AR P315 subwoofer schematic - diyAudio
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Old 8th October 2008, 07:43 PM   #1
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Default AR P315 subwoofer schematic

Looking for a schematic for the Acoustic Research P315HO speaker system. The amp is marked Recoton Home Audio subwoofer amp. Audiovox, AR and Recoton haven't been any help.
I found two transistors shorted in the subwoofer amp, a 2SC3281 and an IRF640. I replaced them but there is still a large dc offset in the output, about 10.5 volts. Without a schematic I'm kind of just fishing.
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Old 8th October 2008, 08:44 PM   #2
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http://home.comcast.net/~jhidley/SubTwoi_Amplifier.pdf
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Old 9th October 2008, 08:32 PM   #3
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That's excellent, thank you Jack for the schematic.

I will do further testing on the amp with your schematic. You guys look like audio buffs par excellance. If you've had any experience with this type of failure do you have any suggestions of what else might cause that large dc offset?

Thanks
Don
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Old 10th October 2008, 12:00 AM   #4
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Don,

Check the DC voltage across each of the output devices (emitter to collector). You can do this by going from the speaker + lead to pin 1 of JP1 and then pin 1 of JP2. These voltages should be around 6-7VDC. If they are higher, don't drive the amplifier very hard at all, the outputs will blow again.

The IRF640 was one of the switches in the tracking down convertor. There is one TDC for the - supply and one for the + supply. Their job is to keep the rail voltage on the output devices about 6-7VDC above the audio signal requirements. RP1 and RP2 adjust the tracking voltages.

This is how the amplifier puts out so much power. There is very little power loss in the outputs since there is very little voltage drop across them. One of the weak spots in the amplifier is the optocoupler (HP-2611). They tended to blow up when one of the IRF640s shorted. The optocoupler is an old part. You have to find someone that has some NOS.

When the amplifier is working correctly, there will be about 250mVDC at the speaker terminals. This is normal.

The entire power amplifier is licensed from Sunfire. It is the same design used in the Sunfire subwoofers. You may be able to get any specific parts (such as the optocoupler) from them.
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Old 11th October 2008, 02:52 AM   #5
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Thanks very much Jack. I will check those components. Looking at the circuit I kind of suspected the down converters would be doing something like following the signal. Your information will be very helpful. I'll let you know what transpires.

Don
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Old 19th November 2008, 04:31 AM   #6
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Hi Jack
I'm finally seeing a light at the end of the tunnel on that amp repair. There were several semi's burned out. Mosfets Q19 and Q20, output transistor Q15, U2 (replaced with LF347), Z2, Z3, U4 and U5 (replaced with 6N137), U6 and U7. The voltage across the output terminals is about 0.2vdc. There's about 10.5 vdc between speaker + lead and JP1, and about 130 volts between speaker + lead and JP2. Looks like there's still a a problem with those mosfets.
U6 and U7 are running quite warm.
Z2 and R19 are running hot. The voltage across R19 is 11.6 vdc, current calculated is 72 ma, about 0.8 watts.
Questions:
What load should I place on the output for testing?
How to adjust RP1 and RP2?
I haven't tried it with an input. What input level should I use? Am I right that the input looks to be a speaker level.

Regards
Don Whyte
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Old 19th November 2008, 03:31 PM   #7
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Not sure if anyone will see this post, but I wanted to see if someone was able to help me out. I believe I have this same Sunfire Amp and it powers up but instantly blows a fuse on the amp board. I really am at a loss, I can solder fairly well, but am not comfortable diagnosing this issue. Would anyone want to take on a repair or walk me through some basic testing/repair. Any help would be appreciated. Thanks
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Old 20th November 2008, 04:00 AM   #8
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Hi remrodbr:
I had the same initial problem with the amp blowing the fuse. The cause appeared to be shorted output transistors and shorted mosfet transistors. Unfortunately several other components farther back in the circuit were also damaged, probably by the shorted transistors. The repair has been made difficult because of the many shorted components - if I replaced an obviously damaged component and then powered up the amp to do further testing there was a chance of damaging the same component. I had to use a variac to keep the ac input low enough to not overheat and burn up more components. Some parts such as the mosfets and the jfet input op amp are static sensitive and require special handling too. Also there are +130 and -130 volt power supply rails that can be dangerous to work with.

Jack Hidley offered some very good insights into how the amp operates and very generously supplied a schematic. See rest of thread.

I don't know if Jack Hidley would have a repair contact. A search for AR repair may net you someone in your area.
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Old 1st January 2009, 09:41 PM   #9
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Don,

I would put a 4-8ohm load on the amp. The input to the amplifier PCB is line level, it is just very low gain. I think it takes 2.5V RMS for full amplifier output. Use an input frequency of 30-80Hz and a level of 300mV or so.

Connect a scope to the output of JP1 and compare it to the output of JP2. There should not be 130V between JP2 and the + output. Something in the - tracker isn't working correctly. If there is 130V at the output of the tracker, either one or all of the FETs are shorted or something in the control circuit has them locked on.

Until you figure out what is still broken, I wouldn't try to adjust the tracking voltages with RP1 and RP2. Once you do get things fixed, raise the input level until the output is about 100W, then adjust the tracking voltages to about 7V.

I'm not sure how the outputs of U4A and U4B should look. I expect that they would be identical.

You can contact http://www.adkhifi.com/contact.html. I know that they can fix the amplifier.
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Old 1st January 2009, 10:52 PM   #10
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Quote:
Originally posted by Jack Hidley
http://home.comcast.net/~jhidley/SubTwoi_Amplifier.pdf
Hello Jack - Happy New Year!

Do you have the complete schematics?
I may be missing something, but I do not see the "main" power supply.
Thanks!
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