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Sunday, December 8, 2019

The D3a LCR Phono Stage


I just finished another D3a phono stage. Before it gets shipped to it's new owner I took a few photos and would like to write some information about it since there seem to be a lot of misconceptions about such phono stages out there.

My primary goal is to build equipment which offers the best possible sound quality at given price points. That includes among others the use of certain technical concepts like transformer coupling, low impedance circuits, 600 Ohm LCR RIAA EQ and low output impedance. Minimized overhead and switching options to avoid noice and deterioration of the signal. Especially phono signals are very tiny and easily impacted by anything in the signal path. Often this means to compromise flexibility. I believe each component should be optimally adapted to the system in which is used. With the right gain structure, generally low impedance connections and large overhead in signal handling.

With these measures I get the transparent and neutral sound I like coupled with strong tone colours and ability to convey the emotional content of a record. The components are designed such that they work without the need for special accessories like expensive interconnects, power conditioners or stands. Of course any user of my components is free to experiment with such accessories as they usually do not harm the result as long as they are sensible.

I prefer XLR connectors and interconnects for their sturdy design and good mechanical properties. So I use them wherever possible. But I typically also include RCA connectors for maximum flexibility. A big topic in the audiophile community is cartridge loading and there are different philosophies about that. Many do not understand that cartridges react differently if loaded with a purely resistive impedance or in addition with a complex load as a MC step up transformer provides. The later do not need additional loading and work over a certain range of cartridge impedances. My standard set up is such that the phono works best with low impedance cartridges with 10 Ohms or less. Up to 25 Ohms had proven to work as well albeit I personally prefer as low impedance as possible. The phono can also be configured for higher impedances which will reduce the gain by 6dB. Those who still want to play with the loading can use RCA plugs with resistors soldered in, which can be simply plugged into the load jacks between the RCA input jacks. I can provide such plugs with a variety of load resistances. This is the simplest way which avoids switches.

The D3a tubes which are used in this phono are high transconductance tubes. Switching the input configuration on the input stage while the unit is turned on can result in plops in the output. Also the wiring from the input to the MC step up transformer is the most sensitive for hum pick up. So I prefer to keep it as short and straight as possible and avoid multiple inputs or switchable configuration. Nevertheless if wanted such input switching can be provided on request.

This phono stage is for MC cartridges only as the step up is built in and part of the biasing of the input tubes, this enables a very minimalistic signal path. MM versions of such a phono can be built as well but use a different biasing scheme.

The phono stage shown here is my best selling unit. Options like partial or full silver are available as well as other versions with fully differential circuit or my new SplitPath RIAA. Of course there are various options in terms of colours. Including gold or orange anodised metal plates. Also different chassis styles.

If you have any questions about the phonos or other equipment I offer, please contact me.

Best regards


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