Schematic of Pleiades 3 K117 JFET Phono Battery Powered MM Preamplifier

At your risk. Please take all safety precautions. A suitable fuse should always be in series with a battery for burn injury or fire prevention hazard.

This is the current schematic without RIAA tests or tuning done yet. So the network used may be wrong, it is just used for initial listening test purpose. Tests will be done using a Lipshitz inverse RIAA networks including the ultrasonic time constant, (please see Wikipedia article on RIAA).

At this prototype stage an input transformer is not used. The Stanton 681EEE calibration standard moving (ultra low mass) iron cantilever cartridge is directly connected to the 47K resistor input.

Two 9 V batteries in series with a fuse are used to power this great sounding very low power consumption and low noise preamplifier.

The sound is warm like a good electron tube design with (no source) cathode bypass capacitors capacitors. Warm may well mean with less distortion, no high frequency overtone artifacts added to the music program. 

The output transformer is used with the 2 secondaries in series, so the ratio is typically 5:1. 2 Channels can drive the Sennheiser HD-580 2x 300 Ohms headphones to a comfortable level with big deep bass, liquid mid and treble. But all these adjectives may be unreal.

The sound is real, close to reality.

I wrongly thought some cartridges like the Stanton 680 series, Ortofon OM series, some Shure were MM. There are variable magnetic reluctance and give MM a very hard time and possibly MC too. For example the cantilever has neither a magnet or a coil attached to it. The mass is so low that the 681 can track at less than 1g. One day i heard by chance n Stanton 680 and that was it. I could not believe how good, warm (natural) and detailed it sounds. The treble...

From AI overview:

The Stanton 681EEE is a highly regarded moving-iron phono cartridge, historically used as a calibration standard in broadcasting due to its flat frequency response (

) and low distortion. It is often sold with a Vivid Line stylus or original Stereohedron stylus and requires precise setup (tracking force 0.75–1.5g, best around 1.5–2g, typically without the brush).

    

Warm Means Undistorted?

 At your risk.

This is how it felt today listening to a mono LP through the Pleiades 3 K117 Jfet battery powered phono preamplifier. 

Without the source bypass capacitors the gain of each stage is much lower. And it sounds much less undistorted like an electron tube preamplifier without cathode bypass capacitors too!

Please see next post for the schematic.

Mina

 

Pleiades 3 K117 18V under construction photo

At your risk. Please take all safety precautions. A suitable fuse must be in series with a battery for injury or fire hazard protection.

Componets are placed in exactly the same order and layout as on the schematic. Signal flow from left to right as usual on electronic engineering schematics.

Sapore di Sale - Gino Paoli, Ennio Moriconne and his Orchestra

 

I head on Yiannis Petridis radio broadcast on Hellenic Radio  that Moriconne had done the arrangement.

Sara perche ti amo

 

Updates to the Pleiades 3 K117 Phono RiAA battery powered preamplifier

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!

How to connect an XLR SM58 studio microphone to a mobile phone with Schematic

 

At your risk.

Schematic of XLR to 3.5mm to USB C adaptor.

External view of XLR to 3.5mm to USB C adaptor.

Internal view of XLR to 3.5 electret mic in adaptor.

The idea behind this is treating the SM58 as it were a condencer electret microphone. 

The SM58 has an internal transformer to step up the moving coil capsule to typicaly 300 Ohms.

The K117 gate is connected to the seconary of this transformer ie to the output of the Shure SM58.

The load drain resistor is on the device to connect to the Pleiades K117 pre preamplifier, and this device supplies the voltage to operate the K117 JFet.

This device can be an older iPhone or iPad or any device with 3.5mm electret mic input.

This of cource includes a modern 3.5mm to USB C adaptor to connect to almost any modern device!

Nice female vocals were recorded at 18in to 24in on a modern mobile phone.

Obviously the further away the microphone from singer the best it sounded as greater distance gives less proximity effect so the listener can now hear more treble detail, breath etc.

To increase further the sensitivity a good quality step up transformer can be connected between any dynamic or ribbon microphone and the Pleiades K117 XLR to USB C adaptor. A small 1:3, or 1:5 ratio may be better to avoid possible overload but it is best to experiment.

It may be worth including enerything on one box, ie input transformer, Pleiades K117 to 3.5mm and Apple 3.5mm to USB C adaptor.

Please also see much older posts on how this has evolved.

Many thanks to ny friends Lefteris and Panos for making clear the inportance of 1 stage electron tube or JFet respectively, microphone amplifiers.

On Increasing Phono Preamplifier Headroom

At your risk.

Please see previous post.

Do source bypass electrolytic capacitors kill musc?

 At your risk.

Experimenting with the Pleiades 3 K117 RIAA phono preamplifier it was found that removing a source bypass capacitor reduces gain as we know so the sound was much softer but it was also more much real. Like the real thing. For example treble detail sounded so real as when having one's ear near the stylus while playing back a record. 

If a gain at say 1st stage is reduced by 26dB, the input headroom is increased by the same amount. If the stage is low noise enough for example by low drain (JFets) or anode (electron tubes) current, it is possible that headroom is increased by removing the source, cathode electrolytic capacitor.

These experiments when done by playing the LP Dromos - Mimis Pleassas, Lefteris Papadopoulos recorded live stereo mix by Stelios Yiannacopoulos at EMI Columbia Athens studios:

So at this time the Pleiades K117 phono preamplifier has evolved to 3 stage K117 with no electrolytic capacitor bypassing the source resistor of any stage! The 2nd stage seems to be receiving an equal amount of low level signal as the 1st stage since the passive RIAA network follows the 1st stage. The 470K potentiometer follows the 2rd stage and then the 3rd stage increases the signal to a louder lever to drive the output transformer which drives the Sennheiser HD-580 150 Ohms headphones.

So the headroom at the input must have been increased a lot and the potentiometer protects the 3rd stage from overload.

It is a concept similar to making nice electron tube studio microphone preamplifiers. You have to arrange the attenuator to be as close a possible to the microphone.

Same as out ears where the 3 liittle bones connected to our ear drum control gain, overload, ie increase headroom,  dynamic range of permissible received sounds.

But the electronics have to be top quality low noise. Pleiades experiments are done with low (say 50 microamperes) electron tube anode current or JFET drain current.

The idea of not using source or cathode capacitors comes from examining the great sounding RIAA stage of the Heathkit AA-32 integrated electron tube class A amplifier.

A NAB test record was used for feeding a 1KHz signal to the Shure 75E Encore cartridge, Metz direct drive turntable.

No bypass capacitors will also allow more meaningful comparison with the Pleiades 3 stage DC90 electron tube battery powered phono preamplifier with most grids at space potential ie nothing connected to grid except a coupling capacitor.

Later addition:

I may be giving a hard time to electrolytic capacitors. The sound may be better, warmer i.e. with less distortion without them because the gain of each stage is now lower. For example less signal appears at the 2nd stage and therefore there is more overload margin. Please visit other posts on the Pleiades 3 K117 battery powered phone RIAA preamplifier. Having said that listening tests and instinct tell that the sound is not only warmer but more real without the capacitors.

   

 

Cover versions of songs

At your risk.

Few people wound make a cover version of a famous painting such a Mona Lisa.

But more would make a cover version of a song such as I wanna hold your hand.

Music Publisher:

https://en.wikipedia.org/wiki/Music_publisher

Boundary Mobile Phone

 At your risk.

Albert told me that his mobile phone sounds with more bass when placed on a table as the larger surface beacomes a soundboard.

Is the sound also more clear as the phone becomes a boundary speaker, ie the listener does not receive a delayed table reflection after the direct sound when the phone is hand held? When the phone is placed on table the listener receives almost the same direct and reflected ray (sound wave).