Need a cheap home stereo amp (I think?)

[atquinn]

So, I've got these wires in my basement:

I've got 4 speakers in the ceiling and I'm guessing that somehow the wires connect to those? Or perhaps 2 of them are related to some speakers in the ceiling in the main floor?

Anyway, I'm looking for a small, cheap amp that I can hook them up to I guess. Anything cheap will do as long as it has at least one input so I can hook up some sort of wireless receiver to it (so I can stream music to it from from my phone/laptop/etc...). I've never had any home stereo equipment other that some stuff I took from my dad years ago when he was upgrading his system (and I have no idea what happened to that), so I don't really even know where to begin to look. Any cheap suggestions would be welcome!

-

Austin

[mathman]

Here is one place to look.

parts-express

[killerteddybear]

You're on Long Island?

craigslist has a bunch of stuff...

[atquinn]

O.k., this looks reasonable I think.

http://www.parts-express.com/pyle-pca4-mini-2x120-watt-stereo-power-amplifier--310-2214

Small, not too expensive and I can hook both sets of speaker wire to it. However, since I don't know anything about this, I don't know if the power is sufficient or even how I would determine that? There are 6 total speakers (4 in the basement and 2 in the dining room) all hooked up through these 2 sets of speaker wire). I was able to get a reasonable volume (a bit low) playing a song from my Samsung S4 through my headphone output on my Behringer Xenyx 502 (I held the speaker pairs against a stereo jack that was plugged into the headphone out), so I figure I don't need anything all that powerful.

Now I need t find some wireless receiver that I can plug into it that will allow me to stream audio from my PC and android phones (and maybe iPhone somewhere down the line). I'd like something that uses wifi so I could use it anywhere, and also the main laptop that I use doesn't have bluetooth. However, it looks like if I don't want to spend too much and have something that works with Android and Windows OS's, I'm going to have to go with bluetooth and maybe get a bluetooth adapter for the laptop that doesn't have it built it?

Any suggestions?

-

Austin

[JohnnyB]

O.k., this looks reasonable I think.

http://www.parts-express.com/pyle-pca4-mini-2x120-watt-stereo-power-amplifier--310-2214

Small, not too expensive and I can hook both sets of speaker wire to it. However, since I don't know anything about this, I don't know if the power is sufficient or even how I would determine that? There are 6 total speakers (4 in the basement and 2 in the dining room) all hooked up through these 2 sets of speaker wire). I was able to get a reasonable volume (a bit low) playing a song from my Samsung S4 through my headphone output on my Behringer Xenyx 502 (I held the speaker pairs against a stereo jack that was plugged into the headphone out), so I figure I don't need anything all that powerful.

Now I need t find some wireless receiver that I can plug into it that will allow me to stream audio from my PC and android phones (and maybe iPhone somewhere down the line). I'd like something that uses wifi so I could use it anywhere, and also the main laptop that I use doesn't have bluetooth. However, it looks like if I don't want to spend too much and have something that works with Android and Windows OS's, I'm going to have to go with bluetooth and maybe get a bluetooth adapter for the laptop that doesn't have it built it?

Any suggestions?

-

Austin

If you read the fine print on that amp's specs, it's only 20 wpc into 4 ohms at 1% distortion, which is on the high side (of distortion, not power). The sound quality at the claimed 120 watts would approach unlistenability. The most usable inexpensive small amp with some guts that I know of is the Emotiva mini-X a-100. It puts out an honest 50 wpc into 8 ohms and 80 into 4.

Since you don't know how that wire is harnessed, you might want to apply an ohmmeter to those leads to see what the nominal impedance is. Then you can adjust your amp shopping accordingly. The impedance could be anything from less than 2 ohms to something north of 32 depending on the combination of series and parallel connections used to send the signal to 3 pairs of speakers. If the impedance is high, you'll want more power; if it's low you'll want more current.

[atquinn]

Thanks for the suggestion! I did some more reading up and, yes, it sound like the Pyle mini-amp stuff might not be too good . I shall get out my meter and figure out how to measue the impedance tonight, but I'm fairly certain the amp you linked to will be fine. I'm not looking to do anything more than background volume. And I have an Airport Express coming to stream music to it wireless. Everything else out there seems crappy and/or outrageously expensive and there is software that will let me use all of my devices to stream to it, so it shouldn't be too painful.

-

Austin

[Toadroller]

You might also want to set that ohmmeter to voltmeter and check that as well.

When we renovated part of our first floor three years ago, we found live, un-protected 240v wires (not even electrical tape on it!) in the walls from the old, mid-70s electric heating sitting there. My guess is they cut the wires and threw the circuit breaker instead of pulling it.

Just another thing in this wonderful, wonderful, stoner-built house.

[Toadroller]

JohnnyB,

Would that Emotiva be a way of powering something like an Avid Eleven Rack's output to a guitar cab, or should one look for a simple used PA amp?

Guitar-> Eleven Rack-> Emotiva -> stereo guitar cab

[mathman]

I guess it is possible it is 70 volt system.

[JohnnyB]

JohnnyB,

Would that Emotiva be a way of powering something like an Avid Eleven Rack's output to a guitar cab, or should one look for a simple used PA amp?

Guitar-> Eleven Rack-> Emotiva -> stereo guitar cab

Yes, that should work for a stereo guitar cab. The fact that this amp has a thermostat-activated fan indicates it should be a good pick for enclosed spaces or being run on the hot side.

The ART SLA1 is more money but it has more power and would probably be a better pick since their target market is pro audio. I've heard really good things about their sound quality. I think it would qualify for 15% off on Cyber Monday, or at least 10%. It also accepts XLR plugs, which is the Eleven Rack's output.

[sixesandsevens]

JohnnyB,

Would that Emotiva be a way of powering something like an Avid Eleven Rack's output to a guitar cab, or should one look for a simple used PA amp?

Guitar-> Eleven Rack-> Emotiva -> stereo guitar cab

Not JB here, but if you want a gizmo that'll do double duty, the Bad Cat Unleash will work that way as well as for reamping.

Only downside for the Unleash is the fan is audible at bedroom volumes. Edit: Well, and maybe the form factor if you want to rackmount the amp.

[atquinn]

Alright, well it looks like I'm dealing with 6, 8 ohm speakers in 2 sets of 3 where the 3 are wired in parallel. So I'm dealing with impedance that is on the low end. How does that affect what I'm looking for? Seems like the mini-x would still have plenty of power, but I'm not sure what I would do to get more current (as opposed to more power)?

-

Austin

[JohnnyB]

Alright, well it looks like I'm dealing with 6, 8 ohm speakers in 2 sets of 3 where the 3 are wired in parallel. So I'm dealing with impedance that is on the low end. How does that affect what I'm looking for? Seems like the mini-x would still have plenty of power, but I'm not sure what I would do to get more current (as opposed to more power)?

-

Austin

Have you used your ohmmeter? If each channel is three 8-ohm speakers wired completely in parallel, then we have an impedance of (8x8x8) / (3x8) or 512/24= 21.33 ohms. This would indicate you need more power, because 21.33 is a high load as speakers go. If an amp is rated at 50w into 8 ohms, it's making a little less than 19w into 21.33 ohms. OTOH, if you were to rewire two speakers in series and then wire the third in parallel to the first two, the overall impedance would be 5.33 ohms. You can tell a high current design by how many watts it puts out into lower loads relative to its 8-ohm rating. For example, some amps that have an 8-ohm rating can't even qualify for a 4-ohm rating because the power supply is too wimpy to come up with the required current, or it lacks sufficient cooling (heat sinks or fans) or both.

A high current amp that puts out 150 watts into 8 ohms will put out 250 or more into 4 ohms. A really high current amp that puts out 150 into 8 ohms will put out a solid 300 into 4 ohms and perhaps even 600 into 2 ohms.

Basically what I'm saying is that if all 3 speakers were in series it would be a load of 24 ohms. In parallel it's 21.33 ohms, and with 2 in series connected to a third in parallel the load is 5.33 ohms. In the first two cases you want an amp that puts out at least 100 watts into 8 ohms because it's only going to put out 33 to 38 watts into 24 and 21.33 ohms respectively. If the load is 5.33 ohms you want something that's FTC rated into 4 ohms to make sure it handles the lower load without overheating.

[atquinn]

Unless, I'm using the wrong formula for the application, 3, 8 ohm resistors in parallel should be about 2.7, which is about what I was measuring, not 21.3. 1/8+1/8+1/8=1/x. So, based on that, I'm assuming I was looking at 3, 8 ohm speakers. In which case, I should look for something rated for 4 ohms.

-

Austin

[JohnnyB]

Unless, I'm using the wrong formula for the application, 3, 8 ohm resistors in parallel should be about 2.7, which is about what I was measuring, not 21.3. 1/8+1/8+1/8=1/x. So, based on that, I'm assuming I was looking at 3, 8 ohm speakers. In which case, I should look for something rated for 4 ohms.

-

Austin

You're right. I should have consulted a system impedance calculator. I was calculating the three drivers multiplied together (256 ohms) divided by the three drivers added together (24). It should have been (as you calculated) the value of two drivers in parallel (4 ohms) wired in parallel to a third 8-ohm load for a total of 2-2/3 ohm. The linked calculator is pretty handy for calculating other scenarios: two in parallel + one in series = 12 ohms; two in series and one in parallel = 5-1/3 ohms. Either of those configurations is an easier load and easier to find an amp that's comfortable with it.

Otherwise if you're facing 2-2/3 ohms you want an amp that is FTC rated into 2 ohms, or at a minimum, 4 ohms as you stated.

Remember, speaker loads fluctuate, which is why the resistance is described as impedance rather than resistance. If you have a nominal impedance of 2-2/3 ohms, you almost certainly will have impedance dips at certain frequencies down to around 1 ohm.

[atquinn]

Holy crap, who knew this stuff was so complicated!?! Well, it's always nice to learn something new I guess

Thanks.

-

Austin

[atquinn]

But wait, there's more!

So, I have impedance matching volume controls. This means, I think, that I don't have to worry as much about the matching amp impedance since, in theory, the volume controls will be set to deliver 4 or 8 ohms regardless of the actual impedance of the speakers. However, if this is the case, why were the resistances I was measuring so low? I know the volume controls work. Are the settings on them incorrect or is it just impossible to get an accurate reading when they're in the circuit? Seems unlikely that they would be set incorrectly since this house has gone through a couple owners since they were installed. Looks like I'm be doing some more research.

-

Austin

[JohnnyB]

Sounds like you could save yourself a bit of trouble with an impedance-matching speaker selector. For $30 you'll know what your amp is facing. As with anything, you can pay more to get more features (such as individual volume controls).

[atquinn]

Perfect! Problem solved. Thank you.

-

Austin