New LM1875 pcb and kit pre-order special

[BrianGT]

Originally posted by Peter Menting
Brian; Could you tell me what the board sizes are? Have a special project in mind.

Thanks,
Pete

The board sizes are:

LM1875 amp board:
1.6" x 1.2"
PSU board:
1.6" x 2.4"

[KT]

Received the kit and boards today, Brian. Thanks!

KT

[korben69]

Hi brain, received the PCBs today.
Thanks !

Do you have some hints to improve LM1875 response in high frequency ?

[sonidos]

Brian,

Thank you!! Got mine today and everything arrived in great shape. Can't wait to get started on this build.

[vonfilm]

Brian,
When will the assembly manual be available on your website?

[sonidos]

I've got it pretty much figured out from the photos, but I want to be sure that I populate the locations for the resistors with the correct values.

I've already got the psu done and I'm heading to our local electronics surplus store at lunch to see if they have heatsinks and other assorted hardware so I can keep moving forward.

Brian, also, on your web page, I found the resistor designators but now I'm not certain what to do about those components that are considered optional. From the images, it looks like the boards are pretty well populated. When you have docs ready, can you address under what circumstances we will want to populate the optional components?

Thanks!

[BrianGT]

Originally posted by vonfilm
Brian,
When will the assembly manual be available on your website?

I will put more time into it this week, and try to get something up by the end of the week.

Originally posted by sonidos
I've got it pretty much figured out from the photos, but I want to be sure that I populate the locations for the resistors with the correct values.

I've already got the psu done and I'm heading to our local electronics surplus store at lunch to see if they have heatsinks and other assorted hardware so I can keep moving forward.

Brian, also, on your web page, I found the resistor designators but now I'm not certain what to do about those components that are considered optional. From the images, it looks like the boards are pretty well populated. When you have docs ready, can you address under what circumstances we will want to populate the optional components?

Thanks!

As for the optional components, they are provided for optimal amplifier stability for using with a variety of output loads/impedances. It depends on your setup, whether you need them or not. Here is a list of optional components:

R1 - not used (optional resistor to ground before C1)
R5 - 2.7 2w (optional - zobel network)
R6 - jumper (optional resistor between input ground and output ground)
C1 - 2.2µF (optional input capacitor)
C2 - 22µF bipolar (optional)

For R1, this is omitted from the kit, and is provided if you wish to put a resistor to ground before the input capacitor. This is not needed, but provided for versatility for various input sources. I had a request for this a long time back, and retained it in the PCB layout, as it doesn't have any side effects if not populated.

For R5/C7, these are for the optional zobel network, which can stabilize the output by creating a pole that reduces high frequency instabilities. If you don't want to use these, simply omit these components from the pcb.

For R6, this is for an optional resistor between the input signal ground, and the output ground. This is specified as a jumper, meaning a simple wire connecting these terminals. You can utilize the extra wire from the 2.2uF film capacitor lead. You should not need to use this, unless you are having ground loop issues.

For C1, this is the optional input capacitor that blocks DC offset from the input source from propagating to the input of the LM1875.

For C2, this is the optional feedback capacitor that ensure unity gain at DC.

As for a bare minimum configuration, here is what you could run:
R1 not populated
R2 22k (input to ground resistor)
R3 1k (gain resistor, gain = 1 + R4/R3)
R4 22k (nfb resistor - on bottom of pcb)
R5 not populated
R6 jumper
C1 jumper, or put input source into pad by C1 label on pcb
C2 jumper
C3 0.1µF (power supply decoupling)
C4 47µF (power supply decoupling)
C5 0.1µF (power supply decoupling)
C6 47µF (power supply decoupling)
C7 not populated

I hope that clears it up for you.

[sonidos]

Brian,

Thanks for your patience and quick response to a noob building his first chip amp!

[vonfilm]

Brian,
Any idea when the 1875 manual will be up?

[Frode]

Very nice amp! Just finished mine and it sounds very nice. I've built it as the minimum configuration suggested by Brian.

Frode