M20 Dual Mono Pre-Ampliﬁer

User Guide1

V1.00 4/2020

M20 True Balanced Dual Mono Pre-Ampliﬁer
Design Criteria
The M20 is a fully diﬀerenBal dual mono preamp. It features 3 inputs; 2 balanced and one unbalanced,
and 3 outputs; 2 balanced and 1 unbalanced.
Each input path has a separate input buﬀer circuit for complete isolaBon between the balanced andunbalanced sources and to allow for diﬀerent gain of each input type. The input stage buﬀers featurehigh speed low noise fast seLling Analog Devices operaBonal amps.
The aLenuator is a discreet ladder of resistors digitally controlled with 60 resistors per phase, followedby very high slew rate fast seLling Analog Devices op-amps in the aLenuator output stage buﬀers, theﬁnal output buﬀers are a proprietary discreet design. Vishay foil resistors are used in key locaBons in
the circuit; we ﬁnd them to have a unique sound so we employed them to impart a tonal character tothe M20, and PCB material is made from ceramic materials with excellent dialecBc properBes. Levelcontrol is in 1db steps and is accomplished using a R2R ladder technique allowing for perfect balance andtonal character at any level with recall, programmable input oﬀset and remote control capabiliBes. All
signal switching and hard output mutes are done using logic controlled relays.
There are 3 separately buﬀered analog outputs, 2 balanced one unbalanced. The output buﬀers are ourown discreet design that is based on our other products like the M1, M12 and M21. With 3 separately
buﬀered outputs the M20 should be ideal for bi amp applicaBons with 2 balanced outs to drive 2 poweramps or running 2 or 3 zones.
The M20 powered by 3 linear power supplies, one for each of the analog secBons and separate supply
for the digital control circuit processor to insure isolaBon from the analog PCB and power supplies. So in
this way the M20 is a full Class A design.
The M20 has a modest amount of gain of 3db, we felt that most sources have enough level and the
majority of the applicaBon for a product like this and modern power amps have high impedance inputsand do no present a load to the outputs.
The M20 comes complete with SBllpoints isolator feet, is available in our Classic ﬁnish of anodized blackand clear aluminum or in the PlaBnum Series with chrome front and brass ﬁYngs.

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Opera<onal Guide
Input:

Selects one of the 3 inputs. # 1 and 2 are balanced and # 3 is the RCA.
Naming the inputs:
The inputs can be renamed by pressing a long press on the input key on the front panel. This willbring up a menu you can scroll through with some common names, M1, M21, M3, phono, CD,
DAC. Once you have found one you like press the Input key again and it will set the name forthat input.
Level oﬀset adjustment:
Pressing a second long press on the input key ( 2 long presses ) that is selected will allow for
seYng a trim oﬀset for that input to match it to other inputs, a^er seYng the level diﬀerence +or – in db. press input to set and return to input select mode.

Status:In this menu you can change the display brightness, view version and temp monitor.

Level:
This is for seYng the level of the main output aLenuator of 90db in 1 db steps from 0 to-89 db. This will be recalled to the last given state when power is cycled on/oﬀ.
Balance:Le^ or Right aLenuaBon oﬀset. Each change is in .5db steps

Reference:

For seYng a favorite preset level of the main aLenuator for reference use.

Mute:

Overall mute to all outputs.

Tigger out:
The trigger out mini jack on the rear can be connected to the our power amps like theM28s or DACs like the M21 to send a 5V DC voltage trigger to power them in and out of standby frompower oﬀ or standby on the M20.
Remote:The M20 is supplied with an IR remote that controls all normal funcBons of the M20.
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Specs
THD+N :Max input level:
Max out level:
Input impedance:
Crosstalk:
Trigger out:
ALenuator:

0.0007% 20-20k typical+20 dbu
Balanced+23 dbu
Balanced+16 dbu
Unbalanced
200k ohm> 120db
TRS mini jack, 5V ring, ground Bp
90 db in 1 db steps from 0 to -89db.

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