Throughly disappointed with my new Yamaha A-3000 Integrated.......

almarg - Your comment really got me thinking about subwoofers connected to the as3000. I knew not to connect a sub via speaker level inputs simply because of what was stated in the owners manual, but I have been considering upgrading to Martin Logan Montis speakers which have an active woofer in each speaker.  I'm not 100% sure that will work after thinking through all of this. And I won't even pretend to understand much about electrical engineering.  I emailed Yamaha but haven't heard back.  Emailed Martin Logan and they suggested the connection will be fine with the as3000.

@arch2
Your question is a good one. And as I indicate below a follow-up question with Martin-Logan will probably be necessary to be confident in their answer. But first I’ll mention that there are two things which make this situation different from connecting a powered sub to the outputs of the amp:

1)Connecting a single powered sub which provides + and - speaker level inputs for two channels to both output channels of the amp would most likely connect the amp’s negative output terminals for the two channels to the sub’s internal circuit ground, and therefore short the two negative output terminals together, potentially causing damage. That will not be an issue in the situation you are asking about, since the amp’s two channels would be connected to different speakers.

2)The suggestion I had made of connecting a sub’s negative input terminal to a chassis screw or the ground shell of an RCA input connector on the amp will not be suitable for this application because it would greatly reduce the amount of power the amp could deliver to the speaker’s electrostatic panel, which of course is not powered by the speaker’s internal amplifier.

3)The remaining concern, assuming that the speaker has a 3-prong IEC receptacle for its AC input, is whether or how it connects the negative input from the amp to AC safety ground. What I suggest that you ask Martin-Logan is as follows:

(a)Does the speaker have a 2-prong IEC connector (AC "hot" and AC neutral) or a 3-prong IEC connector (AC "hot," AC neutral, and AC safety ground)? If the answer is 2-prong, you are good to go.

(b)If the IEC connector has 3-prongs, is the speaker’s negative input terminal completely isolated from AC safety ground? If the answer is yes, you are good to go.

(c)If the answer is no, what is the impedance between the speaker’s negative input terminal and AC safety ground? If they are connected directly together, or are connected together through a low impedance (for example, 10 ohms) I don’t think it would be safe to use the Montis in conjunction with your amp. But if that impedance is high (for example, a few hundred ohms) it should be ok.

Good luck. Regards,
--Al

@almarg 
Thanks for following up Al.  I will contact Martin Logan next week.  From reviewing the owner's manual on line it appears the Montis includes a 3 prong IEC connector.  Thanks again and happy New Year.
Don

If the specs don't give an ohm rating with watt output then chances are it's going to have trouble.  Yamaha rates only at 8 ohms.  And remember that speakers are rated at NOMINAL or AVERAGE ohms.  Those speakers may dip as low as 2 ohms at times and there aren't very many integrateds that are going to handle that.  I remember a friend having this exact same issue with a Denon integrated a couple years back trying to drive Maggie 1.7's.  The thing just kept going into protection mode....sometimes an hour, sometimes 15 minutes.  You could fry an egg on it.  He swapped out for another one a same thing happened. He went to another set of drivers at 8 ohms and never had an issue.

@gkr7007,

Check your facts. Yamaha does provide ratings for lower impedances. The A-S3000 is rated at 150 watts/Ch RMS into 4 ohms. It's maximum dynamic power into 2 ohms is 300 watts/Ch. Even their budget-end, bipolar output integrateds are 2 ohm stable. For future reference, it's quite easy to access owner's manuals online. It's called Google.