Tuesday, May 31, 2011

Old World Audio U33A Vari-Mu

The U33A tube compressor from Old World Audio "is a cross between an Altec 436, EMI RS124, Universal Audio175B and a Fairchild 670. Running channel A into channel B will yield some very interesting pumping and breathing effects". In Stereo mode it works exceptionally well on the 2-buss of a mix.
The controls consist of INPUT LEVEL, OUTPUT LEVEL, THRESHOLD, RELEASE and ATTACK. The threshold determines the compression ratio (turning the threshold clockwise increases the compression ratio). There are also VU MODE and MONO-STEREO switches.
The VU MODE selects between BAL which shows the relative balance of the tubes (nice feature). Normal operation shows no reading. A negative or positive reading implies tube replacement or re-balancing. COMPRESS shows the amount of gain reduction and OUTPUT shows the output level of the unit.
In stereo link mode only the ATTACK and RELEASE are linked (CH A controls are used. CH B is inactive). A 1k test tone is highly recommended to set the INPUT, OUTPUT and THRESHOLD controls so as not to alter your stereo image and balance.

Frequency Response +0/-1 dB 10 Hz- 50 kHz.
Distortion @1 kHz 0.04% +10 Output Level.
Noise A Weighted -90 dB ref from +10 dB Output Level
Maximum Gain 30 dB
Attack Time (variable) 200 microseconds to 47 milliseconds (charging time)
Release Time (variable) 0.08- 1.5 seconds
Compression Ratio Variable 0 to 16:1 typ.
Input Impedance 1 K Transformer Balanced.
Output Impedance 600 Ohms Transformer Balanced.
Output Attenuator range 20 dB
Maximum Output +26 dBu into 600 Ohm load.
Supply voltage 110-130 Volta Ac, 50-60 Hz 60 VA.
Fuse 1 Amp, Time Delay, 5x20 mm.
Size 19” W x 7” (4U) x 14.5” D

The U33A is completely hand built and made to order,

$3450 at
Old World Audio.

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