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Projecttitel: MOTM 830 Mixer

STATUS finished

Startdate: 25.11.2013

Duedate: 15.12.2013

Manufacture link:

further links:

About the module ( copy from synthtech)

The MOTM-830 is a dual mode (audio and/or control voltage) mixer. Using a clever switching scheme, the mixer can configure itself into either 6:1 or dual 3:1 mixers. The mixer is "split" when a patchcord is inserted into the OUT 2 jack.

The MOTM-830 is unique in the modular world: it is optimized for both audio signal quality and DC stability. Other mixers are generic, TL072-type mixers which are OK for audio but suffer from input offset voltage drift over temperature. The MOTM-830 uses special circuitry to provide superior audio specs (less than 0.005% THD, greater than 90dB SNR) while having superior DC specs (less than 1uV/C drift). Other features include:


  • Shielded cables on ALL signals
  • DC Bias generator: module can act as DC source!
  • Mixer #1 (IN1 - 3) uses linear pots, while Mixer #2 (IN4 - 6) uses audio taper pots
  • All pots are sealed, conductive plastic for long life and low noise

Easy to build, the MOTM-830 is a valuable addition to your MOTM system.

Userguide - Buildingguide

MOTM830 User's Guide.pdf


Increase Gain

Changed some resistors to get unity gain from any input to any output.

  1. Changed R8 and R17 from 44.2K to 100K (1%).
  2. Changed R18 from 100K to 49.9K (1%).








RARE Parts:

the Op285 was ordered from littlediode

pots from bridechamber and mouser

PCB, Panel, Bracket, pots from Bridechamber

Radial Electrolytic - tol:+/- 20%         
10μF,50V (this has poles)2MouserXicon140-XRL50V10-RC11$0,062$0,12
Axial Ceramic Caps         
.000022uF (= .022nF = 22pF)1MouserXicon147-75-220-RC11$0,271$0,27
.1uF (= 100nF = 100,000pF)7MouserXicon147-72-104-RC11$0,167$1,12
Caps Subtotal        $1,51
Project Subtotal        $1,51
Resistors - 1/4 W - 5% (unless resistors are specified as otherwise, assume they're 5% - Paul lists them as 5% - extra clear!) note: there is a price breakpoint on the 5% Rs that makes it super-cheap to buy 10 of them.  I always do and put the extras away for when we need them. 
1K ohm (2K2)2MouserXicon291-1K-RC11$0,101$0,10
10 K ohm3MouserXicon291-10K-RC11$0,104$0,40
44.2 K ohm (44K2) 1%2MouserXicon271-44.2K-RC11$0,131$0,13
49.9 K ohm (49K9) 1%2MouserXicon271-49.9K-RC11$0,131$0,13
51K ohm1MouserXicon291-51K-RC11$0,101$0,10
100 K ohm 1%13MouserXicon271-100K-RC11$0,133$0,39
150 K ohm 1%1MouserXicon271-150K-RC11$0,133$0,39
Resistor Subtotal        $1,64
Project Subtotal        $3,15
TL072 dual op amp1MouserSTMicroelectronics595-TL072ACN11$0,951$0,95
OP285GP2Synth Tech these are very hard to find11$8,001$8,00
you may have to sustitute a OP275         
IC Subtotal        $8,95
Project Subtotal        $12,10
Axial Ferrite Beads2MouserFair-Rite623-274300211211$0,123$0,36
MTA .156" Connectors FRCTN LK HDR STR 4P Square post, tin1MouserTyco571-640445411$0,301$0,30
Toggle Switches SPDT on-none-on1MouserNKK633-M201202-RO11$4,501$4,50
Misc Subtotal        $0,66
Project Subtotal        $12,76
Pots / Trimmers         
Set of 100K log taper Spectrol 148 pot - this has 4 pots - these pots are very diffcult to find1Synth Tech  11$30,001$30,00
100K conductive plastic Spectrol 148 log pot3MouserVishay/Spectrolvery very hard to find11   
Set of 100K cermet Spectrol 149 pot - this has 2 pots and ends up being much less expensive than getting them from Mouser1Synth Tech  11$15,001$15,00
100K cermet Spectrol 149 pot1MouserVishay/Spectrol594-149-710411$12,97do the math! If you're doing another module, it pays to buy the set from Paul
Bourns 100K panel mount 95A pots3MouserBourns




Pots Subtotal        $69,24
Project Subtotal        $82,00
2 Conductor Closed Tip 1/4" jack (112A type)7MouserSwitchcraft
Closed tip Closed ring jack (114B type)1MouserSwitchcraft
lock washer8MouserVishay/Spectrol594-512-000811$0,138$1,00
Jacks Subtotal        $17,58
Project Subtotal        $99,58
Power Cable - 20"1Synth Tech  11$7,001$7,00
Wire Assortment1Synth Tech  11$8,001$8,00
Coax assortment1Synth Tech  11$9,001$9,00
OR you could buy a bunch of wire and do it yourself.       
Belden Hook-Up Wire - 22AWG, box of five 100foot spools, different colors MouserBelden CDT566-953111$134,68  
Belden Co-Axial Cable 100 foot spool -   RG174/U 26AWG BLACK MouserBelden CDT566-8216-10011$51,70  
Wire Subtotal        $24,00
Project Subtotal        $123,58
Large BR-1 mounting bracket1Synth Tech  11$8,001$8,00
#6-32 x 1/2 screws4MouserKeystone534-940911$0,084$0,32
1/4" al spacers4MouserKeystone534-39811$0,144$0,56
#6 KEPS nuts - these come in a bag of 10607-P1100$6,70  
count them individaully - here' how they add up:      $0,076$0,40
Tie Wraps9Mouser3M Electronic Specialty517-4193211$0,044$0,16
8 ALCO knobs - so look, if you'r only building this module, you can buy these guys at Mouser… but otherwise think about buying them from Paul - much less expensive1Synth Tech  11$16,001$16,00
knob - Alcoswitch7MouserTyco Electronics / Alcoswitch506-PKES90B1/411$3,33  
Hardware Subtotal        $25,44
Project Subtotal        $123,58
PCB / Panel         
MOTM-830 Mixer pc board1Synth Tech  11$39,001$39,00
MOTM-830 front panel1Synth Tech  11$39,001$39,00
PCB/Panel Subtotal        $78,00
Project Subtotal        $201,58
heat-shrink 1/8" - four foot length - you need this    602-221018-4BK11$1,50  


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