After assembling your α24 boards, follow the procedure below
to make sure that they are functioning properly.
If, at any point you do not pass a check, do not proceed to the next
step until the problem is first corrected.
Perform this procedure one α24 board at a time.
Make sure your regulated power supply is producing the correct
output voltage. The recommended range is between ±8V and ±12V.
Turn off the power supply and let all its capacitors discharge completely.
Do not connect the power supply, input and outputs to the α24
board until the procedure calls for it.
Basic sanity check
- Do a visual once-over to make sure the correct part is
installed in each location. Check that the opamps and
the organic/conductive polymer capacitors are
mounted in the proper orientation. Inspect
all solder joints to make sure they are shiny and smooth.
If in doubt, reflow any that doesn't look good.
- With your multimeter set to Ohms mode (use the lowest resistance
range on a manual-ranging meter), check for short circuits between the
points listed below. If you read less than a few Ohms for any of these,
then there is a short circuit. Carefully locate the short (such as a
solder bridge) and fix it.
Use the J4 connector for these measurements. If you used Phoenix
Contact MPT connectors, turn the screws fully clockwise and use the
screw tops as the test points.
- V+ and G
- V- and G
- V+ and V-
DC offset check
- Install a temporary wire jumper across IN+ and IN- at J1.
- Connect the power supply to the α24 board, making sure
not to mix up the V+, G and V- wires.
- Turn on the power.
- With your multimeter set to DC mV mode, check the voltage
between the following points listed below.
Use the J2 connector for the first three measurements, and J3 for
the fourth. If you used Phoenix Contact MPT connectors, turn
the screws fully clockwise and use the screw tops as the test points.
All of these should read less than a few mV DC (preferably less
- OUT+ and G
- OUT- and G
- OUT+ and OUT-
- OUT and G
- Keep the power turned on.
- Keep the wire jumper (installed in the previous step) in place on J1.
- Set your multimeter to AC mV mode and make the same measurements
as in the DC offset check above. You meter should display a very
low value mV AC (less than 0.1mV AC, or zero).
Repeat the above procedure for any additional boards. If this
is the last board, then proceed with finishing up below.
- Turn off the power.
- Remove the temporary wire jumper from J1.
- Connect the proper inputs and outputs.
- Hook it up to your system and enjoy the music!
- Be sure your input source(s) do not have significant DC offset
at their outputs. The α24 has no coupling capacitors
and such DC offset will be amplified by the gain and appear at
the output. For balanced input, a common mode DC offset
(i.e., same DC offset voltage on IN+ and IN-, relative to G)
- If you are going to be moving the board, desolder parts or otherwise
work on the board after turning off the power, be sure to wait a
moment to allow the capacitors to discharge.
Stored charge in the capacitors could damage parts if board
traces are short-circuited to each other by
contacting other tools, objects or the soldering iron.
- If a SMD chip becomes defective and must be replaced, and if
you don't have specialized reworking equipment, the recommended
method is to use
Chip Quik® SMD removal kit.
Their website has instructions on how to use it. Chip Quik is
available directly from the manufacturer, as well as from
Digi-Key (part number SMD1-ND).
If you don't have Chip Quik, use a sharp knife to cut the leads
off the bad chip near the chip body. Take care not to
score the board. Then, remove the chip from the board.
Heat each solder pad with your soldering iron and scrape away
the residual pin. Then, remove any excess solder using your
iron and a desoldering braid. Be careful with the iron so
you don't melt any surrounding parts. If you are trying to
remove U2 and have polypropylene film capacitors around it,
you may find it easier to remove one or more of these capacitors
first to get better access to the opamp pins. Also, don't heat
the board for prolonged periods of time to avoid delamination.
Soldering in the new chip will be just like the first time.
You need to be careful not to touch the other parts already in
place with your iron.
Main: α24 Main |
Prev: Wiring & ground |