$650 plus shipping
Includes premium construction with C&K Brand Silver contact toggle switches, and Deluxe Gold Plated RCA jacks.
These microphone/input transformers are wired to connect a moving coil cartridge (on a turntable) to a phono preamplifier, phono input of a receiver, or your preamp's phono input.
Switchable for 1:16 (24 dB gain) or 1:30 (30 dB gain).
Into a standard 47k phono preamp, the effective input impedance of the low gain (1:16 ratio) is 184 ohms. At 1:30, the effective input impedance is 52 ohms.
The 150 Ohm tap and the 37.5 ohm taps are specified by the
provide 1:18 and 1:36.5, however 1:16 and 1:30 was measured using a 50
audio signal generator at 1kHz with a 47k output resistance, which
the real situation of a moving coil cartridge load using this
a standard RIAA preamplifier.
OPTIONS: If you prefer a different range, these transformers can optionally be built to be switchable between 1:16 and 1:9 . Additional options are also available
CONSTRUCTION TECHNIQUES: All connections are Resistance soldered using the American Beauty system which avoids heat damage to the delicate insulation on the hair-like wires of the transformers. Test equipment is very low current to avoid saturating the transformer cores. You can count on a premier product that is state-of-the-art.
What about Bob?: I have personally built hundreds of step-ups and tested more than a dozen of the most popular input transformers and several step up pre-amps used to match moving coil MC Cartridges to phono stage preamps.
I listen to each and every unit to make sure it is sonically perfect. My current reference cartridges include: an Accuphase AC-2, Supex SD-900 MKII, Shelter 901, Koetsu Rosewood Signature, Koetsu Rosewood Signature Platinum and a Miyajima Shilabe. I use a VPI Aries Extended turntable with superplatter and JMW 12.7 tonearm and listen through custom Strathearn Ribbon Speakers and Infinity Quantum Full Line Source EMIT Tweeters, bi-amped with Infinity Watson subwoofers using a Bryston Electronic Crossover. I custom make my interconnects and also sell them on this website. If you have any special needs, 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.
A Little about Matching: 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).
What is the difference between a Transformer and 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). Moving Coil Cartridges have low voltage but high current. 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 more on the quality of the components than on which type of step up device is used, but a well crafted SUT has fewer parts than a head amp.
Impedance vs. Output voltage: With transformers used for matching the outputs of 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.) Many folks get caught in the trap of trying to match the cartridge impedance to a step up transformer. If you do attempt to match the impedance, you will “choke out” the cartridge and it will sound flat. With step up transformers, you match voltage, not impedance, but you do need to make sure that there is sufficient head room with the reflected impedance so it does not “choke out” the cartridge.
A conventional RIAA phono preamp has a nominal reference level of 5mV at 1kHz. All phono preamps are different, but typically 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). Phono preamp manufacturers usually specify the input voltage as a minimum that is acceptable. What usually is not specified is the maximum voltage that is acceptable before overloading. The best sound is usually attained toward the high end of the range.
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. (Remember that the 10mV is not the absolute. It depends on the phono preamp you are using.) The standard is 5mV (at 1 Khz), however most folks like to be in the range of around 7mV to match the volume coming from a CD player. Now matching is not always this simple, including the reflected impedance to consider, which is why you should take the time to ask what would be a good match for you.
This 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" mode, the phono system minus sides (negative sides) 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 allows you much flexibility to mitigate for ground loops regardless of the configuration of your other equipment.
I take pride in each and every set and provide customer support to make sure that they work well in your system.
http://www.bobsdevices.com/Grounding.htm contains information on how to best connect this unit to your system including information on grounding and a sketch showing a properly constructed interconnect cable.
You can purchase this for $650.00. Payment by paypal or credit card. Shipping is $12 for US via Priority Mail, and $42 international via Express Mail.
Please email email@example.com to order and to make sure this is a match for your system and to select the switchable gain ratios. Other transformer combinations are available as are choices to upgrade connectors and chassis.
I challenge you to find a better built and quieter SUT anywhere.
Here is a photo of the 3440AH available as the "BLUE" Option
For any questions or to order, please email firstname.lastname@example.org