Speakers sound extremely muffled with new amp..

T

Trackr

[H]ard|Gawd
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Feb 10, 2011
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So, I bought a new SMSL SA-98 100wx2 amp for my Polk Audio Monitor 30 speakers and, well.. it sounds like they're being played within a metal box.

No setting I've found can change this. I've tried virtually everything I can think of.

Please help!
 
Holy shit the THD on that amp is 10%! There's no way that thing is 100watts x 2, you're probably looking at a few watts with acceptable THD before it just tanks. You might've gotten a defective one but personally I'd find a different amp. You need something more robust for those speakers IMO.
 
Wow, 10% THD? I searched and that's what I saw on Amazon, eBay, and some other site. .01% THD would be acceptable, I could understand if 10 was a misprint. Did it come with any documentation saying "10%"?
 
That doesn't mean the amp is 10% THD over its whole output range, it means they are overstating its maximum output. THD varies with output level and is higher on the extreme high and low end. Most manufacturers don't publish the curve, but you can find some that do (like Emotiva) and get an idea of how it works. For example on their UPA-700, which they market at 70 watts in to 8 ohms:

--THD varies from 1%-50% at 100 microwatts. These is a lot of variance between channels because small things can equal large changes when you are talking a signal this low.
--THD is less than 0.1% on all channels by 50 milliwatts.
--THD continues dropping slowly to a low point of 0.01%-0.02% (varying by channel) at 10 watts.
--THD slowly rises to 0.02%- 0.03% (varying by chanel) at 60 watts.
--THD then sharply rises, up to 0.05% at 70 watts, which is where it is rated.
--The sharp increase continues in a basically linear fashion (plotted in log/log space), up to 20% at 110 watts which is where they stop the test.

So a high THD stated at max level doesn't mean a high THD amp overall. It just means they overstate the max level. Not saying it isn't a shady thing to do, just that you have to be wary of drawing inferences from that.


As to why it sounds bad... I dunno. My first guess would be maybe it doesn't have a good feedback setup and thus isn't dampening the speakers properly.

The amp probably isn't very well designed or quality controlled. That can be an issue with cheap no-name amps. If you can send it back, you may wish to do so and look at getting something a little higher quality.
 
I was recommended the SMSL amp on this very forum.. why would people mislead me?

I spent a lot of time and money getting this amp because people told me it was good.. now I have to send it back..?
 
It's probably not that someone mislead you, IMO the amp is probably defective. It happens. Some people believe amps can change the sound quality (we're going to ignore tube amps for this example), I'm not one of them however I've never heard anyone say an amp makes the speakers sound like they're being playing in a metal box so that makes me think that it's probably defective. Usually when someone (of those that believe that amps have sound quality characteristics) they describe an amp sound as something more subtle like warm, neutral, or bright.

Do you have another pair or speakers or another amp to swap between so you can narrow it down at least?
 
Trackr said:
So, I bought a new SMSL SA-98 100wx2 amp for my Polk Audio Monitor 30 speakers and, well.. it sounds like they're being played within a metal box.

No setting I've found can change this. I've tried virtually everything I can think of.

Please help!
Click to expand...

Have you tried reversing the + and - of your other speaker already? It's not unheard of to have + and - in wrong order in cheap devices.

Remember, change only one speakers cable polarity if you change also the other one nothing will change.

The metal boxy sound may also come from a bad switch that doesn't trigger properly. Try cycling all your channel selectors, source buttons etc. and turn volume button high and low repeatedly to see if it changes the sound. Turn the sound low or the amp off before you start cycling.
 
I reversed the polarity by switching the red/blue wires for one of speakers. No change.

I managed to make certain movies sound almost alright by taking down the bass to its lowest (-12dBa) and putting the treble to its highest (+12dBa). I've been fiddling with it up and down, but I can make dialogue sound passable.. the only problem is that it makes everything else sound extremely tinny.

So, how do I tell if my speakers are shit (they only cost $100) or my amp is defective besides having to wait a month for a new one from the seller?

I was told to buy the SMSL because the other amps had a distortion rate of 10%, so I guess I should have done a little more research by myself. I was just so excited to finally hear my Monitor 30's as they were supposed to be heard.
 
Try running one channel with your speakers in series and the other channel undriven.

This'll check if you've got an impedance problem, which is really the only technical downside of Class D amps (practical downsides being higher cost and more complex design). Almost all Class D designs are far more sensitive to speaker impedance (particularly dips in impedance which are hard to drive) than other classes of amp like the common AB.

I specifically said I hadn't tried the amp, but that it looked good based on the info I saw. And I stand by that.

If it's still not good with your speakers in series, it's defective, or you may have gotten a cheap clone with way worse internals.


And about the 10% THD, as mentioned before, that means the power being quoted is BS and that it's really more like half that power. Almost all T-amp manufacturers do this. It's not a respectable thing to do - that's for sure. But you're going to find that from any of its competitors as well. I'm not sure if it's because Tripath itself rates their chips like that or because these are still relatively inexpensive amps that manufacturers don't think will sell well if they were to advertise the real power.
 
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I tried running one speaker by muting the other and they both sound the same.

Question is - how do I know if it's defective or not?

I felt so confident in buying a 100w amp (even if it's only 50w), and using good speakers (I think the Monitor 30's are good).

I get really good quality from them using a Creative G500 receiver.. though, it's been a long time since I compared.

Right now, I'm listening to some shitty 3w portable speakers and they sound better than the Monitor 30's.

Though, I should admit that my girlfriend disagrees. I said that if there is even a comparison between 100w Bookshelf speakers a 3w portable speakers.. something is wrong.
 
Those speakers look like they should be good. I looked at the specs on them though, they have 8 impedance and the sensitivity looks pretty high at 89. You might want to try out a Topping TP20 amp with them, as sensitive speakers like these make a good match for the Topping. You won't be able to get ridiculously loud with it if that's what you're after, but the sound and build quality is great on the Topping. I'm using mine with significantly more expensive speakers and it's working fine.

But first, try exchanging that amp and seeing if it's a defective one. If the new amp does the same you could then either try exchanging the speakers as defective or trying the Topping out instead. If it does the same crap with the Topping you know it's the speakers.

You could also try opening the speakers up and seeing if something looks loose in there I guess.

Just troubleshooting steps.
 
Double-check that you've got things connected on the speaker end properly, in particular the metal jumper. For a single amp connection, the jumper needs to remain connected. You can then use either the top or bottom set of binding posts to connect to the amp, though I think Polk recommends you use the top set. That's how I have mine connected, and they sound just fine on a Dayton t-amp.
 
|Tch0rT| said:
really it all comes down to experience and the amps you have owned personally. their are many who argue amps all sound the same as most of these people never owned various amps - especially high end amplifiers.

Im no expert either, but however comparing my old Denon 3808 (receiver) to my Elektra Theatron is night and day. but then again its not a fair comparison as the denon is a all in one unit while the Elektra is designed as a multi channel power amplifier from ground up with high quality parts and a massive power supply. Question is does quality of parts matter? IMO Yes.
Click to expand...
 
genkifd said:
Im no expert either, but however comparing my old Denon 3808 (receiver) to my Elektra Theatron is night and day.
Click to expand...

One easy way to lose an argument is to overstate your point, something all you golden ears do. "Night and day difference." Classic golden ear bullshit. Even if your higher-end amp has 1% the distortion of your Denon, neither one has audible distortion to begin with and your speakers are several orders of magnitude worse for distortion. Unless you're driving more power than the Denon can do, in which case you don't need a super-high-end amp anyway. If you want to compare your amps without the extreme hyperbole, though, I'm all ears.

I love high-end gear too but really it's better to spend it on things that matter more like speakers, room, and even processing (for example, room calibration systems). That's not to say high-end amps are 100% worthless - they can be better built, drive more power, possibly drive more channels, etc. But don't misrepresent what they do for your sound quality. And very cheap amps can indeed have quality problems, so I normally would say any decently built product.

https://www.youtube.com/watch?v=m7ERMu825m4
 
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Regarding THD, if you are curious, it looks like this particular amp hits 1% THD at 50W/Channel into 8 ohms and at 65W/Channel into 6 ohms (essentially where dandragonrage figured it would be).

It is also worth noting that even if SMSL overstated the amp's power, most persons overestimate how much power they really need for a given speaker anyway, based on the manufacturer's peak power and sometimes unreliable sensitivity ratings.

So don't focus on power handling. Instead, focus on trying out the suggestions in this thread, and if none of those work, I would probably try another unit, perhaps even from another seller.
 
Trackr said:
I reversed the polarity by switching the red/blue wires for one of speakers. No change.

I managed to make certain movies sound almost alright by taking down the bass to its lowest (-12dBa) and putting the treble to its highest (+12dBa). I've been fiddling with it up and down, but I can make dialogue sound passable.. the only problem is that it makes everything else sound extremely tinny.

So, how do I tell if my speakers are shit (they only cost $100) or my amp is defective besides having to wait a month for a new one from the seller?

I was told to buy the SMSL because the other amps had a distortion rate of 10%, so I guess I should have done a little more research by myself. I was just so excited to finally hear my Monitor 30's as they were supposed to be heard.
Click to expand...

Uh, check you didn't connect your speakers between channels. If you connect your speaker to the + of left channel and + of right channel, you get a muddy signal separation output. Double check that your cables are connected to the + and - terminals of left channel for your left speaker and right channel to the + and - terminals for your right speaker. Also, did you speakers sound good initially, you know, before you decided to crank up the volume to see how loud they get? If so you managed to burn up your tweeters with the low power amp and in that case, congratulations.

Outside of that, I have no problems believing a 50 dollar Chinese D-class amp sounds like shit. Get a proper one instead. Actually the easyest thing you can do is borrow an amp from a friend and try it. If it still sounds like shit either your speakers are blown or your signal source (cd/mp3 player, computer) has a problem.
 
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