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Old 21st September 2008, 07:08 PM   #11
K-amps is offline K-amps  United States
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Quote:
Originally posted by AndrewT
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.
As conservative as always Andrew, Good info though!

I am guessing at close to full power the rails would sag to below 80vdc so we might be ok with an unloaded rail of 95... just guessing.
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Old 22nd September 2008, 12:03 AM   #12
AndrewT is offline AndrewT  Scotland
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Hi,
to get the quiescent voltage to fall from +-94.3Vdc to +-80.7Vdc I had to adjust the model to 13% regulation while delivering over 2kW into 1r0. At 1kW that would be around 6% regulation which is a pretty poor 1kVA transformer.

For 4ohm power delivery the regulation has to be set to 18% to fall from 94.9Vdc to 80.1Vdc while delivering 680W. I would consider a PSU that did that to be a disaster.
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Old 22nd September 2008, 01:35 AM   #13
CBS240 is offline CBS240  United States
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Default Re: Buffer Power amp.

Quote:
Originally posted by K-amps
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?

Hi

Opinions are like as$ holes, everybody has one, so as for my opinion, I think you should build a HEC follower circuit using cheap HEXFET's. You would not have any GNF or anything, and it would have a high input impedance with good damping. If you overbuild the gate driving stage, you can add more FETs till your heart contends. Just check out Bob's EC Mosfet amp OPS. Bootstrap the driving stages from the output for the extra drive voltage required.





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Old 22nd September 2008, 03:24 AM   #14
K-amps is offline K-amps  United States
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Thanks CBS... unfortunately my expertise with MOSFETS is even more limited than with BJT's... but TY for the idea!!
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Old 22nd September 2008, 08:25 AM   #15
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"What do the 2 caps do? "

Alow the transition from class A to AB at hiher power.

"Isn't the 5v rating too low (I am sure I am missing something obvious)."

No, the difference between the bases of the two sets of outputs is below 5V.

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

Adjust value for about 100mA through the drivers.

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

No bias circuit required.

"Lastly what kind of gain would this stage have?"

Unity, it's just a buffer/follower. It's called a cool follower because of the caps. There is a hot follower (class A version) that has active current sources instead of the 390R, and no caps.

For unity gain one could also build the Stasis output stage, using ThermalTrack drivers. The Threshold S150/S300/S500 had 3/6/9 pair of outputs.

The basic Stasis output circuit could be modified for a voltage gain of 2X.
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Old 22nd September 2008, 08:18 PM   #16
K-amps is offline K-amps  United States
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TY Dennis:

What kind of current gain will I get form this set-up and what params can be tweaked to change the gain?
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Old 22nd September 2008, 09:24 PM   #17
PMA is offline PMA  Europe
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buffer power amp:
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Old 22nd September 2008, 09:25 PM   #18
PMA is offline PMA  Europe
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CCIF IMD:
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Old 22nd September 2008, 09:29 PM   #19
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Quote:
Originally posted by PMA
buffer power amp:
Mucho better!

But I have to warn: if your nice amp dance well together with your speakers that does nor mean that "the buffer" will do the same...
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Old 22nd September 2008, 09:36 PM   #20
PMA is offline PMA  Europe
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I use it outside NFB loop, just as shown. It must be class A operated, as shown. Some Ccb for driver transistors might be needed, like 220pF.
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