each unit is individually scoped on a dual-trace Oscilloscope, using a low impedance signal generator and a bank of sensitive milli-volt meters, to ensure proper polarity. Then, I personally listen to each one to make sure it is sonically perfect. I also custom build units for special situations, such as using XLR connectors for those with balanced inputs and outputs, or with multiple inputs for those with several turntables or tonearms.
Difference between Step-Up Transformer and Head Amplifier: Moving-coil cartridges have more energy than moving-magnet cartridges due the fact that their magnets are stationary, and can be stronger than those in the moving magnet cartridges. They typically have high current and low voltage, where a moving magnet cartridge has high voltage and low current.
To use a moving coil cartridge, you either have to amplify the voltage prior to reaching the phono preamp (by using a Head Amplifier); or to change the current into voltage that is high enough to be used by the phono preamp (by using a transformer).
Why use a Transformer instead of a Head-Amp: The transformer is a passive device and therefore has certain advantages over a head amp or active device, which is most likely built with solid-state electronics (FETs, i.e. field effect transistors). If you are using a tube system, you would not want to introduce transistors into the system. Moving Coil Cartridges have low voltage but high current. In simplistic terms, the transformer uses the extra current that is not needed and converts it to higher voltage to allow the cartridge to match the input of the phono preamp. Whenever you introduce something into a circuit, there is an insertion loss. Whether there is a greater insertion loss from a transformer or a head amplifier depends on the quality of whatever you put in there. I am not going to visit this topic.
Impedance vs. Output voltage: With transformers used for matching the outputs of moving coil (MC) cartridges, you would want to match the output voltage, rather than the impedance, to get a better match. (This is different from head amplifiers where you would want to match the impedance only.)
A conventional RIAA phono preamp has a nominal reference level of 5mV at 1kHz. Output values below 2.5 mV or above 10 mV will either result in a poor S/N ratio or overload (clipping). The higher the ratio, the higher the gain (the louder it will sound).
The MATH Part: Take the output of your moving coil cartridge which is expressed in milli-Volts (mV) and multiply it by the step-up ratio of the transformer. If this value falls between 2.5 mV and 10 mV, it will work. The standard is 5mV, however most folks like to be in the range of around 7mV to match the volume coming from a CD player. Now, it is not always this simple, since there is reflected impedance to consider, which is why you should take the time to ask what would be a good match for you.
Please contact me if you are not sure, and I can look up your cartridge to ensure a good match. I have many different transformers in stock and can custom build from a variety of transformers to your specifications.
How I determine the step-up ratios: I measure final step-up ratios using a 50 ohm audio signal generator at 1kHz with a 47k output resistance, which approximates the real situation of a moving coil cartridge load using this transformer into a standard RIAA Phono Preamplifier. Then I test each and every one on my own system to make sure it sounds right.
I take pride in each and every set and provide customer support to make sure that they work well in your system.
What about Grounding? Each unit includes a grounding post that can be used to connect your turntable ground and your preamplifier ground. It also includes a ground "lift" switch. In all modes, the transformer cases and faraday shield internal to the transformers are connected to the ground screw. In the "ground in" mode, the phono system ground is connected to the chassis ground. In the "ground out" mode, the phono preamp system ground is connected to the chassis ground. In these modes, the minus sides (negative sides or shields) of the output cables are connected to the grounding lug. This configuration works well for those systems where the turntable ground is connected to the negative leads coming from the phono cartridge or where the negative inputs to the preamp are internally connected to ground. In the "lift" mode, none of the conductors in the RCA jacks are connected to the case, ground, or shield and there is no electrical connection between channels. This design avoids any transformer induced ground loops regardless of the configuration of your other equipment.More about GROUNDING
Here are some of the feedback comments I have received on my custom Step up units on eBay, where my user name is capn-bob:
No handling charge. Domestic priority mail shipping is included in the price. Will ship worldwide via express mail only, charging actual cost.
Here are photos of some of my Step-Up Devices
You are welcome to contact me at: capnbob@toonstudio.com with any questions, suggestions and comments. I will provide you with whatever assistance you need to achieve the best match for your system.
Thank you for viewing my page.
Bob Sattin
www.bobsdevices.com