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Amp cutting out on more efficient speaker. Why?

99.114.214.98
Posted on May 13, 2022 at 00:03:40
voolston
Audiophile

Posts: 3330
Location: New Orleans
Joined: October 14, 1999
 The amp is a SMSL AO200 which is a cheap class D affair using Infineon chips and is rated at about 150/90/50wpc into 2/4/8ohms respectively. I've played it on two very different speakers: Big ass JBL L200's (15" woofer, about 96-97db) and a tiny pair of Definitive Technology Pro Monitor 800's (4.5" woofer, 89db). Amp also has a "smart clipping" setting that apparently cuts the signal and emits a light ticking sound until you turn down and reboot. It apparently keeps things from getting damaged, and it works as I've forced it into action several times. Thing is, it's the JBLs that caused the clipping when the volume hit 35 of 70. On the DTs', I can go up to 45 of 70 and experience no clipping at all. Am I wrong to think I should be able to go to 45 out of 70 (if not higher) with the the JBL's with no issue, since the amp will put out at that level on a more difficult to drive speaker? I'm rather stumped by this.

voolston - audiophile by day, music lover by night!

 

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those power specs are basically imaginary, posted on May 19, 2022 at 20:45:34
LtMandella
 A: anywhere near that power output quoted and the distortion would be horrendous - and unlistenable...

B: other responders are almost certainly correct regarding impedance dips at lower frequencies.

 

a 45 degree phase angle/impedance dip @ 80 to 200 HZ would put a hurting on some amplifiers~nT, posted on May 17, 2022 at 14:01:29
Cleantimestream
Audiophile

Posts: 7551
Location: Kentucky
Joined: June 30, 2005
 ~!
The Mind has No Firewall~ U.S. Army War College.

 

RE: Amp cutting out on more efficient speaker. Why?, posted on May 14, 2022 at 13:32:30
fredtr
Audiophile

Posts: 1987
Location: Phoenix
Joined: January 4, 2005
 What kind of shape are the L200's? Have the crossovers been checked or updated? I remember the L200's being made in the mid 70's, so getting close to 50 years old. I also don't remember them as having an impedance curve with any significant low frequency dips, but I could be wrong.

 

Impedance curve, posted on May 14, 2022 at 21:53:32
voolston
Audiophile

Posts: 3330
Location: New Orleans
Joined: October 14, 1999
 I believe you're correct about the JBL's impedance curve. For what it's worth, the amps that I usually power the JBLs with are OTLs which of course do not tolerate low impedances too well.

voolston - audiophile by day, music lover by night!

 

Speakers, posted on May 14, 2022 at 06:44:14
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 You are over driving your speakers that are rated for lower power, causing them to clip. Also your amp is not interacting with your speakers very well.

 

RE: Amp cutting out on more efficient speaker. Why?, posted on May 13, 2022 at 19:08:55
pictureguy
Audiophile

Posts: 22597
Location: SoCal
Joined: October 19, 2008
 Infineon BOUGHT International Rectifier and may be selling (changed in some fashion?) IR amps under a new name.
I have one of the original IR amps for test.....the 'reference' board version in stereo.

It is Just Possible that the amp doesn't like the REACTANCE of the speaker.....as opposed to a sheer bad 'impedance' match....

I suppose it IS possible for a higher sensitivity speaker (manuf #?) to actually be a worse load to the partnering amp. some wacky low impedance point coupled with 60 degrees reactance?
Too much is never enough

 

SMSL is substandard is Why, posted on May 13, 2022 at 10:15:10
bare
Audiophile

Posts: 1879
Joined: April 14, 2009
 That junky thing is Clipping.. period. NO headroom at all Not withstanding that their 'Power' claims are pure BS.

 

Ok, then why is it only being substandard when..., posted on May 13, 2022 at 11:35:40
voolston
Audiophile

Posts: 3330
Location: New Orleans
Joined: October 14, 1999
 ...powering the more efficient speakers?

voolston - audiophile by day, music lover by night!

 

RE: Ok, then why is it only being substandard when..., posted on May 13, 2022 at 18:48:09
mlsstl
Audiophile

Posts: 1079
Location: Midwest
Joined: September 1, 2015
 My two cents is Story has the answer for you. Somewhere in the speaker's impedance curve it dips too low for the amp. On solid state amps, the output voltage at a given volume stays the same regardless of impedance, but the current draw changes. A 4 ohm load draws twice as many amps compared to an 8 ohm load, and a 2 ohm load tries to draw four times the current compared to 8 ohms. At some point, the amp thinks it is seeing a short circuit and goes into protection mode. Some amps handle this situation better than others.

 

RE: Ok, then why is it only being substandard when..., posted on May 14, 2022 at 08:46:23
Mick Wolfe
Audiophile

Posts: 3365
Location: AZ
Joined: October 10, 1999
Contributor
  Since: September 4, 2000
 Yep and as already mentioned by others, high efficiency isn't much of an advantage if the amp still has to deal with a nasty impedance curve. If I liked the offending speaker, I'd simply buy a better amplifier.

 

FWIW..., posted on May 14, 2022 at 22:25:23
voolston
Audiophile

Posts: 3330
Location: New Orleans
Joined: October 14, 1999
 I did not buy amplifier for the JBLs but wanted to hear it on them since they are my reference, so it's not a problem. The amp is driving the Definitive Technologies just fine. I'm just surprised the outcome came out the way it did.

voolston - audiophile by day, music lover by night!

 

RE: FWIW..., posted on May 15, 2022 at 07:03:30
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 Just be glad that your amp has that protective circuit. I've repaired a few of the old McIntosh MA5100 and 6100 integrated amps that if they saw a 2 ohm dip, they would blow out a zener diode.

It was a little secret that Gordon Gow's son told me.

 

RE: Amp cutting out on more efficient speaker. Why?, posted on May 13, 2022 at 04:22:31
Story
Audiophile

Posts: 10456
Location: NJ
Joined: December 11, 2000
 you would think so as it doesn't seem to make any sense from the appearance of the specs. But the JBL's must have a more complex impedance curve with regard to frequency and it triggers the circuit when it reaches the power/value limitation. In other words it's not a straight line at 8ohms from 20 to 20,000 hz.

Somewhere in the curve it dips low, perhaps to 2 ohms and triggers the protection.



 

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