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Old 26th June 2009, 03:56 AM   #21
swin1 is offline swin1  Australia
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Hi Brian, almost a year later...

I put together one of the lm1875 amplifiers using your PCBs. I have gone with the basic setup to get things going and plan to add zobel etc. later.

Currently on each amplifier PCB I have the lm1875 chip, 22kohm on R2 and 1kohm on R3, and 22k on R4 for feedback, with 2x 0.1uf and 2x 47uf decoupling caps, that is all. I have jumpered C1, C2 and R6.

My DC at output is the same as at input! Power supply is fine, and signals pass via a 50kohm pot.

Do you have any advice on why the output voltage would be the same as the input?? Would I have blown the chips?

Also, there is a buzzing sound near AC in the chassis, could be the transformer. Any input would be appreciated, thanks!
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Old 26th June 2009, 12:07 PM   #22
swin1 is offline swin1  Australia
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Ahh nevermind, I did blow the chips! Lucky I bought a few extras...

Amplifier sounds beautiful even when breaking in. Using a 120VA 18v toroid which idles at 20.8 (as specified by manufacturer) this is ideal for my 6ohm speakers. The input is inaudible with volume turn down and barely audible at full volume! This is a very satisfying build.

Just a thought, bass is a bit thin, I increased the lower frequencies in foobar which is balancing the sound nicely, perhaps a slight increase in filter capacitance is in order, what thoughts on this?
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Old 31st August 2009, 01:51 PM   #23
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Do you have these boards still connected together? I would like to get 2 strips of 3 each for a project.
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Old 14th October 2009, 07:57 PM   #24
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I have exactly the same problem as swin1, DC on output is the same as the supply DC. Fully populated amp board except for jumpered R6. When I jumper R6 (input & output ground?) the DC on output disappears but there is NO output at all. Removing the optional components makes no difference. I think my only mistake was initially using a 25-0-25 toroid (now replaced with 18-0-18) which may have been too high a voltage and fried the chips? I have spare replacements on the way but I'm dying for answers in the meantime!
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Old 10th November 2009, 07:39 PM   #25
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Hi all - Any further word on this amp? I bought a set of these chipamp.com boards and a PT from a guy on EBAY. Did the manual / schematic ever get completed? Thanks very much!
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Old 27th December 2009, 01:00 AM   #26
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Click the image to open in full size.

These things seem to always work for me.
i have made this carrier for a musical instrument project. they are actually to electromagnetically inject signals in to guitar strings.

Neutron Physical Guitar Synth.

because of the possibility of blowing one i made them able to be swapped out by just unscrewing the 1875 and unplugging it from the headers.

There is an option for a star ground on the inputs if it is too noisy using the in/out ground strap.

This is not quite complete, i am waiting for nylon screws and mica washers, but the amps all work fine when tested with no hum, but who knows what will happen once it is in the case with all the other compontents (8 channel ADAT AD/DA converter, some MIDI stuff etc.
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Old 10th January 2010, 02:57 PM   #27
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Quote:
Originally Posted by moonbird View Post
Hi all - Any further word on this amp? I bought a set of these chipamp.com boards and a PT from a guy on EBAY. Did the manual / schematic ever get completed? Thanks very much!
Moonbird, I have yet to see a schematic for this kit. There is a component guide available here. I am currently putting Mouser order together that I would be happy to share with you.

Cheers,

Alan
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Old 10th January 2010, 03:29 PM   #28
AndrewT is offline AndrewT  Scotland
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three 8r2 600mW in parallel are equivalent to 2r73 1.8W
or
four 11r 600mW ~ 2r8 2.4W
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Old 2nd May 2010, 05:27 PM   #29
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Default How

How would I bridge/Parallel the LM1875 to power 4 ohm speakers?
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Old 2nd May 2010, 06:01 PM   #30
AndrewT is offline AndrewT  Scotland
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Badly.

But seriously, the 1875 has a maximum output of 3Apk when it is cold. The limit will reduce at elevated temperatures.

If you use a 4 chip bridged parallel assembly each chipamp sees a load equal to your actual load.

The best you can get is ~6Apk into 4r0. About 72W into 4r0.
Into a real speaker you would need to double the chip count to 8, or preferably 12, i.e. 6off in parallel and then two sets bridged.
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