8/4 ohm switch on integrated amp - what does it do? (1 Viewer)

[John Royster]

I've been playing around with my HK integrated amp and am curious about the 4/8 ohm impedance switch on the back. It is a very heavy duty double pole/single throw.

Are you really supposed to turn this to 4 ohm if you do indeed have 4 ohm nominal speakers that dip very low? I remember reading somewhere that this just lowers the rail voltage and is not a very good idea.

 

[Paul Clarke]

John,

What model are you using? If H/K puts an impedance switch on the back of anything you would be well advised to use it. As you know, their receivers are conservatively rated and do not feature such switches. Different companies handle this issue differently. Some use it to simply lower or limit voltage when selected...effectively limiting output. I am not familiar with H/K's implementation but I would suspect it does anything BUT lower voltage.

 

[Chuck Kent]

John: The 4/8 ohm switches on all receivers and integrated amps do exactly what you've speculated. Lowers the power supply rail voltage when in the 4 ohm position. Typical figures I've seen printed in magazines are 15 to 25% lower output wattage (in the 4 ohm setting.)

The reason for this switch is to lower potential output for heat buildup safety (and pass either UL or CSA heat regulations) when driving lower impedence loads.

In general, if your amp has good ventilation (don't place anything on top of it and leave as much space around it as possible), or if you don't play your programming too loud, then leaving it in the 8 ohm setting is preferable. (Keep in mind that running more power helps to prevent clipping.) If you have limited ventilation or play things at a constant higher volume, then you might want to consider the 4 ohm setting (but you do raise the risk of clipping.)

 

[John Royster]

So basically leave it in 8 ohm mode and continue to use my ears to detect distoration/clipping?

I do like to play loud now and then but the moment I hear any kind of clipping/distortion or loss of dynamics I back it off a notch or two.

Thanks for the tips fellas, it always seemed like the 4 ohm setting didn't have as much punch as 8 ohm. On the ventilation issue the way I see it, that's an amp. Not a darn thing is 6 inches near it.

 

[Chuck Kent]

Yeah, the 8 ohm position is the best place as long as heat is not an issue. You'll have less chance of clipping in the 8 ohm setting (due to the higher output level capability.)

 

[John Royster]

Thanks Chuck. Makes a whole lotta sense now. I remember playing around with the switch/listening and always found my self leaving it at 8 ohm. This is on 6 ohm and 4 ohm speakers.

 

[John Royster]

Just to follow up...
I set off my amp's protection last night on some Janet Jackson. :frowning: Was at a very good listening level about -6 on the pre-amp (previous polk speakers I coud listen to about 0 with no clipping). No clipping...sounded very good.
My poor HK integrated amp. She's been so good to me these last 10 years. :frowning: Actually I was very impressed the protection circutry was VERY fast muting the sound until I turned it down a few notches. She was running pretty hot...don't know if it was thermal or current protction that was engaging.
Good news is now I have a completely plausibly deniable excuse to my wife about purchasing the amp you fine fellows have recommended me.
"Look honey! This amp is incompatible with these new speakers, guess we need to get a different one. "

 

[Mike Veroukis]

John,

I've read about HK receivers that will auto-shut off. I wonder if this is somehow related.

You could also try to improve ventilation by using a small computer case fan to suck warm air out of the reciver's vents. This should make a big difference.

And always be carefull not to run your units too hot as even if it doesn't go into protection mode, heat is the number one killer of electronics, motors and engines. It's best to keep things cool.

- Mike