DESIGNED AND HAND CRAFTED BY MR LABS

BASED ON SWISS PRECISION ENGINEERING

Technical Specifications for VERA Phono Amplifiers

Design Topology Overviews and Technical Specifications

Design Topology Overviews and Complete Technical Specifications for the VERA 10 and VERA 20 Phone Preamplifiers by MR LABS...

VERA 10 Design Topology

The VERA 10 is a three stage design, comprising

  • Active Input Stage
  • Passive Equalization Network
  • Amplifier Stage

The active input stage is designed as a floating balanced complementary current amplifier/voltage converter. In this design, a current flowing between the positive and the negative input terminal is amplified and converted into an proportional output voltage. Specifically, a current in the region of 20µA to 60µA@1khz, as it is typically supplied by a moving coil cartridge connected to the input terminals of the input stage, results in a voltage at the output of the input stage of typically 60 to 180mV@1khz.

Following the input stage, a passive frequency equalization network is provided, yielding the three time constants 3180µs, 318µs and 75µs as required for proper equalization of the RIAA recording curve. It is understood that only the highest quality components are used for this passive network, particularly WIMA film-foil polypropylene capacitors and Vishay CMF precision metal film resistors with excellent high frequency characteristics, exceptionally low noise and low temperature coefficient. Each set of capacitors and resistors of each channel of the VERA 10 phono preamplifier is individually matched to ensure that the specified accuracy of RIAA equalization is met or exceeded.

The equalized signal is fed to the input of the amplifier stage. It has the topology of a discrete fully complementary operational amplifier operated in pure class A, having an open loop gain of around 70db, a unity gain frequency response of >1MHz and an output impedance of <2Ω. The closed loop gain of this stage is user-selectable in five steps. Due to the use of highest grade components and careful manual matching of parts, the behavior of this stage comes very close to an ideal operational amplifier.

VERA 20 Design Topology

The VERA 20 is a five stage design, comprising

  • Active Input Stage
  • Passive Treble Equalization Network
  • First Amplifier Stage
  • Passive Bass Equalization Network
  • Second Amplifier Stage

The active input stage is identical to the one of the VERA 10

Following the input stage, a passive frequency equalization network is provided, yielding the proper treble equalization of the RIAA recording curve. Also in this case, only the highest quality components are used for this passive network, particularly AudioCap Theta polypropylene film and tin foil capacitors and Vishay CMF precision metal film resistors with excellent high frequency characteristics, exceptionally low noise and low temperature coefficient. Each set of capacitors and resistors of each channel of the VERA 20 phono preamplifier is individually matched to ensure that the specified accuracy of RIAA equalization is met or exceeded.

The equalized signal is fed to the input of the first amplifier stage. It has the topology of a discrete fully complementary operational amplifier operated in pure class A, having an open loop gain of around 70db, a unity gain frequency response of >1MHz and an output impedance of <2Ω. The closed loop gain of this stage is user-selectable in five steps. Due to the use of highest grade components and careful manual matching of parts, the behavior of this stage comes very close to an ideal operational amplifier.

A further passive bass equalization stage follows the first amplifier stage. The same is true regarding the components quality and the matching as is outlined in connection with the treble equalization network herein above.

Finally, a second amplifier stage follows the bass equalization network with the same characteristics as the first amplifier stage, except the gain is fixed.

Technical Specifications

INPUT Fully Balanced, Floating (LEMO or XLR Socket)
INPUT IMPEDANCE Dynamic, Cartridge Dependent (Note 1)
GAIN VERA 10: Input Stage: 70db I/V Transfer Ration (Standard Module, Note 2) First Amplifier Stage: 23dB to 43dB, User Selectable in 5 Steps
VERA 20: Input Stage: 70db I/V Transfer Ration (Standard Module, Note 2) First Amplifier Stage: 23dB to 39dB, User Selectable in 5 Steps Second Amplifier Stage: 20db
OUTPUT Single Ended, VAMPIRE RCA Socket
RIAA DEVIATION < ±0.2dB (20 to 20kHz), < ±0.3dB (10 to 50kHz)
THD @ 1kHz <0.002% @ 1V Output
IMD (19kHz+20kHz) <0.005% @ 1V Output
S/N RATIO >100dB @ 1V Output (A-weighted)
  >80dB @ 1V Output (10 to 50kHz, linear, unweighted
HEADROOM >20dB from 20Hz to 20kHz
DIMENSIONS VERA 10: ca. 6¼" wide x 1¼" high x 6½" deep (Note 3) VERA 20: ca. 6¼" wide x 1¼" high x 9½" deep (Note 3)
VERA 10 Power Supply: ca. 6½" wide x 2" high x 8½" deep VERA 20 Power Supply: ca. 6½" wide x 2" high x 10½" deep
WEIGHT VERA 10: ca. 1.9 lbs. VERA 20: ca. 1.9 lbs.
  VERA 10 Power Supply: ca. 3.7 lbs. VERA 20 Power Supply: ca. 5.8 lbs.
Note 1 No cartridge load resistor required
Note 2   A high gain (76db) first stage module for very low output current cartridges and a low gain (64db) first stage module for very high output current cartridges are available as an option.
Note 3 Height of fixed input socket carrier: standard ca. 4", other lengths on request Height of flexible input socket carrier: standard ca. 5.5", other lengths on request