Hey guys, I hope some of you can help me out here as my amp is driving me nuts, and I'm almost at the point of just tossing the whole damn thing out the window...
Technics SA-AX730. I am the first owner, never really had any problems with it, it was always in light use, been in stereo only use for some years now. After spending more then enough time setting up a home theater in my basement the past months, I finally got around to doing the audio installation today, and was hoping to watch something on my 180" projected screen with decent sound finally... but apparently my amp had other ideas...
Technically the amp works. I'm feeding it 6 channels straight from a PC.
Problems:
- The first problem (but least of my worries really) is AC hum... the blasted thing has an un-grounded AC plug, and as soon as the PC is turned on, I get hum. I don't want to compromise sound quality with a decoupling transformer, and I don't want to unhook the ground terminal from the PC... are there any other ways of getting around this issue?
-The second problem is what really put me off... The surround speakers are pretty much useless. Right rear output is okay, though there is some hiss to it, while left rear output is hissing quite loudly, and all output has a tinny sound to it, with technically no mid- to low frequency output to speak of. It sounds like someone put a first order high pass filter on it... Now I read this and that, but google isn't my friend today... I read some people complaining about surround problems, but I didn't find any real descriptions of the problems nor any solutions... Does anyone have any idea what might be wrong? Note: The issue is amp output related for certain. Switching left and right rear inputs the problem stays on the same side, and it's not a wiring problem either, swapping the L/R surround speaker wires at the amp has the problem migrating to the other side.
I'm well versed in electronics, but not too experienced with amp repair. This amp is not something I planned on having to bugger around in, and this problem put me off to the point I've half a mind to smash the thing to bits...
I was considering upgrading to a newer Technics unit that can do optical as well as I was a fan of the brand, but at this point I'm more then hesitant...
Thanks for any help guys!
Technics SA-AX730. I am the first owner, never really had any problems with it, it was always in light use, been in stereo only use for some years now. After spending more then enough time setting up a home theater in my basement the past months, I finally got around to doing the audio installation today, and was hoping to watch something on my 180" projected screen with decent sound finally... but apparently my amp had other ideas...
Technically the amp works. I'm feeding it 6 channels straight from a PC.
Problems:
- The first problem (but least of my worries really) is AC hum... the blasted thing has an un-grounded AC plug, and as soon as the PC is turned on, I get hum. I don't want to compromise sound quality with a decoupling transformer, and I don't want to unhook the ground terminal from the PC... are there any other ways of getting around this issue?
-The second problem is what really put me off... The surround speakers are pretty much useless. Right rear output is okay, though there is some hiss to it, while left rear output is hissing quite loudly, and all output has a tinny sound to it, with technically no mid- to low frequency output to speak of. It sounds like someone put a first order high pass filter on it... Now I read this and that, but google isn't my friend today... I read some people complaining about surround problems, but I didn't find any real descriptions of the problems nor any solutions... Does anyone have any idea what might be wrong? Note: The issue is amp output related for certain. Switching left and right rear inputs the problem stays on the same side, and it's not a wiring problem either, swapping the L/R surround speaker wires at the amp has the problem migrating to the other side.
I'm well versed in electronics, but not too experienced with amp repair. This amp is not something I planned on having to bugger around in, and this problem put me off to the point I've half a mind to smash the thing to bits...
I was considering upgrading to a newer Technics unit that can do optical as well as I was a fan of the brand, but at this point I'm more then hesitant...
Thanks for any help guys!
To check the surround system correctly, I would play the audio from a surround sound DVD or CD. Mains hum? check the connections to your PC.
There's not much to the connections to the PC. Standard jack-cinch cables, all brand new, there shouldn't be a problem there really...
I can only have the PC to feed the amp all 6 channels atm, but swapping inputs for the rear channels, the problem remains on the same speaker, hence it is definitely a problem with the amp :\
I can only have the PC to feed the amp all 6 channels atm, but swapping inputs for the rear channels, the problem remains on the same speaker, hence it is definitely a problem with the amp :\
Hoookay... hum is gone now... the source of the hum was the antenna cable plugged into the dvd writer... strange how it didn't affect tuner or vcr or other modes, but it did interfere with the TV (where the dvd writer is plugged in) and DVD (where the computer is plugged) inputs... anyways, going to bugger the cable company to isolate the cable and that's that...
The surround problem... well... I did some further testing... Previously I did not try adjusting volume while listening, but now I noticed that the volume pot crackled occasionally... then also that the left surround speaker works even at minimum volume... no matter the pot setting, it always stays at consistent volume...
What is weird is that if the pot is indeed a dud, shouldn't that channel just not emit any sound at all ?
The surround problem... well... I did some further testing... Previously I did not try adjusting volume while listening, but now I noticed that the volume pot crackled occasionally... then also that the left surround speaker works even at minimum volume... no matter the pot setting, it always stays at consistent volume...
What is weird is that if the pot is indeed a dud, shouldn't that channel just not emit any sound at all ?
Does anyone know where if at all the 6x100k motorized gang pot used for volume control on these is available? The part of the pot responsible for the aforementioned speaker is open circuit. I don't think this sucker can be dismantled for cleaning without breaking it... I have no idea why it stopped working when this thing is supposedly sealed... :\
SOLVED!
The gang pot can indeed be dismantled with some care. I pulled mine apart as a last-chance solution. Technically there are four metal tabs folded atop the pot that hold it together. Once those are bent straight, the pot pretty much pulls apart. Motor comes off first, then using a small flat screwdriver, prying the cog off the pot's shaft will release the pot bodies. Pulling them off one by one, the problematic piece had an obvious factory defect. The wiper for the affected part was literally broken off from the plastic hub that holds it. Some -very- careful poking with a fine tip soldering iron had the part back in place. Reassembled, and everything seems to be fine. Time will tell how long this will hold... but at least this was not a design fault, but rather a fault of the pot manufacturer. (I do however see the basic design fault with system ventillation, that obviously could be the source of a lot of problems for folks who never read the manual and shoved the unit into a tightly confined rack straight away...)
Now if only I could find a mod to completely eliminate the rear speaker hiss that is inherent to the amp, I wouldn't bother getting a new one for a while 🙂
The gang pot can indeed be dismantled with some care. I pulled mine apart as a last-chance solution. Technically there are four metal tabs folded atop the pot that hold it together. Once those are bent straight, the pot pretty much pulls apart. Motor comes off first, then using a small flat screwdriver, prying the cog off the pot's shaft will release the pot bodies. Pulling them off one by one, the problematic piece had an obvious factory defect. The wiper for the affected part was literally broken off from the plastic hub that holds it. Some -very- careful poking with a fine tip soldering iron had the part back in place. Reassembled, and everything seems to be fine. Time will tell how long this will hold... but at least this was not a design fault, but rather a fault of the pot manufacturer. (I do however see the basic design fault with system ventillation, that obviously could be the source of a lot of problems for folks who never read the manual and shoved the unit into a tightly confined rack straight away...)
Now if only I could find a mod to completely eliminate the rear speaker hiss that is inherent to the amp, I wouldn't bother getting a new one for a while 🙂
- Status
- Not open for further replies.