[Danberg]

I'd like some basic education on a situation that occured when I was auditioning speaker cable.

In simple terms could someone explain the relationship between power amplifiers and output impedence, capcitance of speaker cable.  I think there must have been some type of mismatch between my amp and a speaker cable I auditioned.  I'm not an engineer, I just enjoy music.   I was under the impression that speaker cable is speaker cable, and other than sonic differences, all speaker cable will work with all power amplifiers.

I'll be specific.  Upon hooking up a particular brand of cable to my amplifier and turning on the amplifier, it coming on after it's built-in 30 second delay, an immediate horrible loud buzzing, oscillation sound came from both speakers.  I turned off the amp as quickly as possible, for fear of damaging either the amp, or the speakers.   Fortunately, re-hooking up my usuall speaker wire, all is well, the amp seems to work fine and speakers don't sound as if anything was blown.

I had never experienced such an occurance in auditioning dozens of cables over the years.  Any explainations why this happened?

Here are some specifics about my equipment, including specs from the mfgrs and wire manufacturer.

Tube line stage
output impedance - 300 Ohms SE, 40K Ohms minimum load and 1000pF maximum capacitance
rated outputs - 1V RMS SE into 200K ohm

Solid State power amplifier
200 watts per channel @ 8 ohms, 400 watts @ 4 ohms
sensitivity - 1.3 volts in for rated output
input impedance - 75 KOhm
output impedance - 0.017 Ohm

Speaker Wire
resistance - .0022 Ohms/ft.
capcitance - 0.95 nF/ft.
inductance - 6 nH/ft.
impedance - aproximately 2.5 ohms

Please keep any explaination simple, as I do not know the difference beween capcitance, inductance, impedance, etc.

[*Scotty*]

Bingo! We have a winner! The speaker-cable has way too much capacitance per foot. When you hooked up your amp it immediately went into oscillation and would have died right there without your quick action. It would be advisable to try to stay under 1 nano farad of capacitance for the entire length used to connect the speaker to amp. If you have ten ft. or fifteen feet. your total should be well under that 1 nano farad limit. Lower is better for amplfier compatibility. 
That speaker wire amounts to a ticking time bomb of death for most amplifiers it is connected to.
Scotty
Thank-you for posting all relevant data with your question.

[Danberg]

Thanks for your reply Scotty.

Can you go into more detail about the capacitance of the wire and its relationship to and how it effects the amplifier?

That oscillation the amp was emitting, if I had not turned it off quickly, what would have been damaged with the amp? Would'nt the amp typically have a protective circuit that would have protected it from damage?

Could the speakers or their corossover network have been damaged if I would have not as quickly turned off the amp (which I did in 5 seconds or less)?

[Johnny2Bad]

" ... an immediate ... oscillation  ..."
That's probably what it was.
" ... Please keep any explaination simple, as I do not know the difference beween capcitance, inductance, impedance, etc. ..."
One of those was wrong for the amp you used, causing it to become unstable. Don't use that speaker cable with that amp, and if you have some idea of what kind of speaker cable it was (ie, how it's constructed, etc) don't use a similar kind either. Your amp doesn't like that kind.

Some amplifier designs are more stable into "difficult" loads than others. Yours might be one of the "others", although extreme capacitance values are not expected conditions.

If the specifications for the speaker cable are correct, it has relatively high capacitance.

0.95nF/ft = almost 1,000 pF/ft. A speaker cable with perhaps 300 pF/ft is considered a high value. By way of example, Kimber 4tc is around 45 pF/ft and 8tc is around 100pF/ft.
A foot of your cable has the same capacitance as more than 20 feet of 4tc.

High capacitance is a likely suspect, and high capacitance will cause some amplifiers to go into oscillation.

" ... Could the speakers or their corossover network have been damaged if I would have not as quickly turned off the amp (which I did in 5 seconds or less)? ..."

An oscillating amp is in an unstable condition, and damage to something (amp, speakers, both) is really just a matter of time. There is no hard-and-fast rule about how long you've got; just be quick and hope for the best.

[*Scotty*]

I have this from someone who has been in the business of designing and building High Fidelity electronics for over three decades and he has told me that most solid state amplifiers have a zone of capacitance values that they don't like to see starting around 1 nano farad and running up to 4 nano farads maybe a little more. Many amplifiers have a simple zobel network at their output to help stabilize the amplifier and increase its load tolerance, some amps also have an output inductor which makes them even more load tolerant.
As it happens you can have an amplifier with a certain type of circuit design and the commonly applied stabilizing networks and when you combine this with the right amount capacitance you create the conditions for the prefect storm of destruction. There is really no way to know in advance if the amplifier will tolerate this range of capacitive load from the speaker wire or not so the best thing to do is just run the other way from this sort of speaker wire design. I thought this manufacturer had made available specially designed stabilization networks that were included or were available for purchase with their speaker wire to prevent this problem.
You are not the first person to have this problem result from using this manufacturers speaker wire.
You can burn resistors in the crossover network with this magnitude of oscillation as well as burn up the woofers voice coils if the condition is allowed to persist for any length of time. Of greater concern is the possibility of damaging the amplifier. If it still works
you are lucky and you may have dodged the bullet.
Scotty

[*Scotty*]

Here is a link to a discussion of the compensation network I mentioned in connection with your speaker cable
http://www.audioholics.com/reviews/cables/speaker-cable-reviews-faceoff-2/speaker-cable-reviews-faceoff-2-page-3
If this cable predates the incorporation of the network you should contact the mfgr about purchasing a pair of networks or build your own with the values mentioned in the article in the link.
Scotty

[Danberg]

Thank you both for the responses.

Scotty, you know your stuff, as the mfgr brand you imply as the source of the problem is correct.

The speaker cable I choose and currently use has a value of 8.6 nF/ft.  The length of each cable is 13' and all is fine.

I am considering a future purchase of another solid state amp.  Can I assume that my existing speaker wire will work with it?  What amp manufacturer specifications should I look for, to make sure that it is compatible with my current speaker wire? 

Should I contact the manufacturer, prior to purchasing?   

[Scottdazzle]

Danberg and Scotty,

You would be doing a public service for AC members if you would identify the speaker cable in question.  Thanks for the interesting discussion.

Scott

[toobluvr]

Danberg and Scotty,

You would be doing a public service for AC members if you would identify the speaker cable in question.  Thanks for the interesting discussion.

Scott

Yeah sure!
I got excoriated and basically driven out of my own thread for doing exactly that!

Damned if you do....damned if you don't.

Oh, and be careful if you show yourself to be insufficiently technical.  Some of the natives here will feel threatened that you've invaded their turf.

[*Scotty*]

Yes, contact the manufacturer about possible compatability problems.   
This potential problem can not be avoided by reading through amplifier specifications.
The "secret"was outed in the link to the audioholics article.
I used Google on the 0.95 nF/ft. capacitance parameter.
Goertz is the just about the only mfgr. with cable capacitances in the stratosphere so I was only confirming my suspicions based on experience.
Scotty

[rollo]

Here is a link to a discussion of the compensation network I mentioned in connection with your speaker cable
http://www.audioholics.com/reviews/cables/speaker-cable-reviews-faceoff-2/speaker-cable-reviews-faceoff-2-page-3
If this cable predates the incorporation of the network you should contact the mfgr about purchasing a pair of networks or build your own with the values mentioned in the article in the link.
Scotty

 As always Scotty you come to the recue with educated replies. Thanks for being around and so willing to help. 


charles

[Scottdazzle]

Yeah sure!
I got excoriated and basically driven out of my own thread for doing exactly that!

Damned if you do....damned if you don't.

Oh, and be careful if you show yourself to be insufficiently technical.  Some of the natives here will feel threatened that you've invaded their turf.

I understand your position.  Maybe I'm being naive!  And I'm certainly insufficiently technical -- all I've got is my ears and AC!  But thanks to Scotty for sticking his neck out.

[avahifi]

I agree with Scotty.  You have a speaker wire with which you can actually hear the difference in sound when you use it.

You can even smell the difference when the amp and or speakers burn up. 

Choose both speaker wires and interconnect cables that are flexible, as low a capacitance as possible, and full braid shielding for the interconnects, with solid and reliable connection hardware.  Blue Jeans cables come to mind.

In general, amplifier and preamp output circuits do not like capacitive loads.

Regards,

Frank Van Alstine

[gerald porzio]

I'll 2nd the recommendation of Blue Jeans low capacitance ICs.

[Danberg]

Scotty, you hit the nail on the head.  I confirm that is the speaker cable. 

I would have been furious if it had taken my amp down!  The manufacturer of that cable should warn it's dealers of the protential problems in using it's product!

[*Scotty*]

Danberg, Was the cable a new purchase from a dealer or did you buy it second hand. If it was purchased from a dealer it should have had the stabilization network in place or available. The dealer should also be well aware of the hazard this product poses to the continued functioning of most amplifiers it might be used with. Was the value you gave for your speaker cable in your last post correct or a typo?  If you are still using Nordost Blue Heaven
 it's capacitive value is 1000 times lower than the 8.6 nF/ft. value you gave, being 8.6pF/ft.
Just curious.
Scotty

[markC]

Gotta be a typo as the "problem" cable was listed @ .95 pf/ft and the "no problem" cable is 8.6?

[markC]

I agree with Scotty.  You have a speaker wire with which you can actually hear the difference in sound when you use it.

You can even smell the difference when the amp and or speakers burn up. 

Choose both speaker wires and interconnect cables that are flexible, as low a capacitance as possible, and full braid shielding for the interconnects, with solid and reliable connection hardware.  Blue Jeans cables come to mind.

Why do you recommend full braid shielding on interconnects? I use non shielded and have no issues with noise. I have tried shielded and did not prefer them.

In general, amplifier and preamp output circuits do not like capacitive loads.

Regards,

Frank Van Alstine

[Danberg]

The Goertz was on an "audition" basis from a dealer and no stabilization network was provided or mentioned to me.

Yes, you are correct again, the cable I purchased and am using is Nordost Blue Heaven.

Thanks again for your help & "sound" advice.  AC is a fantistic website!

Not to start a war, but are you aware if anyone has done a study regarding the relationship between a cable's specific capacitance, and the differences between sonic characteristics? 

[markC]

And the Blue Heaven is stated as being 8.6 pf/ft rather than 8.6 nf/ft. BIG difference-like a thousand times difference.