Standard package is 12AX7 + 12AY7 to get 47dB gain.
You can replace 12AY7 with 12AU7, 12AY7, 12AX7 to get 40, 51 or 56dB gain. See below for more information.
Pure Class-A all vacuum tube design with zero negative feedback
Compatible with 12AX7 + 12AU7/ 12AY7/ 12AT7/ 12AX7 for different gains and different sounds.
Premium Quality Parts
Premium power transformer to ensure high performance, low noise and high reliability,
Kiwame resistors at important postions
Obbligato premium film gold capacitors to improve tranparency and clarity
Why do we need adjustable gain? Phono cartridge manufactures produce their own specification with different cartridge’s output level and impedance.
How to make gain adjustable? Typical approaches usually sacrifice sound fidelity. (Note 1)
Therefore we use a different approach – adjusting gain level by changing tubes, therefore there’s no uncessary components that usually distort the sound.
May need another line preamplifier (with +10dB to +20dB gain)
12AU7: linear or well balance sound.
Popular NOS or old production are still easily accessible
12AX7 + 12AY7/6072A
Suitable for most MM cartridges
12AY7: very warm and smooth
12AX7 + 12AT7
Suitable for low output MM cartridges
fast dynamic sound with punchy bass
12AX7 + 12AX7
Suitable for ultra-low output MM cartridges and some MC high output cartridges of +1mV.
12AX7/ECC83 Telefunken is still available though hard to find
Zero Negative Feedback topology
Simple one way feed through circuit arrangement to preserve simplicity in design. By not aiming to lower the distortion with negative feedback we instead design the tube circuit to work into pure class-A and let this linear spot bring out the best no manipulating sound.
The harmonic distortion is less than 0.1% at 4mV input and distortion figure will reduce nicely in linear proportion to the input signal level.
Internal construction of this phono is very simple, elegant and carefully laid out for symmetrical signal between left and right channel.
19 x 26 x 10.5cm (W x D x H) *
* All specification are subject to change without prior notice.
Frequency Response according to RIAA standard
+/- 0.5dB from 20Hz to 20KHz
Total Harmonic Distortion with 4mV input signal
less than 0.1%
S/N ratio (SINAD 20mV input, 400Hz & 30KHz filter on)
+40dB to +56dB adjust by changing output tube (standard +47dB from 12AX7 + 12AY7)
All vacuum tube 2 x 12AX7 (input), 2 x 12AY7 (output)
R/C zero negative feedback type
Maximum input level
20mV from 20Hz to 20KHz
Note 1: Typical approaches usually sacrifice sound fidelity.
1) adjust negative feedback level. The higher dB in negative feedback, the lower the gain. This works like a dream, a nightmare dream. Not only it changes the gain, but it also change the output impedance, frequency response, harmonic distortion, phase shift etc, but because it only requires a few resistors (or trimmer pot) to implement, the cost saving is abundance, thus utilize in many phono stages nowadays.
2) attenuate the signal path of the circuit. This strategy is “Lazy Man” solution that works very much like first method but instead of intruding NFB circuit, it just like adding potentiometer to signal path. Dumping signal away from the next stage and add unwanted impedance into the signal path. Increasing signal impedance means increase noise, reduce bandwidth, reduce current drive.