Synthesis Roma 79DC Phono Stage

Synthesis Roma 79DC is an excellent stand-alone phono stage with a valve output stage. As a result, the sound is sweet with the stunning musicality demanded by vinyl lovers.

It can be used alongside an amplifier from the Roma valve amplifier range or with other hi-fi separates and works with both MM and MC cartridges with 0.5% RIAA accuracy and cartridge loading adjustment to get the best sound from your turntable and phono cartridge.

A high gain JFET stage is used for the MC input and this is switchable on the front panel. Notably, the power supply uses an outsized transformer and the power supply rails are all regulated. The capacitors in the signal path are all Polypropylene long-life components. Finally, Connectivity is simple with RCA inputs and outputs.

Excellent build quality

The high quality PCB holds three amplifier valves as well as a range of top-spec components. There are two ECC83 single triodes and an ECC82 double triode. These provide the necessary low noise, high-gain amplification.

There is also a JFET gain stage. This is needed to boost the low output of a moving coil cartridge. The gain can be set via a front mounted switch.

The power supply uses an oversized transformer and fully regulated supply rails. This provides the very low noise supply needed due to the high gain of the unit. Finally, all of the audio signal capacitors are long life polypropylene types.

Why do you need a phono stage?

Before moving magnet cartridges there were crystal and ceramic cartridges. These did not sound all that great but had a high output. Crystal cartridges could output up to 3V to drive an amplifier directly. Likewise, ceramic cartridges could output several hundred millivolts. However, they need a high input impedance as provided by valves. Unfortunately, transistor amplifiers usually have a low input impedance. As a result ceramic cartridges can sound “Tinny”, which can still be a problem nowadays with cheap audio systems that do not have the correct impedance matching.

As sound quality improved magnetic cartridges came along. These output only a few millivolts and need lots of amplification. Moving coil cartridges output even less, sometimes only a few hundred microvolts. As such, the sound level needs boosting as well as equalising using the now standard RIAA curve.

A phono stage or phono preamps is used to accomplish this and a good design needs to use low noise components to get the best sound from the cartridge without any unwanted noise or hum.

79DC design philosophy

Firstly the PCB has been carefully designed to keep signal paths short. Also the transformer is kept as far away as possible from the signal circuits. The valve heater circuits are fed from a DC source so that there is no possibility of hum being introduced. Another issue with hi-fi amplification can be noise from transistors. The 79DC uses a low noise JFET input. There are also high-grade smoothing capacitors for long life. Finally, valve circuits use high voltages and audio coupling capacitors need to be able to withstand this without going leaky or shorting out. Hence the 79DC uses polypropylene capacitors. Warmth of sound is also a priority and this is where the valves come in - they provide the final stage.