Another Amplifier Check Please

[zox2003]

CAn somebody check this amp and tell me if it looks good and how much power I can expect from this?

Thanks

[darkfenriz]

looks like Pass' Citation
visit http://www.passdiy.com

[Marc Vi.]

I didn't check the amp but if it works well, the power at 4 ohm will be about 175 Watt.

Marc.

[ilimzn]

Looks like an (over)simplified Citation 12 MOSFET mod, which can be found on www.passdiy.com under archived projects, under the name MF12.

A couple of important omissions in the above schematic:

Gate of the top MOSFET should be connected via a diode (reasonably fast, 100V minimum) to + rail. Otherwise the amp will clip asymetrically and may actually overdrive the MOSFET gate above the maximum 20V resulting in it's destruction.
MOSFET gates may need series damper resistors (47-100 ohms).
There is no short circuit protection which may be good and bad, usually good while the amp is working and bad when it stops
In particular, if fuses are added, in a short circuit condition it is likely the amp will not fail due to MOSFET failure, but the failure of the MPSA56 driver for the bottom MOSFET, once that dies, the MOSFETs may follow...
The MPSA56 mentioned above will need a heatsink.
A non-inductive foil cap cca 22-100nF across the Vbe multiplier will help HF distortion.

There are a number of improvements that can be made to this simple amp but it will work fine as it is.

Maximum voltage (before clipping) from this amp will be about 5V less than the power rails. Assuming no rail sag (BIG assumption!!!), that would be 170W into 4 ohms. A more realistic figure would be about 100-120W with a really good power supply.

[zox2003]

Opet si tu....

What quality can i expect from this amp.Would it be better if I replace MJE340 with IRF540 with modified Vgs circuit?


Thanks

[zox2003]

What would be good replacement for MPSA56 in driver stage?
Also should I replace MPSA06 with something else?


ilimzn,
Po kvaliteti dali je bolja sema koju si ti postirao u mom proslom postu ili ova?Da li tvoja verzija moze da radi na +/- 42V bez ikakvih izmjena ( tranzistori,otpornici...)?

[zox2003]

Da li na tvojoj semi mogu da zamijenim 2n5551 sa mpsa06 i 2n5401 sa mpsa56?

hvala


Just question about transistors replacement?

[ilimzn]

The rule is to compensate with the same kind of element as the one being compensated. That way you get the best thermal tracking.

In this case using a Vgs multiplier would not be adequate because the bottom MOSFET and it's MPSA56 driver form Compound Feedback pair (a.k.a. Sziklai pair). Thermally, CFPs behave almost entirely like the first element in the pair, in this case it's a BJT, the MPSA56.

So, you have a BJT and a MOSFET combination. A Vgs multiplier would have too low a temperature coefficient for the BJT part so you have to use a Vbe multiplier to account for this. Still, the total combo will have a lower tempco than the Vbe multiplier, which is why there is a resistor added in the Vbe multiplier's emitter, to make it a better match.

[ilimzn]

2N5551/2N5401 could be substituted with MPSA06/56 but in this amplifier as well as the one I posted the MPSA parts are at the limit (Vcemax=80V, the rule is Vcemax>(|-rail|+|+rail|). Not for all transistors in the circuit, but in the case of the above amp, definitely the MPSA06 VAS transistor is at it's limit (it will need a heatsink but that should have been obvious).
Fortunately, you are not violating Vcemax by much (4V) so you might get away with it - if it was me, I'd be looking at other transistors.

[zox2003]

So you still did not answer on my question:

What quality can I expect from this amp?

and


Which one would be better: your amp you posted 3 in my last post or this one?

Also is it better to use two n mosfets( like in this amp) or n and p mosfets (like in your)?

regards,

zox