AU-717 & AU-777 & 4 ohm loads

[brunswick]

Hello all,
In the next week or so I will be receiving an AU-717 and AU-777 via the mail. My question today regards the ability of these amps to drive 4 ohm loads.
Specifically, a pair of Klipsch KG4s, which have a quoted impedance of 4 ohms.
Many people have commented (some on AK) that these speakers sound great with tubes, so I thought the AU-777 (which is supposed to sound tube like) would be an ideal match, however I don't won't to 'brick' my newly acquired toys.
Any thoughts on this matter would be appreciated,

Cheers,
Richard

 

[Hyperion]

In the specifications I can find for both of these amps it does not mention a power output into 4 ohms - only 8 ohms. - might be a clue :scratch2:

If the question was regarding 2 pairs of 8 ohm speakers in parallel (giving a resultant ~4 ohms), I would say a definite NO - as this combination could result in a very low impedance being presented to the amps at some frequencies.

As for 1 pair just 'maybe' the KG4's may be an easy load as a speaker - others may be able to advise, however DO NOT try it before you get a definitive answer.

Just my 3 ha'pence worth

 

[SoCal Sam]

KG4's don't look particularly hard to drive. 94 dB/1m is efficient.

http://www.klipsch.com/na-en/products/kg-4-specifications/

 

[Hyperion]

Well efficiency is one thing - but the key here is impedance vs frequency - some speakers rated at even 8 ohms nominal have alarming plunges to 3 ohms and below at some frequencies.

 

[LBPete]

As long as the amps are properly adjusted, they will have no problems with a single set of 4 ohm speakers. Just be sure the heat sinks are not getting hot at low volumn.

Also, DO NOT connect two sets of 4 ohm speakers and play them at the same time.

Keep in mind that the AU-777 in particular is a very old amp so it could die of old age regardless of what speakers are connected. But, if it should happen, it can be fixed.

- Pete

 

[SoCal Sam]

Well efficiency is one thing - but the key here is impedance vs frequency - some speakers rated at even 8 ohms nominal have alarming plunges to 3 ohms and below at some frequencies.

That's why I prefer 8 ohm speakers.

 

[brunswick]

Thanks everyone.
I have looked around but cannot find a frequency v impedance curve, so I think I'll be cautious, I paid too much for the AU-777 (what can I say, I've wanted one for ages) to break it. I thought the 777 might cope, as the Au-222 & Au-555 both were rated for 4 ohm loads, as well as the Au-777D. Oh well.
Does anybody have any experience with the AU-777 & AU-717 regarding appropriate speakers?
Cheers,
Richard.

 

[brunswick]

I posted a question in the Klipsch area, somebody kindly posted a Impedance curve for the KG4s; I don't think I'll be using them with the 777 or 717.

http://www.audiokarma.org/forums/showthread.php?t=277665

 

[LBPete]

You worry too much. No reason at all not to pair them with either of these fine amplifiers. Even if the impedance drops a little below 4 ohms it's not an issue at all. Judging by that curve, the majority of the time it will be well above 8 ohms and when it dips below that it will be just a few micro seconds at a time. Those amps are very robust. They can handle it.

- Pete

 

[brunswick]

Thanks for the reassurance Pete.
I'll give it a shot.
I was a bit nervous mainly because the AU-717 actually is coming from the States (the unit has international voltage selector) and on arrival will have been a long time coming. I had a friend working in Pasadena at Caltech for a couple of years. He is bringing back some gear for me when he moves home.
While Au-717s and better do on occasion come up for sale down here, they can get very expensive, there just isn't the variety and volume of gear available here.
I almost weep when I see what people can get stateside and what they pay for it. Very Jealous!

Cheers,
Richard.

 

[LBPete]

Well, it sound like you need a California vacation. Quantas has been advertising some very reasonable airfare.

- Pete

 

[usedto]

I've been running a pair of KG4s on my 417, 717, and 719 for four or five years now with no ill effects yet.

 

[SoCal Sam]

Thanks for the reassurance Pete.
I'll give it a shot.
I was a bit nervous mainly because the AU-717 actually is coming from the States (the unit has international voltage selector) and on arrival will have been a long time coming. I had a friend working in Pasadena at Caltech for a couple of years. He is bringing back some gear for me when he moves home.
While Au-717s and better do on occasion come up for sale down here, they can get very expensive, there just isn't the variety and volume of gear available here.
I almost weep when I see what people can get stateside and what they pay for it. Very Jealous!

Cheers,
Richard.

There is enough vintage in Southern California for everyone!

 

[SoCal Sam]

Thanks everyone.
I have looked around but cannot find a frequency v impedance curve, so I think I'll be cautious, I paid too much for the AU-777 (what can I say, I've wanted one for ages) to break it. I thought the 777 might cope, as the Au-222 & Au-555 both were rated for 4 ohm loads, as well as the Au-777D. Oh well.
Does anybody have any experience with the AU-777 & AU-717 regarding appropriate speakers?
Cheers,
Richard.

The AU-717 with the Yamaha NS-200M is a very nice pairing. Superb balance and voicing together.

 

[noveltone]

Well efficiency is one thing - but the key here is impedance vs frequency - some speakers rated at even 8 ohms nominal have alarming plunges to 3 ohms and below at some frequencies.

The impedance curve for the Klipsch speakers (rated at 6 ohms) actually looks easier to drive that my own speakers' which are rated at 8 ohms. I don't know how they come up with this "nominal impedance" number. Check out the attachment -- these things are all over the place. They are B&W DM603s3.

Seems like you're in the clear from what the other folks have been saying. Good luck.

 

[brunswick]

Everyone's advice was spot on, the KG4s are no problem to drive at all. The AU-777 arrived and was plugged in; didn't miss a beat.
I was surprised how damn good it sounded, I must admit to buying it out of curiosity and an appreciation of its looks (I think that series look great), but I was blown away by the sound. Really smooth and very tube like. They are an excellent match for the KG4s.
Just have to wait for the AU-717 which is making its way slowly across the pacific.

Cheers,
Richard.

 

[SoCal Sam]

I think you will enjoy your AU-717 very much. I just cleaned one up this afternoon and was comparing it against a very well known and expensive 200 wpc power amplifier which shall I shall not name. It was a draw.

 

[brunswick]

Sorry about the delay, I meant to put these pictures up a week or three ago. The AU-777 & AU-717 both sound great with the KG4s

 

[Les Lammers]

Thanks for the reassurance Pete.
I'll give it a shot.
I was a bit nervous mainly because the AU-717 actually is coming from the States (the unit has international voltage selector) and on arrival will have been a long time coming. I had a friend working in Pasadena at Caltech for a couple of years. He is bringing back some gear for me when he moves home.
While Au-717s and better do on occasion come up for sale down here, they can get very expensive, there just isn't the variety and volume of gear available here.
I almost weep when I see what people can get stateside and what they pay for it. Very Jealous!

Cheers,
Richard.

I would definitely have the 717 checked, adjusted and re-capped before putting it into daily service. Driving KG4's will be fine. :thmbsp:

Enjoy it.

From a reliable source:

SPEAKER WARNING!:

Do NOT connect 4 speakers to this amp if the impedance of any of the speakers is 4 ohms. This will definitely damage the amp sooner or later.
If you must use 4 speakers, then all 4 speakers must be 8 Ohms (not 6 or 4 ohms). This was specified by the manufacuter. Please pay attention to this. We have found many amplifiers damaged this way.
If you must use 4 speakers that are 4 ohms, then you must connect each pair in series and connect either to system A or B but not both. If you need help, contact us before you connect your amp.


Just do not run four 4 ohm speakers at the same time. This is a good read: http://audiokarma.org/forums/showthread.php?t=60386

 

[plbeard]

Hello all,
In the next week or so I will be receiving an AU-717 and AU-777 via the mail. My question today regards the ability of these amps to drive 4 ohm loads.
Specifically, a pair of Klipsch KG4s, which have a quoted impedance of 4 ohms.
Many people have commented (some on AK) that these speakers sound great with tubes, so I thought the AU-777 (which is supposed to sound tube like) would be an ideal match, however I don't won't to 'brick' my newly acquired toys.
Any thoughts on this matter would be appreciated,

Cheers,
Richard

I am jumping into an antique thread, but for anyone else with this question: of all the late 60s Sansui amps, the 777 line specifically warns in the manual against using any speaker under 8 ohms. The 555 and 999 manuals say
"anything from 4 to 16" ohms, which was typical of many solid state amps c. 1970. Not so the 777. The 777 manual says "8 to 16," period. (The manuals for these are helpfully available on line at hifiengine).