Sunn Concert Buzz

[Rajio]

I recently bought a used 1975 Sunn Concert Lead and I noticed that it has a bit of buzz. The buzz seems to get louder with the volume and I have no idea what to do about it. I checked the speakers in the cabinet and the cables and they're fine. I don't know much about amps, so is there an easy way of fixing this problem?

[tube]

hi rajio,

 it could be a ground problem in the preamp stages or a bad capacitor, again in the preamp stages. if the "buzz" you describe changes with the position of the volume control, it indicates troubles in the gain section.

 as an experiment, try moving the physical location of the amp to check for interference from another source (power line hum or radio frequencies bleeding across the preamp.) if you still hear the noise (without anything jacked into the inputs) it's probably a capacitor that has gone bad. they have a defined shelf life of around 7 years (give or take a couple of decades, hehe.)

 for anything outside of induced interference or a raunchy guitar cord you should find a qualified technician to diagnose the trouble and make the repairs. it isn't something you want to poke around at.

 best regards, tube

[Babs]

I have a 1973 Concert Bass that had the same type of problem. I opened it up and found that most of the larger electrolytic capacitors has leaked. They had fuzzy, crusty bubbles on the their positive sides. Electrolytic are fluid-filled (most anyway), so the leakage will significantly affect their filtering capability.

I am an electrical engineer and pretty familiar with a soldering iron, so I removed the pre and power amp boards and replaced these capacitors. The amp sounds great now.

If you have ever soldered a component onto a circuit board, replacing the capacitors is something you can do. If not, I agree that you should leave the work to a pro (or, if you are anywhere near Milwaukee, I can do the job for a nominal fee :).

Babs

[Rajio]

Actually, I live on the east side in Milwaukee! What a coincidence!!!!!!!!!!!!!    I would really appreciate if you could take a look at it for me. I'll give you my email and maybe we can set up a time so you could take a look at it. I don't know anything about electronics so this would be a huge help. Here's my email:

smartpopboyidol@aol.com

Thank you very much!

[tube]

babs,

 as a precaution, i'd suggest that you bench test the electrolytic caps that you will substitute for the bad ones. in the lab, i'd always use a suitable power supply, current limiting resistor, bleed resistor and cover the test component with a pickle bucket. if the caps are weak, you'll want to know about it before you install them and they spew electrolyte all over the circuit board.

 since electrolytic capacitor technology has gotten better since this old amp was built, you can select low esm, low inductance caps wired into capacitive "banks" to replace those big, ugly, noisy ones. the new ones handle in-rush currents much better and will really increase the stability of the amp's power supply, not to mention make it much "punchier."

 you'd be surprised at how many times i've proven aando peraandi's theoretical "noise emitting capacitor" model - screw up and your new caps will explode with a loud pop.

 the outgrowth of peraandi's continued research gave birth to the "confetti generator" - that can be experienced by connecting a high current power supply to the capacitor in reverse polarity.

 best regards, tube