Is a moderately powerful amp too much for my console speakers?

[mstrane21]

I bought an old console with a tube amp. It is missing tubes and just to get it out of the garage for now I'm going to stick a more modern amp in the bottom of it just to make it function. It has two 15s, mids, and tweeters. No idea on the impedance.

Hooked the speakers up to a couple of newer amps ranging from 40-80 wpc. They do fine until I turn the volume up just slightly past casual listening level. At that point the receiver clicks like it is going into protect mode and the music is inaudible. Is this what y'all refer to as clipping?

Is my amp too powerful for these speakers, or vice versa? I have to think it's the former since there's no way that old tube amp puts out much wattage. Any recs for a cheap low powered amp I could stick in there as a stopgap that won't this? Would one of those TPA 3116 amps be worth trying out? I really want something that won't shut down when the volume is reasonably loud. Any help would be appreciated.

 

[cnolanh]

Sounds like the amp is giving up and going into a protective mode indeed. The speakers may want more current than the amp is ready to provide, especially if they are low-impedance. Old tube amps usually have different taps for various speaker impedances (4, 8, 16, etc.).

Clipping is a little different, in that when the amp runs out of juice the sonic waveform gets clipped (flattened) at the top and bottom. This quickly becomes audible distortion. If the amp is clipping, the music may stay just as loud but will sound obviously worse.

 

[Chris Brown]

There should be some audible distortion before you got to the point where your amp is going into protection, but exact behavior will vary among amps.

You said you "Hooked the speakers up to a couple of newer amps". Do you mean that you've experienced this same behavior on several different amps?

I would verify the impedance of the speakers you are trying to use. Many tube consoles used 16ohm speakers, which means your amp would have basically half the power output it's rated for at 8ohms, making a 40wpc amp more like a 20wpc amp. Lower impedance loads will instead increase the power output from your amp, to the extent that it's able to deliver increasing amounts of current. An impedance too low can result in your amp trying to deliver more current than it's capable of. So there are situations where the speakers being too low, or too high impedance might cause issues. Also keep in mind that unless you're connecting to the individual drivers, how they are hooked up via the crossover can affect the overall impedance.

I can't really imagine any situation where the amp being overpowered relative to the speaker it's hooked up to would cause the issues that you describe. I doubt going to a lower powered amp is the answer.

 

[mstrane21]

So you think it's lack of enough juice from the amp? If that is the case I am wondering how on earth this old tube amp ever functioned with these speakers?

I've got an old 100 wpc Optimus receiver I could try next. If the speakers truly need more juice then there's no point in buying tubes for the old amp, and least for the purpose of pairing with these speakers, right?

 

[mstrane21]

Chris, yes, it did this with 4 different amps, and I forgot I also hooked a 100 wpc Yamaha amp up. Same thing. I bet you are right about the speakers being 16 ohm, but wouldn't a modern receiver be a heckuva lot more equipped to drive these speakers than the old tube amp? I really don't want to bother buying a few tubes for the original amp and then run into the same issue.

Sorry for the newbie questions.

 

[Chris Brown]

So you think it's lack of enough juice from the amp? If that is the case I am wondering how on earth this old tube amp ever functioned with these speakers?

It's not that simple. Tube gear tends to excel at delivering Voltage, whereas solid state gear is better at delivering current. High impedance speakers require lots of voltage, not so much current. Low impedance speakers require lots of current, not so much voltage. If the speakers are high impedance, they might be better suited to that tube amp than might be immediately obvious.

 

[Superampman]

16ohms is a relatively easy load. Those old console speakers are also probably very efficient. But it's possible they are 32-36ohm speakers. If they are, you have your answer. Serious clipping going on.

 

[sKiZo]

If the amp was clipping, it'd recover after the hot spots ... not saying damage wouldn't ensue ...

Got a pic of the speakers and original amp? Depending on the age of the console, they may require a transformer that might have been on the original amp to drive them properly ...

 

[mibag6]

Do you have a schematic that shows how the speakers are wired? Some of those consoles don't have much in the way of crossovers, simple band pass caps maybe. If there are caps, they're likely bad so check those. Also, check how the drivers are wired, parallel or series and see if you can make out impedance ratings. If you have 3-8ohm drivers in parallel I can see that a lot of SS amps might not like the low impedance load.

 

[Superampman]

If the amp was clipping, it'd recover after the hot spots ... not saying damage wouldn't ensue ...

Got a pic of the speakers and original amp? Depending on the age of the console, they may require a transformer that might have been on the original amp to drive them properly ...

I'm imagining the kind you hear when turning the volume all the way up on a battery powered transistor radio. Seems like the op's description.

 

[mstrane21]

Just to close the matter in case anyone else has a similar problem in the future, the culprit was apparently my use of some crummy speaker wire I had laying around the garage. Hooked it up to the thick stuff and this old Yamaha is blasting.

 

[whoaru99]

May have been somehow related to the speaker wire having a defect, but it's very doubtful that it was simply the gauge that mattered in this regard.

 

[toxcrusadr]

The earlier posts about the speakers being 16 or 32 ohm impedance do not explain the issues either. An amp will deliver half the power into a 16 ohm speaker that it would into an 8 ohm speaker. I was beginning to suspect that this console had 4 ohm speakers, and your amp was having trouble with the load. But even that was a bit of a stretch.

Maybe that old speaker wire had shorts in it, and the amp was delivering a lot more than it sounded like.

Also wondering what kind of a crossover is in the console, i.e. how the drivers were hooked up.

 

[Chris Brown]

The earlier posts about the speakers being 16 or 32 ohm impedance do not explain the issues either.

Why not?

An amp will deliver half the power into a 16 ohm speaker that it would into an 8 ohm speaker.

Exactly. The amp being able to deliver significantly less power into the speakers than expected, and thus likely running out of power, seemed like a reasonable explanation to the OP's problems:

They do fine until I turn the volume up just slightly past casual listening level. At that point the receiver clicks like it is going into protect mode and the music is inaudible. Is this what y'all refer to as clipping?

 

[whoaru99]

Why not?



Exactly. The amp being able to deliver significantly less power into the speakers than expected, and thus likely running out of power, seemed like a reasonable explanation to the OP's problems:

An easier load shouldn't cause the receiver/amp to shut down prematurely.

 

[toxcrusadr]

Exactly. It's the opposite of a low-ohm speaker situation where the amp is being asked to deliver more and can't.

Edit: That's all a moot point anyway, if the changing the cables fixed it, there had to be something wrong with that wire. There's no way an 80 wpc amp should go into protection driving efficient console speakers at any kind of level below stupid loud.

 

[Chris Brown]

An easier load shouldn't cause the receiver/amp to shut down prematurely.

In what context is it "easier"?

If the amp is putting out less power, as it would when using higher impedance speakers, it will run out of power more quickly.

If the amp is behaving as it might when it runs out of power, how is there not a direct correlation between the two?

Edit: That's all a moot point anyway, if the changing the cables fixed it, there had to be something wrong with that wire. There's no way an 80 wpc amp should go into protection driving efficient console speakers at any kind of level below stupid loud.

But if it's 80wpc at 8ohms, it would be ~20wpc at 32ohms.

 

[johnr66]

Amplifiers run out of voltage headroom due to the supply rails. If the voltage supply to the output stage is +40 and -40 volts, for example, and the signal driving the output is pushing it to 45 volts peak, it can't do that and the top and bottom of the waveform get flattened down to 40 volts (actually less, but I won't get into that here). This is clipping. it doesn't matter if the load is 4 or 4,000 ohms, the amp still clips.

The maximum clean power the amp can deliver (just before clipping) is figured as (Vrms)^2/R = watts, with R being the load resistance (to keep it simple I'm not concerned with impedance here). If the amp can make 28 Vrms into a 4 ohm load, the load is dissapating 196 watts. Into a 16 ohm load it is 49 watts, into a 4K ohm load it is only 196 milliwatts.

I've had amps go into protection with light loads or heavy loads when performing power tests using 4,8 and 16 ohm non inductive loads. I assume the engineer who designed the protection scheme didn't want the amp to be clipping too much as it is bad for speakers. Some amps do this, some don't. Most seem to go into protection only when there is too much output current.

Careful with the console speakers, They are often really weak on power handling if they came from a single ended tube console. I rebuilt an old Telefunken console into a stereo rack and rebuilt its speakers with modern components. I took the old drivers and hooked them to a 15 watt amplifier and cranked them up until the coils smoked.

 

[jhtstone]

There was likely a short somewhere with the old speaker wire. Even a stray strand from between + and - terminals.

It could have been an impedance issue but that is more likely when impedance is too low for an amp. It is not likely a wattage issue as the original tube amp would not have been hard to beat with SS for power.

 

[toxcrusadr]

If the amp is putting out less power, as it would when using higher impedance speakers, it will run out of power more quickly.
/QUOTE]

I don't know if we're having terminology problems, but this doesn't make sense. All else being equal (speakers, acoustic output power, etc.), the same amp will be less likely to be driven into clipping with the higher impedance load, and more likely with a lower impedance load. Unless I've failed my fundamentals somewhere. :scratch2:

Edit: Rereading john's post above, the amp can deliver 196W into a 4 ohm load and only 49W into a 16 ohm load. Which amount of power coursing through the outputs would overheat them faster? I'm going to guess 196W.