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Old 21st September 2008, 12:06 PM   #1
K-amps is offline K-amps  United States
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Default Buffer Power amp.

Anyone know of a simple enough circuit that acts as a power amp for a power amp? i.e. A load buffer (current dumper?)

i.e. What i want is a power amp that has 1x to 2x voltage gain that it accepts 10v to 80v inputs form other power amplifer and drives the load (basically acts as a load buffer for the signal amp).

In other words lets say I have an integrated amp which sounds awesome at 8 ohm loads but like crap on 4 or 2 ohm loads... that I connect it to this supposed buffer amp that drives the load using the integrated amp as it's pre-amp....

It will basically be an output stage with 1 or 2x voltage gain (no need for input diff/ VA stages hopefully)...

Any ideas?
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Old 21st September 2008, 12:18 PM   #2
Horexx is offline Horexx  Germany
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It would be a power amp for low impedances with good stability at low amplification. The idea is not so good imho.

1) What about an approved "normal" power amp and dropping the old one?
2) Add to your integrated amp some power transistors. But you will lose output protection and the amp will presumably deterioate.

Regards
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Old 21st September 2008, 12:21 PM   #3
Zen Mod is offline Zen Mod  Serbia
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what's wrong with Papa's F4?
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Old 21st September 2008, 12:43 PM   #4
AndrewT is offline AndrewT  Scotland
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if you have some 4ohm speakers then build some 4ohm capable power amps to drive them.
Forget the bastardisation of an add on.
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Old 21st September 2008, 12:54 PM   #5
K-amps is offline K-amps  United States
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Yes.... but this is for an AV room that needs a high WAF among other considerations... The main AV processor will drive this behemoth (which will be behind a wall) plus I can try different amps and see which do I prefer the sonics of. This buffer amp will let me do all that... not to mention drive any speaker out there without re-doing the rest of my system....

I do believe it will afford me the kind of freedom, that folks who never saw a pre-power combo could never dream of... Isn't it taking it to the next level?

By the way I misspoke about 1x gain.... it needs to be 2x gain.

Now Gimmie some ideas / circuits

Here's what I might end up with. 24 TO-3P (NJW1302/3281) per channel. Powered by Dual 1kVA Toroids with 50kuF per rail per channel CLC. But I need the precursor cuircuit.... The driver will also be a NJW1302/3281 or maybe just switchers driven by the integrated power amp (but then I lose My 2x gain) rails about +/- 95 vdc or so...
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Old 21st September 2008, 12:59 PM   #6
K-amps is offline K-amps  United States
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Quote:
Originally posted by Zen Mod
what's wrong with Papa's F4?

Mucho Dinero?

Plus I really wanna use the new NJW1302/3281 devices from ON... this project seems like a good use for those high beta devices.
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Old 21st September 2008, 01:02 PM   #7
K-amps is offline K-amps  United States
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Quote:
Originally posted by Horexx
It would be a power amp for low impedances with good stability at low amplification. The idea is not so good imho.

1) What about an approved "normal" power amp and dropping the old one?
2) Add to your integrated amp some power transistors. But you will lose output protection and the amp will presumably deterioate.

Regards


A few transistors won't cut it... adding a turbo to a corolla does not make it a Cummins v12.
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Old 21st September 2008, 01:50 PM   #8
AndrewT is offline AndrewT  Scotland
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for a 12pair NJW1302/3281 I would recommend a maximum of +-85Vdc
At this quiescent supply voltage (Ibias=500mA Re=0r47) the stage should give about 700W into 4ohm @ 60degree phase angle and 1250W into 2ohm @ 41degree phase angle, provided you keep the Tc<=55degC i.e. Heatsink Ts<=45degC.
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Old 21st September 2008, 04:13 PM   #9
djk is online now djk
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Old 21st September 2008, 07:06 PM   #10
K-amps is offline K-amps  United States
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Thanks Dennis: This is a start....

What do the 2 caps do? Isn't the 5v rating too low (I am sure I am missing something obvious).

What resistor values you recommend for +/-90v?

This would need a bias circuit of sorts because the pre-amp will not pass any DC... what do you recommend?

Lastly what kind of gain would this stage have?
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