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New LM1875 pcb and kit pre-order special

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BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
I should receive the next batch of LM1875 boards soon, and have put them up on my website for pre-order.

Details on boards here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=122793
and here:
http://chipamp.com/lm1875.shtml

I should begin shipping out the new kits in 2 weeks. I have put up a pre-order special for the kits, including an extra stereo pcb set along with the purchase of a kit. I will run this special until the kits start shipping out.

Drop me a mail if you have any questions. Sorry it took so long to get these kits out. I have been really busy at work, and wanted to make sure to get a few amps built with the boards and used for a while before making them available on the webpage.

Pic from initial prototype:
An externally hosted image should be here but it was not working when we last tested it.

I will see if I can get pics posted from the assembled amp soon also.

--
Brian
 
M

morepower4me

Member
Joined 2008
Looks fantastic, thank you.

Do you think this would make a good first amp DIY project (as compared to your 3886 kit?)

It will be driving bookshelf speakers in a medium sized room.

And for the other newbs... What else besides your kit, the PE transformer, soldering equipment (and patience,) will I need?
 
P

ppcblaster

Member
Joined 2006
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
The boards have arrived, and I have started putting the kits together. They will ship out on Monday, and I will remove the special at that point.

morepower4me said:
Looks fantastic, thank you.

Do you think this would make a good first amp DIY project (as compared to your 3886 kit?)

It will be driving bookshelf speakers in a medium sized room.

And for the other newbs... What else besides your kit, the PE transformer, soldering equipment (and patience,) will I need?
Click to expand...

The LM1875 is just as simple as the LM3886 kit, and will be a great project for a beginner.

tschrama said:
just ordered two LM1875 PCB sets...

I messed up, so I had to send the money in to paypal transmission.. but I hope everything goes allright...:att'n:

Thanks,
Thijs
Click to expand...

Everything looks good. Orders will go out Monday.

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

Thanks,
Pete
Click to expand...

The amp boards are roughly 1/2 the size of the LM3886/LM3875 boards. I don't have dimensions on me now, but I will look then up when I get home.

Sorry for the delay, let me know if any of you guys have more questions,

--
Brian
 
K

korben69

Member
Joined 2006
Hi Brian I've got one.

In my system, Tri active amp, DEQ/DCX 2496, I'm wondering wich amp will be the more accurate in driving a CP21F, 105dB tweeter, 6.1 Ohms ? 3886 or 1875 ? Freq range from 2KHz to 20KHz.
I don't need a lot of power, but definition.
Your opinion ?
Thanks
 
BrianGT

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
korben69 said:
Hi Brian I've got one.

In my system, Tri active amp, DEQ/DCX 2496, I'm wondering wich amp will be the more accurate in driving a CP21F, 105dB tweeter, 6.1 Ohms ? 3886 or 1875 ? Freq range from 2KHz to 20KHz.
I don't need a lot of power, but definition.
Your opinion ?
Thanks
Click to expand...

If you don't need the power, I would try the LM1875.

--
Brian
 
sonidos

sonidos

Member
Joined 2007
Paid Member
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

BrianGT

Retired diyAudio Moderator
Joined 2002
chipamp.com
vonfilm said:
Brian,
When will the assembly manual be available on your website?
Click to expand...

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

sonidos said:
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!
Click to expand...

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.
 
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