Overheating Amp?

**scottdawg** · 06-22-2003 01:29 PM

I have a problem, my new (used) B & K ST3030 seems to be getting hot. I know an amp will get hot but this seems to me to be excessive. Areas of the cover directly surrounding the heat sinks are too hot to touch. I have the amp in open space providing free air all around it. The problem is that when playing at approx. 50% of volume the amp will lose the highs and bass gets real muddy, as soon as I turn the volume down for a couple seconds the treble and bass return to normal, it seems that the right side goes away first and then the left. The problem is only apparent during times when a track gets into heavy jams with demanding bass. The reason I have focused on overheating is that when I first listened to it the amp was in an area that did not provide free air around it and was without a doubt getting too hot. After moving it the amp did not get as hot and the problem occured less frequent at at the higher volume. Any comments or suggestions to resolve this problem? Could it be the AC supply cord/circuit or something internal that needs to be repaired or will cooling fans patch it until it breaks? Thanks in advance. Scott

**polkatese** · 06-22-2003 01:38 PM

Scott,
sounds like a potential voltage drop problem to me. Do you have access to a voltmeter? I use a Panamax 5500 that has ammeter and voltmeter, and I noticed (especially at night) at moderate volume level, the voltage could dip a bit, although it doesn't go down below 117 volts. Normal is about 124 volts. I have dedicated outlets for the gear, and my B&K AV125.7 also gets warm, especially during movies and multichannels audio listening. I installed a small fan to help circulate air inside the cabinet and it helps a lot.

**Tour2ma** · 06-22-2003 02:05 PM

Good call polka... be my first guess as well.

Not ultra surprising that it's not comfortable to keep your hand on a class A/B amp when driven, but it shouldn't drive itself into protection mode.

What model speakers are you running scott? 4 or 8-ohm?

Other question is whether it is the amp or the speakers that are going into the protect mode?

**scottdawg** · 06-22-2003 02:43 PM

Polka, I would be lost without my Fluke 177 multimeter. I use it all the time as a contractor here in Augusta specializing in industrial electrical construction. I just checked the voltage at the receptacle and it measures 120.7 volts which is good, that leads to the point in your reply stating that it could drop during listening which I have not measured. I will perform a continuous reading while listening sometime later today. I should just get in the attic and install a circuit using some #10 wire and eliminate that potential cause. I will do the test though to see whats happening with the voltage. Thanks
Tour, My SDA SRS 2's @ 5 ohms are what I am driving. The JBL's havent had any play time yet. I didnt even consider it to be the speakers, the ST3030 is rated at 200@8 ohms, 300@4, I dont know what the SDA's are limited at but ass u med at least that.

**Tour2ma** · 06-22-2003 03:54 PM

Are you running the SDA's with the standard SDA cable in place?

If yes, maybe the 3030 is not a common ground design... Other members running a SDA/ non-common ground combo report overheating, amp shut-downs, etc. Apparently it's like there's a partial short producing huge current draws on the amp. Which leads to over heating, etc.

Try disconnecting the SDA cable and see if that solves it.

**scottdawg** · 06-22-2003 04:29 PM

Tour, I am using the standard cable. The amp doesnt specify common ground or not. Is there a way to tell by looking inside? I will try what you suggested now.
P.S. The voltage is not dropping below 119 volts measuring the other plug on the same receptacle. The problem did occur while the measurement was being taken.

**scottdawg** · 06-22-2003 05:23 PM

Tour, I did about a 30 minute test without the interface cable connected, the amp is warm but not hot. I did check the resistance on my 2 negative speaker terminals without the speaker wire connected and they check .2 ohms which means they are connected internally, however they are open or isolated from the incoming or chassis ground. I dont know what common should be. In searching previous posts with "common ground" I read where the sound was horrible from a non common ground amp using the intereface cable and that is not the case with mine. It sounded great until the amp or speakers go into protection mode. Is there a loss in quality using the modified interface cable for non common ground amps. I was thinking I should try one. Without the interface cable the system was a little less than sucky.

**Tour2ma** · 06-22-2003 08:32 PM

scott,

My gut tells me that 0.2 ohm is too high for common ground. I get 0.0 on mine.

Suggest you ring up B&K CS this week and see what they have to say.

One member, at his amp manufacturer's suggestion, created a common ground amp by using a piece of wire to connect the negative terminals on his amp. It's not a universal fix, so I wouldn't try it if I were you, but it shows there are potential easy fixes.

Don't sweat it. Youll be back in SDA heaven in no time.

**scottdawg** · 06-22-2003 09:24 PM

Thanks for the help tour, I made an incorrect statement earlier. If I knew what was meant by common ground I could figure it out. So far I have determined that my source ground from the ground prong on the power cord is isolated from the chassis and the negative of the speaker connections. The chassis is common to the negative of the speaker connections at .2 ohms, you may be right about .2 being too high but I think it would be either infinity or somewhere close to 0.0 ohms. Did you check your amps incoming ground to the chassis for resistance I am curious to know what that is. My speculation is that common ground means everything in the component is grounded to the source ground. If I am correct then I have a non common ground amp.

**peckgary** · 06-23-2003 04:35 PM

Hi Scott,

I had the same type of thing going on when I upgraded from an Adcom GFA-555 to the GFA-5500. The amp did not actually get hot, but the sound was really muddy and nasty on my SDA 2B's. I contacted Ken at polk customer support and he sent me the instructions to make an SDA interconnect cable with an isolation transformer in it. This seemed to have solved the problem. I lost a some volume out of the SDA drivers, but it sounds alot better then it did with out the isolation transformer.

My understanding on what a common ground amp is, that the left and right channel grounds are shared. On a non common ground amp it is like having two monoblock amps inside. Both are completely separated. I could be wrong, and if so I would appreciate somebody explaining the difference.

Hope this helps,

Gary

**goingganzo** · 06-23-2003 04:46 PM

comonground is that all the amps ground to the same point. the jumper between the negetives will not work that is kist like hooking yp the sda to the amp same efect. the olny way is to seperater the grounds. ps curent flows negetive to positive.

**Tour2ma** · 06-23-2003 04:56 PM

Correct pg, common ground refers to the "negative" speaker posts on the amp. The ohm reading between them should be 0.00 for a common ground design. I'm not sure non-common amps are completely like mono blocks, in that they may not include two power transformers, etc., but you are obviously right that two mono's would not share negative speaker terminals.

I don't know the SDA circuitry (need to get Ken S. to share a schematic), but as I mentioned earlier, I believe the common ground is needed to keep the SDA connector from acting as a short in the amp's output. May have to do with the amp's external feedback loop.

BYW, scott, when I mentioned wiring the negative posts together, I did not mean to say don't do it period. I just meant don't try it before you ask B&K about it and see what they say.

**scottdawg** · 06-23-2003 10:18 PM

Cant call B & K anytime soon due to work load. I did email Ken and hope to get a reply tomorrow. This gives me a chance to demo the JBLs until I come up with a solution. Thanks for the help guys, I welcome any other input from those electronic gurus out there. I know my big wire stuff but this small wire stuff takes to much thinking.

**F1nut** · 06-23-2003 10:39 PM

Send mantis a email, he's a B&K kinda guy. Maybe he can help you.

**Tour2ma** · 06-23-2003 11:07 PM

F1,
Good thought, Dan just might know.

Originally posted by scottdawg
Without the interface cable the system was a little less than sucky.

Scott,
I missed the above part of an earlier post of yours. It concerns me a bit.

I'd expect the imaging to collapse and the bass to fall off a bit, but not the performance to go from great to "less than sucky".

I think you should still follow through with Polk CS on the troubleshooting guide.

**scottdawg** · 06-23-2003 11:53 PM

Tour, after posting that my tubes warmed up and it got better, not as good as when the IC was installed and understandable. One thing I didnt mention was that the amp seemed to push a hell of alot more without the IC hooked up. At near 50% was louder without the IC than with it.
F1, I will email mantis thanks.

**Tour2ma** · 06-24-2003 02:15 AM

Scott,
Excellent... I think the volume gain is confirming a ground loop with the SDA cable in place.

**F1nut** · 06-24-2003 02:27 AM

Tour, way to help the bro out! I concur with your findings.

**scottdawg** · 06-24-2003 06:04 AM

I cant frickin believe it, Alls I have to do is get a amp that is a common ground amp. What happens I get a non common ground amp. Dayum!! I guess it could be worse I could have got a non working amp. OK so can someone e-mail me the drawings for making the cable that I need. Thanks
Scott

**mantis** · 06-24-2003 07:03 AM

Scott,
you got mail......

By the way by the sound of this thead,I believe the amp is not a common ground amp.If you connect the sda cable and the amp gets hot,remove the cable and it just gets warm,then I believe your answer is there.

Do you like the way your speakers sound without the cable in place????I know your kinda of taking away from the design of the speakers sda but just curious......

The Isolator inline on the cable.I wonder if it takes away performance from sda????I assume it's Isotating the ground,lifting it if you will.

If the B&K st3030 isn't a common ground amp,then I suggest if you really love your sda's,look of a high quality amp that is.....

**F1nut** · 06-24-2003 11:41 AM

There is no need to look for another amp and the AI-1 interface cable does not take anything away. It's a must have for using mono-blocks, I tried it and it sounds great.

**scottdawg** · 06-24-2003 10:52 PM

Tour, Polk, PG, Mantis and F1, Your input and time has been greatly appreciated. In Kens reply he states that the volume knob at the 12 oclock position ( what I call 50%) is actually the amps full output. I didnt know that. I really dont think I gave him enough info though cause he is suggesting that the amp just might be getting hot due to high volume. The non common ground problem would be very apparent. ?? Mantis If you could find out for sure that would end any more speculation.
Thanks
Scott

**mantis** · 06-24-2003 11:04 PM

In the middle of a big job( really nice Sonus Faber HT and REL)

Niles 6 room Multiroom system with the Gloria(4630)

I will find time to call my guy tomarrow about your 3030...Sorry I didn't get a chance today....

**mantis** · 06-30-2003 10:11 PM

the amp is a floating ground amp.Not a common ground

**scottdawg** · 06-30-2003 10:56 PM

mantis, Thank You.
That solves my speculation even though it wasnt what I wanted to hear. Thanks to F1nut I will construct the cable I need. Hope I can help you all out in the future.
Scott

**mantis** · 07-01-2003 06:45 AM

Your Welcome.

**F1nut** · 07-01-2003 02:46 PM

Scott,

Glad we could help you. Let us know how cable works out.

F1

**scottdawg** · 07-01-2003 06:13 PM

Well not so fast Scott. Guess what guys I just learned that since my speakers, SDA 2's pre 1987 with the twin blade interconnect will not work with the isolation transformer for whatever reason. This was from Ken S. at polk. I replied about any modifications I can make and should get a reply tomorrow.

**peckgary** · 07-02-2003 09:00 PM

I have 2 pair of SDA 2B's and my original pair was a pain to get working with the isolation transformer. I had the blade/blade interconnect cable and the top blade was actually not connected to anything at all. The bottom was the only blade that had any connectivity. To finally get them to work, I had to hook the bottom blade to the one wire on the isolation transformer and then the other wire to the negative ground of the speaker. This completed the circuit and I got sound out of the SDA driver. You will have to do the same for the other speaker.

You will have to remove your passive radiator out of one speaker to see if one or 2 wires are hooked to the interconnect cable.

Also ask Ken to fax you the schematics. He faxed me all of them for all of the SDA2 speakers. It was really the only way I figured out how to get it to work.

I banged my head on the wall for 3 weeks trying to figure it out.

I just had to make another cable for my second pair of SDA2B's.

I found out because of this thread my B&K ST1430 amp also is not common ground. It was running a little warm, but other then that I did not have any problems. It runs alot cooler now thought.

Let me know if I can be of any assistance. I would be glad to try and help you out.

Gary

**scottdawg** · 07-02-2003 11:31 PM

Gary, According to Ken the only way I could make them work is to replace the entire crossover network. He recommended getting a common ground amp over that task. For now I am on pause, I will have my L100's in place tomorrow. I might even put the SDA's in my bedroom hooked to my old Yamaha amp until I can get another for my main system.

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