Ascend Sierra Tower + Emotiva XPA-11 = Burnt Voicecoil

[jeeper]

Hi there,
I started this thread over at Audioholics, and was encouraged (Pogre) to post here as well for additional feedback and sharing with the community.

I have my HT setup with a Marantz AV7705, Emotiva XPA-11, and a bunch of speakers from Ascend Acoustics (front/surrounds) and RSL for Atmos.

The front L/R are the Ascend Sierra Towers, and Center is a Sierra Horizon. These are connected to the mono-blocks of the amp.

I was recently playing some music in stereo mode, not that loud (-8, -6 db tops), and turns out that I busted my midrange woofers. There was the distinct smell of burned rubber, and it the midrange from both towers were done. One completely gave out (no sound at all), while the other was distorted.

Contacted Ascend, and Dina was super nice and Dave pretty responsive via email as well. They suspected a burnt voice coil, and from the smell it does appear to be so, and I bought two replacement midranges.

Dave recommended that I test with some cheaper speakers and there was no hum or pops when on, playing music, or when switching on/off.

The best theory that I've come across (thanks, TLS Guy) is that a power transistor of the amp is starting to fail at a certain temperature, sending a DC offset. Also, that because of the speaker design there's no capacitor in series with the woofer to prevent a DC offset from reaching the woofers. The capacitor is a theory, and I'm waiting on Dave to confirm.

I've reached out to Emotiva about getting the amp tested; waiting on reply.

Any thoughts or feedback from anyone to share?

[Mag_Neato]

That Emotiva is a strange design, IMO. Not familiar with it so I cannot give an educated guess.

My old Adcom amp had me concerned about the possibility of DC offset. Occasionally I'd pop the cover off and adjust it using a multimeter. For peace of mind I sold it and now use a Audio by Van Alstine SET-120 amp. It's design is DC stable and will not generate DC drift even into clipping.

That said, you obviously require multiple channels of amplification for an HT setup, so you probably want to stay with a big multi-channel model.

[Pogre]

It's odd that both mids burned out like that and DC offset from the amp is a proposed possibility. I know there's a lot of "it depends" with different systems, source, etc, but I've had my towers cranked up pretty good myself (dial at 0, 103 dB peaks at mlp 14.5' away) and never experienced anything like this. It's starting to look like maybe that amp needs to go.

I was wondering if Dave might have some input on the DC offset hypothesis.

[Pogre]

That Emotiva is a strange design, IMO. Not familiar with it so I cannot give an educated guess.

My old Adcom amp had me concerned about the possibility of DC offset. Occasionally I'd pop the cover off and adjust it using a multimeter. For peace of mind I sold it and now use a Audio by Van Alstine SET-120 amp. It's design is DC stable and will not generate DC drift even into clipping.

That said, you obviously require multiple channels of amplification for an HT setup, so you probably want to stay with a big multi-channel model.

Clipping of course, was discussed also, but wouldn't the tweeters be more prone to damage from clipping? I'd guess they would go before the mids.

That's why DC offset was proposed.

[davef]

Hi there,
I started this thread over at Audioholics, and was encouraged (Pogre) to post here as well for additional feedback and sharing with the community.

I have my HT setup with a Marantz AV7705, Emotiva XPA-11, and a bunch of speakers from Ascend Acoustics (front/surrounds) and RSL for Atmos.

The front L/R are the Ascend Sierra Towers, and Center is a Sierra Horizon. These are connected to the mono-blocks of the amp.

I was recently playing some music in stereo mode, not that loud (-8, -6 db tops), and turns out that I busted my midrange woofers. There was the distinct smell of burned rubber, and it the midrange from both towers were done. One completely gave out (no sound at all), while the other was distorted.

Contacted Ascend, and Dina was super nice and Dave pretty responsive via email as well. They suspected a burnt voice coil, and from the smell it does appear to be so, and I bought two replacement midranges.

Dave recommended that I test with some cheaper speakers and there was no hum or pops when on, playing music, or when switching on/off.

The best theory that I've come across (thanks, TLS Guy) is that a power transistor of the amp is starting to fail at a certain temperature, sending a DC offset. Also, that because of the speaker design there's no capacitor in series with the woofer to prevent a DC offset from reaching the woofers. The capacitor is a theory, and I'm waiting on Dave to confirm.

I've reached out to Emotiva about getting the amp tested; waiting on reply.

Any thoughts or feedback from anyone to share?

Hi Jeeper,

I haven't been over to the audioholics forum in well over a year, I don't even know if I am still a member . That said - Dina did inform me that both mid-woofers have burned coils.

A DC offset in your amplifier is what I was alluding to when I asked you if you heard any low level hums or "pops" when you turn your amp on or off. Typically, with a DC offset, you can hear a low level hum in the background or pops on amp power on/off etc, or see the woofers move in/out during amp power on/off. However, this is very much dependent on the amp design.

Something definitely happened, it is rare enough for a voice coil to burn, but for both of them at the same time to go, it is a sure sign *something* happened.

Another possibility is low AC line voltage, and I have seen this more often these days - especially here in California. If your line voltage drops, this will cause your amp to clip and the distortion this produces can be quite damaging, especially if there is a DC component to it, which can happen depending on the amp design. Luckily, the RAAL 70-20 has good protection from the damaging effects of transverse waves caused by clipping and DC can't hit the tweeter.

Do you have access to a voltmeter?

I should probably also mention that I have come across this same issue before with the same amplifier (DC Offset)

[davef]

Clipping of course, was discussed also, but wouldn't the tweeters be more prone to damage from clipping? I'd guess they would go before the mids.

That's why DC offset was proposed.

For any other tweeter, yes - heavy clipping would take the tweeter out first. However, the RAAL 70-20 has a unique damping feature (unique only to the 70-20) which enables the ribbon to better handle the problems associated with a clipped signal. This is one of the reasons why I love this tweeter and am willing to pay a fortune to use them...

[jeeper]

Hi Jeeper,

I haven't been over to the audioholics forum in well over a year, I don't even know if I am still a member . That said - Dina did inform me that both mid-woofers have burned coils.

A DC offset in your amplifier is what I was alluding to when I asked you if you heard any low level hums or "pops" when you turn your amp on or off. Typically, with a DC offset, you can hear a low level hum in the background or pops on amp power on/off etc, or see the woofers move in/out during amp power on/off. However, this is very much dependent on the amp design.

Something definitely happened, it is rare enough for a voice coil to burn, but for both of them at the same time to go, it is a sure sign *something* happened.

Another possibility is low AC line voltage, and I have seen this more often these days - especially here in California. If your line voltage drops, this will cause your amp to clip and the distortion this produces can be quite damaging, especially if there is a DC component to it, which can happen depending on the amp design. Luckily, the RAAL 70-20 has good protection from the damaging effects of transverse waves caused by clipping and DC can't hit the tweeter.

Do you have access to a voltmeter?

I should probably also mention that I have come across this same issue before with the same amplifier (DC Offset)

Hi Dave, thanks for the reply! I did test the amp with an old speaker and didn't hear anything. That's why I like the theory of failure at a certain temperature idea... perhaps under a heavier load.

I do have a multimeter...

[Pogre]

Hi Jeeper,

I should probably also mention that I have come across this same issue before with the same amplifier (DC Offset)

Interesting. TLS Guy mentioned that in his opinion that amp is very questionably designed, but he can be a curmudgeon sometimes, chasing the neighborhood kids off his lawn, lol.

[jeeper]

Emotiva confirmed that the XPA series has buit-in DC offset protection, along with protection in the event of a short at the speaker connection, and a bunch of others. According to them, if there was a dc offset, the amp should've shut down. That never happened, and the amp still turns on.

[racrawford65]

Typical Emotiva - never an issue with any of their products.