Hi Renzo,
Thank you for your comments about the GK-1MP. I'm thrilled that you, along with Mal and Mark, feel the phono is very good, as I spent more time in the pcb design than the circuit design!
This is in contrast to most of my work, where the many choices of topology, component and operating points consume huge time, much of it in cafes drinking strong coffee and idling watching the girls walk by........ (I call this 'Bistromathics', the complex study of the relationships between the number in the party, the size of the bill, the time of day and the identity of the one who finally pays the bill!
)
Phono design offers more flexibility than almost any other area of hifi. This makes it very interesting, but it is a huge challenge to keep costs down. The tube pres are quite complex, as they must use cascaded tube stages to achieve the necessary voltage amplification. The big complications with tubes are noise, filament hum, and capacitive coupling, which is critical. It is also true that too many tubes can adversely 'round' the sound. Many designs use interstage transformers, but they have their problems and are very expensive. I like tubes, but like fine food (particularly chocolate, my weakness!), they must be used sparingly.
Since I was using a tube in the output stage of the preamp, I reasoned that we already had the marvellous tube sonics, so the emphasis should be on low noise and moderate price. This led to an IC design, fairly conventional, but with considerable effort put into the choice of IC (trade secret!), the power supply topologies, and dimensioning the RIAA/feedback network. While I worked hard to enhance the focus, soundstaging and good bass, the way in which it deals with the troublesome clicks and plops which is a fact of life with vinyl was just good luck, so I can't really claim credit for that!
Earthing is always a big issue with very small voltage inputs, and is greatly exacerbated when the Zout of the voltage source, the cartridge, is high. My suggestion would be to run an earth wire from the body of the turntable, including the arm (which is likely electrically connected to the T/T anyway) right through to the 0V connection on the phono section. This will ensure that all earths and shields are on the same page, and will prevent tiny circulating earth currents from creating noise and hum.
Renzo, did I include the extender bar for the source selector in the kit? If not, let me know, and any other GK-1 owners who may not have it yet, since I have not had them long and am now ready to ship them out.
I would be very interested to hear your comments after you have played your entire collection, Renzo! Thank you for your post,
Ciao,
Hugh
