Reduction 1.1 Phono Preamplifier Kit

PJ and Doc had planned to revise the Seduction phono preamp kit as much as five years ago. But the kit sold so well that we didn’t want to throw everyone a curve by making some small changes that were more about easing production than radically changing the sound of the preamp. So it stayed in the lineup from 2001 until early 2013. The unfortunate side effect was that the assembly manual became more and more out of date as the visual appearance of various parts were forced to change over the 12 year run. This made building the kit a little more difficult than necessary.

And even so the recent retirement of the Seduction kit create a small tempest. To those unhappy with the demise of Seduction, rest assured that we have a replacement! The new Reduction phono preamp kit employs the same 6922 based circuit that was in Seduction. The biggest cosmetic changes to the basic kit is that the power transformer is the PT-5 that we use in the Eros kit, and the chassis plate is 8 x 10″. The use of the PT-5 is a very cool change, partly because it is more quiet EM-wise than the old PT-1, which lowers the noise floor of the preamp a bit, partly because it allows the use of a regulator on the DC heater supply, which lowers it even more and partly because it is available in a 240VAC mains version (which Seduction never was). As quiet as the Seduction was, the Reduction is even more quiet.

A design by Paul Joppa, the Reduction is a two stage stereo phono preamplifier (one 6DJ8 tube per channel) with passive RIAA equalization.The solid state high voltage supply uses fast recovery soft start rectifiers. The heaters are supplied with filtered DC from Schottky rectifiers, which do not exhibit the switching spikes of lesser rectifiers, the supply is shunt regulated, and the heaters themselves are bypassed with wide bandwidth ceramic capacitors to filter out interference. The passive RIAA components are high quality Vishay Dale 1% metal film resistors and close tolerance metallized polypropylene capacitors. Grid and plate stopper resistors round out the RFI filtering that lets this 6DJ8/6922/7308 based preamp perform without the edginess sometimes associated with this fast, articulate tube. Tube bias is set via Agilent LEDs, a special model that has excellent noise and linearity characteristics for this application.

The kits assembles on a 10″ X 8″ .080″ laser cut random brushed aluminum chassis plate like our other kits and comes with a beautiful Pacific Northwest alder wood base that you can assemble and finish to taste. RCA jacks are high quality gold plated, and the ceramic sockets feature bayonet mount shields for additional RFI protection. This kit also employs a power entry module that allows the use of IEC terminated power cords. A standard IEC type cord is included and you can try out our Bottlehead power cord as well. Wiring is point to point and a ground post serves as the tie point for all of the sensitive low level signal wiring.

The phono preamp has a gain of approximately 36 dB at 1 kHz and is intended for use with phono cartridges of 2.5mV and higher output, with 5mV output being the design center. Higher than 5mV output is certainly fine, and one may also use lower output cartridges with a suitable step up device. Input impedance is 47.5K ohms, input capacitance is 50pF. Remember that your phono cable’s capacitance will add to this figure and increase your cartridge’s capacitive load somewhat. Frequency response exhibits +/- 0.3dB RIAA curve accuracy. The Reduction is designed to operate into line stages with 50K or higher input impedance through interconnects of 1M or shorter length. At 4.5mV input THD is 0.12%, THD+noise is 0.6%

Here’s how the production prototype tested out for RIAA accuracy –

This kit is designed for the builder who has built one kit before or for a beginner who is willing to take on a slightly more challenging kit than our easiest ones (lots of first timers have successfully completed this kit). Assembly is a one or two evening affair, designed for the builder with minimal level soldering experience in mind. A very thorough assembly manual is included, containing step by step printed instructions you check off as you go, detailed photos of the chassis underside and components. All the builder needs to supply is solder. As with our other kits the Bottlehead Forum serves as the builders online tech support resource, with literally hundreds of experienced builders participating to help you with your questions.

Recommended Cartridges:
Here are some phono cartridges that should perform well with the Reduction, listed more or less from highest output level to lowest. This is certainly nothing close to an exhaustive list. Please understand that we are listing these cartridges because they have an advertised output level that will work well with the Reduction’s gain factor, not because they have any other specific sonic characteristics. In theory a cartridge with a higher output level will give a better signal to noise ratio than a lower output cartridge, so bear this in mind if you are sensitive to the potential noise problems typical of phonograph setups – cable/cartridge/tonearm hum pickup, ground loops, electromagnetic interference, etc. We have done our best to minimize the noise level of the Reduction itself, and to accommodate the best approaches in turntable/tonearm/cartridge/preamp grounding, but we cannot predict how all of the myriad turntables, tonearms, cartridges and phono cables out there will perform together.

Rega cartridges

Roksan Corus Black

Grado Reference Series, Prestige Series

Goldring Elan, Elektra, 1000 Series

Reson Reca cartridge

Audio Technica moving magnet cartridges

Ortofon moving magnet cartridges

Shure cartridges

Sumiko Oyster, Black Pearl, Pearl, Blue Point