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pinnocchio 16th November 2012 01:13 PM


Originally Posted by rho (
I'm sorry if this is already made clear somewhere in the previous 101 pages, but I have a simple question about this amp: Is it designed to drive a 4 ohm load? Or can I drive a 4 ohm load when lowering the supply voltage?

Sorry for my laziness, but I didn;t feel like plowing trough 100 pages of replies to find the answer.

Hi rho,

My main speakers are 4ohms and I have yet to see an issue with this amp. Runs cool and sounds amazing!


ratbagp 16th November 2012 01:26 PM

I have been driving Apogee Stages (4 ohms or less) for some time on classical music. The 50 watts is a bit marginal when it gets really loud.


rho 16th November 2012 03:05 PM

Thank you very much for replying so quickly. :)
So it's safe to run 4 ohm speakers with this amp in a normal hifi configuration. That's good news.

meanman1964 16th November 2012 04:07 PM

rho,I even have drive magnepans with this amp

AKSA 16th November 2012 09:23 PM

My golly, Ratbagp, the Apogees get down to 1.8R, IIRC. I wouldn't have expected a single pair of lateral FETS would driving these very difficult loudspeakers, but, hey, the FetZilla seems to be OK!! Maybe this is a welterweight prizefighter, huh?

Thanks for the leap of faith, and for passing the revelation to us.....



rho 17th November 2012 08:02 AM

What's the minimum load the amp is designed for at the recommended maximum supply voltage?

ratbagp 17th November 2012 11:48 AM

As I seem to remember, the larger Apogee models were the ones that got down that low in impedance. The Stages are reasonably flat in the 3 - 4 ohm range with a rise about 500hz due to the crossover. The curves can be seen in this reprint of the old Stereophile review (see figures 5 & 6).
Stage Stereophile review

It still is impressive that it works. Remember most of the time I play classical music and not to earsplitting volumes.


JKC 18th November 2012 04:13 AM

I am driving 6 ohm speakers and they can get as low as 3 ohm at some frequencies. No problems here. It has been one year since I built this amp and I really like it.


RKH 5th February 2013 07:11 AM

Before I connect speakers...
Hello All,
I am almost there... I have done biasing etc. as described in the building guide. One channel dials into 37 mV just fine. The other gets to 38.1 mV and then I run out of travel on the potentiometer. On both channels, everything else adjusted as prescribed.

a. Is there a need to be concerned about the 38 mV channel?
b. I neglected (forgot) to ground the inputs when I set the bias. Should I go back and redo it?

Can't wait to get this baby going and see what it sounds like. I will post some pictures if there is any interest. I've put this in the new DIYAudio 4U chassis.



meanman1964 5th February 2013 07:47 AM

What value did you use for P3?

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