So now that I have all this stuff...
May 23, 2006 3:21 PM   Subscribe

Speaker/ReceiverFilter: I have a recently acquired NAD 7240PE receiver, and a pair of older but fairly decent (I think) floorstanding speakers. The input source is clean (its a CD player that has its own headphones jack, and that's clean), but I'm running into a problem with the speakers + receiver.

Basically, when I first turn on the system, there's quite a lot of hiss/buzz. When the speakers are selected on the receiver, this is also audible through the headphones jack on the receiver (when the speakers are turned off on the receiver, the headphones jack is clean). About 4 or 5 minutes into the speakers being on, there's a loud pop & the hiss/buzz goes away, and I get very nice high quality sound. Also occasionally, for the first few minutes, the right channel doesn't work. I assume these are separate problems. Where should I be looking? I'm decently comfortable with electronics in general, although I don't know much about stereo/audio electronics other than the absolute basics.

Bonus question: The receiver has RCA inputs. I have a SBLive card. What would be the cheapest solution to get good audio quality from PC->Receiver? Are 3.5mm -> RCA cables sufficient, or is there a medium step before SPDIF->DAC->Reciever? What's my range of options with this?

Bonus question #2: Is there a good standard book for stereo/audio stuff of this nature?
posted by devilsbrigade to Media & Arts (10 answers total) 1 user marked this as a favorite
Response by poster: Ugh. Bonus question #3: If I buy a cheaper equalizer, will this entirely defeat the purpose of a nice equalizer & good quality input? How much would I be looking to spend for a functional/fairly simple/not-going-to-kill-my-sound-quality eq?
posted by devilsbrigade at 3:27 PM on May 23, 2006

Best answer: I'm not an electronics expert, but I'll answer this:

Are 3.5mm -> RCA cables sufficient?

With a "yes", in that, I do this all the time and the sound is generally very good. Be sure to use the "line out" and not an amplified speaker output.
posted by knave at 3:28 PM on May 23, 2006

Your amp is ill, very likely a loose connection or ailing component that heals itself after the warm-up. Disconnect everything, put the amp on your bench, and first of all open it and clean it up - tumbleweeds, dust, etc. Now start looking for a loose wire, loose connector, loose transistor socket, questionable solder joint, etc.

(Safety disclaimer - do this with everything disconnected, and amplifier NOT plugged in. )

Bonus answer #2. Start with the 3.5 mm to RCA cable, and see how you like it. SBLive are fairly clean cards.
posted by Artful Codger at 3:32 PM on May 23, 2006

(Safety disclaimer - do this with everything disconnected, and amplifier NOT plugged in. )

Even if it's not plugged in, it can still be dangerous. It'll be full of capacitors that'll be still holding a charge.
posted by clarahamster at 4:05 PM on May 23, 2006

Best answer: I found several service manuals on eBay for this receiver (scanned reproducions from Vintage Audio Manuals) for reasonable prices. One of them would be handy for examining what is wrong.

On the 'charged cap' issue mentioned by clarahamster, he/she's generally right, but the caps in this unit are probably not high voltage. I presume it's a transistor amp/receiver. Old vacuum tube units had high voltages and were notorious for knocking your socks off if you weren't cautious, but I haven't found excessively high voltages in transistor gear, as a general rule. Still, it does pay to assume you are going to get shocked...

When I first examine a piece of used gear, I also do a thorough cleaning, including working all the contact surfaces a lot. (By this I mean vigorously working all the switches, knobs, sliders, jacks, etc. do dislodge dust, etc.) Compressed air in a can is good for blasting out crap you can't see. 90% of the problems I find are related to contacts.

The temporary and intermittent noises can have a variety of sources. One possibility is actually the aformentioned power supply filter caps, which do go bad with age. They usually DON'T get better in a few minutes, though. Same with transistors, though thermal problems aren't unusual. I'd think more along the lines of faulty solder joints or interconnects. These would respond to expansion/contraction from heat/cooling and be somewhat unpredictable. A review on an audio review site mentioned poor solder quality, so it may be endemic to the receiver. You'd have to take it down fairly far to get to all the solder joints for inspection, but that's the way to eliminate it. Look for dull joints... sort of sugary instead of shiny.

The site I was mentioning is below:

Also, I'd check the Tuner INformation Center ( for info on the unit. Good place for the best info on tuners and some integrated tuner/amps.
posted by FauxScot at 4:55 PM on May 23, 2006

Amplifier- Your capacitors are probably drying out. I had a similar problem with an older amplifier; after spending $38 to have the volume pots and connections cleaned the problem persisted, and I learned that in time the oil in the capacitors dries out and the sound degrades.

An electrical engineer I trust advised me to leave my stereo on at all times in order to maintain a more constant operating temperature, thereby improving sound quality and increasing the longevity of the equipment (fewer temperature shocks, less expansion/contraction to weaken the connection points).

Especially if you enjoy great sound after the warm-up period, I suggest keeping it in that state.

Equalizer- The fewer devices that process your signal, the cleaner the sound you will enjoy. If you can avoid an equalizer altogether, you will retain more of the subtleties of your source. That's why many NAD and other higher end amplifiers let you bypass even the tone controls.
posted by reeddavid at 5:02 PM on May 23, 2006

Best answer: (when the speakers are turned off on the receiver, the headphones jack is clean)

That sounds like a key symptom.. Speaker relay maybe? The headphone jack will be pretty close to parallel with the speaker outputs. They add a resistor to reduce the volume, and a relay to allow you to turn off the speakers, maybe a couple of other minor parts..

Equalizer's are evil :P Make sure you spend some time working on speaker placement (haven't read it, just the first hit on google).
posted by Chuckles at 6:50 PM on May 23, 2006

You should not add a crappy EQ.

You should compressed-air blow your amp.

You should check for loose or blocked connections in the amp.

And I hope it all works out. NAD equipment can be great, I have a real affordable NAD setup myself with Acoustic Energy speakers that has treated me so well in my small apartment.
posted by Joseph Gurl at 8:31 PM on May 23, 2006

Response by poster: I got the mini plug -> RCA, and that seems to be working well, although still not the same as CD quality. I also got some compressed air, and I'll try that tomorrow, along with tightening up anything I see loose. If that doesn't work, I'll start looking at the soldering. I'll leave the EQ off.

Thanks all.
posted by devilsbrigade at 10:21 PM on May 23, 2006

As for PC to receiver.. Make sure you are comparing apples to apples - rip a favorite CD test track to a wav file, and compare against that. Some sound cards only do 48kHz, or 48 and 96kHz, but not 44.1kHz. They can still output 44.1kHz by resampling it, but the sound quality suffers. Also, see some of the links below for a discussion of ASIO, and how windows mangles audio data.

Check out places like avsforum and the computer forum at audio asylum for the latest in sound card recommendations. You might get away with the analogue outs on a good (but not necessarily expensive) sound card. Whatever that sound card turns out to be, it probably won't be a soundblaster.

This looks like as good a starting place as any.
posted by Chuckles at 11:42 PM on May 23, 2006

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