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Old 1st October 2009, 10:36 PM   #1031
Electrons are yellow and more is better!
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Are the LM3886 on the heatsink? Without heatsink they will pretty hot.
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Old 2nd October 2009, 03:12 PM   #1032
shmulik is offline shmulik  Israel
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I gathered my wits, replaced the faulty LM and after meticulously checking placed the PA150 back on power. it now function well in the sense no smoke is coming out and heating is similar to the other board (hot, though). trying to kill the DC offset, I found myself running out of resistance and still have 6-20mv on the various LMs.
P-A, you write it is important to match the LMs' gain in each triplet, but the only control I have is over the dc offset. the gain is fixed by the fixed resistors.
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Old 2nd October 2009, 03:20 PM   #1033
Electrons are yellow and more is better!
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The gain is one thing. The other thing to trim away the offset with the pot but I'll guess you may experience perhaps more offset in rare occasions since the offset voltage can be 0-10 mV times the gain. 20 mV offset at the output is good but the current flowing between the chips is the offset divided by you series resistance and this is a compromise. High resistor value, lower heat, higher output impedance, hotter resistors at high output power.
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Old 3rd October 2009, 10:19 PM   #1034
shmulik is offline shmulik  Israel
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Default DRV134 hiss

getting one step further, I assembled a DRV134 circuit (chip, 2 capacitors, connectors) on a strip board. as others before me, I encountered an excessive hiss on the drv outputs. I suspect it is circuit layout dependent, but I don't know how to verify or contradict it. I need to test the drv board in a more insulated environment.
I also suffer from another dreaded power amp problem - subtle hum. however, this hum seems to be picked up by the input cable, as it is there even when the cable is not connected on the other end.
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Old 4th October 2009, 07:18 AM   #1035
Electrons are yellow and more is better!
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Do you have shielded wires? If not, you will create a perfect antenna.
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Old 4th October 2009, 12:22 PM   #1036
shmulik is offline shmulik  Israel
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P-A,
do you mean cabling between the RCA plug/PA150 and the circuit? they are all shielded and shield acts as ground. the noise is present only when the drv134 is powered. when fully connected (power, in and out) but not powered, or when I remove the circuit and let the wires to the PA150 hang free on air on one side there is no noise. when pulling the input to ground using 1K resistor the noise is almost totally muted. however, checking with an oscilloscope, I suspect the noise on the individual phases is about the same as without the resistor, but less correlated, and hence does not cancels out when bridging.

have you completed checking your implementation of a DRV board? do you have any noise issues?
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Old 4th October 2009, 04:40 PM   #1037
Electrons are yellow and more is better!
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I haven't tested my board yet.

Have you connected the DRV134 according the datasheet (or like I have done). What kind of power supply do you have for your board?
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Old 4th October 2009, 04:49 PM   #1038
Electrons are yellow and more is better!
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Quote:
Originally Posted by rhysh View Post
You should have another package tracking code by wednesday. I will keep posting updates.
Just wanted to remind you, it's soon the 10th of October.
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Old 4th October 2009, 09:06 PM   #1039
shmulik is offline shmulik  Israel
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Quote:
Originally Posted by peranders View Post
Have you connected the DRV134 according the datasheet (or like I have done). What kind of power supply do you have for your board?
for PS I'm using TeddyReg from PinkFishMedia :
http://www.pinkfishmedia.net/forum/s...ad.php?t=39990 with added LED on each rail.

the drv implementation has only connectors, and 2 electrolytic capacitors in parallel to 2 film capacitors between the +-V and ground for smoothing whatever is caught on the PS relatively long lines. I've tried adding a pulldown 100k resistor on the input with no change in behavior. also tried 1k resistors between outputs and ground - nothing changed.
The main abnormality I can spot is a difference in the level of noise (and DC offset) between normal and inverted phase pins. I cannot find an external cause for that difference.

any wild ideas are welcomed.

Shmulik

Last edited by shmulik; 4th October 2009 at 09:11 PM.
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Old 4th October 2009, 09:16 PM   #1040
Electrons are yellow and more is better!
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If you compare my design with yours, what differs?
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