Carverfest tube amp capabilities at 4 ohms

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Don
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Carverfest tube amp capabilities at 4 ohms

Post by Don » Mon Oct 31, 2011 10:45 am

Has anyone tried their Carverfest tube amp on any efficient 4 ohm speakers yet? Don't want to blow mine up. Thinking of trying out on my Legacy Whisper XD's. Would temporarily pull out Sunfire 400 X 7 and insert tube amp. See if I can hear differences and what exactly they are. Don't have any idea how Carverfest tube amp will react to 4 amp load. Would not be driving Subwoofers, as they have their own built in amp.

Didn't want to risk damaging speakers or amp. However, thought it would be interesting to compare two at lower volumes. Believe at 95 db. speakers are efficient enough to try out Carverfest tube amp. Just don't know enough about amp performing at 4 ohms.

Thoughts from some of you tube-o-philes? Is it safe to insert in loop and use at lower volumes?

Whisper XD
Specs:
System Type:
10 driver, 4 way
Tweeter:
(1) 1" dual pole neo ribbon, folded Kapton diaphram
Midrange:
(1) 3" dual pole neo ribbon, vapor deposited kapton diaphram
Midwoofer:
(4) 7" Rohacell reinforced-Silver Graphite, cast frame
Subwoofer:
(4) 15" carbon/pulp composite
Low Frequency Alignment:
2nd order differential
Freq. Response (Hz, +/-2dB):
22-30K, includes 24 bit processor
Impedance:
4 Ohm
Sensitivity:
(Room, dB@ 2.83V): 95 dB
Recommended Amplification:
10-600 Watts

Crossover:
300, 3K, 10K
Binding Post:
2 Pair
Dimensions: HxWxD (inches):
63 x 17 x 13
Weight:
210 lbs. each
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Martin1970
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Re: Carverfest tube amp capabilities at 4 ohms

Post by Martin1970 » Mon Oct 31, 2011 10:52 am

Don wrote:Has anyone tried their Carverfest tube amp on any efficient 4 ohm speakers yet? Don't want to blow mine up.
I'm driving my 4 ohm 60" Amazing ribbons with one of them.
(Edit: The amp is being fed 190 Hz up and just feeding the ribbons themselves.)

They haven't blown up.
I still haven't put the zener in yet, but using those Sovtek EBay tubes Bob suggested.
Last edited by Martin1970 on Mon Oct 31, 2011 10:59 am, edited 2 times in total.
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jjptkd
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Re: Carverfest tube amp capabilities at 4 ohms

Post by jjptkd » Mon Oct 31, 2011 10:53 am

Damn! Those are some awesome looking speakers!! =D> =D>
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Re: Carverfest tube amp capabilities at 4 ohms

Post by frankieD » Mon Oct 31, 2011 10:54 am

Hey Don, I think you will be allright.

Your speaker specs say 10-600 watts, so 20 watts is in there.

As Bob would say "Try it and see".

Just be careful with the volumes. Turn it up slowly & carefully.

Let us know what you find.

I would try mine but it is STILL in Pittsburgh.

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Chauss
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Re: Carverfest tube amp capabilities at 4 ohms

Post by Chauss » Mon Oct 31, 2011 11:30 am

Don- you will be OK so long as you do not try to rock out (the amp should be good to at least 95db). I think the power rating on Bob's CarverFest amp is good from 2 ohm to 8ohm if I am not mistaken. He made a comment to the group something like that when we were in Cabin 5 doing the build- but I can not remember EXACTLY what he said.....Have FUN exploring tubes! :D

Cheers!~
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Re: Carverfest tube amp capabilities at 4 ohms

Post by radioeng2 » Mon Oct 31, 2011 12:27 pm

Transformers are exactly that, transformers. They have a turns ration, not a specific impedance on one side without the appropriate load on the other side.

We installed 10K/8 ohm transformers. That means that the tube is driving 10K load whenever an 8 ohm is reflected from the speaker. All drivers (ok ribbons are a little diff) have peaks and dips in their impedance, so tubes happily drive other than 8 ohms all the time.

A 4 ohm load means the tube drives, on a whole, a stiffer load than it's optimum. The penalty in tubes as you deviate from the design center is either higher power/higher distortion or lower power/lower distortion depending on which way you're going. Driving a nominal stiffer load means you're going in the higher power/higher distortion direction.

But unlike the extreme harmonics that clipping in solid state can create (what can blow tweeters), with tubes, overdriving just starts to flat top the waveform. But it doesn't create the same risk of driver destruction or amplifier outputs letting the magic smoke out. IE...overload a tube and it just starts sounding like shit!

So no harm in hooking up loads other than 8 ohms, just means that you'll reach a point where going louder just starts getting messy sounding and going more loud it just progressively gets worse. No fear...we're not dealing with the danger of SS devices here....

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Re: Carverfest tube amp capabilities at 4 ohms

Post by angelod307 » Mon Oct 31, 2011 2:25 pm

jjptkd wrote:Damn! Those are some awesome looking speakers!! =D> =D>

now that my friends is a man-ly man speaker. wimps need not apply. wifes need not apply for fear of being rejected as well. but the guys that have them, wow, i commend you. ata'boy.
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Don
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Re: Carverfest tube amp capabilities at 4 ohms

Post by Don » Mon Oct 31, 2011 2:30 pm

Thanks everyone for the response.

Mark, thanks also for explaining the tube vs SS clip difference. Had no idea, since a SS man all my life. Knew SS clip could get me in trouble fast. Didn't know what to expect with tubes. Wasn't quite ready to break out my Carverfest soldering gun. :lol:

Halloween tonight. Therefore, probably insert Carverfest tube amp tomorrow and sit down for some critical listening differences vs Sunfire.
To argue with a person who has renounced the use of reason is like administering medicine to the dead.
— Thomas Paine


"Try not to become a man of success, but rather a man of value" Albert Einstein

"Politicians are the only people in the world who create problems and then campaign against them". Charlie Reese

"The problems we face today exist because the people who work for a living are outnumbered by those who vote for a living." Brad Shurett


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RIP BILL D. RIP WRABBIT

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Re: Carverfest tube amp capabilities at 4 ohms

Post by BillD » Mon Oct 31, 2011 2:41 pm

Tube amp overdriving is interesting. When it happens, you sort of "squeeze" the bottom of the waveform into a narrower space and blunt the top, because the transfer function is assymetrical (bends). In SS amps (AB), the transfer function is always symmetrical, which squashes the linear transfer function both at the top and the bottom, causing "clipping".
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