This Audio Alto’s compact series reflects maximum effort and knowledge, as it presents quite a different solution with its built-in electronic tubes as voltage amplifiers. Result of design and construction is its acoustic-inertial and elegant shape.
The AA DMI 3H is designed as dual mono amplifier and with modularly designed enables an insertion of different input modules (Phono RIAA MM etc). AA DMI 3H power supply is realized with two150VA toroid transformer with a static screen winding and magnetic screen that provides power to each set of the amplifier individually. Heating of electronic tubes is regulated and is time-controlled for optimum operation and for achieving their life expectancy of over 5.000 hours. Power supply voltage for tubes is time delayed and regulated.
All the internal voltage amplifier stages work in Class A mode of operation. The input stages are realized with low noise low distortion circuits and are also working in class A mode. The voltage amplification is realized with a double triode vacuum tube configured in CCDA (Constant Current Draw Amplifier) single ended topology to eliminate the supply voltage fluctuations due to audio signal changes. The selected tube 6922 or E88CC (NOS 6DJ8) are among the best audio triodes providing low input capacity, high standby current, low output impedance and very low distortion levels even without negative feedback. The tube glass is dumped with a special silicone ring.
A complementary MOSFET output transistor transforms the CCDA output with output impedance of few hundreds of ohms to low impedance (high current) output required by speakers. The output transistors are biased with an innovative dedicated circuit that keeps both output transistors biased during the whole signal phase (360°) reducing the low power related distortions (no typical class A/B turn off that is the cause of unpleasing crossover distortion).The circuit significantly reduces the distortion caused by the effects of nonlinear transconductance in the output transistors resulting in a sound almost identical as it would be produced with an pure class A output stage.
AA DMI 3H is handmade and all components are tested prior to installation.
The voltage and current amplifiers work without any negative feedback loop!
|Inputs||I2 – RCA 220Kohm, 500 mVeff sensitivity (line input), Noise -95dB
I3 – RCA 220Kohm, 200 mVeff sensitivity (line input), Noise -95dB
Tape in – RCA 220Kohm, 200 mVeff sensitivity (line input), Noise -95dB
|Output||Tape out – RCA, 200 mVeff
Headphone – 0.9 Veff @ 32 Ohms
7,5Veff @ 600 Ohms
4 x Speakers posts 4 mm
|Gain||30 dB (70 dB Phono MM)|
|Output Power||Model A:
2 x 30W @ 8 Ohm
2 x 50W @ 4 Ohm
2 x 60W @ 8 Ohm
2 x 100W @ 4 Ohm
|Frequency response||5Hz to 60.000Hz -1dB|
|Vaccum tubes||2 x 6922 (E88CC or NOS 6DJ8)|
|Dimensions (W x D x H)||295 x 465 x 93 mm|
|Finish||Dark Shadow, Silver, Inox, Chrome, natural solid wood (i.e. walnut) or upon special order in various colors|
High Fidelity review – Link
Positive Feedback review – Link