Ask MetaFilter questions tagged with audio and electronics

Mic level vs. Line level FIGHT!

knowles — Sun, 25 Jan 2009 07:50:00 -0800

How do I build a microphone preamp for a Macbook Pro? Oh hai. I just recently learned that the 3.5mm input on my MBP (core duo, 2.16ghz, 17in) is not actually a 3.5mm mic in, but a 3.5mm stereo line-in. What's the simplest circuit I can build to remedy this? What about more complex ones?

I bought a Zalman ZM-MIC1 and assumed that it would work out of box, not knowing that I would need some kind of preamp. I have soldering skills and a decent understanding of what electronic components do, how do I get the mic output up to line level for like six bucks at Radio Shack?

If you're so inclined, explain what is making the loudness happen and suggest cool modifications for this circuit as well.

Lite Rock, Less Talk? I'd like neither, please.

strangecargo — Thu, 15 Jan 2009 00:59:16 -0800

(Electronics|Stereo)filter: What is causing this infuriating noise in my preamp and how do I fix it? Links to sound files and long list of symptoms in extended. I have this preamp and ever since moving to my current apartment in San Francisco, it generates a really loud noise that sounds like a combination of 60 Hz hum and FM radio broadcasts. The noise is loudest when the volume knob is turned all the way down, but it doesn't go away when you turn the volume up. And this is what it sounds like when you go from zero gain to full gain and back. The noises don't sound that loud when played back on a computer, but that level of noise is pretty dang loud when sent to the input of a power amp.

The maybe pertinent facts (numbered because there are a lot of them):

1. I recorded the linked sound files by plugging in the output of the preamp into the line in of a MacBook Pro. No mixing or diddling with the file other than that.

2. You can clearly hear the station identifier for KOIT in the first sound file I linked. This is an FM station. What the heck? I was under the impression that FM was way too complicated for equipment to randomly pick up unless it was designed specifically to, you know, receive FM radio.

3. Changing the vacuum tubes inside the preamp doesn't change the nature of the noise.

4. I have other audio equipment (both solid-state and tubed) that doesn't make this sort of noise.

5. The noise is generated independent of what I have connected as an input or output (or if there's anything connected at all).

6. I can't seem to reproduce this noise outside of my apartment (friends' places, hifi shops, etc). Whenever I try, the preamp is noiseless and dead silent.

7. Physically moving the preamp around my apartment doesn't seem to change the noise either.

8. I live in an old apartment without grounding in most of the electrical sockets, but the noise doesn't change if I plug the preamp into a grounded outlet. I've checked that the grounded outlets in my apartment are indeed grounded with one of these devices.

9. I live sort of near Sutro Tower (but who in SF doesn't?). Wikipedia tells me that KOIT broadcasts from Sutro Tower. I also live right next to the N Judah MUNI line. Sometimes my lights dim when it goes by. I suspect the power is probably kind of dirty.

10. Using a different power cable doesn't do anything.

11. For what it's worth, here's a look at the circuitry inside the preamp.

I've been investigating this problem on and off for the last year or so and I still haven't figured out what's causing the problem. Do any electrical engineer types have an suggestions for further testing or solutions to this problem? I have a digital multimeter and oscilloscope at my disposal for the collection of further data.

I'm quite attached to this preamp (more so when it isn't making this noise), so please don't tell me to replace it.

what are my options when/if my aging speakers (z680's) break?

weakcore — Fri, 21 Nov 2008 21:35:41 -0800

Seeking advice on what to do with (or looking for resources explaining how to fix) aging 5.1 PC speakers for when/if parts start breaking. So I've got a set of 5 or 6 year old set of Logitech z680 speakers (http://images.google.com/images?q=z680) that have served me well over the years but have recently begun to make popping/ppptttfff-ing noises sporadically (cycling through the 'effect' button makes it go away for a bit, but it ends up coming back eventually. I fear the command module is on its way out) Is there a buyer's market for replacement parts for these speakers? It would appear that Logitech has replaced this line with a newer set, therefore no longer supporting them.

I've seen the satellite speakers available on ebay for an affordable price (at least for now), but I am more concerned with replacement command module/preamp (the console part with the volume knob and buttons on it) or subwoofer parts.

1) Are there places that sell replacement command modules/preamp or am I SOL if this breaks? I have seen the entire set still being sold, but not the individual components.

2) Will I be stuck with trying to dismantle the sub and spend hours reading up on how to fix it (and perhaps fry something) if that goes out (any resources you audiophiles frequent?)? What are some ways to tell if it's the sub or the command module or something else that's bad?

3) The remote control ceased to function long ago, but it would be nice to be able to replace that too ...

4) What's the life expectancy of these type of things anyways? I would ideally like to migrate them over to use for my secondary 'media' center speakers (I prefer

While I am not averse to dismantling things and I consider myself to have somewhat above average mechanical aptitude (perhaps not when comparing within the set of mefites), when it comes to troubleshooting electronic innards/circuitry like what might be in the sub or pre-amp, I feel quite ignorant (learning resources welcome!).

What should I do with my broken Tascam FW1082?

JZig — Thu, 18 Sep 2008 12:20:18 -0800

I have a Tascam FW1082 midi/audio interface board. Over the last few months, there's been a more consistent and very loud high-pitched whine in the audio output, making it fairly useless for what I need. What should I do to get this fixed? The whine appears to be some sort of artifact of power, because when I connect it to my UPS instead of my wall jack (so it's a noise-free power supply) the whine gets louder and higher pitched. It also seems to change based on features I turn off or on. So, it seems that somehow the power is bleeding through to the D/A converter or something. I'm not an expert on complicated audio hardware.

It's out of warranty and it's $600 new, so it's in the weird zone where I don't know if I should try to send it in for repair (where do you send complicated audio equipment for repair?), buy a new one, or try and fix it myself somehow.

Manual for obsolete test equipment wanted.

kc8nod — Thu, 29 May 2008 08:20:28 -0800

I need a manual for a Panasonic VP-8121B AM-FM Stereo Signal Generator. This is an obsolete piece of test equipment that Panasonic doesn't support anymore. Apparently, they're out of the test equipment business altogether.
There are a few used equipment dealers like http://www.testequipmenthq.com/ and http://www.alternativetest.co.uk/ who will sell me a (like) new unit, but won't sell me just the manual.
I have also tried:

http://www.manualsplus.com/

http://www.ebaman.com/

http://bama.sbc.edu/

http://www.consolidatedsurplus.com/

I would hate to have to replace this thing only for the lack of a manual. Help!

Is my mp3 player frying my headphones?

keith0718 — Thu, 24 Apr 2008 11:28:10 -0800

Is my mp3 player frying my headphones? Is this even possible; if so, how? I've been using a Cowon D2 with Shure se530 earbuds for over a month with no problems at all. Tuesday, after enjoying the player/earbuds for the first half of work, I shut the player off for lunch, but left it and the earbuds on my body as they were. (I wear an armband and make sure that nothing touches where the headphones go into the player's jack.) When I started the player up after lunch, there was no sound in the right earbud. This was not precipitated by any kind of warning at all and no amount of wriggling can coax out any kind of short anywhere. The right earbud won't work in other mp3 players either. Wednesday, I went to work with a different/brand new headphones (but same mp3 player) and after just a few hours, the right earbud started to fade in/out. It seemed to be most noticeable after the player has been off for a few minutes, but this could be coincidence. Is is possible for an mp3 player to fry headphones? What do you think is going on?

Homemade guitar amp filter

Grundlebug — Mon, 17 Mar 2008 09:13:45 -0800

I built this mini guitar amp based on this circuit. But I used a 4 watt speaker rather than the 8 watts specified. What are the consequences of that change? I'm trying to understand the concepts of the circuit, not just how to assemble it. I know Ohm's law, P=IV, series vs. parallel, etc. But I have no idea how to apply it practically.

So I used a lower resistance speaker. Will this increase my current through the whole circuit? Does that change the power output of the amp? Will that drain the 9V battery quicker? Is it louder than the 8 ohm speaker would be? Does it clip the sound signal at lower volume?

Bonus Question 1: And how about all those capacitors? I understand they are low and high-pass filters, but that's it. Will fiddling with those change the quality of the sound produced by the amp?

I've read a bunch of websites on speaker impedance, but they're generally geared toward home audiophile types and aren't answering this low level questions. And websites dealing with the low level concepts don't seem to step up a level to practical applications.

So any tips on resources for hobbyist level electronics, especially sound related, are also appreciated.

Please help my find a pair of headphones that won't hurt my head or ears.

Afroblanco — Thu, 29 Nov 2007 12:45:16 -0800

Please help my find a pair of headphones that won't hurt my head or ears. I used the same pair of Radioshack headphones for at least two years. They weren't great headphones, but were very comfortable - lightweight, with a nice, loose fit. They died recently, and I am forced to find new ones.

Unfortunately, every pair I've tried has been way too tight. I've tried both circumaural (around the ear) and supraural (on top of the ear) types. Neither have made me happy. The circumaural ones give me headaches, and the supraural ones made my ears hurt. I'm not a fan of the in-ear or earbud type - they're leaky, the sound quality tends to be poor, and I don't really think they're that comfortable.

Do they still make headphones that don't hurt? I should mention that I wear them for close to 8 hours a day, so comfort is really really important. I've returned, like, 5 pairs at this point, and am beginning to feel a bit discouraged.

All the pairs I've tried have been in the $50 range, and that's about as much as I'd like to spend. I could go as high as $75 - $100, but they'd have to be *really really* good.

Home Audio 101

10ch — Tue, 20 Nov 2007 06:49:09 -0800

What components do I need to buy to have a solid stereo system for my home? I know nothing about home audio and I want to buy a quality turntable for playing records (including 78s) as a gift for my one and only.

I took a look at other mefi questions about turntables and found some good resources, but I quickly realized that there's a lot of vocabulary and hip-bone-connected-to-the-assumptions going on that leave me clueless. I need someone that isn't trying to sell me something to help me figure out what I need.

Fer'instance... am I better going with separate parts (and if so, what are those parts specifically) or with a "home system" (I want to avoid crappy parts just to get the 78 feature, for example).

Here are the things I'd like the system to do, in priority:

- Cost around $500
- Sound good
- Play records (78s, 33s and 45s)
- Play cds
- Play cassettes
- Play FM/AM radio
- BONUS, BUT NOT REQUIRED: Record across the above (ideally on CD)
- BONUS, BUT NOT REQUIRED: Be aesthetically pleasing

Speak jargon as long as you provide clarification (parenthetically). Links and specific make/model recommendations are appreciated. I'll be happy to converse in thread if I'm leaving details out. Thanks for your help.

Help me not screw up.

tmcw — Sun, 21 Oct 2007 12:01:22 -0800

I'm going to embark on a stompbox-building adventure, and I'd like to know how much one can mess things up. I'm aiming to make a Fuzz Face (not sure about the specific plan yet, any suggestions welcome). Also, if I can find an incredibly cheap delay pedal (I guess I'll trawl eBay...), I'd like to modify it to produce some good stutter effects. So, as far as experimenting with this... what is the fact that's preventing 9V from running straight into an amp and blowing it up? I'll probably be testing on a Princeton 112 turned way down, but what are the risks and methods of reducing them with this stuff? Are people using tiny amps to test things?

Thanks

What's wrong with my reel-to-reel?

waxboy — Mon, 08 Oct 2007 14:08:18 -0800

I recently acquired an older reel-to-reel tape recorder, and it works fine except for inconsistent tape speed. I recorded a test tone and it plays back at a varying pitch. Can this be fixed, or should I put it out with the trash tomorrow? The machine came from a university auction and had previously lived in the library. It looks like it's in good shape, and there are no obvious problems under the hood. It came with a box of blank tapes, probably a decade or two old, that I've been using. Could the tape be slipping or stretching? Or is this more likely to be a problem with the drive system, like a bad motor?

Crass consumerism strikes again

FelliniBlank — Fri, 27 Jul 2007 19:34:25 -0800

Tell me how much I need to spend on audio preamp(s) and amplifier(s) to make my home stereo system sound jaw-droppingly great. Ze muzeek, she eez my life, so two years ago I upgraded some of my very low-end stereo components to these moderately better ones:

Goldring GR2 turntable

NAD C542 CD player, and

Orb Audio speaker system (two "MOD2" double-satellite assemblies + a subwoofer)

WAY better sound, baby, but that's when the money ran out, so I couldn't replace the basic Onkyo receiver with a nice preamp(s) + amp(s) to make the most of the other components.

Now I have some pennies saved and have started looking at equipment and reviews. This is where you come in. I might could swing $1500 tops for the whole enchilada if absolutely necessary, but I'd like to spend as little as it takes to get good quality gear -- new or used -- that actually makes an audible improvement to my non-audiophile, non-engineer ears. And even if I do drop the whole $1500, I'm not exactly sure how to divide it between the different components so that I'm investing the right proportion in each one.

The question:
To get preamp and amp equipment that is of comparable quality to the rest of my system and that will help it live up to its full potential, how much should I be looking to spend on each of the following:

1) phono preamp
2) line preamp
3) or instead of 1+2, a single preamp with phono stage
and
4) monoblock or two-channel amp(s) with max 110 wpc output (25-75 watts is probably plenty for my small, decently efficient speakers in a 13x20ish foot room)

Or if you think the existing Onkyo receiver is up to the job and I should put my wallet away, g'head and say so.

Other info:
-- This is just for music; I have zero interest in home theater audio. My musical tastes run the gamut.

-- SS or tube is fine, but I doubt that decently isolated hybrids are within my budget. As a vinyl-loving middle-aged Luddite who digs warm, rich sound, I'm drawn to the concept of vacuum tubes, and the basic Antique Sound Labs preamp and monoblock amps are appealing and affordable. But I don't know if I'd like the reality of tube gear. It would have to go in this type of open rack and would have at most a few inches of clearance above it, and I'm not sure that's sufficient for ventilating tube components. Also, I'd get cranky if I had to let the thing warm up for an hour before it stopped sounding like shit.

Please take it easy on the acousticalese; IANAPhysicist.

Keeping electronics cool in enclosed spaces?

mphuie — Thu, 04 Jan 2007 13:56:57 -0800

What is the best way to keep electronic devices that are in enclosed areas cool? (ie. stereo receiver, game console, etc). I'm just got a new AV cabinet/stand that is a lot smaller than my previous one and my components are getting a lot warmer than they used to. My receiver has about 1" leeway on each side and about .5" on top. 1/3 of the rear of the cabinet is open. I also have my HTPC in there as well as my Xbox 360. Anyone know of a simple way to keep them cooler (without adding noise or uglyness to my setup)? Would not like to cut anything. Some ideas... Separate the exhaust and intake (so no hot air gets recycled) by blocking the sides and top at the rear of the unit. Put a small computer fan at the back of the stand to improve airflow? Put a exhaust hose (a la dryer) on the receiver where the fan is.. maybe put a fan at the end of the hose to pull more air through? Any tried and true methods that arent too complicated?

What is a "starving plate" design?

goodnewsfortheinsane — Sun, 27 Aug 2006 14:55:34 -0800

In tube ciruitry, what is a "starving plate" design?

I'll take "A New Stereo" for $200, Alex.

exceptinsects — Tue, 08 Aug 2006 12:33:02 -0800

So, the stereo I won on Jeopardy is about to break...what should I replace it with? What I already have and would like to hook up:
Surround sound speakers
TV
DVD player
iPod
iBook

I would like to also have a basic CD player [the old one was a 24-disc changer and completely irritating--1 CD at a time is plenty] and AM/FM radio. A tape deck would be nice but not at all necessary.

So...should I get one of those integrated stereo things again? A receiver and separate CD player? A wireless doodad so I don't have to actually plug in the computer/iPod?

I'm not a big audiophile, so it doesn't have to be AMAZING sound quality, and I don't want to spend more than 2 or 3 hundred bucks at most. I also would prefer not to have to build it myself out of parts from Radio Shack. (Do they still have Radio Shack?)

Any advice would be greatly appreciated.

The sound of silence.

The White Hat — Thu, 18 May 2006 21:33:55 -0800

Laptop power supply interfering with PA speakers. The Problem: My laptop power supply is interfering with my speakers, givng off very unpleasant, persistant interfereance. I know that it's the power supply because when the laptop is running on its battery, the interference is nonexistant. I'd like to be able to plug in my laptop without the interference.

What Works: The PA system has two volume controls- one for the tape in, and a master control as well. When I turn both knobs to around 7, the interference goes down in volume, but is still noticeable.

Equipment chain:

US Grounded Wall Outlet
-----Furman PL-8 Power Conditioner
----------Dell 65w AC Adapter
---------------Dell Inspiron 6000
--------------------Creative Labs 24-Bit Sound card
----------Phonic Powerpod 408 PA Amplifier (120W)
---------------Phonic PA Speakers

The sound card is wired to the PA system using a 1/8" to RCA cable from the soundcard's output to the PA's "Tape in."

MXL 990

ludwig_van — Sun, 29 Jan 2006 08:41:43 -0800

I dropped my MXL 990 condenser mic. The grill is slightly dented and the capsule inside has come loose. Can I repair it myself? Can I get it repaired in London? I'm a clumsy idiot, and I shouldn't have left my mic out on the stand, and I shouldn't have left the cable where I could trip over it. That said, can anyone tell me how to fix it, or recommend a repair shop in London? I don't have a soldering iron or any specialized tools, and I'm located in New Cross.

airtunes vs. tivoli deathmatch

luriete — Sat, 07 Jan 2006 19:33:06 -0800

i just bought a tivoli system (kloss model 2, extra speaker and cd) and have it on the bookshelf but some questions: The Tivoli staffperson I emailed said it had an aux in and would work fine with my airtunes setup. However, there's an aux in (for the CD player, I think?) and a "mix in" which is also a single (mono?) mini rca. My old stereo went mini RCA (airtunes) > full size right and left stereo jacks (stereo), so now I've run a single mini RCA cable (on both ends) from airtunes to the "mix in" jack and it sounds just OK. Not as good as the cheapie sony boombox we used to have. Is this because before I had stereo sound coming in and now I just have mono? Is there a better way to hook this stuff together? I really like the warm sound of the Kloss speakers and it looks very pretty, and I like the big knobs ... I assume there must be some way to make the music from my powerbook sound better than it does on my crummy powerbook speakers; right now they sound about the same.

Humless DC->AC Power Inverter?

odinsdream — Tue, 15 Nov 2005 18:44:16 -0800

What DC to AC power inverter can I buy for use in a car that won't contribute hum to an audio signal from devices it powers? I've currently got a cheap one-outlet low wattage DC -> AC converter that I use to power my laptop in the car. I use a tape adapter to play music from the laptop through my car stereo.* When I have the laptop plugged in to the power, there's a considerable hum in the audio coming through the speakers. I can almost completely eliminate it by unplugging the power. Of course, this means the laptop eventually dies.

What DC->AC power box will let me keep the laptop plugged in without the hum in the audio? I'm hoping to pick it up tomorrow, perhaps at Best Buy or similar Box Store.

*using predefined playlists with the lid closed and all that jazz - let's not discuss driving distractions and all that.

What's that noise??

dead_ — Fri, 26 Aug 2005 12:24:05 -0800

Why, when a TV is turned on--even in another room--can I detect some kind of buzzing/electronic noise, that many other people around me can't detect?

48 or 12 Volts for my condenser mic?

goodnewsfortheinsane — Mon, 25 Jul 2005 17:01:50 -0800

MicrophoneFilter: Should I connect my MXL 990 condenser mics to preamps providing 12V or 48V of phantom power? I recently purchased a pair of MXL 990 capacitor mics, as well as an Audiotrak MAYA 1010 audio interface. The MAYA provides 12V of phantom power, and I also have a small mixer with two channels of 48V phantom. The MXL 990 info sheet specifically states:

IMPORTANT - This unit requires phantom power at 48 volts, +/- 4 volts.

I can, of course, steer on the safe side and just use the mixer's preamps, but I know I'm going to use more mics/inputs for a project soon and the MAYA's preamps will come in very handy.

So what I would like to know is: does it matter which preamp I use? More specifically, is there any influence of the phantom voltage on the signal quality or is it merely a matter of "it works or it doesn't"?

What is the name of this audio effect?

Mars Saxman — Mon, 02 May 2005 18:13:29 -0800

I'm looking for a device that processes an audio signal by sweeping the center frequency of a bandpass filter back and forth across a frequency range. What is this effect called, and what sort of effects processor might provide it? This seems like a really simple idea, so I'm sure somebody must have tried it, but I don't know what such a gadget might be called. I've found schematics for bandpass filters and for LFOs, and a project that combines the two is probably (barely) within the range of my electronics ability, but it would take a lot of time and I'd rather just buy the gadget if it exists. I'd like to be able to set the low and high ends of the frequency range, and it should be possible to set the sweep rate to at least around 5sec/cycle. The perfect solution would be a simple guitar stompbox type device, since I'd like to run this on battery power.

Which manufacturers make well-built home theater equipment at a reasonable price?

danwalker — Fri, 04 Feb 2005 19:21:06 -0800

Over the past several years, I have been burned by poor quality in home electronics from various manufacturers. I have purchased pieces by Sony (home stereo), Panasonic (theatre-in-a-box) and RCA (various pieces of junk), and all have given out in one way or another far too quickly for my liking. In a renewed attempt to build a proper home theatre system (DVD/CD, receiver, speakers, etc), and recognizing that I haven't the money for really high-end stuff but will avoid anything cheap, I seek outside opinions as to which manufacturers are making products that are of reasonable quality, and reasonably priced. Your experiences, please.

Diagnose computer speakers or replace them?

JoanArkham — Wed, 23 Jun 2004 05:55:41 -0800

When I got home from work yesterday, my computer speakers were making an incredibly horrible noise. When I unplugged them, the transformer was hot to the touch. There were storms in the area yesterday, although the surge protector plugged into the same outlet wasn't tripped and nothing else in the house seems to have been damaged. (The speakers were plugged directly into the wall, not the surge protector, because I had run out of room.)

So my question: would it be dangerous to plug them back in tonight and see if they're a lost cause? Should I just buy some new speakers and be done with it? (The speakers were expensive, but about 6 years old.)

Ghost Music

bkeaggy — Tue, 27 Apr 2004 09:13:05 -0800

Why do my speakers play music when no music is playing? (More inside) I have a set of pretty low-quality Benwin BW2000 flat-panel speakers connected to my iBook. Have used them for several years on several computers. I recently rearranged my home office and now they're right by the window. When I turn them on they pick up a classical music radio station that can be heard at a low volume, but not really through the actual speaker set -- just from inside the mini woofer. If I play MY music loud enough it gets covered up, but it's annoying anyway. Why does this happen and can I stop it? (Aside from moving them away from the window.)