AVD Audio MP312-4 User manual

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Assembly Manual
MP312-4 Four Channels Mic Preamp.
Hello DIY lovers!
Thanks for choosing AVDAUDIO!
We are proud to introduce our new MP312-4 Four Channels Mic Preamp.
This unit was made based on vintage API312 version preamp.
Unit has four independent channels. Each channel has:
input gain and output attenuator
phantom power supply bottom +48v
-20Db pad input gain bottom
phase reverse bottom
mute bottom
The box is with external power supply.
If you had bought this DIY Kit, hope this manual help you to complete this
unit. And we hope it will be easy to build and will give you pleasure!
We wish you happy DIY moments with this kit and please contact us at
[email protected] if you have any questions.
Let's start this build!

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
•Descriptions and material for building.
The MP312-4 DIY kit contains:
•Metal case with front panel and power supply case.
•PCBs (Main PCB and power supply boards)
•Power transformer (115V or 230V included)
•Four variable potentiometers for preamp gain
•Four T-Pad 600ohm attenuators
All parts are marked on PCB. This includes two markings –NAME and VALUE.
These parts can be found in the BOM here download MP312-4 BOM>>>
Or follow this link: http://www.avdaudio.com/files/boms/BOM3124.pdf
What you will need for build:
•soldering station
•basic understanding of components
•DIGITAL MULTIMETER to check VALUE of capacitors and
resistors.
•You can also use a table with resistor color codes, which
can be found here: resistor color code information>>>>
Or copy this link: http://www.resistorguide.com/resistor-color-code/
All capacitors (electrolytic, ceramic) are clearly labeled, but you may also check these
values with a digital MULTIMETER!
Electrolytic capacitor:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Ceramic capacitor:
IMPORTANT!
To avoid any mistakes after the order of the components check each component by
multimeter! Make sure that it corresponds to the nominal value indicated on the PCB
and place them on a blank sheet with the measured values. Want to remind to you:
•Resistors are not polarized elements
•All diodes are directional! Make sure you insert them in the correct direction.
•Film capacitors are polarized elements
•But ceramic capacitors are not polarized
Remember please!
Unit has four same channels. We will build this, based only on the one channel. Others
channels be assembled by the same way. But other important steps we will show
separately.
2) Second step we start to build preamp with main PCB.
All parts you need for this board you can find in the BOM. Marked “Preamp parts”
Here is a picture of Preamp PCB:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Preamp PCB has four same channels. All channels are identical. Manual shows building
of one channel only. Build other channels by the same way. Others important moment
will show you separately.
Let’s start main PCB!
Solder all resistors and diodes.
Each channel has one diode 1N4004 and eleven resistors. Next nominal of resistors you
can use per channel: 160R, 200R, 510R, two of 750R, 5K1, two of 6K98, 10K, 20K, 150K.
Do the same on each other channels!
In the end of this step you must solder two diodes 1N4004 on the power side of the
board! You can soldering two power capacitor (100uf/50v) this step as well. Or soldering
as we do it after! But it helps you to do this easily now!

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Don’t forget about one 10K resistor. It is on the right side of board for power led diode!
Find three different ceramic capacitors on the each channel: 120pf, 220pf and two ps of
1000pf. Each capacitor is marked:
120pf capacitors are marked as:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
220pf capacitors are marked as:
1000pf capacitors are marked as:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Placed each capacitor and solder these:
1000pf capacitor is (two ps):

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
220pf and 120pf capacitors are placed:
Place 4 pushbuttons per each channel on the board:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
To be sure before solder! Push button placed directly on the PCB. Must not have any
distance from PCB!
Turn up board and solder each push button. You can solder at first only one leg of each
pushbutton. Try to press switch to pin on PCB. Then check you have all switches directly
on PCB. And solder other legs.

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Do not recommend cut push button’s legs.
For DOA we use HARWIN sockets.

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
You need one completed DOA. Insert sockets to DOA as I show below:
To be sure all sockets are installed fully on DOA!
Install this to PCB.

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Pull the sockets on 1mm from PCB.
Solder only one leg first! Then solder on the other side. Solder the three far legs. Then
solder the rest. Or do as we do below:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Check our result from other side.
Ready to do to next step!
Find four T-Pads and four Gain potentiometers:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Install each T-Pad to T-Pad’s place on the board marked T-Pad:
Place the potentiometer directly on the PCB!

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Check again the distance from PCB. We must have not any distance!
Go to the down side and solder T-Pads.
Solder first only one leg. During soldering push T-pad. Then you solder other legs. We
are not recommend to cut this legs after.

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Check you are done right.
And all T-Pads are on the board:
Hope you have done this step good!

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
And we are ready to go the next step.
Take four Gain potentiometers. This one must to be placed directly on PCB too.
Look to the next picture and start solder Gain potentiometers.
Install Gain potentiometer to their place marked GAIN:
Check please the potentiometer is directly on the PCB and solder this:

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
Break off the locking pin on all potentiometers and T-pads!
You need 9ps from 14 black screws. This screws are in the ordered package.
Tighten all bolts on back wall and bottom cover.

FOUR CHANNELS MIC PREAMP MP312-4
©2019 WWW.AVDAUDIO.COM
How to looks the case with installed bottom cover:
The bottom cover has 7 standoffs for PCB. Near future will install PCB to these places.