Polk XT15 amp noise

[Mike710]

Hi all,

New here although I use to follow/surf the Audiokarma and Gearslutz forums as a musician and vintage hi-fi enthusiast some years ago (90´s-00´s).

I have recently got Into all this D-amp and small format hi-fi gear by trying out a SMSL A100 paired with a set of Polk Audio XT15´s as starters. I use a DAP (Hiby R3) as my listening source plugged via the RCA Inputs. Using the headphone/line and switching to line out on the app of the R3, and use a Y RCA connector cable with TRS tip.

I have run Into what appears to be a Issue and that I need to solve soon so I can return what ever Is causing the Issue to Amazon before It´s to late.

The Issue Is that the A100 makes this "blowing" noise when turned on and stays there. When the speakers are not plugged In there Is no noise from the amp. I have tried a different pair of speakers (Infinity EL-20 @8 Ohms) and no amp noise although I did get some distortion from them. They are old and I really can´t trust them, the speaker ring Is all worn out and most has deteriorated over time from no use and heat In my old house. Surprisingly the EL-20´s sounded a lot louder then these XT15´s. Also, there Is some digital pop when past the 50% of volume on the amp on one of the XT15 speakers.

I have also tried different speaker cables and banana plugs but as above, same Issue. So I have a dilema now as to what Is going on, Is It the speakers or the amp? Any help Is much appreciated, all this new Tech, Is well new to me now.

Never had a amp or speakers that can run on both 4 and 8 Ohms without switching. At first I thought It could be a ground Issue, but now IDK.

Thank you.

 

[Mike710]

Well, returning the SMSL A100 tomorrow. Thinking of getting the Aiyima A07 Max, going to stick with the stock 36V PS for now. Will see how It goes...

 

[AnalogSteph]

The Issue Is that the A100 makes this "blowing" noise when turned on and stays there.

So it's coming from the amplifier itself?

I vaguely remember such issues cropping up with another small Class D amp here (possibly a Loxjie, or another SMSL? MA12070 as well, I think, so could be the A30?). There even kind of was a fix for it. Has something to do with the output filters.

I have tried a different pair of speakers (Infinity EL-20 @8 Ohms) and no amp noise although I did get some distortion from them. They are old and I really can´t trust them, the speaker ring Is all worn out and most has deteriorated over time from no use and heat In my old house.

These "rings" are called surrounds, and the older foam variety is well known for falling apart after 15-20ish years. You may want to look around for a set of replacement surrounds (refoam kit). A quick Google search turned up an offer for a new midrange surround, for starters. For the woofer you may have to go by measurements, nominal diameter is 210 mm. It's a very fiddly procedure (especially on smaller drivers) but doable if you're handy enough; watching lots of tutorials is advised.

Surprisingly the EL-20´s sounded a lot louder then these XT15´s.

They're a 3-way with an 8" woofer and a rated sensitivity of 90 dB, vs. a 5" 2-way rated 86 dB, so them being louder should actually not be a surprise at all. Speaker drivers are always a compromise between sensitivity and how low they will go, but a larger one starts out higher. The EL20 is only rated to 60 Hz at -3 dB, which is not very deep for an 8" at all, supporting the notion that the drivers may be more geared towards sensitivity.

Had a look at the manual, they're 8 ohms with a bit of a following wind at best. The woofer almost makes the cut at 6 ohms DC (the usual rule of thumb is that a 8 ohm driver should be around 6.4 ohms at DC), the midrange at 4.2 ohms DC isn't even a 6 ohm driver.

The EL-20 is a pretty basic 3-way with 1st-order crossovers, but you can definitely get worse as well (if you buy a $100 class 3-way chances are the crossover will consist of a grand total of 2 electrolytic caps, the Infinity has 2 caps and 2 inductors at least). A higher-order XO would also eat into sensitivity a bit. Port is not flared by the looks of it, probably not an expensive speaker at the time. You could make quite a racket with these even on a small Class D amp. I wouldn't use them nearfield, but they'd make some good TV speakers or the like.

 

[Mike710]

Hi @AnalogSteph

Thank you so much for you´re concern and help/guidance, very kind of you.

I have no way of knowing If It´s from the amp or speakers because I don´t have another amp to try the XT15´s on. Well I do, a Sansui A-40 of which I had my EL-20´s hooked up to, but I am afraid that too needs some maintenance. The volume nob (pot) needs cleaning and one channel Is failing, might be due to the volume pot. I had another Sansui AU 555 but sold It last year. The 555 sounded great though with the EL-20´s and with vinyl (LP´s).

Not sure the EL-20´s are worth the trouble with all the new tech now day´s. But It´s good to know you can do that, I´ll think about It.

Either way, I do have a bad feeling with the A100 so I sent It back. Worst case scenario would be that with whatever class D amp I get I have the same Issue, which In that case would make the matter very clear that the Issue Is with the speakers. The Idea Is to have a small set-up for my desktop and the XT15´s are quite small and don´t sound bad for what they are and what I want.

Still not sure what amp though, reading through a A70 Max thread here on ASR for more Info on that. BTW, great forum you all got here!

 

[Chrispy]

By blowing noise are you referring to a bit of amp hiss?

 

[Mike710]

By blowing noise are you referring to a bit of amp hiss?

It´s like static but without the crackle and smoother, If that makes sense.

 

[Chrispy]

It´s like static but without the crackle and smoother, If that makes sense.

Yeah that kinda sounds like amp hiss. Is it just when you put your ears near the speaker or even from your seat?

 

[Mike710]

Yeah that kinda sounds like amp hiss. Is it just when you put your ears near the speaker or even from your seat?

Hi Chrispy, sorry for the late reply, just got back from work (EU zone)...

It´s not coming from the speakers, It´s coming from the amp It´s self.

 

[Chrispy]

Hi Chrispy, sorry for the late reply, just got back from work (EU zone)...

It´s not coming from the speakers, It´s coming from the amp It´s self.

I've had some amps with transformer buzzing, maybe its more along those lines. Are there fans in these amps?

 

[Mike710]

I've had some amps with transformer buzzing, maybe its more along those lines. Are there fans in these amps?

I don´t think so, they are quite small, at most a heat sink on the amp chip.

 

[Chrispy]

I don´t think so, they are quite small, at most a heat sink on the amp chip.

How loud is it, is it audible from your seat or only when near the amp? Nothing comes thru the speakers at all? I'd probably still return it....more curious than anything just what is making a noise like that.

 

[Mike710]

How loud is it, is it audible from your seat or only when near the amp? Nothing comes thru the speakers at all? I'd probably still return it....more curious than anything just what is making a noise like that.

It´s loud enough that you can hear It while playing music at low volume. Yeah I already returned It and got a refund. Now I am looking to buy another similar amp, this was was a dud me thinks.

 

[Mike710]

I received my Aiyima A07 Max order yesterday and have been trying It out today. I am happy to report that there are no Issues with the XT15´s and that the noise Issue was from what I gather, a defective SMSL A100 unit.

When I decided to return the A100 I noticed that the box that came with It (shipped In) had some humidity stains. Getting old and without my reading glasses I miss some details sometimes! Anyhow, I find It strange that being shipped from the SMSL warehouse (according to Amazon), something like this could have slipped by. Luckily Amazon has a good return policy!

 

[ninetylol]

I received my Aiyima A07 Max order yesterday and have been trying It out today. I am happy to report that there are no Issues with the XT15´s and that the noise Issue was from what I gather, a defective SMSL A100 unit.

Sounds like a great bang for the buck combo!

 

[Mike710]

Sounds like a great bang for the buck combo!

Listening to both as I read through the forum. Very pleased so far, sound Is pleasant and BIG for such a small unit. Also surprised at how much bass these little XT15´s can put out with the A07 Max. Have been running It for the past 4hrs. unit Is slightly warm to the touch and that´s about It. No noise, no fuss, runs like a charm!

When compared to the SMSL A100, the A100 sounded a bit more analytical and with a tad more separation, It also sounded quite good but I find that the A07 Max sounds fuller. Of course this Is all subjective but that´s the first Impressions that I felt. Both the A07 Max and XT´s need the usual work In so I can only guess It will all get better.

If I were to listen behind a wall, I would get the Impression that I am listening to a bigger set-up. How things have changed since my teenage years!

Just ordered the Topping E50 a few hours ago (Black Friday sale) on Amazon, at a pretty good price (126€). Yes I know their are other more up to date DAC´s with maybe more bells and whistles now days, but I like to stick with one trick ponies. It just makes more sense to me.

It´s great to be able to listen to my music without headphones for a change, was looking forward to that. Now I am In for a cool ride and some G.A.S