This is a printed circuit board suitable for building a single channel moving coil / moving magnet RIAA phono preamp to the classic JLH (John Linsley-Hood) K1450 design.
The circuit board design is Copyright © 2020 Robert Jenkins. The preamplifier schematic design is absolutely the property of John Linsley-Hood.
In my opinion it is the best of the classic designs, but as far as I have been able to find, the people or businesses previously making suitable PCBs for the K1450 have all ceased trading and no other source of boards is available.
Especially with the revival of interest in LPs or "vinyl" it seems a great shame that this superb design is not available in an easy to build form, and this project it intended to correct that omission.
These are a totally original artwork, created to suit the published circuit and with no reference to any other PCB version.
They are plated through hole PCBs with a top side ground plane and built to take the best practical components: 1% Polystyrene capacitors are used where appropriate, with polyester film for larger values, or low ESR electrolytics in high value locations. The resistor lead spacing is 0.4", suitable for MRS25 or similar metal film resistors.
The schematic and specifications are taken from Paul Kemble's page, here: paulkemble_sound3
Specifications, as given for the JLH design; I make no claims re. these, other than they do appear to be excellent when built on my PCBs (See below for audio samples):
Moving coil (mc) or moving magnet (mm) input - link selectable.
Frequency response: +/- 0.25bD to RIAA curve.
Signal to noise ratio: 26dB below record surface noise.
Sensitivity (for 500mV output): 37mV (mm), 340pV (mc).
Input impedance: 47K Ohms (mm), 100 Ohms (mc).
Gain: 134 (mm), 1460 (mc).
Overload: 670mV (mm), 60mV (mc).
Two jumper link points J1 and J2 are included in the board; left unconnected they are as the "mm" (moving magnet) configuration, with wire links fitted to close the jumpers they are in the "mc" (moving coil) configuration.
Bare PCBs are £14.99 each plus postage (£2.99 presently, for two PCB sent to an address in the UK.) A full parts list with suggested sources will be included with each purchase.
Note that each PCB is for a single channel; two are needed for a stereo preamp.
For order enquiries or postage / shipping costs, email audioparts (at) robertjenkins.co.uk
These can be supplied built and tested, to order. The price including all components and assembly would be £179.00 each, or £350 for a stereo pair (plus postage at cost). Note these would be built but uncased circuit boards, requiring a 15-0-15V power supply, enclosure, wiring, connectors etc.
Complete cased ready-to-use preamplifiers could be an option, at additional cost.
A suitable 15-0-15V power supply board is presently being tested and should be available in the next few days. It is designed to be able to function from either a transformer for AC supply, or appropriate batteries for absolute avoidance of possible interference.
Completed preamp PCBs look similar to the prototypes on test in the photo below; the final boards have one additional capacitor changed to a polystyrene type and some minor changes to text etc. Also all later prototypes (and any ordered) us the larger diameter electrolytics throughout.
Audio examples recorded using the prototype setup in the photo above
These were made using a JVC L-E22 linear tracking turntable with its original JVC cartridge and a new Audio-Technica elliptical stylus.
The preamps are fed in to a Focusrite Scarlett 2i2, using 24 bit samples at 96KHz sample rate, with the levels adjusted to just below clipping and then unchanged for all LPs. The files below are unmodified in any way other than trimming the fragment lengths.
Other than the turntable, all items were battery powered to minimise external interference or hum loops.
(And please note that all the discs are my original 70s - 80s ones, which have had a lot of use and are not all in particularly good condition; the preamps are not to blame for the clicks and scratches!)
The example fragments are provided as technical examples and are no more than around 10-15 seconds each, in respect of the copyright holders rights.
Credits: Artists, album and publisher for each of the original tracks that the fragments are taken from are given below. All copyrights fully acknowledged.
These files are 96K 24 bit stereo FLAC format. If you have difficulty playing them, try VLC.
Sample 1: From Queen - Keep Yourself Alive; BBC Old Grey Whistle Test performance compilation album. BBC BELP004, © 1973
Sample 2: From Black Sabbath - Evil Woman; Black Sabbath - Black Sabbath album. Vertigo WMA 006, © 1970
Sample 3: From Jean Michel Jarre - Equinoxe Part 5; Equinoxe album. Polydor POLD 5007, © 1978
Sample 4: From Pink Floyd - One Of These Days; Meddle album. EMI Harvest SHVL 795, © 1971
Sample 5: From Pink Floyd - One Of These Days; Meddle album. EMI Harvest SHVL 795, © 1971
Sample 6: From New Order - Blue Monday; 12" Single version. B Music / Factory Records FAC 73, © 1983 [Recording gain reduced slightly for this extract as it's a higher level than the 33rpm LPs].
Sample 7: From Deep Purple - Child In Time; from Made In Japan album. Deep Purple Overseas Ltd / EMI TPSP 351, © 1972
Sample zero - noise level test: setup and gain etc unchanged from the album tests above, but the stylus lifted from the disc. There is noise present, but it is at a low level and not obvious unless the file gain is boosted: