Aboutcleggsan Expertise Consumer Electronics of all kinds. Audio, video, tv. Digital equipment for consumer use. Ham radio and automotive electronics.
Experience Electrical Engineering; recording, broadcasting, design, international standards, tv and radio theory and practice.
Organizations FELLOW of AES (Audio Engineering Society)
Senior Life Member of IEEE (Institute of Electronic and Electrical Engineers)
International Consulting Organization
Publications IEEE Spectrum
Various Consumer Electronic publications
Education/Credentials BSEE
MSCS
MBA
Awards and Honors Famous Engineer for Digital Audio
Expert: cleggsan Date: 7/11/2008 Subject: Sony STR-SE501 dreaded buzzing
Question QUESTION: I've read many posts on this topic but I couldn't find one that did what mine does. I'll try to explain as much as possible.
Vol. at 0 = no buzz
Vol. at 1 = buzz (not 60Hz hum)
Buzz gets louder with vol. up to MAX
Doesn't matter what "Input" I select (DVD, Tuner, Video, Aux, etc.)
No sources connected to receiver, different outlets don't help, buzz comes from all speakers (L, R, C, Sub)
Sub is connected using RCA to powered sub unit.
I've swapped speakers to different channels, swapped speaker wire (short, long, small gauge, large gauge)
I am a 20 year vet of 12 volt goods in cars but I don't do much at all with home stereo stuff. I have built C-Moy headphone amps and even a headphone amp for my bass guitar using a schematic from a guy on the web.
Also, the tuner part has not worked in a few years. I get nothing but static. Antenna not the problem.
ANSWER: Let me make sure: The buzz is there even when there are no input connections of any kind? Right? And, the buzz is heard as soon as the volume control starts coming up? Right? And, the level of the buzz continues to increase as you increase the volume control (until is saturates out)? Right?
The buzz is power supply ripple buzz and it is at 120 Hz, twice the frequency of the 60 Hz line. It is a buzz because it is a voltage coming out of the full-wave bridge rectifier which is NOT a sine wave but has many harmonics in it and therefore the buzzing sound.
The cause is the loss of one or more filter capacitors in the section of the power supply that feeds the amplifier section ahead of the volume control. The solution is to replace all the electrolytic capacitors in the power supply. The fact that one or two have gone means the others are likely on their way out as well.
Let me know how it goes!
C
---------- FOLLOW-UP ----------
QUESTION: That sounds like an EASY fix! Now if I only knew which caps I was replacing. I found a service manual and I have my main board out of the chassis. I found the 2 amplifiers. If I email you the service manual, could you take a look and point me in the right direction?
Answer Oh, but it is much easier than that. Electrolytic capacitors are mounted in tubular cans and are usually mounted vertically, but the telling feature is they are polarized! They are clearly marked with "+" and "-" markings on them. They virtually always have the microfarad value and voltage rating marked on the can or outside covering. If you aren't clear you can use the parts list from the service manual.
Also, the ones of greatest interest are usually somewhere near the main power supply components (which are mostly not mounted on a pc board).
But, if you get stuck, do send the manual and I can guide you in more detail.
