Tube Preamplifier With Expander

Our answer to Loudness Wars.

As many of you noticed, in many cases there appear unconvenient listening feeling about overwhelming compression of dynamic range related mostly to those modern recordings, causing the music to sound like a "sausage". Compressing natural dynamics out, therefore making music sounding "flat", is for some reasons believed to make the music to sound "better", but actually and sadly it will kill a lot of liveliness out from recorded music.
This phenomena of heavily compressed audio is caused by some reasons, like masking faults in digital recording techniques, hoping to get recordings play more decently in lower level systems and in the end there stand demand from music production marketing departments, who consider such a dynamically compressed "better sounding" music, without natural Piano's and Forte's, is easier to sell.
It's not rare when dynamics of modern digital recordings may be compressed as hard as into 4 dB dynamic range window only! Here is appropriate to remind that a full symphonic orchestra can have a 120 dB of dynamic range in live performance. And even those real analog LP-records can produce about 30 dB dynamic range and good digital recordings even more, but producers in many cases do not utilize these possibilities for reasons ment before.

So in here steps a device named expander, in other words widener of dynamics.

Expander is mostly known from recording studio devices, being not common in High-End home audio yet. Positive effect of expandering audio signal appear as it widdens the dynamic range, restoring the naturality of live performance to recorded music - making vocals closer as performed by a living person and instruments to sound more natural. Principle of expander is to make a loud part of signal more louder, while lower level signals remain unchanged. Expander does not affect audio signals below 300 Hz as these do not need in expandering. In this pre-amp the expandering level is adjustable by user demand.
Integrated with classical fully-tube pre-amplifier this expander is also tube-based and no solid-state components included in signal path. Audio signal handling is all analog ofcourse.
Those nice "Magic Eye" tubes give a visual hint about ongoing expandering level and help to adjust the "Angel Wings" touch amount just right.
Output Volume adjustment is a big handy knob and it is also IR-remote controlled.
There is five inputs available to connect different line-level audio source devices to this pre-amplifier.
The Gain setting give a control about input sensitivity of the pre-amplifier. Both Gain and Expander settings are independent.
All power supplies are stabilized to minimize interferences.

Parameters:
Frequency band: 20 Hz - 20 kHz
Inputs: 5x RCA
Outputs: 1x RCA
Input signal level: 250 mV...2V
Output signal level: 1V...2V
Input impedance: 50 kOhm
Output impedance: 100 Ohm
Amplifying factor: max 6
Amplification is adjustable with Gain button
Expandering is adjustable up to +10 dB (300 Hz - 20000 Hz)
All potentiometers: Alps RK27 series
Output signal is adjustable manually or by IR remote control
Input commutation: by relays
Input indication: NIXIE numeric
Tubes: 7 tubes (6Н2П, EBC81, EM80), 1 NIXIE (ИН-12)

February 2022