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Old 17th June 2012, 10:10 AM   #1
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Default Memphis 16-ST3004

Well I will just jump right in. I have a St3004 I have been running bridged to my fronts. I started to notice that it sound like the right side didn't have the mid range lows. after swapping the crossovers and the speakers no change. So that leaves the amp. So in the past I have collected a few classic hi-fi receivers and Amplifiers "60's~ 70's Sansui, Yamaha ,Pioneers. Most of the time with those I would do a full recap . Maybe replace a bad resistor ,set the bias and the Dc offset and They would come out sounding great. Very noticeable difference in how they sound.
So I was thinking that hey this amp is is 12 years old, in a hot car all the time. It was over due for a re-cap so I did a full re-cap.
So the only problem was that after channel 1 has a dc offset of 20mv the rest are 4~8mv. I did not check it before so I don't know if that's something I did. So I would like to know if there is anything I can do about that.

The Next part, the bone head part. Is when I was hooking up my test speakers I think two strands of copper speaker wire shorted out the number 4 channel. After that my Power supply would shut down when ever I tried to power up the amp. Now with the help of Perry Babin how to repair audio amplifiers DVD. "Great stuff buy the way". I found a shorted "Output mosfet?" Q462? I pulled it out along with the one in parallel Q461. After I put it back on the power supple and it started right up. So I would like some advice on if there is anything else I should look at before I put my order in for the fets. Also should I replace them on all 4 channels or just the two on the channel that went bad?

The Mosfet that I am replacing Reads IRF 540 IR 116e. Is the "IRF 116e" a batch number? There are few different types of this Mosfet. Are there any brands that stand out over the others. Would this be a good one to go with? http://www.mouser.com/ProductDetail/Vishay-Siliconix/IRF540/?qs=zorda86t5M84bzifvTBSvlVViIR1Cf%252bo4feVM7od2ZU %3d
Also Is this one the same , just $3 cheaper? http://www.mouser.com/ProductDetail/...jNOOiOrz9Ek%3d
Would there be an advantage to picking one that has a higher amperage. Would it last longer? The last one is how do I ask for mosfets from the same lot when I order them , so they will be matching?

I would also like to thank all that post here. I have doing a lot of searching the past couple of days and this forum has been a gold mine of info.

Thank you
Jake

Last edited by Outerlimits; 11th June 2013 at 02:44 AM.
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Old 18th June 2012, 12:09 PM   #2
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The PBF version is the same (functionally) as the non-PBF version in most all instances.

Use the same part number as the original (don't try to substitute for a different part with higher current ratings. There can be various problems that can cause the amp to fail.

If you order by phone, you can ask if they can send matching date codes. If ordering from the site, order 10 or more or in multiples of 10 or 25. That will generally get you matched sets.
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Old 18th June 2012, 04:56 PM   #3
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Any recommendations on how to lower the DC offset on channel 1 or is that with in spec for the amp?

Thank you
Jake
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Old 19th June 2012, 10:29 AM   #4
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20mv is insignificant. You could try replacing the differential amplifier transistors but you're just as likely to make it worse than make it better.
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Old 11th June 2013, 03:17 AM   #5
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Hello,
Well it's been a year now since I repaired this amp. When I had this amp on my bench my car was broken into and had my stereo stolen. I finally got around to put a stereo back in using this amp for my fronts. So today I had my oscilloscope out setting the gains on my amps. When I was checking this Memphis amp. One of the output channels the polarity was reversed. Meaning that to view the signal on my scope I touch the prob to the positive speaker output to view it. But one channel I had to touch the negative speaker output to view the signal. So I guess my first question is how bad is this, It's signal looks ok on the scope and it sounds good as far as i can tell. My second question what could be the cause. Like I said up above I have done a Re-Cap and replaced the transistors. So would a backward Cap cause that? Well any help would be appreciated.

Thanks
Jake
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Old 11th June 2013, 07:11 PM   #6
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That is perfectly normal, so don't worry or loose any sleep over it. All (most of today's) amplifiers have an inverted channel this is so you can bridge them (mono) without having an external bridging module....like the old school amps did.
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Old 11th June 2013, 09:03 PM   #7
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So when I hook up the speakers should I reverse the connections. Postive speaker to the negative amp terminal? Thank you for the answer.

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Old 11th June 2013, 10:25 PM   #8
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Hook them exactly the way the label shows. Read the manual and hook speakers the way it specifies.

Click the image to open in full size.


As you can see from the picture above, the two middle speaker terminals are the "signal ground" so if you use your DMM you'll notice 0 resistance between those two.....but wait one shows negative and one is positive how can that be..right? that's because one channel is inverted.
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Old 12th June 2013, 05:52 AM   #9
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Thank you for the info. One question is this amp is a 4 channel amp. Why is it not reversed on the other side. On the other side channels 3 and 4 polarity match how there labeled? Just wondering ?

Thanks Again!!

Jake
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