Elma 47 Position Autoformers
Clamor for a higher quality switch version of the autoformers lead me to designing a custom circuit board with hard gold plated contacts that integrates to an elma switch mounted directly on the board. The top of the line unit is a 47 position stereo attenuator that goes seamlessly from +5dB to -51.25dB in 47 1.25dB steps. This stereo unit can also be wired as a mono balanced unit. For the ultimate, a version in all silver is available. (Dimensions 2.9” wide by 2.25” tall and 3.3” deep with the knob being offset and 0.6" from the edge)
Elma 24 Position Autoformers
This unit has a 24 positions and can be from 1-4 decks so it covers the range from mono to balanced stereo in one unit. Pictured above is a stereo unit / balanced mono unit. For balanced stereo two additional decks can be added. (Dimensions 4.7” wide by 2.25” tall and 2.75” deep)
23 Position Autoformers
The basic building block of the family is a compact 23 step autoformer that measures 2.4" X 1.6" and is 1.8" deep. They can have any taper desired and the stadard version comes with the following dB steps. (0, -3, -6, -9, -12, -14, -16, -18, -20, -22, -24, -26, -28, -30, -32, -34, -36, -39, -42, -45, -48, -52 and Mute)
Stereo 23 Position Autoformers With Balance Control.
Two of the 23 position autoformers are placed on a single board with a "penalty free" balance control between them. Each autoformer step is 2.5dB and the balance control allows for a 1.25dB shift to the left or right. Maximum attenuaton is 52.5dB. They measure 2.5" X 4" and are 1.8" deep.
One of the biggest complaints about the $200 autoformers is that they are a real pain in the you know what to wire up. In one of my many discussions with John Chapman of Bent Audio we came up with a simple switching arrangement to make the units a breeze ot install. They are dual mono units with 1.25dB steps and give a maximum attenuation of 41.25dB. Complete details are available Here
The $200 Autoformer Volume Control (AVC)
Pictured above is our first off the shelf device. It is intended as a high bang for the buck entry into the magnetic volume control arena. It allows attenuation from 0dB to -42db in -3dB steps. It has an 80% nickel core, all brass hardware and sounds every bit as good as our custom units. For more information please check out the FAQ, Wiring Directions and visit the Forum.
Price: $200 a pair
The $400 Autoformer Volume Control (AVC)
The Demand for more positions and finer attenuation steps has brought about a second product. This device has 28 steps and provides attenuation from 0dB to -52dB in 2dB steps.This uses a similar approach as the $200 kit but has a 28 pin bobbin in place of the 14 pin. When wiring this device to a switch with fewer than 28 taps you simply assess your gain structure and choose the appropriate steps.
Price: $400 a pair.
Speaker Level Autoformer Modules
These turn-key tapped units make a perfect replacement for resistive L-pads. They allow for a 10.5dB attenuation range in 0.5dB steps. The 49% nickel core can handle an 18V input singal at frequencies above 100hz. The nature of an autoformer transforming the excess voltage into current drive makes this an ideal solution for matching driver efficiency.
The $20 switch.
I sourced a bunch of these two deck 24 position shorting switches and will include one with any autoformer purchase for $20. (Click on either picture for a larger view)
Custom Magnetic Volume Controls.
For those of you who need a bit more control or a special taper, we can offer the perfect MVC to fit your needs. We can help you choose between transformer and autoformer and help you select the proper values of inductance and attenuation to best fit your system. Please check out the $200 autoformer FAQ and join us on the forum to discuss your needs. Please note that the leads of the custom volume controls should not be cut under any circumstances!
Price: Starting at $400 a pair.