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Old 28th January 2007, 10:12 PM   #1
MikeW is offline MikeW  United States
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Default Frequency response vs. output power

How much does the frequency response change for one watt output to full rated output power on a Pass labs amp? All the reviews I read are for small signal frequency response. Is there a difference. Does anyone have some data?
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Old 28th January 2007, 10:58 PM   #2
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Mike,
Bode is the keyword you're searching for. As in Bode plot. Yes, the bandwidth shrinks as the power (interpret this as gain) increases.
Chip opamps have really stupid open loop bandwidths...like 100Hz. It's only after you apply gonzo amounts of feedback that the bandwidth becomes tolerable.
If you meditate on all the ramifications and implications of this junk you're likely to end up like me--meaning someone who thinks that 250kHz to 300kHz open loop bandwidth is a good start. I say that having just come up from the Dungeon wherein my Evil Experiments managed a whole, astounding 10kHz. Unsatisfactory. Need to stop and think things over. Bummer.

Grey

P.S.: Good talking to you. There's no one to talk audio with out here in the hinterlands.
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Old 28th January 2007, 11:16 PM   #3
flg is offline flg  United States
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Grey, Southern R.I. isn't any better. But, MikeW, your only a stone's throw away...
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Old 29th January 2007, 01:26 AM   #4
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Quote:
Originally posted by GRollins


Yes, the bandwidth shrinks as the power (interpret this as gain) increases.

Somewhat difficult for me to understand.
I am simplified. Nevertheless, as the rolloff is hapenning
depending purely on the RC network, I understand that the
rolloff point is independant of the power level.
I.e. the bandwidth of an amp is the same at any power level.
The distortion might be increased at the power increase, though.

Where I'm wrong . . . ?
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Old 29th January 2007, 02:17 AM   #5
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Quote:
Originally posted by GRollins
P.S.: Good talking to you. There's no one to talk audio with out here in the hinterlands.

the hinterlands aren't in SC -- at least you guys know what a "grit" is.
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Old 29th January 2007, 06:18 PM   #6
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Default Re: Frequency response vs. output power

Quote:
Originally posted by MikeW
How much does the frequency response change for one watt output to full rated output power on a Pass labs amp? All the reviews I read are for small signal frequency response. Is there a difference. Does anyone have some data?
It's pretty much the same.

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Old 29th January 2007, 06:24 PM   #7
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A little later:

Since there was an XA100.5 on the bench being tested for
frequency response, I checked it at 2W, 50W and 100W.

It was 2 dB down at 100 KHz at 2W, 2 db at 50W, and 2.2 dB
at 100W.

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Old 29th January 2007, 11:28 PM   #8
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So Nelson,

I don't recall having heard of an XA100.5 previously. What is the difference between it and the the XA100? Thanks.

Graeme
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Old 30th January 2007, 12:49 AM   #9
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Quote:
Originally posted by Nelson Pass


It was 2 dB down at 100 KHz at 2W, 2 db at 50W, and 2.2 dB
at 100W.



I guess the last value, 2.2dB, must be due to
the accuracy tolerance of your farsighted glasses
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Old 30th January 2007, 04:31 PM   #10
MikeW is offline MikeW  United States
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Quote:
Originally posted by Nelson Pass
A little later:

Since there was an XA100.5 on the bench being tested for
frequency response, I checked it at 2W, 50W and 100W.

It was 2 dB down at 100 KHz at 2W, 2 db at 50W, and 2.2 dB
at 100W.

Thanks
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