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Questions about my Yamaha AX-750

R

ryeman

New Member
Hey Everyone. Long-time lurker at Audiokarma. Maybe I can puzzle some of you.

So after years with some interesting combos, I got a that early 80s Yamaha amp with no controls, and it came with two different cartridges - one for the special speakers, and one for regular speakers. I can never remember the model. Anyway, I adored the "Natural Sound" and I'm all in on Yamaha ever since.

So I gave that amp away and moved, and I'm starting over. I got an AX-750 that's in pretty good shape and two Canton GLE-50 three-way speakers... and I was having a birthday party the day they arrived, so I had very little time to do anything right.

Anyway, the Northern European model of the AX-750 says 6 ohms right on the back, even though it also says 270 watts, which is rated at 4 ohms. The other models are all rated for 4 ohms. Likewise, the speakers say 4 ohms, even though all the similar Canton speakers of that era say "4-6 ohms," because the Germans went through a period where they expressed both the rated ohms and the "lowest ohms" you can get with a speaker.

Additionally, I'm sending 270 watts to two speakers that are rated for like 60 watts each, although in all the forums, they say these Canton's are power hungry speakers. And I believe it, because right now they can haul ass.

So I am assuming that these Canton GLE speakers are not dropping below 4 ohms and are possibly 6 ohms, and that the amp can pull 4 ohms without blowing up. Because hell, it's a flagship amp and it should be able to pull 4 ohms.

The input selector switch is wonky and caused the right channel out when the amp arrived in the mail, an hour before the party... which led to a cascade of poor decisions. It causes all kinds of sound issues... from the L or R going out completely to delivering just parts of the sound. So at this party, I setup the speakers in series because I was moderately worried about the ohms and because the R was out. However, it was actually in parallel because I was drinking. So I ran the amp/speakers below 4 ohms all night... but not particularly loud. This means I was sending I don't know how many watts into these little speakers, as well as potentially killing the amp. Anyway, I discovered this the next day, and also discovered the wonky input selector.

So I don't have any spray to clean the switch yet. But I worked it back and forth pretty good, wired up the speakers as they were intended, and low and behold it sounded great. Really nice speakers... almost too accurate... but amazing on any record that had good production. The high damping of the amp is actually spectacular to behold, but woe to any poorly produced record. The speakers can really haul ass.

Now, I don't know if my ear was just off initially, or if this was going on the whole time, but it turns out that the mid-range speaker is completely out in both speakers. This may have happened in the last few days. I had them cranked up a couple times. But I have a hunch they must have died at some point between the party and today... though I can't be sure of that.

So - what in the hell do I have to do, and what tools do I need? Where do I start? I'm eager to take matters into my own hands here. I'm gonna do whatever it takes.

And I'll not be abandoning the thread.
 
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ryeman said:
However, it was actually in parallel because I was drinking.
Click to expand...
2 -- 4Ω in parallel = 2Ω / 2-- 6Ω in parallel = 3Ω So you were running a single channel in the neighborhood of 2 - 3Ω . Your speaker's mid-range drivers are history.
 
avionic said:
Not anymore.You need to find some replacement mid-range drivers.
Click to expand...

Right-o. I am not surprised... it was a silly mistake made in some weird circumstances.

But so - why did the midrange fail?

Maybe I'll ask James if I can really run 4 ohms too. I had already found that thread, but it seemed like a different sort of project.
 
I'm also surprised you didn't burn up the amplifier as well.
 
ryeman said:
Right-o. I am not surprised... it was a silly mistake made in some weird circumstances.

But so - why did the midrange fail?
Maybe I'll ask James if I can really run 4 ohms too. I had already found that thread, but it seemed like a different sort of project.
Click to expand...

I mean specifically the midrange.
 
ryeman said:
I mean specifically the midrange.
Click to expand...
I'd need to see the speaker crossover schematic. But 2-3Ω load is a way to low impedance for the AX. So clipping would occur at a much lower volume level. Clipping is almost DC to the speakers. Speakers and DC don't get along together. I would suspect the midrange voice coils are burnt open.
 
avionic said:
I'm also surprised you didn't burn up the amplifier as well.
Click to expand...

Not sure how much of a difference it makes, but the music wasn't loud at all and did not clip during the party. I was sort of checking on the amp all night, because the whole thing was wonky from the beginning.

I had read about the GLEs and the AX series before buying, but I had to have this stuff shipped in... and I asked the seller, who had both amp and speakers (and had dozens of others), to verify that the combination made sense ohms-wise. Did not make sense.

The amp seems just fine. It's quite a beast, and despite the weirdness in the rating, I'm not surprised it made it. Test of a champion!
 
Who knows exactly. Perhaps the drivers were toast before you got them.
 
ryeman said:
Not sure how much of a difference it makes, but the music wasn't loud at all and did not clip during the party. I was sort of checking on the amp all night, because the whole thing was wonky from the beginning.

I had read about the GLEs and the AX series before buying, but I had to have this stuff shipped in... and I asked the seller, who had both amp and speakers (and had dozens of others), to verify that the combination made sense ohms-wise. Did not make sense.

The amp seems just fine. It's quite a beast, and despite the weirdness in the rating, I'm not surprised it made it. Test of a champion!
Click to expand...

Or maybe it did clip. :/ I guess I'm going to have to buy all these MB Quarts that have turned up today... :D
 
Alright - well end of story is I have to find some 3154 Canton mid-range drivers or a junky GLE 50 pair... not impossible. And I have to figure out why the European AX-750 isn't rated for 4 ohms, even if the wattage on the unit is clearly for 4 ohms.
 
Hi ryeman,

I think that I answered part of your questions in the AX-750 thread:

The 270w printed on the back panel of the amp relates to the maximum power that the amp will draw at the plug/wall. It has nothing direct to do with the amps power output to the speakers.

The manuals sure state a mishmash of figures concerning output power.
20hz - 20khz 0.015% THD 8 ohm ... 110wpc

But note this: "DIN Standard Output Power Per Channel (European Model) = 1khz 0.1% THD 4 ohm ...185w." (Peak power, at 1khz not to be confused with continuous RMS power). I'll make the WAG that the amp will deliver roughly around 120wpc RMS 20hz-20khz into 4 ohms with decent THD.

In any case the amp has no problem driving 4 ohm loads. In fact the one in my AX-750 thread has only driven 4 ohm speakers while I had it and is now owned by a friend and he is using my old Canton Karat 60 speakers as daily drivers. The 60's are 90w speakers and the amp has no problems at all driving them cleanly. (In fact the older and less robustly built AX-700 had no problems driving those same speakers cleanly). I would not however ever connect 2 pairs of 4 ohm speakers to the amp and drive them at the same time. Only one pair of 4 ohm speakers at a time!

Concerning your GLE 50's. Your AX-750 can cleanly drive them with ease and lots of headroom. You only need to limit how much you turn the volume up. You are in the drivers seat. ;)
My suggestion is to start a separate thread for your speakers in the Speakers sub-forum. Finding some new mids for you should be no problem with a little patience. I'm fairly close to the source after all.

It would be helpful to know roughly what part of the world you reside in. :)

Cheers,
James
 
TBH I couldn't follow most of your story, but there are some errors in your assumptions. First the AX-750 actually delivers only 110 watts per channel into 8Ω (stereo)
20Hz to 20kHz Total harmonic distortion: 0.008% which is a good deal less. The 270 watts is the maximum power it will take off wall outlets.

Also speakers ratings tend to be guesstimates by the maker because speaker impedance varies with frequency. If you had only 1 pair of speakers hooked up it seems unlikely that you were overdriving the amp unless you were really cranking it:rockon: which is certainly possible in your blitzed condition:beerchug:. What seems surprising is that you didn't blow up the tweeters also which make me suspect that the mids may have been defective to start. Certainly I would take them out of the speaker and test them with an ohm meter or if you don't have that with a AA or 9 volt battery. Hook wires to the battery and the mid speaker terminals and see if you get any sound.

I would also be suspicious of the amp until you can clean the controls with a contact cleaner and can get a clean sound with no static or dropouts. Best of luck.:thumbsup:
 
The motorized input switch is the Achilles Heel of all of the AX-xx50+ amps and their only real weak point imho. The contacts oxidize and one gets channel dropouts. When it happened to my AX-1090 I was able to cure it with a good amount of Deoxit and a lot of excersizing of the switch. In a worst case the board will have to be pulled from the amp and the switch de-soldered from the board. They are open on the bottom and a person can get at the contacts better from there.

There are replacements with gold contacts that can be found from time to time on ebay etc. The correct 7-position gold contact replacement switch for the AX-750 is P/N: VT148400.

DSC03958.jpg

The photo is of a VT148000 9-input switch that I bought by mistake. But it at least shows what they look like from the underside.

Cheers,
James
 
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