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Technics SU-G91... clipped out @ high volume. Disassembled, sleaned and applied new grease to heat sinks. Amp worked great for a while, clipped out and now occasionally will not light up the front dis

Tried cleaning, applied new grease for heat sinks, checked board for any burn marks. Amplifier worked well for hours, then clipped out and now the front display will occasionally light and the unit will work. The fuses are good, still can not find any burn marks on board or any burnt components. I have much newer & better equipment, but would like to fire this up for my man cave. I know it probably isn't worth doing, but if anyone has an answer to this, let me know. I've driven 4 HUGE Klipsch speakers with this since 1990, and it more than paid for itself. If I can repair it cheaply, I will. Thanks, Kirk!

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  • Kirk Bo
    Kirk Bo Dec 02, 2014

    The volume does not have to be on very loud at all for this to occur. Granted, the problem started when the volume was up around 60%. I didn't have to go any harder than that as the sound quality and volume was absolutely incredible at that level. Now it can be on low and shut down. For the time being I took my Yamaha home theater unit from my man cave so I can have my big speakers going....but I can only power 1 set with this unit, the other outputs are for the surround speakers and I DESPISE music through a surround system. I'm going to play with it one more time when I get a chance...but i'm pretty much sold on replacing it with a big Yamaha non home theater amp that delivers over 100 watts per channel and will power up an "A" & "B" set of Klipsch monsters! I do thank you kindly for your time. Kirk.



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  • 924 Answers

First off, why do you drive the amp into clipping? It's not good for amp, nor your Klipsch. We won't even mention the terrible load that Klipsch in parallel presents to your amplifier, nor the distortion. I would suggest to you, that the amp goes into thermal overload. Trying turning it down by 20-30db, and see if it stays on-line. It can be fixed, if turning it down doesn't help, it can be repaired, but not inexpensively.

Posted on Dec 01, 2014

Testimonial: "The amp never clipped @ high volume in its 20+ years of usage. It is a new development. When I say driving @ high volume, it is far from at the maximum amount. Besides, what difference in the world does it make what kind of speakers the amp is driving?"

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  • Audio Service Clinic Dec 01, 2014

    I'm sorry, but you said "clipped out" a few times. I had believed you meant you were driving the amp beyond what the rail voltage would support. I guess the next step would be to understand what you mean by "clipped out @ high volume". As for the Klipsch speakers/wiring, I assume you had them wired in paralel. This would drop the drop the impedance looking back into the amp by 1/2, so yes, that could be an issue as well, meaning that, if the nomial rating of the speakers is 9

  • Kirk Bo
    Kirk Bo Dec 01, 2014

    Maybe I used the word improperly. I am a certified Master Auto Tech with close to 30 years experience. What the amp would do is shut off, which I assumed to mean "clipped out".... after it was allowed to cool it would come back, which led me to disassemble the unit, check the boards and apply the super conductive heat sink grease from radio shack to the heat sinks. The unit worked flawlessly for 3 albums at a high volume, then the same thing occurred. Now it will come on & work intermittently. I'm looking for what direction to go in, as I like this unit and would set it up in my man cave. I am looking to save up to buy a big Yamaha non surround unit, but having 2 teenaged sons and being disabled makes that very difficult to do.

  • Kirk Bo
    Kirk Bo Dec 01, 2014

    Add a CommentThe one thing that strikes me as odd is that when the unit stops working, the front panel goes blank, as if the power is off. I checked the fuses and the power supply, all test good.

  • Audio Service Clinic Dec 01, 2014

    Oh, I forgot to mention this. The numeric value on the volume control, in your reality, means relatively nothing. As you have a fixed preamp, and fixed, but separate amp, the actual volume in decibels, is a combination of the preamp output, and how the volume control is set on your amp. In other words, if the output on your preamp is turned up, you will not be able to turn up the volume on your amp as much, before you drive it into clipping. For an example of clipping, draw yourself a picture of a circle. Now, draw a line about 1/3 down from the top of the ball figgure horizontally;straight across. You now have a circle with the top cut flat. That circle is akin to a sine wave from an audio oscillator. The circle, or ball, in this example, rises untl that line(the full rail, or amplifier voltage), then suddenly flattens out, much like any amplifier that runs into clipping. I hope the ball scenario works for you, but if it still doesn't make sense, Google up "amp clipping". This can definately have an issue as to why it's shutting down, but the display can be from so many other issues. I suggest this...When the amp shuts down, and refuses to turn on, make sure the power is off to the amp. Carefully listen to the top of the amp, volume turned down, and push the power button. You should immediately hear one click, followed by another about 5-20 seconds later. I'm going to guess and say you hear the first click, but not the second, pointing to amplifier issues of a thermal nature. As to one or two comments of the same question, this entire scenario, does not apply to only one channel out. Instead, try reversing the patchcord between the preamp and amp, and see if the sound changes sides. If not at the amp side, try the preamp side. If you need more assistance, please visit my website listed in earlier answers.

  • Audio Service Clinic Dec 02, 2014

    Hello Kirk.There are many more issues that you'll encounter with buying a new 2 channel amp, that maybe you aren't aware of. All may result in exactly the same condition when you're done with your upgrade. One quick example, if your current amp is at 50wrms, to get a 3db increase is sound pressure level(which is just a barely perceptable increase from what you have now, takes double the power, 100wrms, another 3db up, brings you to 200wrms and on, and on, expotentially. I could go on and on, but not here. If you would like more info, please contact me through my website. Thank you.



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Posted on Jan 02, 2017

  • 1 Answer


I had the same problem. As soon as the volume reached about 24db it would go into overload. I was able to fix it by soldering all the connections on the larger power module. The one connected the the heat sink. When I took it apart there where several solder points that had come loose.

Posted on Dec 01, 2007

SOURCE: Technics SU-G91 Left channel bad

Did you ever find the solution to the left channel issue? I have the same problem with mine.

Posted on Jan 23, 2008

  • 5 Answers

SOURCE: su-g91

Have you checked the fuse in the unit?

Posted on Aug 31, 2008

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SU-G91 amp over load wont reset.

Technics SuG91 uses a couple of SVI ( I think they are SVI ) packs for driving the speakers. These are big black plastic things mounted to the silver finned heat sinks. 95 % of the time, this is the problem. They are not very tolerant to any type of abuse, and all the amp has to do is overheat once and they are toast. 1 The SVI packs are expensive and that amp may not be worth fixing. If you know how to de-solder something, and are comfortable working with voltages that can kill you, you can unplug the amp, make sure it has been unplugged for at least 20 minutes, and gain access to the area of the circuit board that the SVI packs are soldered to. De-solder one of the packs and remove it from the unit. Make sure that when you de-soldered the SVI pack that you DID NOT accidentally solder one solder hole to another ( create a connection from one hole to another that shouldnt be there ) . Re-assemble the unit correctly, plug it in and turn it on. If the display lights up, you have removed the offending unit and need another one. If it is still in protection, then mark the one you took out as "possibly good", and repeat the removal procedure for the other SVI pack. NOTE if you decide to replace the SVI pack yourself, you will need heat sink compound ( that goo that stuck the original pack to the heat sink ). you will need to remove the old stuff ( a rag and some alcohol will work ) before you apply new heat sink compound. If you are uncomfortable with ANY OF THAT, then take it to a shop that offers free estimates. Good luck and BE CAREFUL....Rob

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Unit was clipping out @ high volume.

First of all, I would need to know the make and model number, rather than guessing. Second question, why are you driving the amp into clipping, if that's what you mean? That will destroy tweeter and midrange drivers. Certainly, if you are driving it into clipping, the heatsinks have got to be hot, and I don't believe an external fan will cool the right places. If you can get back to me with more information, you can contact me at my website,, to inquire about a repair. Thank you.

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Keep me posted.

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Did you ever find the solution to the left channel issue? I have the same problem with mine.

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I had the same problem. As soon as the volume reached about 24db it would go into overload. I was able to fix it by soldering all the connections on the larger power module. The one connected the the heat sink. When I took it apart there where several solder points that had come loose.

Oct 10, 2007 | Technics SA-AX540 Receiver

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