Question Yamaha AS-801 help

Special K 2

Novice Member
Hi

These questions apply to UK equipment

I have just taken delivery of a Yamaha as801 amplifier from yourselves.


I wonder if you could confirm something.


The amp has a impedance selector switch, it is currently set to high.

I am running one pair of speakers that are 6ohm impedance, and according to the instructions for speaker set up A or B

6 and 8 ohm should be set to high, but in brackets it says Asia models Only

Then it says 4ohm and higher set to low.

Could you confirm which it should be as I am a little confused as my impression it should be set to 4ohms and ie low,

so that would require a change of the switch fro where it is, correct?


Cheers


Chris
 

BlueWizard

Distinguished Member
Actually this question comes up a lot, and while the switch is there for a purpose, a vast majority of people and the conventional wisdom is that you leave it set to HIGH regardless of what speakers you have.

According to Internet Rumors, when you switch to LOW what really happens is it drops the voltage on the Power Stages to keep the temperatures lower. Lower Impedance means more Current, and more Current means more Heat.

But, if your amps is reasonably well ventilated, this action is unnecessary. I've been using a Yamaha Amp for many years, and at one point even used it with a pair of 8 ohms speakers combined with a pair of 6 ohms speakers. It ran fine until one night I was listening to "Lord of the Rings" at about 50% volume, and the amp overheated and shut down. I gave it a change to cool and started again, and everything was fine.

Now using the same speakers, I simply use TWO Amps to solve the problem. But ...again... conventional wisdom is that you leave the Impedance Switch set to HIGH for all speakers. That way you always get the full power capability from the Amp.

But this also assume you have some Common Sense, and have the amp in an unconstricted and well ventilated space.

I think you will find a vast majority of people with amps that have this switch leave it on HIGH and never have a problem.

Steve/bluewizard
 

dannnielll

Prominent Member
Steves explanation is on the money, but a marginal different take. , slightly more technical is this:/
. In the 4 ohm position, a different winding on the main power transformer is used , this reduces the voltage on the power transistors. As a 4 ohm speaker will draw more current than an 8 ohm speaker (actually 2 times as much) , it will be consuming / developing 4 times the power, at the same signal voltage as would the 8 ohm one. The heat sinks,capacitors and power transistors cannot handle this , and at a sustained high signal level will overheat.
In the 4 ohm position, it will never overheat (assuming any ventilation), but you lose some headroom with 8 ohm speakers. In that 8 ohm position, you get more headroom before any distortion, but with potential thermal overload.
 

BlueWizard

Distinguished Member
Steve's explanation is on the money, but a marginal different take. , slightly more technical is this:/
... The heat sinks,capacitors and power transistors cannot handle this , and at a sustained high signal level will overheat.
... you get more headroom before any distortion, but with potential thermal overload.

In my experience, you have to be pushing the speakers ridiculously hard to overheat the Amp. Again, I ran 3.4 ohms and was good up to an hour of high volume "Lord of the Rings" before the amp shut down (Yamaha RX797 100w/ch Stereo Receiver).

I wonder if there isn't some Health/Safety Regulation coming into play here? Don't know, but I wonder.

If you amp is in a cramped space with limited ventilation, I would use the Low Setting. But with normal and reasonable ventilation, most will recommend that you put it on HIGH and leave it there.

Keep in mind also, the Internet Forum Recommendations are not guarantees. Ultimately Common Sense is the greatest protection for your system.

Steve/bluewizard
 

Special K 2

Novice Member
Hi

Thanks for replies.

It was just the words regarding the 'Asia model only' that added more confusion.
The amp is well ventilated, got space all around and I won't be driving it too hard, I have neighbours!

So will leave the selector on the high setting.
As a separate point I wonder how many people are oblivious to the selector and just plug their speaker in it anyway?

Cheers

Chris
 

muljao

Prominent Member
If it we're me I'd look at what ohms the speakers are rated at and set the switch on the amp to the corresponding position and not worry about the Asia only in brackets, 4 ohm speakers would be considered low 6 and 8 wouldn't
 

BlueWizard

Distinguished Member
[QUOTE="muljao, post: 26905432, member: 776448"... 4 ohm speakers would be considered low 6 and 8 wouldn't[/QUOTE]

Right, 4 ohm speakers are really the only concern, and if you have them, it is still a judgement call whether to use the Impedance switch. It is all about heat, but a well ventilated amp will not be a problem even with 4 ohm speakers unless you are pushing it to ridiculously high volumes.

In ...my opinion.

Steve/bluewizard
 

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