Need help with Peavey Tour 700

[GoodyearThrust]

SO... my friend may have just learned the hard way that there is a big difference between a 1/4 inch instrument cable and 1/4 inch speaker cable while using my Peavey Tour Series 700 Watt amp and my TVX 4x10.

It turns out that he lost the speaker cable that I gave him to use between the head and cabinet and decided to use one of his own 3 footers... :scowl:

I'll be getting the amp back later this week, and I'll be sure to make him buy another speaker cable, but my question is...

My friend said that the amp was clipping sound for a couple seconds while he was playing which sounds like a good thing to me since the amp recognizes that it cant push that much current across a cable with that high of a resistance and clips the signal. Is that wrong? Can using an instrument cable really damage the head? If so, what is blown?


Cheers

 

[GoodyearThrust]

C'mon guys! Help me out a little!

 

[nashvillebill]

An amp, or any electrical power source, won't "push" current. That's not the way electricity works...current flow increases when there is lower resistance. Speakers draw current. A 4 ohm speaker has lower resistance than a 8 ohm speaker, so it draws more current than a 8 ohm speaker (from a constant voltage source like a SS amp). A dead short has zero resistance and draws infinite current.

Now, there are a couple of scenarios. It's possible your "friend", apparently being irresponsible enough to lose your speaker cable, also was irresponsible and cranked the amp up until it, or the speaker cab, started distorting and clipping--especially if he boosted the bass. It's even possible the voice coil in the speaker has been damaged.

Or the instrument cable started breaking down under the high current being asked to flow through it. Ordinarily there would be a very high resistance between the conductors in any cable (whether instrument or speaker), but instrument cables have very tiny wires which heat up rapidly under high current. Heat breaks down insulation, the cable begins to short. A short in a cable is bad news for a power amp.

Get the amp away from your idiot friend, take it home, plug in a proper speaker cable, try it out and see if it sounds okay.

 

[GoodyearThrust]

An amp, or any electrical power source, won't "push" current. That's not the way electricity works...current flow increases when there is lower resistance. Speakers draw current. A 4 ohm speaker has lower resistance than a 8 ohm speaker, so it draws more current than a 4 ohm speaker (from a constant voltage source like a SS amp). A dead short has zero resistance and draws infinite current.

Now, there are a couple of scenarios. It's possible your "friend", apparently being irresponsible enough to lose your speaker cable, also was irresponsible and cranked the amp up until it, or the speaker cab, started distorting and clipping--especially if he boosted the bass. It's even possible the voice coil in the speaker has been damaged.

Or the instrument cable started breaking down under the high current being asked to flow through it. Ordinarily there would be a very high resistance between the conductors in any cable (whether instrument or speaker), but instrument cables have very tiny wires which heat up rapidly under high current. Heat breaks down insulation, the cable begins to short. A short in a cable is bad news for a power amp.

Get the amp away from your idiot friend, take it home, plug in a proper speaker cable, try it out and see if it sounds okay.

My idiot friend is paying for the new cable and the amp if it's busted. Thanks for your help man.

Cheers.

 

[B-string]

An amp, or any electrical power source, won't "push" current. That's not the way electricity works...current flow increases when there is lower resistance. Speakers draw current. A 4 ohm speaker has lower resistance than a 8 ohm speaker, so it draws more current than a 8 ohm speaker (from a constant voltage source like a SS amp). A dead short has zero resistance and draws infinite current.

Now, there are a couple of scenarios. It's possible your "friend", apparently being irresponsible enough to lose your speaker cable, also was irresponsible and cranked the amp up until it, or the speaker cab, started distorting and clipping--especially if he boosted the bass. It's even possible the voice coil in the speaker has been damaged.

Or the instrument cable started breaking down under the high current being asked to flow through it. Ordinarily there would be a very high resistance between the conductors in any cable (whether instrument or speaker), but instrument cables have very tiny wires which heat up rapidly under high current. Heat breaks down insulation, the cable begins to short. A short in a cable is bad news for a power amp.

Get the amp away from your idiot friend, take it home, plug in a proper speaker cable, try it out and see if it sounds okay.

Just a little correction on an excellent post . Hope the amp survived!

 

[GoodyearThrust]

I get the amp back Thursday, will let you know how it goes. Hope I don't have to get it fixed/replaced.

 

[nashvillebill]

Just a little correction on an excellent post . Hope the amp survived!

thanks, i fat-fingered that number....i'll correct my original post.

 

[GreggBummer]

I'd like to see if I understand this correctly.

I have an amp that is rated at 450 watts at 4ohm. The instruction manual, and conventional wisdom, say that I should not put a 2 ohm load on the amp. For example, two 4 ohm cabinets.

So, the way I understand the post above, the resistance is lower and the cabinets would draw more current. Because my amp is rated down to 4ohms, the draw would exceed the maximum amount and I could damage the amplifier, specifically the power amp section.

If that is correct (and likely I butchered your well written post), why is it that when I add cabinets, the amount of resistance goes DOWN?

I could go the rest of my life not knowing why... But I'm interested.

 

[Floyd Eye]

Ohms kinda go backwards. The more you add, the lower the impedance.

 

[nashvillebill]

When you add cabinets, they are almost always connected in parallel.

Two resistors in parallel will produce a resistance lower than either of the resistors alone.

Series resistors are additive; parallel are not.

 

[nashvillebill]

Here is the math behind the parallel resistance" Invalid Link Removed

Note the sentence in the tutorial :

The equivalent resistance is always less than the smallest resistor in the parallel network so the total resistance, RT will always decrease as additional parallel resistors are added.

 

[craig.p]

why is it that when I add cabinets, the amount of resistance goes DOWN?

Basic electrical theory. Invalid Link Removed. Maybe you're letting the physical cabling fool you into believing it's a series (rather than parallel) connection? If you dig into the cabling internals and draw it out on paper, the parallel connection will become clear.

...Gah! On a preview I see Bill beat me to it. Oh well, I'll post this anyway.

 

[GreggBummer]

Thanks!

I think, one I'm finished paramedic school, I may indulge myself with with a basic electronics class at the local community college. I would like a little background in basic electronics.

Thanks again for the links and explanations.