At your risk. Please take all safety precautions. Any battery should have a suitable series fuse to prevent personal injury or fire hazard.
A great encouragement while developping this phono preamplifier is accidentaly overhearing Alekos at Orpheous Hi-End shop in Athens say how the mains power supply is dirty.
Another factor leading to the beauty of the Pleiades 3 K117 is almost by accident connecting a phono cartrdge output to the mic input of the Realistic disco mixer. Yes the mic in has no de emphasis EQ so one would expect a very treble heavy sound devoid of bass. Yes but is sounded so bad and distorted as if all treble was clipped.
So there may have come a greater tendency to suspect even the 1st stage of a preamp for overload. After all since records are almost cut at constant displacement with respect to frequency, this means by Faraday's law that the treble input to a phono preamp is too much, increasing as frequency rises. (EMF ie output voltage of a coil is proportional to the rate of change of magnetic flux).
So with the thought that a phono preamplifier may in fact overload at the input rather than at the output stage, it was decided to keep each stage at very low or low gain. It was done by removing the source resistor bypass electrolytic capacitors on all 3 stages. (please visit older post)
Bingo! Now almost no violin sounds harsh. Bass is huge. There is depth and warmth to the sound. And there is amazing bass, mid and treble detail.
But most of all it sounds like the real thing. As if the instruments are alive in the room or in my head when wearing the reference Sennheiser HD-580 300 ohm headphones. In fact each channel's output transformer can drive the headphones directly to a comfortable substantial level.
In the begining there was a motorboating (put-put-put) effect when both channels were operated from the same kind of exhausted 2 12V garage door remote control batteries. The problem was solved by using new batteries. In fact it worked greatly with 2 New 9V batteries. It seems the high output impedance of the drained batteries causes the problem of energy being fed back positively to the 1st stage sustaining oscillation.
Now operated at 18V we have a fantastic sounding phono preamplifier which can operate with no electrolytic capacitor at all, not even in the power supply which is 2 9V batteries connected in series.
Very low noise too.
The K117 JFets are treated like electron tubes. In fact the smoothness of the sound reminds a lot well designed (gain structure again) vacuum tube or electronic valve phono preamplifiers. This amplifier is based on the so nice sounding Heathkit AA-32 electron tube integrated amplifier.
The load resistors are aas follows. 1st stage, 100K. 2nd stage 220K and 3rd stage 10K. The passive RIAA network is after the 1st stage, before the 2nd. It consists of a series 220K resistor feeding a 22K is series with 15n. And also feeding another low R (for the 5th supersonic frequency time constant) in series with 5nF. (please visit the RIAA wikipedea article which presumably gives a hard time but good popularity to Allen Wright (Tube Cookbook) who may be right! after all).
Presumably the 2nd stage receives a low input voltage comparable to the 1st stage due to the RIAA de emphasis network which is really a potential divider made of 220K and 22K. ie 10:1?
A 470K potentiometer is after the 2nd stage.
The 3rd stage through a Philips MKT capacitor feeds a Belclere step down transformer.
At this stage the preamp is made on 1 breadboard for each chanel. Everything is now inside an aluminium box with some loss of sound quality compared to the paper cardboard box (non conductive). Electrons are jealous.
Looking at the box from the user's angle. The power on off swich will be at the left side. The volume potentiometer is at mid right. The Bulgin 2 9V battery holder at rear right. Neutrik input and output RCA female chassis connectors are at left and mid respectively. The Neutrik stereo headphone female connector is at front right.
It may be a good idea to keep the preamp in breadboard mode so that any knowledgable user can adapt his, her preamp to perfection. The low component count, low battery voltage make this ideal.
The life of this preamp may be higher that the user life as there is no electrolytic capacitor.
As my philosopher friend Michalis says: "In 150 years we won't remember anything."
The power consumption of this preamplifier is so low, 2mA? at 18V that the batteries should give plenty of hours of music pleasuse from our magical records.
And the sound quality makes it all worth!
