Finally made a LM1875 amp

[BrianGT]

Testing Procedure once boards are assembled:
-first, make sure to wire up the fuse and AC terminals correctly. Test with a multimeter set on ACV to make sure that your switch works. Wire from the AC H terminal on the AC socket to a fuse holder, and then into a switch.
-connect the first wire of the transformer primary to the AC H connection on the power switch
-connect the second wire of the transformer primary to the AC N connection on the ac input terminal.
-connect the earth ground from the ac inlet to the main chassis ground
-for US or other 120v countries, if your transformer has dual primaries and is specified for either 115vac or 230vac, such as the Avel Lindberg common transformers, wire both the pairs of primary parallel with each other.

Here is a picture of the Avel Lindberg transformer wiring:


-For the Avel Lindberg transformer in the US, connect the Blue and Violet wires to the AC H connection on the switch, and the Gray and Brown wires to the AC N connection on the AC input terminal. For 230vac, connect the transformer primaries in series, as shown in the above image.
-Make sure to isolate the secondary wires from the transformer, and power up the amp to verify the voltages from the transformer secondary windings. If you have a 2x18vac transformer, you should now measure 18vac across each secondary (secondary 1 = black/red and secondary 2 = Orange/Yellow)
-power off the amp, and wire the secondary windings from the transformer into the AC1 and AC2 terminals on the power supply board. Here is a picture:


(AC1 = black, AC1(bar) = red, AC2 = orange, AC2(bar) = yellow)

-Wire one of the GND connections on the PSU board to the chassis ground.

-Once the transformer secondaries are connected to the PSU board along with the chassis ground connection, power up the amp to check the output DC voltages. Measuring from GND to V+ and from V- to GND should show ~25vdc if you are using a 2x18vac transformer.
-The LED on the PSU board should also be lit up, if installed correctly.
-Once the power supply voltages are verified, power the amp down, and wire up one amplifier board to the V+, V- and GND connections from the PSU board to the amp board.
-power up the amp again, and check the DC offset of the amplifier with the multimeter, by setting it to the minimum DC voltage setting, and measuring from OUT to OG. You should measure between 10-30mV, but under 100mV is acceptable.
-if all checks out, power down amp, and hook up the other channel and test it.
-once both channels are verified, connect the RCA input terminals to the IN and SG connections on the amp boards for both channels. Also connect the OUT and OG connections on the amp boards to the output terminals on the chassis.
-power the amp up again, and test the amp with a test speaker for both channels.
-Once all is verified, connect to your system and enjoy!

(note, this is a quick rough draft of the manual, and I will work this into a manual for putting together an LM1875. Let me know if you spot any issues, or have any comments)

--
Brian

[BrianGT]

Here is a picture of the wired up amplifier board:


Note: I would highly recommend using different colors for V+ and V-. For this amp, the wiring as done with what I had on hand, and will be rewired for the final chassis setup.

I also installed output terminals for the output connections under the pcb, so that I could wire the test speakers directly into the PCB. For the final chassis wriing, the wires going to the output terminals will be wired directly to the PCB.

For heatsinks, I tested with the small heatsinks that I had on hand. With a single heatsink per channel, they got quite hot, so I connected 3 together to obtain a reasonable temperature for the heatsinks. We were able to run the amplifier at full power, and easily overwhelm the test speakers. At full power, the heatsinks were a bit warm, but not to hot to touch.

Note: make sure to insulate the heatsink from the LM1875 package, as it is not insulated like the LM3886TF chips.

--
Brian

[KT]

Brian,

Are you selling (or going to be selling) these on the chipamp.com site?

I've been looking at trying out the lm1875 but haven't had the time or motivation to hardwire one together. A PCB would make things much easier.

Cool project.

Best,
KT

[zymurgn]

Brian we need to make a correction on that amp pcb part list. We are using the 47µF for c4 instead of the 0.1µF. I'm working on a manual for this project and it should be out soon. This is just something I noticed while doing a walkthrough.

[BrianGT]

Originally posted by zymurgn
Brian we need to make a correction on that amp pcb part list. We are using the 47�F for c4 instead of the 0.1�F. I'm working on a manual for this project and it should be out soon. This is just something I noticed while doing a walkthrough.

Yeah, that was a typo that I made, thanks for catching it,


-Brian

[korben69]

Nice job Brian !
I'd like to buy some boards when available...

Some questions
PSU
Is one PSU board enough for two LM1875 modules ?
C1/C2 : I've got 1800µF/35v from Panansonic, does it fit ?
C3/C4/C5/C6 : 5mm footprint ?
R0 : 10k/.6W is Ok ?

AMP Boards
C2 : 3.5mm footprint ?
C3/C5 : 5mm footprint ?
C4/C6 : 2.5mm footprint ?
C7 : 5mm footprint ?
C1 : Philips MKT/250v is Ok ?

Many thanks

[ppcblaster]

Please post the Parts Express part number.

"......Transformer selection:
I used a 160va 2x18vac Avel Lindberg transformer from Parts Express, and anything similar should work. The acceptable power supply range from V+ to V- is 16-60v. See the datasheet for power output levels with various supply voltage......"

Thank You

[BrianGT]

Originally posted by ppcblaster
Please post the Parts Express part number.

"......Transformer selection:
I used a 160va 2x18vac Avel Lindberg transformer from Parts Express, and anything similar should work. The acceptable power supply range from V+ to V- is 16-60v. See the datasheet for power output levels with various supply voltage......"

Thank You

http://www.partsexpress.com/pe/showd...number=122-610

[ppcblaster]

Thank You,

I hope you have kits for this amp and PSU.

[korben69]

Brian YGM