ADC B100 Preamplifier

An obscure high end Mark Deneen design

If you have any information, marketing info, opinions, ads, etc., please forward. (jrw-at-thewayners-dot-org)

Design Highlights

100% Dual mono construction
Fully regulated hi-voltage supplies and heater supplies for each channel
Two Moving Magnet and Moving Coil (Jensen JE44K-DX transformer) phono inputs with separate tube sections
Variable phono load for capacitance and impedance matching (DIP switches) on Mag2 input
Cascode front end on phono stages and voltage gain stages, cathode follower outputs for low impedance, no loop feedback.
Low output impedence
Delayed startup
14 6DJ8 tubes

Selected Specifications
Moving Coil Input

Voltage gain: 19.7 dB
Frequency Response (re: 1kHz)
-.3 dB @ 20 Hz
-.02 dB @ 20 kHz
Phase response +2 degrees at 20 Hz, -10 degrees at 20 kHz
THD .065% @ 30 Hz, .03% @ 50 Hz, .006% @ 1Khz
Transformer Noise Figure 1.7 dB re: 36.1 ohms

Magnetic Input
Separate input stage for each phono input (3) with all cascode voltage amplifiers. Low impedance cathode follower output. No loop feedback.

38.6 dB Voltage Gain @ 1 kHz
Input Impedence: Phono 1 - 47K, Phono2 - Selectable
+/- .1 dB deviation from RIAA response curve (individually calibrated)
S/N greater than 70 dB below 10 mV input (unweighted)
Less than .1% THD @ 1 kHz at .5 volt output
Input Overload: 300 mV

Note: When fed through an accurate inverse RIAA network, the preamplifier will produce proper square waves without overshoot or ringing at any frequency between 20 Hz and 20 kHz.

High Level Amplifier
All cascode voltage amplifiers with interstage level controls. Low impedance cathode follower output. No loop feedback.

20 dB voltage gain
100 k ohm input impedance
20 Hz to 20 kHz +/- .2 dB Frequency response
Bandwidth: -3 dB @ 2 Hz, -3 dB @ 150 kHz
THD less than .1% from 20 Hz to 30 kHz @ 2 volt output
IM less than .1% SMPTE
S/N greater than 80 dB below 2 volt output

Power Supplies
Each channel has an independent transformer, high voltage, and filament supply.

Hi Voltage: Three transistor feedback regulator with zener diode reference. 150 uF local decoupling for each phono stage and 10 uF local decoupling for each high level stage giving a decoupling time constant of 1.5 second and .1 second respectively.
Filament Supply: 3 amp monolithic integrated circuit regulator
.1% load regulation

Device Complement

14 6DJ8 tubes
6 transistors
18 silicon diodes
2 zener diodes

Comments from the designer, Mark Deneen, on the Klipsch forums:
"I designed this in 1980 for the ADC division of BSR. They were introduced at the 1981 CES show in Las Vegas. When we got back ,we began a production run of about 200 units. I know for sure that perhaps 50 units were shipped to dealers." ... "If I recall the 1981 retail price was $1495."

I have listened to many of these preamps. It's a great sounding preamp and back in the early eighties was a worthy competitor for Audio Research and other premium tube gear. There are still a good number of these in the Milwaukee area. I suspect this is because a local high end audio dealer picked on them early and sold a bunch of them.

Here's a scan of a poor photocopy of the schematic. (Sorry, it's the best I have.)