Another JFET phono preamplifier

[andreidaniel]

Hello guys! I remembered recently about a Romanian magazine since 1994 where was presented an interesting phono preamplifier based on FET transistors. As previously most listeners preffered to buy or construct either "Le Pacific" or "Boozhound" preamplifier, I decided to come in help for them with this diagram.

Short description:
"The preamplifier for the magnetic cartridge presented can satisfy a series of lately wishes such as:
-very good signal/noise raport thanks to using the FETs;
-very low THD for a high gain and a high output voltage;
-high capacitance for preloading the signal peaks.

Technical characteristics:
-Gain at 1KHz = 40dB;
-V out = 250mV;
-S/N = 82dB;
-overload for the normal output voltage (250mV) = 40dB;
-THD = 0,01%;
-Z in = 220K;
-minimum Z out = 1K.

The preamplifier is built after the pattern of an OA equipped with FETs at the input in a differential mode. The stage mixes or combines the advantages of the BJT (regard frequency and high amplification) with the low noise of the P-channel FETs.

Regarding to the type of cardridge, C1 can vary between 10-90pF.

Here are the diagram, the power supply, the part list and the PCB 45 x 55mm

 

[Audioguru]

This is the year 2016. You show a preamp designed 30 or 40 years ago using discrete parts. Today and for many previous years we use audio opamps to do it.
Its input resistance is much too high for a moving magnet cartridge that needs 47k ohms.

By the way, does anybody play old vinyl records anymore? The last time I was in a discotech was 1975.

 

[chuckey]

I sometimes play my 45s. I gave away my 78s about 4 years ago when we moved house.
Frank

 

[BradtheRad]

I still have a few boxes of vinyl records. I've wanted to play more of them into my computer to convert to mp3's. I hope to take others to a secondhand store and get money for them.

Not long ago I heard that vinyl records are making a comeback, and turntables are rising in sales, and aging baby-boomers throw 60's parties where they play oldies records on old-fashioned phonographs.

 

[c_mitra]

By the way, does anybody play old vinyl records anymore? The last time I was in a discotech was 1975.

I still have few 33RPM LPs and I sometimes play them. I recently bought a turntable with an USB interface (I am not very happy with it). I have seen being played at several place.

They are dead but refuse to lie down.

 

[ftsolutions]

Alot of albums are now coming out on vinyl. Whether it is a short lived fad, or lasts another 30-40 years, who knows. But, there are not many decent record turntables available at local stores anymore, and many of the new, cheap turntables with hard ceramic stylus and have tone arm pressure are as likely to wear out the vinyl as play it.

 

[andreidaniel]

I also saw this type of cheap turntable in my country. There are splitted in two categories:

A) The cheapest and the worst stereo systems which includes radio, usb, aux and a phono with toxic plastic chasis and mechanics and of course a ceramic cartridge. The entire mechanics of plastics if is touched moves arround, is not fixed strong. Even the platter is made of plastic without having a slipmate. Most of the models have 33,45 and 78rpm but the speed isn't fixed properly. These cost about up to 90-100$

B) The other cheap turntables cost a little bit more than 100$ and are from Pioneer or Sony or Denon or maranz. I saw the same design of maranz and Denon and only brand makes the difference. I want to add that :
- the counterweight is fixed (a metal piece) and maybe the cartridge as shown is an AT91
- they are belt drive but with a width belt rolled by a tape motor with two speeds, not with a special cone with two diameters placed on the AC motor axis and the belt driven only by a fork on differents diameters like those TESLA / UNITRA models
- the platter is not from plastic, but from a cheap alluminium, placed very low to the bottom of the turntable with a high balanced and not a massive platter put on a drum like again other good vintage turntables which had a role of calibrating the speed if some line (110-220V) differences would occur
- there is a torture puting the belt between the motor axis and the fixed soldered drum of the platter. you have to be very careful when you move the fingers
- I didn't even see an antiskate adj on them

Personally I have two TT with different technologies TESLA NC430 belt driven, AC motor with a cone on the motor axis, full stop or manual, arm lift, antiskate adj, massive platter on the drum, Kenwood KD 44R direct dive, DC motor, full stop automatic return, arm lift, antiskate adj, massive platter, quartz locked.

Have a look here: **broken link removed** and here: https://www.flanco.ro/tv-electronice-foto/audio-hi-fi/pick-up.html

 

[Audioguru]

I have a Shure V-15 cartridge from the '60ies on a Dual (German?) automatic turntable. It does not change discs, instead it has simple automatic start and stop.
It still plays fine (click, pop, click, pop).

 

[c_mitra]

I have a Shure V-15 cartridge from the '60ies .

They are the Saks fifth Avenue of Sound Snobbery!!

 

[Audioguru]

Each year a new Shure cartridge came out my friend bought it and gave me his slightly used one.