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Old 27th August 2012, 07:14 PM   #1
keaster is offline keaster  Canada
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Default ESP P3A more power

I currently have 2 P3A's running and they sound great but have wondered about more power. I read about running 2 in bridge mode and also adding more power transistors. My question is what is the pro's and con's of this.

Does bridge mode double the power output? and what about adding more transistors does it double the power too just without all the other components?
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Old 27th August 2012, 07:27 PM   #2
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Adding only more output device will drop the output impedance and change the bandwidth characteristics somewhat you may then use say a 4 ohm speaker (provided the power supply enough power for the purpose)

Bridging theoretically quaraplies the output, but one would safely stick with doubling without straining the output too much. (Again provided the power supply is able to)

Four times the power is do-able if you observe the SOA and increase the output devices and power supply accordingly.
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Old 27th August 2012, 07:34 PM   #3
wahab is offline wahab  Algeria
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The compound output stage is not as easily parralelizable
as a double emitter follower output stage.

This latter configuration better suits your needs , although
the Vbe multiplier should then be slightly modded to match
the EF higher total VBE.
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Old 28th August 2012, 01:19 AM   #4
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Try reading Douglas Self on doubling the output stage devices in chapter 5 of his manual and also the discussion on the CFP "Load Invariant" amplifier. http://www.bgaudioclub.org/uploads/d...th_Edition.pdf

Wahab is right that its not straightforward, like an EF design, to double the output transistors but if you convert to an EF design, it will not be a P3a or sound quite like one anyway.
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Old 28th August 2012, 07:39 AM   #5
amptech is offline amptech  Scotland
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At nico ras read rod's info, the circuit is not meant to designed for higher dc rails.. In b-tied mode your get 200w at 8 ohms plenty for that amp.
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Old 28th August 2012, 12:02 PM   #6
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Quote:
Originally Posted by amptech View Post
At nico ras read rod's info, the circuit is not meant to designed for higher dc rails.. In b-tied mode your get 200w at 8 ohms plenty for that amp.
Why should At nico ras read rod's info? I don't follow your English amptech or understand "b-tied mode". Is this some "audio specific" jargon or definition.

What I did say is that you should upgrade your power supply capability for delivering higher power since invariably amplifier power is directly related to the power delivery of the supply. You do not get something for nothing
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Last edited by Nico Ras; 28th August 2012 at 12:21 PM.
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Old 28th August 2012, 12:15 PM   #7
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Hi Ian,

I did not realise that Doug's book is available on the internet for free.
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Old 28th August 2012, 01:06 PM   #8
amptech is offline amptech  Scotland
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Hi nico, the project a3 was built rod elliot if you type in your inter Elliot sound page then follow his information on this amp and what it can and can't do. B-tied mode means bridging both amps together to get more power... At nico means giving you your answer to the question. So the safe way to get more out put from this amp is to bridge them. Also using same power supply of 40volts.
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Old 28th August 2012, 01:12 PM   #9
amptech is offline amptech  Scotland
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Keaster, check rod Elliot's audio page on his amp.
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Old 28th August 2012, 01:36 PM   #10
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It should be possible to add more power devices by retaining the structure.
Add a duplicate set for R11,R13,Q5, Q7 and R12,R14,Q6,Q8. Then it retains the same form of the P3A. However you'd have to determine if the VAS must have a higher quiescent current to handle the load. Supply could also be raised to get more wattage. The input stage transistors might have to be changed to 2SC types I guess. Not to mention looking at the compensation again.
Maybe someone could sim it.
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