Phono audio tube preamplifier with R.I.A.A. passive correction
for turntable's MC cartridge with 4 x ECC83 ( 12AX7 )
Metal work
LM317 regulated PSU (1A - 12.60V for filaments)
Filaments test (DC voltages insulated, no ground common connection)
Preamplifier progress
Sound test
The "hum" and ground noise was not totally erased from preamplifier to audio sound test
so project will continue
- capacitors added across the diodes in the rectifier bridge for filament's PSU.
- tube's sockets was grounded in short
- new capacitor added in the anode PSU (anode voltage PSU - 300Vdc unregulated)
to new audio sound test the result was better, I can not go up to 1/3 volume's limit because ... hum and ground
noise still there (especially al low level and most of all in the pause between melodies)
so project will continue
With 2 trafos have not good results so I put a new one with technical specification:
Secondary : 1 x 16V / 1A
1 x 240V / 0,1A
New capacitors added :
- on the anode high voltages (final value = 300Vcc)
- on the filaments pins
- on the every stage
but the hum... still there...and out of idea (for the moment)
Sound fantastic but only at low level, even if I use a mixer, the hum it's there.
Update 10.12.2016
I understand that the problem it's not from the RIAA preamplifier so I extended my "search" to my turntable.
modified turntable
new setup
passive DI (direct imported) added
and now no more hum, no more ground noise.
All quiet and have in the output the best bass ever
Tested in club with 3 way active crossover and:
2400 W on low/1300W on mid/600W on high
sound fantastic.