Spectral DMC-10 Preamplifier modified by Dr. Arthur Loesch

From his estate, this Spectral DMC-10 full-function preamplifier was updated and rebuilt by renowned audio designer Dr. Arthur Loesch. The major changes are closely matched, higher quality parts and a complete reworking of the RIAA phono circuit.

This unit was modified at a time when Arthur was experimenting with solid state amps and preamps. A friend of his named Harry Paller asked him to develop a solid state alternative to his well-known tubed phono preamp. In the course of this work, Arthur acquired a high-end transistor curve-tracer (the equivalent of a tube tester for FETs) and discovered that most of the amplification devices (MOSFETs) used in modern solid state components were completely mis-matched in their characteristics. It's as if the tubes in a tubed circuit were selected at random from an available pool without testing and matching beforehand. This often resulted in a much higher level of distortion than published specs would indicate. By carefully matching the devices, this distortion could be reduced to levels that actually exceed the manufacturer's specs, as is the case with the DMC-10 in this sale.

As a side note, many designers know this and get around the distortion issue by using more devices in a circuit than necessary, figuring that the law of averages will work in their favor. The reason most manufacturers don't bother to match them is the time, equipment, and added cost it takes to properly sort them. It partially accounts for why solid state components from some companies, like Goldmund (which closely matches them), seem to be disproportionately expensive when compared to similar components from other sources.

The mods to this unit were done about 15 years ago as a prelude to what became Paller's TAG Model One preamp, which for a time was The Absolute Sound's "State of the Art" preamp. The work on the DMC-10's phono board appears to be an early implementation of that design and Arthur's collection of notes support this hypothesis. Comparing the board with a photo of the original, I can see that he replaced many of the Spectral caps and resistors with higher quality parts. The original volume control appears to have been upgraded to an Alps pot. Arthur also changed the way the phono load is implemented. Though the default load is still 47K ohms, instead of using shorting blocks across a fixed array of soldered-in-place resistors, resistors of any value can now be plugged in. The Plexiglas cover was added to show off the jewel-like construction quality and the original metal cover is provided, too.

Included are a large collection of notes (including curve traces), schematics, Spectral literature, and a separate, original Spectral power supply. This is an exquisite one-of-a-kind unit and a unique piece of audio history!

The power supply is wired for 115V, 60Hz use in North America.

Free shipping only to any continental USA address (lower 48) at the "Buy It Now" price. If you are located outside of the US, before you buy or make an offer, please contact me for a shipping estimate. Remember, if you "Buy It Now" or your offer is accepted, you are obligated to complete this sale. Shipment is typically within three days of completed payment.

This item is offered for sale elsewhere and is subject to prior sale. Returns accepted only if non-working or not as described.