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Author Topic: Subwoofer amps - what are we REALLY hearing?  (Read 31350 times)

Tim McCulloch

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Re: Subwoofer amps - what are we REALLY hearing?
« Reply #170 on: February 18, 2008, 06:47:13 pm »

Mac Kerr wrote on Mon, 18 February 2008 17:43

Tim McCulloch wrote on Mon, 18 February 2008 18:42

Can we stick a fork in this thread?  It's done....

Tim Mc
It was done on day one.

Mac


Hmmmm... Let's carve it up and serve it...  lots of tofu; most of the real meat went unnoticed.

Tim Mc
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John Roberts {JR}

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Re: Sound Is Subjective
« Reply #171 on: February 18, 2008, 07:03:42 pm »

Mac Kerr wrote on Mon, 18 February 2008 17:41

I don't know if it's what you were thinking of, but that was a claim to fame of Spectrasonics amps. The Spectrasonics 700 was a 70W amp on a card. You could load up to 8 of them in the card cage. they were very sensitive to wiring issues, I smoked a cage full of them when they went into ultrasonic oscillation because there was a grounding issue.

Mac



No not Spectrasonics.. they were around for quite a while IIRC.. The amp company I had in mind was a flash in the pan, didn't last more than a year or two...

WRT the Spectra's I was always nervous about running power amp power et al through PCB edge connectors, but people liked the modularity.

JR

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Ted Olausson

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Re: Sound Is Subjective
« Reply #172 on: February 18, 2008, 07:37:04 pm »

Andy Peters wrote on Sun, 17 February 2008 19:57

Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a


No, typo, 80 KILO hertz is it bandlimited to.
It can only handle 300KHz at full power, but the risetime is 0,5uS and slewrate is 180v/uS.

Should i mention the brand!? Naah Twisted Evil

Andy Peters

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Re: Sound Is Subjective
« Reply #173 on: February 18, 2008, 07:52:28 pm »

Ted Olausson wrote on Mon, 18 February 2008 17:37

Andy Peters wrote on Sun, 17 February 2008 19:57

Ted Olausson wrote on Sun, 17 February 2008 06:50

(One of the amps is also very close to "2xpower" from DC to 80MHz and has perfect stepresponse, the other is a normal amp)


80 MEGAHERTZ?

Why does it need bandwidth out that far, if it's an audio amplifier?

-a


No, typo, 80 KILO hertz is it bandlimited to.


And this is EXACTLY why I'm a pedantic asshole.

There is a significant difference between 80 MHz and kHz. (And if anyone writes mHz, that's a very small bandwidth.) So, at least proofread before posting. (And yes, I expect to be called on my typos, and I always admit to making mistakes.)

Anyways -- I'm not significantly impressed by 80 kHz bandwidth.

-a
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Ted Olausson

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Re: Sound Is Subjective
« Reply #174 on: February 18, 2008, 08:11:51 pm »

Andy Peters wrote on Tue, 19 February 2008 01:52


And this is EXACTLY why I'm a pedantic asshole.

There is a significant difference between 80 MHz and kHz. (And if anyone writes mHz, that's a very small bandwidth.) So, at least proofread before posting. (And yes, I expect to be called on my typos, and I always admit to making mistakes.)

Anyways -- I'm not significantly impressed by 80 kHz bandwidth.

-a


It is easy to remove the 80KHzfilter, its just a cap and a resistor on the input but i dont expect it to do any difference.

Andy Peters

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Re: Sound Is Subjective
« Reply #175 on: February 18, 2008, 08:14:25 pm »

Ted Olausson wrote on Mon, 18 February 2008 18:11

Andy Peters wrote on Tue, 19 February 2008 01:52


And this is EXACTLY why I'm a pedantic asshole.

There is a significant difference between 80 MHz and kHz. (And if anyone writes mHz, that's a very small bandwidth.) So, at least proofread before posting. (And yes, I expect to be called on my typos, and I always admit to making mistakes.)

Anyways -- I'm not significantly impressed by 80 kHz bandwidth.

-a


It is easy to remove the 80KHzfilter, its just a cap and a resistor on the input but i dont expect it to do any difference.


OK, smart guy, why not try it -- remove the filter and see how long the amp lasts before ultrasonic oscillation destroys the output stage.

-a

PS: it's kHz, not KHz. K is absolute temperature in Kelvin. Kower-case k is kilo-.
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Mac Kerr

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Re: Sound Is Subjective
« Reply #176 on: February 18, 2008, 08:18:08 pm »

Andy Peters wrote on Mon, 18 February 2008 20:14

PS: it's kHz, not KHz. K is absolute temperature in Kelvin. Kower-case k is kilo-.
Oh Andy, you pedant you.  Laughing

Mac

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Ted Olausson

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Re: Sound Is Subjective
« Reply #177 on: February 18, 2008, 08:20:46 pm »

Andy Peters wrote on Tue, 19 February 2008 02:14


OK, smart guy, why not try it -- remove the filter and see how long the amp lasts before ultrasonic oscillation destroys the output stage.


What does inputcap have to do with oscilliation!? it is a inputbuffer after the cap...
-If so, it would oscilliate when there wasnt any connector in the amp....

John Roberts {JR}

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Re: Sound Is Subjective
« Reply #178 on: February 18, 2008, 08:22:16 pm »

Ted Olausson wrote on Mon, 18 February 2008 18:37



No, typo, 80 KILO hertz is it bandlimited to.
It can only handle 300KHz at full power, but the risetime is 0,5uS and slewrate is 180v/uS.

Should i mention the brand!? Naah Twisted Evil


Well that doesn't exactly clear it up for me... Band limited to 80 kHz but only handles 300 kHz at full power. Is that another typo?

I am an advocate of rise time instead of slew rate specifications. For the record the rise time spec implies a low pass filter either before or incorporated into the input gain stage. The few times I've seen rise specs for power amps there is often a foot note that the rise time filter is disabled during the slew rate measurement. Because customers insist on hearing high slew rate numbers in a "more is better" contest despite having little clue about what they actually mean. Another archaic specification that used to mean something when amps were slow.

Since slew limiting is like clipping in the time domain, a properly low passed amp can't be slew limited with a valid input signal, making such measurements a little difficult. A max slew rate could be imputed from the power bandwidth frequency and voltage, but a well designed circuit is typically faster than that.

If the power bandwidth really is 300 kHz that is excessive for audio reproduction.  

My only possible interest in the brand name is to look up a data sheet and see what the specs really are, but nah..  Twisted Evil  

JR


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SteveKirby

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Re: Sound Is Subjective
« Reply #179 on: February 18, 2008, 08:40:47 pm »

John Roberts  {JR} wrote on Mon, 18 February 2008 17:32

The name of the company escapes me now, but there was an amp company back in the late '70s or early '80s whose claim to fame was strip line (?)  technology and Mhz bandwidth, I doubt even they were pushing 80 Mhz power bandwidth but they were faster than your average Fender...

Needless to say there was no "there" there and they faded into oblivion. Something about "you can't fool all the people all the time..." (without a huge marketing budget).

JR

 

Are you thinking of Spectral?  I think they were based in SF and founded on the premise that bandlimiting to 20kHz created slew limiting bluring time base information that provided directional cues.
There was an arm of the company that made records,  Reference Recordings.  I have one record of theirs with Stephen Gordon playing Chopin.  Lots of ambience that sounds like the rear third of the hall.
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