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Hey folks, I'm looking for some help with troubleshooting my Technics SE-A900S power amplifier which distorts in the right channel at higher volumes only. Sorry about the long post by the way! I've already spent some time looking for the issue and so have plenty of context, which I'll try and make as succinct as possible. Troubleshooting notes and context: The distortion is in the right channel only, in both speakers A and B. Tested with two different sets of speakers and have also tried switching the speakers around. Distortion is always on the right channel - ruling out speaker issues. I don't hear any distortion on headphones plugged into the headphones jack on the front of the amp at any volume. There is no distortion at low sound levels. It only kicks in at higher volumes and I was able to confirm this with a scope as well (More details in linked pictures below). There seems to be no distortion in the output if I remove the speakers at any volume levels (confirmed with a scope). Visual inspection of the circuit board shows no signs of damage, burns, faulty components like bulging capacitors etc. When I first opened the case, I noticed a weird plastic/metallic looking film stuck across a couple of the legs of the IC SVI3205B (which is the power amplifier IC). Removing this made no difference to the issue. Continuity test showed that this material isn't conductive. I'm assuming this was never a problem but thought I'd mentioned this anyways. (I know the film looks little like what might be used in electrolytic capacitors, but I have spent a fair bit of time hunting for any blown caps but I see none.) Scope output at various frequencies. I used an audio signal generator as source and then plugged my scope in parallel with a speaker to measure amplifier output. Source signal was always a sine wave at various different frequencies. 200Hz Right channel, distorted 200Hz Right channel, clean 800Hz Right channel, distorted 800Hz Right channel, clean 1.6KHz Right channel, distorted 1.6KHz Right channel, clean 3.2KHz Right channel, distorted 3.2KHz Right channel, clean 6KHz Right channel, distorted 6KHz Right channel, clean 12.8KHz Right channel, high volume distorted 12.8KHz Right channel at low volume, clean 12.8KHz Left channel, high volume clean It also seems like the signal starts distorting at lower volumes at lower frequencies and requires a lot more volume before it starts distorting at higher frequencies. [Circuit diagram of the amp from the service manual (I've tried to trace the Left and Right channel signal path in the circuit diagram using Yellow and Orange colours respectively) as context for the following notes.] I traced the distorted signal through the circuit and can see it all the way up to pin 16 of the preamp IC AN7062N, however, there is no distortion at pin 17. (This is located at the far left of the circuit diagram I linked above, not too for from the signal input posts) I've swapped out the transistors Q402 and Q452 with the equivalent transistors Q401 and Q451 on the left channel respectively and the distortion remains in the right channel. I have also spent a bit of time testing most electrolytic capacitors in-circuit with an ESR meter but don't have much to report here. I've also re soldered some joints along the right channel, but definitely not the entire path... this was random and seemed like a waste of time. While asking for help elsewhere, I took pictures of the actual circuit board, linked below in case they are helpful. Circuit top shot (stitched, there is a fair bit of overlap so may look weird) Circuit top shot Preamp side of the circuit Shot of the MOSFET module Power amp module and the adjacent circuit Shot of some of the transistors across the L and R channels The main caps A shot of the bottom of the circuit board showing the traces (stitched, again there is a fair bit of overlap so may look weird) Circuit board bottom Would appreciate any help I can get in hunting down the root cause here. Thank you for your time and help

Hey guys, Got handed down a sick sound system from a relative that's downsizing, and he said he's not sure whether or not the subwoofer actually works. He's not a massive hifi/electrical guy so it's up to me to diagnose it. For now I just need help knowing what the correct way to connect it is, so I can know whether it actually works under normal conditions, and if not then I'll open it up and get the multimeter out. Receiving this system is what spurred me on the join this site because I really want to optimise it and learn how to use it well, because I don't have any hardcore hifi experience, just tinkering with cheap junk over the years. So far I've just tried connecting the amp's subwoofer port directly to the "low level input" with a 1 to 2 RCA cable, and didn't get anything. Fuse is intact. So: Looking at the photos of the inputs, are this sub and amplifier actually compatible, and if so, what's the best way to connect them? Should I care about the speaker out part on the sub or just throw the speakers directly onto the amplifier? Also, can someone give me a rundown on the gain/Freq knobs as well as the on/auto/off and phase switches? Like, I know what gain is from playing my guitar, and I understand that the frequency knob will be probably focusing the sub on a particular frequency to thump out or isolate, but I don't know what kind of range I want to keep it on for it to be good. Absolutely no clue what the phase bit is for. Cheers, and happy listening

I'm having an issue with an electrical buzzing noise coming out of the tweeters of my active monitors, I'm trying to determine the cause so I can fix it (ideally without having to resort to ground loop isolators). On Monday I received a new JDS Labs Element II DAC/amp unit to replace my dying Audio GD NFB 15.32. The Element is USB only, where-as I was using an optical cable with the Audio GD. Upon changing over to the Element, I noticed a 'dirty' buzzing sound coming from the tweeters (JBL 305P MkIIs) that was not there before. This buzzing is totally independent of the volume pot on the Element or volume in Windows. It ceases when I switch to headphone output on the Element or when I turn my computer off. Additionally, this buzzing behaviour is not present when I plug the Element II into other devices. I've tested it with two laptops (a dell and a macbook air) as well as my android phone. The noise seems to correlate with system load (it becomes considerably more pronounced when running a game, sounding sort of like coil whine) but also changes in pitch when I move the mouse and takes on an even buzzier sound when I use the scroll-wheel. I'm not electrically knowledgeable, so please enlighten me if I'm totally mislead on this, but if this buzzing was a regular good old fashioned ground loop issue, wouldn't it still occur even if I had the element plugged into a different source? FWIW; everything in my system is plugged into the one power-board, which is plugged into the wall via an extension cable. I can only conclude, with my layman lack of knowledge and the process of elimination I've done so far, that it's an issue with my computer since it's fine with the laptops and phone. When I think about what could be wrong with my PC to cause this issue, my mind immediately goes to my power supply, which has made a buzzing noise when running since the day I bought it last year. Does it make any sense that a bad power supply might cause something like this? If it does, I'm strongly considering buying a new different PSU and cross my fingers that it fixes it. It's not too risky as I would return my current one anyway (I've just been too lazy to do so and it hasn't appeared to have caused or been related to any real issue until this). Sorry for the wall of text, would appreciate any insight or thoughts on this! tl;dr - Active speakers buzzing since getting JDS Element II. Buzzing seems to be correlated with PSU buzzing. Speakers do not buzz with other computers used as source.

Trying to fix the issue with this Luxman amp. Takes a while to get out of protection on start-up. When outputting more than about 1W, speaker makes popping sound, if left playing, makes one really loud pop and turns itself back to protection mode. I took it open and got some pictures. Seems like the amp had been repaired before. One of the amp board looks like it's been blown up before. the main power transistors looks different on the power amps, is that a concern? The 2SA679 is swapped for 2SB655A and 2SC1079 is swapped to 2SD675A. Any ideas what would be causing the issue? Any help is appreciated.

Hello! I'm new to the forum, and seeking some help. I have been given a Cutec L-200 amplifier. I've hooked it up, etc. On powering up, it's showing as receiving good consistent signal, but no sound is being sent to speakers, and the status light on the amp is showing as being in standby; red. instead of showing; in operation, green. Has anyone got any experience with this amp? Thanks!!