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Old 19th May 2008, 05:59 PM   #1
Elkaid is offline Elkaid  Canada
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Question LM49810 amplifier

Hi everyone,

I ordered a few weeks ago 2 amplifiers LM49810-based modules from this website : www.chip-pcb.cn

The problem is that I'm experiencing problems adjusting bias. According to the documentation, I should adjust the potentiometer in order to read 22mV across "Re". Unfortunately, I read 0mV whatever position the potentiometer is.

When I powered up the amplifier module, everything went fine. (No explosion, red-hot resistor or magic smoke). The LM49810 becomes very slightly warm after a few minutes which seems perfectly normal)

Being a complete ignorant concerning amplifier debugging, I suspect the module to be stucked in "Mute" mode but I have absolutely no idea how to confirm this. Datasheet mention the LM49810 needs 50žA to 100žA on Mute pin to swich to "play" mode.

How can I read such a low value ?

I'm reading 0-1mV on module's output which may be due to my multimeter Fluke 111 imprecision.

I'm feeding 44VDC to the modules using conventional non-rectified power supply. Could it be the voltage too low ?

I've attached the schematic

Any help would be greatly appreciated. Thanks !
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Old 19th May 2008, 06:08 PM   #2
Elkaid is offline Elkaid  Canada
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Here's a picture of the assembled modules
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File Type: jpg dsc_0045b.jpg (75.0 KB, 1209 views)
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Old 19th May 2008, 06:50 PM   #3
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check to see if there is a place for a switch that leads to pin two "2" "mute" on the chip, thats how you switch it on and off. it should be before resistor RM and zener diode DW, if not then it should be on constantly.
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Old 19th May 2008, 07:56 PM   #4
Elkaid is offline Elkaid  Canada
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Hi !

First of all, thank you.

In response to your comment, unfortunately there's no pads provided to switch mute on/off. As you wrote, it should be constatly on.

I'm not very familiar with zener diode but is there a way to calculate which voltage should I read on LM49810's pin 2 or on the mute circuitry (Rw, Cw, Dw, Rm)

Thank you for your help !
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Old 19th May 2008, 08:14 PM   #5
AndrewT is online now AndrewT  Scotland
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T5 is drawn upside down.
How is it fitted?
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regards Andrew T.
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Old 19th May 2008, 08:40 PM   #6
Elkaid is offline Elkaid  Canada
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Hello !

Here's a picture how T5 is mounted. By looking at the pcb traces :
T5 pin labeled G(b) is tied to Rz (100ohms)
T5 pin labeled D(c) is tied to CL (0,1uF)
T5 pin labeled S(e) is tied to Re (0,22ohms)

I suppose if T5 would have been installed backward, something would have blown up right ?

Thank you very much for your help guys

Emmanuel
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Old 19th May 2008, 10:59 PM   #7
sidiy is offline sidiy  Canada
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Hi,
I have a similar kit from them and I presume they tested it for supply voltages close to 100V. Rw=22k is marginally good at those voltages.

For 44V rail voltage I think Rw should be lower. A 4k7 / 1W should do a proper job to bias the Zener and keep it at 5.1V even when the LED is on. Assuming 4mA through the LED then Rx should be around 820 ohm. The other values seem to be OK. (Rm=33k, Cw=47u, Dw=5V1 type)
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Old 19th May 2008, 11:44 PM   #8
Elkaid is offline Elkaid  Canada
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Thank you very much !

I can't wait to try those values. I'll keep you posted.

Thanks again

Emmanuel
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Old 20th May 2008, 12:12 AM   #9
ttan98 is offline ttan98  Australia
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Default Re: LM49810 amplifier

Quote:
Originally posted by Elkaid
Hi everyone,

I ordered a few weeks ago 2 amplifiers LM49810-based modules from this website : www.chip-pcb.cn

The problem is that I'm experiencing problems adjusting bias. According to the documentation, I should adjust the potentiometer in order to read 22mV across "Re". Unfortunately, I read 0mV whatever position the potentiometer is.

When I powered up the amplifier module, everything went fine. (No explosion, red-hot resistor or magic smoke). The LM49810 becomes very slightly warm after a few minutes which seems perfectly normal)

Being a complete ignorant concerning amplifier debugging, I suspect the module to be stucked in "Mute" mode but I have absolutely no idea how to confirm this. Datasheet mention the LM49810 needs 50žA to 100žA on Mute pin to swich to "play" mode.

How can I read such a low value ?

I'm reading 0-1mV on module's output which may be due to my multimeter Fluke 111 imprecision.

I'm feeding 44VDC to the modules using conventional non-rectified power supply. Could it be the voltage too low ?

I've attached the schematic

Any help would be greatly appreciated. Thanks !

I have a pair of the same amp y0u ordered, I think it is NOT a good idea to release to the public the commercial in confidence the circuit diagram that has been given to you. Did you get permission to do so?

The developer took many hours/days to come up with the circuit, intellectual property from the East is the same as from the West.
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Old 22nd May 2008, 02:38 PM   #10
larzman is offline larzman  United States
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Default Diagram release violating copyright

Ttan98, pardon your poor English, but the way I have viewed this thread, there is no issue about violating any IP or copyright in Elkaid's posts. He simply showed a photo of a pcb assembly. Exactly how is that any IP or copyright violation?
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