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Carver CT-28v Tuner preamp - Has a hum/buzz (soundls like a ground loop) that is heard as soon as the unit is turned on. Does not increase with volume, just stays the same and is continuous. Changing cables/connectors/etc between it and all other compnents has no effect. Any suggestions as to what might cause this problem? Any one have a service manual I can use to fix?

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Reverse the polarity of the AC plug and try it. Is there a headphone jack on the preamp? Try headphones with the preamp standalone without the amp attached.

Are you sure the preamp is the problem? I assume you also have an amp or you wouldn't hear anything. Power up the amp with nothing but speakers attached. Hum??? It's in the amp. No Hum? Attach just the preamp with no external components. Hum now? It's the CT-28. Turn it off an exercise every switch and knob throughout its range numerous times. Try again. Still humming? Manipulate source selections, Tape Monitor, everything.

Posted on Nov 20, 2009

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Hum can come from a jillion different places. Is this hum coming from the unit with no speakers connected, or is it heard through the speakers? What sources are being used? What cables? Are thereany common sources of interference near? Troubleshooting is difficult without much information.

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Power supply noise lg 42LV3730?


If your tv uses rca a jacks to connect it up to the reciever, You coul try what is called a ground loop iceilator, It hooks up to the patch cord,If they are still availible.They were use on car Stereo,s when you have a amp hook up to it,In some vehicles you would get a ground loop hum. Radio Shack might still sell them. You could try one.It work for me with a (Carver) Power amp that i use to own.

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After a power outage I have a loud hum.


Hi, The Ground Rules Of all the annoyances that can afflict any audio/video home theater or even a simple stereo installation, the notorious "ground loop" may well be the most difficult and persistent one to track down and eliminate. A "ground loop" is caused by the difference in electrical potential at different grounding points in an audio/video system. (All the grounds in an A/V system should ideally be at "0" potential.) A ground loop typically adds a loud low-frequency hum or buzz as soon as you plug in any of various audio or video components, including subwoofers, cable-TV outboard boxes, satellite-TV feeds, TV displays, amplifiers, A/V receivers or turntables. The buzz/hum is a byproduct of the multiple power supply cables and a ground voltage differential within your system and its network of interconnecting cables.

Here are some methods to help you get rid of ground loops. Try these first and don't waste money on a power "conditioner" which, in most cases, won't help. (There is no need to "condition" the AC power for your system. Your receiver or amplifier already has a power supply with its own filters and transformers. No further filtering is normally required.)

If you get your system up and running and hear an audible buzz or hum, the first culprit to look at is either the powered subwoofer or your cable-TV or satellite-box feed at the entry point to your system.

First, the subwoofer: unplug the coaxial cable that connects to your powered subwoofer to see if the ground-loop hum disappears. If it does, it's likely coming in through your cable/satellite TV feed.

Reconnect your subwoofer's coaxial cable from the subwoofer input to your receiver's subwoofer output and disconnect the cable-TV feed (or satellite feed) from your outboard set-top cable box or satellite tuner. Be sure and disconnect the cable before any splitters. Now see if the hum/buzz from your subwoofer stops.

If that eliminates the hum, you can install one of these inexpensive in-line ground isolators from Parts Express or Bass Home. Note that these transformer-based ground isolators will work fine with analog cable-TV feeds, but depending on their design they may interfere with or block reception of HDTV signals via a digital cable or satellite dish feed.

Install the ground isolator between the cable-TV feed and the input of your outboard cable-TV box or satellite tuner (or the TV display's antenna or cable input if you have a set with a built-in TV tuner or a cable-card ready set). In many cases, the ground isolator will "break" the loop and remove the annoying hum or buzz by isolating the TV-cable ground.

If a hum remains with the TV cable completely disconnected from your system, or you don't want to risk degrading reception of HD signals from a cable or satellite system, then you may have to add a ground isolator like this Radio Shack Model 270-054 between the line-level coaxial subwoofer cable from your A/V receiver and the line-level input jack on your powered subwoofer.

In all cases, if your subwoofer has a ground-lift screw like some of Axiom's subwoofers, try first removing the screw (or replacing it) to see if it increases or eliminates the hum. It may or may not make a difference.

If you do not have easy access to the aforementioned ground isolators, here are a few more tips:

Try plugging the subwoofer into a different AC outlet in the room, one that isn't supplying power to your components (A/V receiver, TV, cable box, etc.). That might fix it.

Try reversing the AC plug for your A/V receiver or the powered subwoofer. If it's a 3-wire plug or a polarized plug, which has one prong wider than the other, you won't be able to reverse the plug. For safety, do not use a "cheater plug" to bypass the 3-wire plug.

With the power OFF, reverse the AC plugs one by one of any other components that have a standard 2-prong AC plug that isn't polarized. Each time you reverse a plug, turn on the system with the attached component and your subwoofer and see if the hum disappears. In some cases, reversing one or more plugs will eliminate the hum.

If you have a turntable, try connecting a separate ground wire to a chassis screw on your preamp or receiver and see if the hum disappears. If you already have a turntable ground wire, try removing it from the preamp. One or the other may eliminate the hum.

Finally, here is another solution that worked well for a member of our message boards who decided to discard his ground-loop isolator on his subwoofer: "I took off the ground-loop isolator I'd been using and connected a plain 14-gauge wire to chassis screws on the sub and the receiver then powered everything on. Although hum was still there, it was far lower than before. Next I unscrewed the ground-loop screw on the back of the sub and that took care of the hum completely."

Almost certainly sounds like an earth loop to me, but can be caused by a poorly made transformer or phase shifts on the mains supply. Visit some power conditioner web-sites like Isotek or Isol-8 (or google "earth loop") where there's plenty of advice on how to reduce/eliminate earth loops and other causes of mains-induced hum (transformer problems etc).

Hum on the speakers usually indicates that there is a DC voltage on the speaker line. DC voltage on the output lines would be caused by a shorted output transistor.


Have a nice day...

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1-shut down all flourecent lamp and check.
2-check for your cables in a good condition and no touching of wires to the body of amp.
3-connect(ground loop isolator)code number(270-054)from radio shack near you and connect it between your audio device(like cd player and amp)

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first of all you must connect as follows.
1-preamp/mixer-------equalizer/reverb unit------amp-----speakers(keep all equalizer control to 0db).
2-check your cables for good connector no touching of any inner wire to chassis of any equipment.
3-go to radio shack and buy(ground-loop isolator).
parts code(270-054)-----better to buy two pieces and connect it between your equipment.

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Hi John...
Are the caps completely destroyed?

http://www.free-service-manuals.com/Audio___Hi_Fi/Carver/index.html

For $14.00 / 3 months D/L as many as 3 manuals a day.
I use it A LOT.

Cheers,
Scott in Verrrrrrrrrrrrrrmont

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