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Old 21st February 2011, 01:52 PM   #1091
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Quote:
Originally Posted by tinitus View Post
if you want 100% pure classA, it seems to me that both low impedance speakers and balanced design is a bit of a 'pain'
With MOSFET output stages, balanced is always a bit of a pain, Class A or no Class A.
For low impedance loads, Class A is a bit of a pain only if the LSP also has low efficiency.
Plenty examples of high quiescent current level, low power Class A amps for high efficiency loudspeaker systems, both commercial and non-commercial designs.

ZM, stop spitting against the paper.
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Old 21st February 2011, 02:39 PM   #1092
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Originally Posted by tinitus View Post
ahh, yes
and that we do

but why do I get a reminder of old days when some amps were 'marketed' with their 'music wattage'
hey, Im not trying to be sarchastic, not at all, and I know it may not be quite the same thing
but I still get this..hmmm

but hey, Im doing it too
That's because you cannot sell a 20Kg amplifier costing 5.000$ by advertising their "just" 25w per channel.

Other mainstream manufacturers choose to say the real ratings, but they seem so small that use to show them in a shy and small thypography.
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Old 21st February 2011, 02:45 PM   #1093
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Originally Posted by regiregi22 View Post
That's because you cannot sell a 20Kg amplifier costing 5.000$ by advertising ........25w per channel.
Yes, you can, if you identify your market and tailor your output to satisfy that market.

A bit like JC did with the Blowtorch.
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Old 21st February 2011, 02:46 PM   #1094
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Quote:
Originally Posted by regiregi22 View Post
That's because you cannot sell a 20Kg amplifier costing 5.000$ by advertising their "just" 25w per channel.
22KG the pair, at roughly $5000 in the early '90s, for 30W Class A power per channel.
Quite a few sold, actually.

(Oh Dear, these were used Bridged, and MOSFET output stage amps on top of that !)
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Old 21st February 2011, 03:11 PM   #1095
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Quote:
Originally Posted by Melon Head View Post
Sorry if someone has already answered this.

P=V^2/r, Therefore if you double the voltage you quadruple the power. I am not sure if that has answered your question.

Also you get less class A current. That is you get half the class A current compared to a regular F5 biased in the same manner.
yes that answers it perfectly thanks, joules law yes? but how does this fit with ohms law over a set resistance?


nvm, i've been too stuck on ohms law, but we are dealing with reactive devices here and the effect of increased voltage over the fets and speaker is not linear.

back to the books
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Old 21st February 2011, 03:19 PM   #1096
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Quote:
Originally Posted by jacco vermeulen View Post
22KG the pair, at roughly $5000 in the early '90s, for 30W Class A power per channel.
Quite a few sold, actually.

(Oh Dear, these were used Bridged, and MOSFET output stage amps on top of that !)
you really like them ......
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Old 21st February 2011, 03:36 PM   #1097
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When was the last time something really good, and attractive, came out of the Philips lab overhere ?

Look Ma, no spaghetti.
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Old 21st February 2011, 05:42 PM   #1098
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Originally Posted by jacco vermeulen View Post
...

Look Ma, no spaghetti.
Actually, I prefer straight, short and thick piece of wire instead of false tidiness of endless spaghetti tracks on the pcb...
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Old 21st February 2011, 08:58 PM   #1099
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Originally Posted by qusp View Post
yes that answers it perfectly thanks, joules law yes? but how does this fit with ohms law over a set resistance?


nvm, i've been too stuck on ohms law, but we are dealing with reactive devices here and the effect of increased voltage over the fets and speaker is not linear.

back to the books
Ok to make it simple lets assume no losses.
The best way to do this is with an example.
We have two amps:
A) Stock standard F5 with 20V rails
B) Balanced F5 with 20V rails

Assuming no losses:
the max power of amp A is (20^2)/8 = 50W pk (25W avg) power into 8 Ohms
the max power of amp B is (40^2)/8 = 200W pk (100W avg) power into 8 Ohms.

To determine required current use V=IR or I=V/R
Amp A requires 20/8 A = 2.5A for max Class A power (ie 25W avg) into 8 Ohms, however we only need to bias at 2.5/2 = 1.25A since a push pull amp provides double the bias current

Amp B requires 40/8 A = 5A for max Class A power (ie 100W avg) into 8 Ohms, however the balanced F5 does not provide double the bias so we need to bias at 5 A (thats 2.5A from each half of the circuit)

So a balanced F5 will produce 4 x the power of a regular F5 using the same rail voltages, but depending on the bias current it may not all be in Class A.

There is no reason why you couldn't build a Balanced F5 with 20V rails and a bias current of 2.5A. That will give you 25W Class A and up to 100W in class B.

Hope that all makes sense.
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Old 21st February 2011, 09:15 PM   #1100
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Quote:
20V rails
I think you mean 24v rails, 20v available.

Quote:
Amp B requires 40/8 A = 5A for max Class A power (ie 100W avg) into 8 Ohms, however the balanced F5 does not provide double the bias so we need to bias at 5 A (thats 2.5A from each half of the circuit)
That's two output pairs

Last edited by bobodioulasso; 21st February 2011 at 09:19 PM.
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