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Pass XA25?
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Old 12th June 2017, 10:12 PM   #441
Zen Mod is offline Zen Mod  Serbia
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Pass XA25?
I have a way for first (shutting Iq of drivers and pucks) while I'm lazy to even think of mains killing

though , Papa naturally is obliged to make it foolproof , while I can't** make it (my own) proof of this fool

**(and doesn't need)
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Old 12th June 2017, 10:26 PM   #442
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Pass XA25?
in fact , I implemented stand by in my basic iteration

hopefully it'll work
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Old 15th June 2017, 02:14 PM   #443
Alexiss is offline Alexiss  Sweden
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Conceptual Schematics XXII

Well, I put together the conceptual FE and BE of the previous posts - to produce a possible iteration of the whole circuit.

I have simulated the whole circuit. Although I have not had the time to search
for the correct pspice-models of the semiconductors, it measures very well indeed with the IRFP240/9240 and the dubious models of the rest of the semiconductors.

Please take a look.
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Old 15th June 2017, 02:23 PM   #444
Alexiss is offline Alexiss  Sweden
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Comments
R30, C4, C5 are not a necessity, they bootstrap the power-feed resistors
for a slightly better PSSR and a litter higher Open-Loop Gain. They may be left out.

The circuit features very low distortion. The Square-Law characteristics of each half of the circuit
produces lower order harmonics that readily cancels out in the complementary arrangement.

The bias regulator-circuit keeps the Idc VERY stable regardless of temperature variations.
It is possible to just use a silicon-diode and a voltage divider to create the required
reference voltage.
It is not necessary to use the temp-compensated voltage reference as shown.

fft of output 20W in 8 ohms.

Bias is = 2.5 Adc
Voffset out = 1.5 mVdc
bode.jpg

fft.jpg

Last edited by Alexiss; 15th June 2017 at 02:43 PM.
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Old 16th June 2017, 03:21 PM   #445
Alexiss is offline Alexiss  Sweden
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THD vs POWER in 8 ohms

Another interesting simulation results is the Total THD vs power into 8 ohms.

As can be seen, in spite of questionable psipce models used, the measured thd and the simulated thd vs power match pretty closely.
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Old 16th June 2017, 06:46 PM   #446
Nelson Pass is offline Nelson Pass  United States
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Pass XA25?
Probably a coincidence, given the simple models.
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Old 19th June 2017, 12:42 PM   #447
Alexiss is offline Alexiss  Sweden
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Conceptual Schematics XXIII

For the more ambitious diy:ers, it would be possible to incorporate an additional
DC-servo for controlling the output offset voltage, eliminating the need for
adjustments.

Please look at the schematics below:
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Old 29th June 2017, 10:21 AM   #448
Alexiss is offline Alexiss  Sweden
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Conceptual Schematics XXIII - simplified

A few fellow diy:ers have expressed concerns about the complexity of the conceptual schematics and the number of OP amps and servos used.

Remember that this is not the original XA25 circuit, it is only a possible solution.
I am sure Pass Labs has a much better and more optimized circuit.

It is possible to slightly simplify the circuit though.
That would be to remove the DC offset servo and replace the reference voltage source with a simpler one.

But remember that it will exhibit thermal drift in "simple" simulations, but in real life it will work very nicely indeed (as long as the diode and the heatsinks
are not thermally coupled).


Please have a look:
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Old 8th July 2017, 10:11 PM   #449
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Quote:
Originally Posted by Nelson Pass View Post
About 2 milliseconds, and then shutdown, regardless off how many
amps above 10A.
Is that over current protection necessary because there are no degeneration resistors that would otherwise limit the current? Is it recommended for safety reasons to implement that kind of over current protection also in our home brewed amps? Or does it just help to reduce the amount of amps that are returned to be repaired?
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Old 8th July 2017, 11:45 PM   #450
wayne is offline wayne  United States
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Pass XA25?
Mostly done for safety compliance. They think up all kinds of strange tests to do on our amplifiers some of them don't make much sense to me. We very seldom see an output stage failure.
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