Axiom Home Page Forums General Discussion Stereo New M60s

The resistors are free of charge from Axiom. Just give customer service a call and they'll send you out a set.

As far as sound is concerned, I still have them on to this day and I should probably take them off and do a critical comparison when I've got some extra time. But with them on, I really think my system has never sounded better. I would probably say that they haven't comprimised the sound or that they haven't made the speakers sound drastically different. The best way to describe it would be that the highs are less fatiguing now.

If you get a set, please post your thoughts on them. I'm interested to read what you think.

-Kevin

Well, the NAD742 lasted less than a week. I had instrumented the amplifier to measure its power output, frequency response flatness and distortion with the M60s attached. This involved driving the input with a low distortion sine output from a function generator while the output was probed for voltage and current.

A Tektronix TDS360 digital sampling scope was used; CH1 measured the NAD742 ouput voltage while CH2 connected to a Tek 503 Hall-effect current probe to measure output current. Data was taken at 10, 20, 50Hz, 100, 200, 500Hz, 1kHz, etc.

First the good news: At lower frequencies the NAD742 output began clipping at +/-35 volts peak. The current was 4.6A peak meaning the M60 impedance was 7.6 Ohms calculated. RMS power output was calculated as 80.5 Watts before clipping. Harmonic distortion measured 0.9% at 500Hz and 80W.

The bad news (my stupidity): I left the output amplitude at +/-35 volts while I swept the frequency from 1kHz to 2kHz, my next data point. The first sign of trouble was the speaker current going to zero phase angle and rising to 16.8A. The second (and final) sign of trouble was a blue flash of light from a blowing fuse inside the NAD. The scope hardcopy showed 294 Watts RMS being deliverd to the load at the time of failure. The speaker resistance calculated out as 2.1 Ohms at 2kHz. I opened the NAD and measured damage consistent with secondary avalanche failure of both output transistors. The NAD was a serious pain in the rear to get to the failed devices; it had to be nearly completely disassembled.

What I learned: It's really bone-headed to input a continuous sinewave to drive an amp at high power levels until you have mapped the load impedance versus frequency characteristics. Second, I was surprised a premium amp does not have SOA protective shutdown. SOA limits are published for power semiconductors; it does not take a rocket scientist to fashion a protection circuit to prevent this type of failure.

Mariss

I saw that bright blue spark - purple actually, the first time I powered up my Anthem PVA 5 amplifier. The Purple Bolt was accompanied by a great whomping sound from the amp. Anthem replaced it no questions, just a bit of head scratching.

BTW, what source are you using for material which produces sibilance?

Well I'm laughing, but only at your articulate, self-deprecating, and humorous description of the catastrophe, NOT at the catastrophe itself.

I would wager money that there isn't one person on this forum who, at one time or another, hasn't stuck, figuratively speaking, his finger in the electrical outlet. Overlooking the fact that it was your knowhow that precipitated the problem, at least you have the knowhow to repair it. I'd be out the cost of the unit AND the cost of the repair.

Hang in there.

The only sibilance presently audible is from the choice 4-letter words I'm uttering about myself. The M60s have fallen silent until I repair the wounded NAD. I cannot in good conscience play dumb and try to foist it off as a warantee repair. Also, it builds character to clean up my own mess; it'll help remind me not to do something as stupid as this again.

While on this subject, any recommendations for an integrated stereo amplifier or stereo receiver? Denon, Rotel, something else? I really didn't want an AVR as it turns out; 2 X 125W makes more sense for me than 5 X 50W. I may give the NAD to my son after I fix it. He is into all that 5.1 stuff, I'm not.

Mariss

Kevin,

Thanks for the info. My M22's are supposed to come in mid-August, but I think that I will send the $40 tomorrow so I can get them sooner. You never stated how hard they are to install. I'm decent with my hands, but electrical components scare the hell out of me, that and I don't want to screw up my new speakers. I like the forward sound that they are supposed to present as well as the clarity and soundstage. Based off of descriptions, I think I will love these speakers. It's the alleged schreeching highs that worry me. I figure the resistors would help alleviate the problem. I will try to do extensive listening without the resistors and then try them with them on and see if the sound is improved to me. While I'm doing this, I will try to A/B the PSB image 2b's and do a comparison. Hell, I might even A'B my old Bose 301's for shits and giggles.

Mariss,

If you liked the NAD sound, their integrateds get very good reviews. The C372 would be a good option.

No worries. I didn't realize you were asking about the resistors for you M22's opposed to the M60's. I'm not sure, but I thought the resistors were meant mainly for the 60's or the 80's. Not that you can't use them on the 22's, but moreso that you probably won't need them. I believe the tweeters are different between the 22's and the 60's (or 80's) which is probably why I thought the resistors were meant for the two larger floor models.

But with that said, if you do get them they are incredibly easy to install. You just need a hex/allen wrench to remove the screws on the tweeters. Be sure to turn off all your equipment first. Remove the tweeters. Then insert the connectors in between the tweeters and the correct wires. The end of the resistor caps have connectors that only work one way. There's no way for you to get them installed incorrectly. Brilliant, especially since I had the same question as you did about them.

Good luck, regardless. Let us know how you make out.

Nope, all of Axiom's speakers currently use the exact same tweeters.

Very interesting. You learn something every day. Thanks for the info.

-Kev