Hi all,
I picked up an old NHT SA-2 and SW2P over the weekend and have had a couple of issues with the SA-2 amp.
First issue is the volume control doesn't work, it seems to be stuck on full volume. Not a big problem as I can reduce the output level on the AV receiver to balance it out.
The amp and sub were working fine for an hour or 2 but I paused the movie I was watching and ducked out of the room for about 20 - 30 mins. The amp went into standby mode but switched back on when I restarted the movie however there was no output from the sub. I had a closer look at the sub and when the amp switches on, the speaker cone gets sucked back into the magnet. Turn off the amp and it pops back out again.
I tested the sub with another amp and it works fine, so the problem is definitely the SA-2.
My electronics knowledge and toolkit is very basic, so I don't know where to start to diagnose the problem. Assuming its not an easy and obvious fix it will probably involve taking it to a service tech to get it repaired.
So my 2 questions are - is this a fault that an absolute beginner is likely to be able to fix?
If not, and it needs to go to a service tech, is it worth it? The cost of diagnosis and repair is probably going to be more than buying something like this Aiyima A3001 - AIYIMA TPA3255 Subwoofer Power Speaker Amplifier 300W Mono Hifi Home Audio Amplifier NE5532 OP AMP Bass Treble Adjust - AliExpress - 11.11_Double 11_Singles Day
Thanks in advance!
I picked up an old NHT SA-2 and SW2P over the weekend and have had a couple of issues with the SA-2 amp.
First issue is the volume control doesn't work, it seems to be stuck on full volume. Not a big problem as I can reduce the output level on the AV receiver to balance it out.
The amp and sub were working fine for an hour or 2 but I paused the movie I was watching and ducked out of the room for about 20 - 30 mins. The amp went into standby mode but switched back on when I restarted the movie however there was no output from the sub. I had a closer look at the sub and when the amp switches on, the speaker cone gets sucked back into the magnet. Turn off the amp and it pops back out again.
I tested the sub with another amp and it works fine, so the problem is definitely the SA-2.
My electronics knowledge and toolkit is very basic, so I don't know where to start to diagnose the problem. Assuming its not an easy and obvious fix it will probably involve taking it to a service tech to get it repaired.
So my 2 questions are - is this a fault that an absolute beginner is likely to be able to fix?
If not, and it needs to go to a service tech, is it worth it? The cost of diagnosis and repair is probably going to be more than buying something like this Aiyima A3001 - AIYIMA TPA3255 Subwoofer Power Speaker Amplifier 300W Mono Hifi Home Audio Amplifier NE5532 OP AMP Bass Treble Adjust - AliExpress - 11.11_Double 11_Singles Day
Thanks in advance!
Maybe someone's been in there and disabled it, otherwise it looks like a bad connection at the pot or a bad pot.
Not good - there is a good amount of DC offset on there, and the protection circuitry is failing to catch it. Which is odd but not impossible - the relay contacts may be welded together. Measure output DC voltage.
What colour is the power LED? Protection mode should be red, normal is green, and standby is amber.
Only with a lot of luck and a major following wind. A schematic does seem to be out there, which is a good start.
Do you have a multimeter? Have you watched someone troubleshoot electronics before at least? Are you generally comfortable working on things (even if just mechanically)?
The matching power supply is likely to set you back about the same on top of that, and then you still don't have quite the same feature level. Also note THD 0.03% at 1 W vs. full power (not like it matters that much for a sub, but still)...
Glancing over the schematic, this looks like all through-hole parts. Should be quite repairable, assuming the construction isn't too service-unfriendly. Would almost be a shame not to.
I'd say have it diagnosed by someone with experience in audio amps and see what they'd be charging. Bonus points if they have any upgrade ideas (the XO seems to be a TL072 grave for one, there may be some better options for the highpass section assuming you're using that at all).
Thanks very much for the detailed reply! The volume pot appears to be a common failure from what I have read online, so hopefully an easy replacement, but some of the comments suggest it has to be a genuine nht replacement which costs $130, which seems odd..
When the amp powers on the power light is amber briefly then green. With no input signal I checked the voltage at the speaker output and got -3.0v initially but it kept increasing to -8.7v. I turned it off for a minute and tried again, it went straight to -8.7v and kept climbing slowly. I wasn't sure if this was a user error on my part or if the multimeter was possessed so I checked it against a new 9v battery and got a steady 9.6v so the user and meter appear to be ok.
I've got some basic tools like a soldering iron and multimeter and with the aid of Prof Google and YouTube University I have built a 2.1 speaker system, but have never worked with a PCB.
I have ordered the Aiyima amp as I could use a second sub amp for another project. Doing some research on repair options, the local audio forums have recommended a repair shop 5 minutes away so I'll take it there for assessment and quote. As much as I would like to learn how to work on amps, I think I would prefer to have this one fixed professionally if it is economical enough to do so, as it would be a great way to add a subwoofer to a system powered by a Cambridge audio A1, which doesn't have a sub output. The Aiyima can go with the AV receiver as it does have 2 sub outputs.
When the amp powers on the power light is amber briefly then green. With no input signal I checked the voltage at the speaker output and got -3.0v initially but it kept increasing to -8.7v. I turned it off for a minute and tried again, it went straight to -8.7v and kept climbing slowly. I wasn't sure if this was a user error on my part or if the multimeter was possessed so I checked it against a new 9v battery and got a steady 9.6v so the user and meter appear to be ok.
I've got some basic tools like a soldering iron and multimeter and with the aid of Prof Google and YouTube University I have built a 2.1 speaker system, but have never worked with a PCB.
I have ordered the Aiyima amp as I could use a second sub amp for another project. Doing some research on repair options, the local audio forums have recommended a repair shop 5 minutes away so I'll take it there for assessment and quote. As much as I would like to learn how to work on amps, I think I would prefer to have this one fixed professionally if it is economical enough to do so, as it would be a great way to add a subwoofer to a system powered by a Cambridge audio A1, which doesn't have a sub output. The Aiyima can go with the AV receiver as it does have 2 sub outputs.
The repair shop called today with the quote - $240 to replace the volume pot and some resistors and transistors at the power amp.. I'm guessing much of this will be the labour cost as I don't imagine the parts will be too expensive. I'm not going ahead with the repair for the moment, I found the schematics and will do some research on how to troubleshoot, hopefully I can find the faulty parts and replace them.
I'm quite happy with the Aiyima and bought a second one not long after for a second system.
The first one is part of the 5.1 home theatre setup in the lounge room, powering the NHT sub. The other is at my desk, part of a 2.1 system powering a harman kardon 10" sub in a ported enclosure I built myself.
No issues at all with heat and power capacity. How clean is a bit hard to quantify when driving a sub.. but with the 10" subs and the right source it is capable of being felt throughout the house.
The home theatre is powered by an entry level Denon receiver (X550BT) and after allowing the amp to do it's auto calibration the sub blends in seamlessly.
So overall I'm quite satisfied with the price / performance.
The first one is part of the 5.1 home theatre setup in the lounge room, powering the NHT sub. The other is at my desk, part of a 2.1 system powering a harman kardon 10" sub in a ported enclosure I built myself.
No issues at all with heat and power capacity. How clean is a bit hard to quantify when driving a sub.. but with the 10" subs and the right source it is capable of being felt throughout the house.
The home theatre is powered by an entry level Denon receiver (X550BT) and after allowing the amp to do it's auto calibration the sub blends in seamlessly.
So overall I'm quite satisfied with the price / performance.
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