[vintage9594]

I have recently bought a 20 w per channel Carver Black Magic EL 84 tube amplifier, Audible Illusions M3a preamp and Zu Audio Omen speakers(98db).  I am experiencing a higher then normal level of tube noise.

Looking for some advice to lower the noise without having to change anything out.  I think a big part of the noise is the gain of the preamp but I also noticed the same noise but a little less of volume when I used the volume control of the amp with preamp removed..

Thanks
Don

[Bob in St. Louis]

I'm probably the least knowledgeable tube guy in STL, but my first guess would be to clean the sockets and pins.   

[macrojack]

If the problem persists with the preamp removed, you can direct your attention toward the amp. Follow Bob's suggestion first, and if that doesn't solve the problem, consider finding someone in St. Louis who has a tube tester. Also might consider your sources. You didn't mention what you are using but the problem may be coming from upstream.

[Bob in St. Louis]

Since we're cleaning things, might want to clean the cables and jacks.
I don't have any EL84's, otherwise I'd loan you some to try.

[Mr Peabody]

You sound like a tube guy, I'm assuming you biased the tubes after taking possession of the amp.  Unfortunately, that Zu super tweeter will expose any noise in the system, you may notice hiss on certain recordings that wasn't so evident before.

Have you tried any aftermarket power cords or see if different interconnects help?  If it's a tube making the noise though nothing will help except replacing it.   I bought some tubes one time and switched them in and out just to make sure they worked and one caused noise, it happens sometimes, I think it's called eufonic.

[galyons]

Try to isolate the suspect component.  With the system running, but no signal, power down each source connected.  Noise go away? Then it's a source. Noise still there, power down the pre. If the noise goes, it's the pre.  Still noise? Then the amps are the culprit.

Do you have a DMM that measures frequency? If so, set it to frequency.  Power up the equipment, no signal, and put the probes on your speaker terminals. What is the frequency of the noise?  60Hz, AC grounding issue.  120Hz, transformer issue. Other? You'll have to let us know.

To test for AC on the outputs of the amp, put shorting plugs into the inputs.  Put your DMM probes into the speaker jacks. (with the speaker wires removed). Power up the amp and let it warm up for 10 minutes. Set the DMM for millivolts if the DMM is not autoranging. How much AC is on each channel?  With 98dB speakers AC probably needs to be 5mV or less to be quiet at the listening position.

High efficiency speakers do not mate well with amps not designed for them.  They will show every design and/or build flaw.  Good, quiet power supplies are critical for quality, quiet, low power amps.

Cheers,
Geary

[vintage9594]

Thanks for the responses......narrowed it down to the preamp.  Maybe tubes no way of testing them and volume control are a resistor based stepped attenuator x2.  When both volume controls are turned they make a static noise at each click of the rotation on both sides.  Been reading some different forums and could be as simple as cleaning the mute switch or could have a bad resistor or 2 in the volume controls(not sure why that would make every turn of the volume controls on both side make noise?)

Thanks for the tips and it looks like it will make a trip to the repair shop on Monday.

[Bob in St. Louis]

Geary, that was a very informative post, thank you. 

[bladesmith]

I would suspect the tubes first... then connections and then the pots...

good luck..