Avalon Design VT 737 SP Class A Mic Preamp Overview
Class A Inst/Mic PreampThe VT-737SP has 3 input selections:
1. The VT-737SP features a higher-performance microphone input transformer with +48v phantom selection.
2. Instrument DI high source input with jack located on front panel.
3. Balanced line input, discrete high-level Class A.
The Class A preamplifier utilizes 2 cascaded, dual vacuum tube triodes configured with minimum negative feedback. A high gain switch boosts the overall gain of the preamplifier. The 4 high quality tubes are configured as singled ended anode coupled followers. A passive-variable high pass filter and hard-wire relay bypass completes the input signal conditioning. The phase reverse relay is available on all 3 inputs.
Opto-Compressor
The opto-compressor features a minimum signal path design with twin Class A vacuum tube triodes for gain matching. The optical attenuator acts as a simple passive level controller. Full dynamic control from soft compression to hard- knee limiting can be achieved with threshold, ratio-compression, attack, and release controls plus gain reduction selection on the large VU meter. Special spectral control including de-ess is available with the dual sweep mid EQ to side-chain switch. The EQ section can be flipped pre or post the opto-compressor via a front panel switch for alternate effects and tone shaping. Two VT-737SPs can be linked via a rear panel link cable for stereo tracking. The compressor bypass is a sealed silver relay for the most direct signal path.
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- Circuit topology
- 4 dual triode vacuum tubes (Sovtek 6922), high-voltage discrete Class A
- Gain Range
- Microphone: Transformer balanced 850/2500 ohm, 0dB to 58dB Instrument: Unbalanced 1 meg ohm, 0dB to 30dB Line: Balanced Class A 20k ohms, -27dB to 28dB
- Maximum input level and connector types
- Microphone26dB@25Hz, 30dB@1kHz balanced XLR Instrument 30dB unbalanced front panel jack socket, Line 36dB balanced XLR
- Maximum output level
- 30dB balanced 600 ohms, DC coupled, discrete Class A
- Output type and gain
- XLR connector, output trim gain -45dB to20dB
- Noise 20kHz unweighted
- -92dB
- Noise microphone EIN
- -116dB, 22Hz to 22kHz unweighted
- Distortion THD, IMD
- 0.5%
- Frequency response -/2.5dB
- 10Hz to 120kHz input filter included
- Frequency response -3dB
- 1Hz to 200kHz line in-out
- VU meter and gain reduction
- High quality illuminated OVU = 4dB and gain reduction to -20dB
- High cut filter
- Variable 6dB per octave 30Hz to 140Hz
- Compressor type
- Optical passive attenuator incorporating twin vacuum tubes and stereo link
- Threshold - Ratio
- Threshold variable -30dB to 20dB, ratio-compression variable 1:1 to 20:1
- Attack - Release
- Attack variable 2mS to 200mS, release variable 100mS to 5 seconds
- Equalizer type
- Discrete Class A, variable active and switched passive design
- Frequency bands (4)
- Treble - switched 10kHz, 15kHz, 20kHz, 32kHz, /- 20dB range, shelf High mid - variable 200Hz to 2k8Hz and 2kHz to 28kHz, /- 16dB range, hi-lo Q Low mid - variable 30Hz to 450Hz and 300Hz to 4k5Hz, /- 16dB range, hi-lo Q Bass - switched 15Hz, 30Hz, 60Hz, 150Hz, /- 24dB range, shelf
- AC power
- Internal toroidal 100v to 240v, 50-60Hz selectable, 75 watts maximum
- Dimensions
- 19 x 12 x 3.5 in (482 x 305 x 89mm)
- Weight
- 22 lbs (10 kg)
- Dimensions - Shipping Carton
- 21 x 18 x 8 in. (533 x 457 x 203mm)
- Weight - Packed
- 26 lbs (11.8 kg)
