Hello all:
I have a problem with two Chipamp LM1875 amplifier boards. I emailed Brian with the question, but haven't heard back. Not sure if he is still supporting these kits or not, so I'd like to post the question here:
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The output goes to the + power supply value. I built a second board and have the same problem. There is one capacitor (47 uf, I believe it is C6) on the board that appears to be an electrolytic but the board shows no polarity for installation. So I am suspicious of this. Is the circuit the same as shown on the first page of the National data sheet for the LM1875?
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The power supply is fine (it is the board that came with the amp kit). Without knowing the exact schematic it is hard to figure out diagnostics. Also, a few of the components are labelled as "optional" without any information on what they can do for you.
Any help would be appreciated.
Thanks,
Mark
I have a problem with two Chipamp LM1875 amplifier boards. I emailed Brian with the question, but haven't heard back. Not sure if he is still supporting these kits or not, so I'd like to post the question here:
=================
The output goes to the + power supply value. I built a second board and have the same problem. There is one capacitor (47 uf, I believe it is C6) on the board that appears to be an electrolytic but the board shows no polarity for installation. So I am suspicious of this. Is the circuit the same as shown on the first page of the National data sheet for the LM1875?
=================
The power supply is fine (it is the board that came with the amp kit). Without knowing the exact schematic it is hard to figure out diagnostics. Also, a few of the components are labelled as "optional" without any information on what they can do for you.
Any help would be appreciated.
Thanks,
Mark
Hi mbohn.
This was a picture of the very first Chipamp.com 1875 boards they posted on this forum. The picture links are broken in the build thread now unfortunately.
http://i703.photobucket.com/albums/ww35/Jblackburn_photos/ampboard.jpg
You can see the positive symbol for C6 marked on the board. Compare your board to the photo before you act on it though as there could have been revisions since then.
Hope it helps.
John
This was a picture of the very first Chipamp.com 1875 boards they posted on this forum. The picture links are broken in the build thread now unfortunately.
http://i703.photobucket.com/albums/ww35/Jblackburn_photos/ampboard.jpg
You can see the positive symbol for C6 marked on the board. Compare your board to the photo before you act on it though as there could have been revisions since then.
Hope it helps.
John
My board does not have the 0711 (date?) stamp on it but I do now see the polarity indication and I do have C6 installed correctly on both boards.
I now see that it is C2 that is shown on the schematic as polarized but on the board polarity is not shown. C2 is also one of the optional components. I've got it installed in one board and not in the other.
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photos:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Hi Mark.
There is a snapshot of the original parts listing here.
http://i703.photobucket.com/albums/ww35/Jblackburn_photos/forumpage.jpg
C2 is listed as a non polarised capacitor and as optional on the BOM. I would be tempted to reflow the soldering on your boards and maybe look at getting bigger heatsinks once you have it working. I found the little 1875s run hotter than the 3875s I have used previously.
On your photo, follow the trace down from the SG pad. Do you have an unsoldered wire in the next hole down?
John
There is a snapshot of the original parts listing here.
http://i703.photobucket.com/albums/ww35/Jblackburn_photos/forumpage.jpg
C2 is listed as a non polarised capacitor and as optional on the BOM. I would be tempted to reflow the soldering on your boards and maybe look at getting bigger heatsinks once you have it working. I found the little 1875s run hotter than the 3875s I have used previously.
On your photo, follow the trace down from the SG pad. Do you have an unsoldered wire in the next hole down?
John
That hole is for R6 listed as
"jumper (optional resistor between input ground and output ground)"
I was not sure how a jumper could be a resistor so I left it out. Could the option be between a jumper and a resistor, not between a resistor or jumper or leaving it out?
Greetings! C4 is same as C6 47uf,probably is better to put there 100-220uf.You must put C2 22uf,C7 0.1uf and R6 jumper or 10 ohm resistor and that should work.
Your explanation of R6 answers my most recent posted question.
C4 is shown (next to the V+ pad) as round and polarized on the board but the supplied part is square and unpolarized.
Can you explain what the other optional components are for, C1, C2, C7, R1 (listed as optional and not used), and R5?
Some of those were listed as optional without any explanation of what they were for or when you might want to use them. Others were described ambiguously, e.g "R1 not used (optional..)
Hi Mark.
The R6 jumper is mentioned here, well spotted basi.
http://www.diyaudio.com/forums/chip-amps/122793-finally-made-lm1875-amp.html#post1508448
John
The R6 jumper is mentioned here, well spotted basi.
http://www.diyaudio.com/forums/chip-amps/122793-finally-made-lm1875-amp.html#post1508448
John
Hello again!C4 must be Elko same as C6 your's supplied part is mistake.
C1,C2,C7 and R5 are good values there's no need for 'optional'.
The heatsink pictured in post #6 will cause failures in at least two ways:
It is far too small, and that is a mistake because LM1875 are easily damaged by heat (explode).
It is not insulated, and that is a mistake because the tab of LM1875 has voltage and will explode unless you install insulator pad, thermal paste, and shoulder washer to block voltage properly.
There are two errors that may cause infinite gain (explode): R6 is not optional. It can be from 0 ohms (wire) to 10 ohms. I use 2 ohms.
C2 is not optional. If either R6 or C2 is omitted, the amplifier explodes. Why does a kit have so many documented options for explode?
Other errors:
If C2 is too small, it will omit the bass (sounds like loud mids) and thus should be at least 100uF or more.
If R6 is shorted, the amplifier might hum, so use a resistor, not a wire.
R1 should be approximately 100pF capacitor parallel with a 1M resistor.
R2 should probably be 10K.
If you want a mids-n-treble amp, 47uF for C4 and C6 can work okay to get the midrange especially loud (implying also using a subwoofer). Most people won't like that. SO, for full bandwidth amp, C4 and C6 should both be 220uF or more, and you can fit good size caps on that board if you solder the little gray box caps trackside.
It is far too small, and that is a mistake because LM1875 are easily damaged by heat (explode).
It is not insulated, and that is a mistake because the tab of LM1875 has voltage and will explode unless you install insulator pad, thermal paste, and shoulder washer to block voltage properly.
There are two errors that may cause infinite gain (explode): R6 is not optional. It can be from 0 ohms (wire) to 10 ohms. I use 2 ohms.
C2 is not optional. If either R6 or C2 is omitted, the amplifier explodes. Why does a kit have so many documented options for explode?
Other errors:
If C2 is too small, it will omit the bass (sounds like loud mids) and thus should be at least 100uF or more.
If R6 is shorted, the amplifier might hum, so use a resistor, not a wire.
R1 should be approximately 100pF capacitor parallel with a 1M resistor.
R2 should probably be 10K.
If you want a mids-n-treble amp, 47uF for C4 and C6 can work okay to get the midrange especially loud (implying also using a subwoofer). Most people won't like that. SO, for full bandwidth amp, C4 and C6 should both be 220uF or more, and you can fit good size caps on that board if you solder the little gray box caps trackside.
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