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Thread: Weird Noise Thru Amp

  1. #26
    Registered User almeriastrings's Avatar
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    Default Re: Weird Noise Thru Amp

    Very possible. This is a Class D amplifier module on the output and one thing that can cause issues with these is if the output inductor or the power transistors themselves get too hot (they use very little heat sinking compared to class A or AB circuits as normally, they don't need it), but external heat hitting them could do it. Symptoms can be distortion, cutouts or sudden bursts of noise - so it could be.

    No electronics gear likes being subjected to direct hot sunshine. Bad news all round. If your air temperatures were in the 90's, the gear would have been way, way, hotter as it is absorbing the direct solar heat... adding its own heat.. unable to lose it easily via convection... and positively cooking the boards in there.

    Shade gear in hot weather, never expose to direct sunshine, and consider adding an extra, external fan to boost convection.
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  3. #27
    Registered User Mandobart's Avatar
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    Default Re: Weird Noise Thru Amp

    Here's another update: I played another Farmer's Market Gig today with my Carvin AG300. Plugged in to the AC receptacle there - not using my inverter. Outdoors, Carvin up on a speaker stand, did not use an extension cabinet this time. Temperature was ~90F and we started out in the full sun at first. I brought along a small fan which I placed on top of my amp, blowing straight down onto the amp. Played for about 2 hours, 15 minutes without ever turning off. Plugged my mandocello into channel one and a SM58 into channel 2. All volumes set at about half way. No problems at all, no unusual noise, everything sounded fine. It is either a single one or combination of the following that may explain why I had no problems today:

    1. Temperature was a little cooler (90 F vs 93 F last time)
    2. Cooling fan on top of the amp
    3. Did not use the extension cabinet which draws a little more power from the amp
    4. Moved an umbrella to shade the amp after about an hour
    5. I brought along a friend's acoustasonic as a spare if my amp flaked out

    I'll keep posting on this, more for my personal log than anything else but hopefully this info is useful to someone else at some point as well. Never did hear back from Carvin on this subject - they just keep sending me ads.

  4. #28
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    Default Re: Weird Noise Thru Amp

    Mandobart, I have called Carvin before with problems and they have been very helpful, you might try giving them a call and asking for their tech department. Sounds like the temp is a probable cause.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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  6. #29

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    I can't help with the troubleshooting, but I have dealt with Carvin several times in the past. In my experience, calling on the phone is much more effective than sending an E-mail. They are wonderful to deal with once you reach them, but I concluded that there is nobody assigned to reading E-mail.

    Ed

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  8. #30
    Registered User Mandobart's Avatar
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    Default Re: Weird Noise Thru Amp

    Good suggestions about calling. I'm in the same time zone so I'll try and reach them tomorrow.

  9. #31
    Registered User Mandobart's Avatar
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    Default Re: Weird Noise Thru Amp

    Latest, hopefully last update. I called Carvin about a month ago and reached a real person in their tech department. Since I was still in the 1 year warranty they told me to remove the power amp from the cabinet and send it to them and they would fix it. So I did that. When I took the amp out I was surprised to see great gobs of silicone RTV deposited like some kind of random incontinent rubber bug got loose in there:
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    I packaged up my amp along with a long letter explaining the symptoms I outlined above. I also stated that since the problem is temperature-sensitive, and RTV is a good thermal as well as electrical insulator, I was concerned about the non-workmanlike manner in which it was so liberally applied. I contacted the guy I spoke with and asked him directly what he thought of it.

    Never did get an answer, but last week (about 2-1/2 weeks after I sent it to them) I received an email saying they fixed my amp and were sending it back. I replied with a thanks and also asked if they could tell me what the cause of the problem was and how I can prevent it from recurring. They answered "gee we don't know, I don't have the tech's notes, but we fixed it and you're all set." The amp arrived today, looking like they gobbed a bunch more RTV on it:

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    So I re-installed the amp and tested it out. Works fine, sounds just as good as ever, but I won't know until next summer if it really is fixed as our 90 F days are over here. So I give Carvin a medium-high (7 out of 10) rating for customer service - they were responsive over the phone, they kept me informed on the repair status, shipped back to me no charge. But they weren't able to tell me what the problem was and as a former nuclear submarine electronics tech I hate to see such sloppy work, and I wonder about the silent treatment when I called them on it.

  10. #32
    Registered User almeriastrings's Avatar
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    Default Re: Weird Noise Thru Amp

    Hmm... well, they (at least some brands) sometimes add this stuff to amps that are in active speakers or combo amps to reduce microphony or vibrations from affecting inductors or caps. Certainly looks like that is the intent here, and they have been very generous with it. Maybe there was a bad pcb connection, or dry joint on an inductor or cap and they resoldered it and glued the things down even more? As you rightly say, it does not help with heat dissipation..
    Last edited by almeriastrings; Sep-21-2016 at 3:17am.
    Gibson F5 'Harvey' Fern, Gibson F5 'Derrington' Fern
    Distressed Silverangel F 'Esmerelda' aka 'Maxx'
    Northfield Big Mon #127
    Ellis F5 Special #288
    '39 & '45 D-18's, 1950 D-28.

  11. #33

    Default Re: Weird Noise Thru Amp

    Hello all, new user here. I found this thread via google search. I have an AG300 amp that has the same problems that the OP described, I'm wondering if the amp ever got cured? And if so, what was done to cure it? Any help is appreciated!

    What mine amp does: operates fine for one hour, or ten, then suddenly puts out white noise, like an AM radio that's not tuned to a station. This has happened indoors and outdoors, in heat and cool, and medium and low volumes, even with the amp just idling with a guitar plugged in but not being played. When the noise happens it's noticeable louder than the music that preceded it. Once the noise pops up, it stays there regardless of the volume settings of channels 1,2,3. When the noise is there, it goes up and down with the master volume. I have seen the noise go up and down with the master level for Effects 1 (not channel 1), and it may have also done that with Effects 2 but can't remember. Rebooting cures it, but the problem comes back and it comes back faster than it did the first time.

    Sigh. I've bought used gear for decades, this was my first time buying a new piece of fairly expensive gear. I really wanted to like it. But about a year after I got it, it would just suddenly cut off on me, no sound, and not driven that loud either. It was ~2 weeks out of warranty but I talked to their very helpful technician, then Carvin fixed it for the cost of shipping ($14). But several months later this problem rose up. Spent 45 minutes yesterday just to talk to a sales guy who recommended sending it in for repair or trading it in to get 30% off a new one. I'll see if I can get hold of the technician today. But I am pretty disappointed with Carvin, over $500 and I hardly got a few gigs out of this amp. When it works it's a great, but cutting out or spitting out white noise, can't risk it on a gig.

    Thanks all,
    -Steve

  12. #34
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    Default Re: Weird Noise Thru Amp

    Could be a couple of things, one is a bad component, but what I suspect is a cold solder. Works until the solder joint heats up then your noise. Comes back faster as it has not cooled completely. Sometimes you can find these by just looking at all the connections, but it's a real PITA to get the board out and flipped over. I have had good luck with Carvin in the past, hopefully they will step up for you, good luck.
    THE WORLD IS A BETTER PLACE JUST FOR YOUR SMILE!

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  14. #35
    Registered User Mandobart's Avatar
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    Default Re: Weird Noise Thru Amp

    Quote Originally Posted by Steve Granger View Post
    Hello all, new user here. I found this thread via google search. I have an AG300 amp that has the same problems that the OP described, I'm wondering if the amp ever got cured? And if so, what was done to cure it? Any help is appreciated!

    What mine amp does: operates fine for one hour, or ten, then suddenly puts out white noise, like an AM radio that's not tuned to a station. This has happened indoors and outdoors, in heat and cool, and medium and low volumes, even with the amp just idling with a guitar plugged in but not being played. When the noise happens it's noticeable louder than the music that preceded it. Once the noise pops up, it stays there regardless of the volume settings of channels 1,2,3. When the noise is there, it goes up and down with the master volume. I have seen the noise go up and down with the master level for Effects 1 (not channel 1), and it may have also done that with Effects 2 but can't remember. Rebooting cures it, but the problem comes back and it comes back faster than it did the first time.

    Sigh. I've bought used gear for decades, this was my first time buying a new piece of fairly expensive gear. I really wanted to like it. But about a year after I got it, it would just suddenly cut off on me, no sound, and not driven that loud either. It was ~2 weeks out of warranty but I talked to their very helpful technician, then Carvin fixed it for the cost of shipping ($14). But several months later this problem rose up. Spent 45 minutes yesterday just to talk to a sales guy who recommended sending it in for repair or trading it in to get 30% off a new one. I'll see if I can get hold of the technician today. But I am pretty disappointed with Carvin, over $500 and I hardly got a few gigs out of this amp. When it works it's a great, but cutting out or spitting out white noise, can't risk it on a gig.

    Thanks all,
    -Steve
    Hi Steve - I'm the OP. I sent just the amp removed from the speaker cabinet back to Carvin for repair late last summer. They fixed it (?) at no cost to me even though it was about three weeks out of warranty. I use a (?) about the fix because though I've used the amp several times since the repair, I haven't used it in a high heat/direct sun application so I can't say it is fixed, as the only two times it exhibited the problem was when used outdoors in direct sun on hot summer days. I could not reproduce the problem at home even leaving my amp on all night.

    I recommend you put an inconspicuous mark with a sharpie somewhere on each circuit board when you send the amp back. Then you'll know if they actually replace a board. They were unable to tell me how they "fixed" mine. I also bring a small portable fan with me now to try to keep things cooler. Best of luck! Sorry to hear of your trouble.

  15. #36

    Default Re: Weird Noise Thru Amp

    Thanks Mandobart. Glad to hear your troubles are seemingly over, fingers crossed for you. When they fixed (?) my amp for the cutting_out_suddenly problem, they didn't tell me exactly what they changed either, just that they did an 'upgrade'. My guess is it was a poorly designed protection circuit kicking in, and they just reworked it. I'm an electrical engineer with an analog and power supply background, so I have a fair idea of where to look for problems.
    Good idea with the sharpie, I'll do that. Although I'd rather they replace a circuit, honestly. I have a feeling that they know there's a bug in the design and have probably corrected it. Most people seem quite happy with this product, it's one of the reasons I went for it. Here's hoping.
    -Steve

  16. #37

    Default Re: Weird Noise Thru Amp

    Originally Posted by Fatocaster View Post
    I posted recently in the Carvin acoustic amp forum about this problem and in the course of investigating I discovered posts concerning the same problem I was having.
    I purchased my amp in July 2014 and it started having issues Sep. 2016 I had taken it to a local amp guru that could find nothing wrong. It had been doing fine until last week when the "white noise" returned!
    I contacted A Carvin tech that told me my options but at the end of our conversation he suggested that they may be able to sell me just the module (the "brain" of the amp) since my cabinet and speakers were not the issue.
    So I called a sales rep and sure enough... A replacement is on the way for $191 shipped. I probably could have got off with $95 repair by shipping it to them, but I figure I may as well just spend the extra $$ and get basically a brand new amp. Here is a YouTube link where I was lucky enough to catch the problem on video!
    https://youtu.be/N2nW1MmIszE

  17. #38
    Registered User Mandobart's Avatar
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    Default Re: Weird Noise Thru Amp

    Wow Fatocaster - that's pretty much what mine did too. Only twice, and only when playing outdoors in the full sun on a hot day. I couldn't reproduce it at home.

  18. #39

    Default Re: Weird Noise Thru Amp

    Hey if anyone is still here ... I recommended the AG300 to a student Xmas 2016, and here it is almost out of warranty and Carvin Audio is busted outa business. This AG300 amp has a little crackle/fizz/AM-radio whine coming out of the speaker even with input volumes and master all the way down...but NOT that loud hiss that fatocaster caught on video. No noise in the headphone output nor the stereo music input jack with my iPod sound fine. So that means the preamp section is OK. So what's the problem? And has anybody found the schematic?

  19. #40
    Registered User Mandobart's Avatar
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    Default Re: Weird Noise Thru Amp

    I can only offer basic troubleshooting suggestions, which you may have already done. Trying cycling the pots several times through full range with the amp off to try to wipe them clean. Try swapping out instrument cords and instruments. Try original instrument and cord thru a different amp. Try all the channels on the amp. One thing I found is I get a similar noise if I'm playing an iPod thru the aux channel while also charging it with the USB connection. I know some other people had the same issue.

  20. #41

    Default Re: Weird Noise Thru Amp

    Quote Originally Posted by Mandobart View Post
    I can only offer basic troubleshooting suggestions...
    Thanks Mandobart, I'm fairly certain that the preamp section is fine given that there is no noise on the headphone output (I haven't listened to the DI out yet, but it's probably OK for the same reason). Stands to reason that the noise therefore is coming from the power amp section -- right? Also, the noise is present with the master all the way down, therefore the noise is being injected POST master volume pot -- right??

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