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Old 18th June 2009, 01:35 PM   #4111
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by AndrewT
you normally set power and sensitivity and normal listening volume so that the peak SPL at the listener's location to about 20dB greater than the average music level.

Quote:
Originally posted by thanh1973

I didn't see what the efficiency of his speakers were.
Are you making an assumption here?
If so what assumption are you making?
do want yet more numbers?

I have already posted them.
Gedlee has also posted numbers.
Many others have posted numbers.
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Old 18th June 2009, 01:40 PM   #4112
tinitus is offline tinitus  Europe
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F5 power amplifier
Quote:
Originally posted by thanh1973
Hi tinitus
This is a push pull design not a single ended design.
Therefore it stays in class A up to twice the bias current then goes into class B.


Obviously I dont understand as I expected bias current to be the same for all loads

So its 25watt classA in all loads, is that what you are saying

Anyway, I dont think anything else have ever been promissed

Maybe thats why 300VA trafos are still ok for both channels

25watt classA in 16ohm, 25watt classA in 8ohm, 25wattt classA in 4ohm, 25watt classA in 2ohm, 25watt classA in 1ohm

And the rest is just rubbish
Makes sense
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Old 18th June 2009, 01:40 PM   #4113
jackinnj is offline jackinnj  United States
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F5 power amplifier
Quote:
Originally posted by pro
Is it a good tweek, to put a cap beetwen the mosfet gates? Did anybody try it?
No need -- there is no instability in this amplifier until you run it up into the Megahertz.

The F5 has that wonderful combination of speed, stability and very low distortion.

If you have to tweak, some electrolytics like the Elna Silk 220uF on the rails almost immediately next to the MOSFETs will help. I tweaked up mine to adjust the gate input resistors to the JFETs which has no effect on sound, but makes the slew perfectly symettrical.
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Old 18th June 2009, 01:47 PM   #4114
pro is offline pro  Italy
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It's not for stability, but it, from simulation, looks to lower alot the even harmonics.
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Old 18th June 2009, 01:48 PM   #4115
tinitus is offline tinitus  Europe
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Quote:
Originally posted by jackinnj


If you have to tweak, some electrolytics like the Elna Silk 220uF on the rails almost immediately next to the MOSFETs will help.

Or even better, place your last main supply cap close to amp board

I usually prefer a single pair of caps
But this time I may have multiple caps placed along the entire supply line from bridge to amp board conection

Anyway, I have never understood the use of those small signal supply caps in poweramps
They are not fit for high ripple currents
How that works is beyond me
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Old 18th June 2009, 01:51 PM   #4116
Melon Head is offline Melon Head  Australia
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Sorry I am a bit too lazy to give a long explanation.
But it is like this if the output is 25W Class A into 8 Ohms, then it will be 12.5W Class A into 4Ohms, and 6W Class A into 2 Ohms.
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Old 18th June 2009, 02:02 PM   #4117
Melon Head is offline Melon Head  Australia
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Sorry Andrew
I was asking a genuine question.
If the speakers he has are 100db/w/m then your calculations would be a lot different for someone elses speakers which might only be 85db/w/m.
Wouldn't they?
Please explain?
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Old 18th June 2009, 02:08 PM   #4118
jackinnj is offline jackinnj  United States
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F5 power amplifier
Quote:
Originally posted by pro
It's not for stability, but it, from simulation, looks to lower alot the even harmonics.
Regards
That's because you bandwidth limit the amplifier when you add more capacitance to the output device -- usually you do something like this to cure some instability arising from poor lead dressing etc. When you bw limit the amplifier you slow the slew rate as well.
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Old 18th June 2009, 02:14 PM   #4119
Melon Head is offline Melon Head  Australia
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Hi Pro
Just to be sure I hope you are not talking about my suggested tweak.
I never suggested putting caps at the gate.
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Old 18th June 2009, 02:15 PM   #4120
R-K Rønningstad is offline R-K Rønningstad  Norway
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Quote:
Originally posted by AndrewT




your logic is right.

But, you normally set power and sensitivity and normal listening volume so that the peak SPL at the listener's location to about 20dB greater than the average music level.

Based on that 20dB headroom for transients, your maximum average power input to your speakers will be ~ 0.25W.
This is well within ClassA into 4ohm speakers.

If the output goes to 2.5W into your 4ohm speakers (average +10dB) then the peak voltage is still only 4.5Vpk. The maximum current to meet this transient peak is likely to be <=3.2Apk for severe reactance speakers. This is just outside the ClassA limit for a standard F5.
If you increase the bias to 1.65A or 1.7A, then that +10dB transient will be within the ClassA limit.
Only transients that are above the +10dB level will drive the speakers harder. and only if that transient is either very fast starting or very fast stopping will it demand the highest of current to be sent to your reactive speakers.
There's a good chance that you will only go out of ClassA once or twice a recording (if it's very dynamic) when your average listening level is <=0.25W

Seems the First Watt or so are Class A .....
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