CMoy Hardwire Power Problems

TheHusker · 12th August 2010, 05:12 AM

I just finished a simple modified CMoy for my motorcycle. It plugs into my bike stereo's aux in. It is powered by my cigarette lighter circuit, which is switched with the ignition. Given this application, I didn't include a power switch or a volume pot since the volume could be controlled both at the input device (my mp3 player or GPS) or at the stereo and the power turns off when I turn the bike off. It worked great on my office desk. Then I connected power from the plug on my bike. No music at all, just a soft hum. When I connect a 9-volt battery to it, the sound is great again. I have verified that I have 12.4V at the plug from the motorcyle to the amp. I have also verified the polarity. I mounted the CMoy in a plastic enclosure to make sure I don't have a grounding issue. Any other thoughts?

Additionally, I used this same power plug on my bike to power an amp purchased from BioScienceGeek on Ebay. That worked just fine. I'm not sure it's relavent, but I'm using an OPA2227 amp chip, the amp has a gain of 11, 220uf electrolytic power caps, .1uf poly input caps. I'm certainly no audiophile or electrical engineer, though I don't have trouble following electrical schematics.

Thanks in advance for any help or advice.

wwenze · 12th August 2010, 07:42 AM

The DC from your cigarette lighter may be fluctuating too much. Try extra capacitance.

Or an LC filter might be better in this case.

TheHusker · 12th August 2010, 12:07 PM

I'm leaving tomorrow for a trip and would like to use it. If I was going to add capacitance, can I just throw in a single electrolytic on the +12V input to the CMoy? Can you recommend how much capacitance?

I appreciate the help.

wwenze · 12th August 2010, 01:28 PM

You can refer to what your BioScienceGeek amp used for its power supply.

TheHusker · 12th August 2010, 07:01 PM

I tried a 1000uf cap, similar to the one in the BSG amp and still no sound at all. I go back to the 9V battery (no 1000uf cap) and it sounds great again. Do you have any other thoughts?

theAnonymous1 · 12th August 2010, 10:26 PM

Doesn't that CMOY design use some kind of rail splitting for the power supply?

If that is the case, you are shorting out the negative rail of the CMOY when you connect it to the bikes 12V power and the bikes audio ground.

DigitalJunkie · 12th August 2010, 10:58 PM

Quote:

Originally Posted by theAnonymous1

Doesn't that CMOY design use some kind of rail splitting for the power supply?

If that is the case, you are shorting out the negative rail of the CMOY when you connect it to the bikes 12V power and the bikes audio ground.

X2 It is a split supply.

theAnonymous1 · 12th August 2010, 11:11 PM

I think you need to completely isolate the entire CMOY circuit with DC blocking caps. Input, output, and one between the feedback resistor and ground.

wwenze · 12th August 2010, 11:16 PM

Wait... the amp is connected to the input of a stereo?

X3 @ three posts above, but why would you want an amp between your source and another amp?

TheHusker · 13th August 2010, 12:09 AM

The output of the mp3 player is too weak (or the amplification of the stereo from the aux input is too weak). I connect an mp3 player or my GPS to the aux input to my stereo, then have to turn the stereo all the way up to hear it at 55mph. At 80mph, I can't hear much at all.

12th August 2010, 05:12 AM	#1
TheHusker diyAudio Member Join Date: Aug 2010	CMoy Hardwire Power Problems I just finished a simple modified CMoy for my motorcycle. It plugs into my bike stereo's aux in. It is powered by my cigarette lighter circuit, which is switched with the ignition. Given this application, I didn't include a power switch or a volume pot since the volume could be controlled both at the input device (my mp3 player or GPS) or at the stereo and the power turns off when I turn the bike off. It worked great on my office desk. Then I connected power from the plug on my bike. No music at all, just a soft hum. When I connect a 9-volt battery to it, the sound is great again. I have verified that I have 12.4V at the plug from the motorcyle to the amp. I have also verified the polarity. I mounted the CMoy in a plastic enclosure to make sure I don't have a grounding issue. Any other thoughts? Additionally, I used this same power plug on my bike to power an amp purchased from BioScienceGeek on Ebay. That worked just fine. I'm not sure it's relavent, but I'm using an OPA2227 amp chip, the amp has a gain of 11, 220uf electrolytic power caps, .1uf poly input caps. I'm certainly no audiophile or electrical engineer, though I don't have trouble following electrical schematics. Thanks in advance for any help or advice.

12th August 2010, 10:26 PM	#6
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	Doesn't that CMOY design use some kind of rail splitting for the power supply? If that is the case, you are shorting out the negative rail of the CMOY when you connect it to the bikes 12V power and the bikes audio ground. __________________ "If you don't like funerals don't kick sand in Ninja's face." - Ninja

12th August 2010, 11:11 PM	#8
theAnonymous1 diyAudio Member Join Date: Feb 2004 Location: Anonymityville	I think you need to completely isolate the entire CMOY circuit with DC blocking caps. Input, output, and one between the feedback resistor and ground. __________________ "If you don't like funerals don't kick sand in Ninja's face." - Ninja

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12th August 2010, 07:42 AM	#2
wwenze diyAudio Member Join Date: Mar 2008	The DC from your cigarette lighter may be fluctuating too much. Try extra capacitance. Or an LC filter might be better in this case.

12th August 2010, 12:07 PM	#3
TheHusker diyAudio Member Join Date: Aug 2010	I'm leaving tomorrow for a trip and would like to use it. If I was going to add capacitance, can I just throw in a single electrolytic on the +12V input to the CMoy? Can you recommend how much capacitance? I appreciate the help.

12th August 2010, 01:28 PM	#4
wwenze diyAudio Member Join Date: Mar 2008	You can refer to what your BioScienceGeek amp used for its power supply.

12th August 2010, 07:01 PM	#5
TheHusker diyAudio Member Join Date: Aug 2010	I tried a 1000uf cap, similar to the one in the BSG amp and still no sound at all. I go back to the 9V battery (no 1000uf cap) and it sounds great again. Do you have any other thoughts?

12th August 2010, 11:16 PM	#9
wwenze diyAudio Member Join Date: Mar 2008	Wait... the amp is connected to the input of a stereo? X3 @ three posts above, but why would you want an amp between your source and another amp?

13th August 2010, 12:09 AM	#10
TheHusker diyAudio Member Join Date: Aug 2010	The output of the mp3 player is too weak (or the amplification of the stereo from the aux input is too weak). I connect an mp3 player or my GPS to the aux input to my stereo, then have to turn the stereo all the way up to hear it at 55mph. At 80mph, I can't hear much at all.

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