Amps and Power hungry speakers.

[Papajoe 221]

Up to this point, I have been one of the people who has thought that our beloved Carver amps can power any speaker.  But, what has made me question that belief is a pair of  Thiel speakers that run in the 2-4 Ohm range. They are noted to be very power hungry and only will be at their best when they are supplied by the proper amp. The amp in question is a TFM 42. Plenty of power and rated in the 4 Ohm range. But, is it the proper one to power those speakers?

What do you think?

Papajoe

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[RodH 4,866]

It somewhat  depends on the sound level you hope to achieve.

 

An increase of 3 db requires a doubling of power, so it can add up fast. I have a buddy who clips his Bryston 14B-SST into a set of Vandersteen 2Ce's on an alarmingly regular frequency. WAY too loud for me, but not apparently for him. 

 

One issue with speakers that run down to that 2-4 Ohm load is going to be supplying enough current at raised volumes. Finding an amp that will handle the load might be a more important task than looking at raw power numbers.

 

Uncontrolled (hard) clipping kills speakers, not high power amps - unless you are pushing them beyond their maximum SPL output limits. 

 

Whatever you use - it'll need to be a biggun'

[UncleMeat 1,173]

TFM-45 should be enough; 600WPC @ 4 Ohms. The TFM-45 drives my ALS Originals W/60" ribbons just fine all the way up to it's max power output. If the impedance of the speakers were too low the amp would go into protection.

[Ar9Jim 6,512]

Hard to imagine that TFM-42 having issues and not providing enough current to at least 99 % of speakers IMHO.. Has the amp been serviced yet? Could be an issue if not, and putting under heavy load.. My basic understanding for sake of conversation, is that the lower impedance speakers show a load similar to a smaller rated resistor, or closer to a short circuit. This causes the amp to need the capacity to flow more current to carry the load (actually a lighter load but makes the amp work harder).

Most of my experience has been with AR9s and 90s. They are 4 way 5 drivers each. 3.6 ohms.. Ran a couple different pairs over many years with M400s, M500T M1.0Ts both stock and MkII, TFM 25, Silver 7Ts and several tube amps that should have been poor match but worked great. Never had a problem.. With a stock M500T I can tell when the amp runs out of gas, the power meter needles become reluctant to move higher and the volume doesn't increase, I never leave it that way, but always turn it down, back to where the amp can be comfortable with the load, never leave it running on the ragged edge of its capacity, back it down and give it some room to work. Guys running un serviced amps this hard will find trouble at some point. But if the 42 is in good shape and the speakers are not being abused by the owner with a clipped amp or excessive power and overheating, then I still bet on the crossovers bleeding signals and taking out the fragile higher end drivers..

[loner_t 2,568]

The Sunfires have patented tracking downconverters, which seem to handle such speakers very well. If you can find a Sunfire 300x2 or 600x2 (a bit rare), it would be a good comparison.  

 

The 42s should handle the Vandys well, though (unless you want to have a block party   ). Carver Pro series are also a good bet.

[fill35U 1,846]

Hard to imagine that TFM-42 having issues and not providing enough current to at least 99 % of speakers IMHO.. Has the amp been serviced yet? Could be an issue if not, and putting under heavy load..

 

Guys running un serviced amps this hard will find trouble at some point.

 

Servicing is better sooner than later! At this age they all need some kind of TLC. The TFM-42 I'm working on now ran pretty good at first glance, but on recapping I found two caps that had dried out so bad that they might as well have not even been there: a VAS decoupling cap and the -11.4V supply filter. Half of the rest of the small caps were merely in poor shape, par for the course...

 

My basic understanding for sake of conversation, is that the lower impedance speakers show a load similar to a smaller rated resistor, or closer to a short circuit. This causes the amp to need the capacity to flow more current to carry the load (actually a lighter load but makes the amp work harder).

 

Jim, I don't understand when you say a lower impedance speaker presents a lighter load to the amp, or how a lighter load makes the amp work harder?  

[fill35U 1,846]

Carver Pro series are also a good bet.

 

The Carver Pro amps have a wide range of power ratings and topologies. Just because it's "pro" doesn't mean it's "better" (or "worse"). Professionals have to choose the right tools for the job, too. 

 

The salient difference is that most of the Pro amps have a clipping eliminator, usually switchable. While definitely neither a panacea nor without drawbacks, it can help. But in home use, you should be able to see the TFM-42's clipping indicator LED's and hear the effects of clipping, and reduce the volume before things get too bad. If you're playing that loud and long, power compression comes into play- and that can help you or hurt you, depending on what you do next...

[Ar9Jim 6,512]

 

 

 

Hard to imagine that TFM-42 having issues and not providing enough current to at least 99 % of speakers IMHO.. Has the amp been serviced yet? Could be an issue if not, and putting under heavy load..

 

 

Guys running un serviced amps this hard will find trouble at some point.

 

Servicing is better sooner than later! At this age they all need some kind of TLC. The TFM-42 I'm working on now ran pretty good at first glance, but on recapping I found two caps that had dried out so bad that they might as well have not even been there: a VAS decoupling cap and the -11.4V supply filter. Half of the rest of the small caps were merely in poor shape, par for the course...

 

 

My basic understanding for sake of conversation, is that the lower impedance speakers show a load similar to a smaller rated resistor, or closer to a short circuit. This causes the amp to need the capacity to flow more current to carry the load (actually a lighter load but makes the amp work harder).

 

Jim, I don't understand when you say a lower impedance speaker presents a lighter load to the amp, or how a lighter load makes the amp work harder?  

Lighter load from a resistance viewpoint.. Working harder because of increased current demand into a less resistive load..

[Papajoe 221]

The TFM-42 was recently refurbished by the previous owner, so that is not a contention. After doing more research, I have found that the Thiels are rated 300-500W, but at 4 OHMs.  The TFM-42 can easily drive loads at 4 Ohms; but, the fact is that it will be putting out much higher wattage than the speakers can handle. It is also a know fact that the Thiels are power hungry. Putting more need to "turn it up".   Time to find another amp to power those beasts. 

Papajoe

• 

[fill35U 1,846]

Sorry, if I'm still confused!

 

My basic understanding for sake of conversation, is that the lower impedance speakers show a load similar to a smaller rated resistor, or closer to a short circuit. This causes the amp to need the capacity to flow more current to carry the load

 

I'm with you all the way up to this point 

 

(actually a lighter load but makes the amp work harder).

 

Jim, I don't understand when you say a lower impedance speaker presents a lighter load to the amp, or how a lighter load makes the amp work harder?  

Lighter load from a resistance viewpoint.. Working harder because of increased current demand into a less resistive load..

 

Increasing the resistance of the load makes (the typical voltage source) amp work less hard. 

 

I think you're saying the more reactive the load, the less its overall impedance is due to resistance? And that highly reactive loads, especially low impedance, can be very difficult for an amp? I'd certainly agree with that.  But everything is frequency dependent, including how much the amp cares.

 

 

[Ar9Jim 6,512]

 

 

Sorry, if I'm still confused!

 

 

My basic understanding for sake of conversation, is that the lower impedance speakers show a load similar to a smaller rated resistor, or closer to a short circuit. This causes the amp to need the capacity to flow more current to carry the load

 

I'm with you all the way up to this point 

 

 

(actually a lighter load but makes the amp work harder).

 

 

 

Jim, I don't understand when you say a lower impedance speaker presents a lighter load to the amp, or how a lighter load makes the amp work harder?  

Lighter load from a resistance viewpoint.. Working harder because of increased current demand into a less resistive load..

 

Increasing the resistance of the load makes (the typical voltage source) amp work less hard. 

 

I think you're saying the more reactive the load, the less its overall impedance is due to resistance? And that highly reactive loads, especially low impedance, can be very difficult for an amp? I'd certainly agree with that.  But everything is frequency dependent, including how much the amp cares.

 

 

Fill, I apologize if my terms were improper and confusing. My basic point that I attempted to make is this. The lower the ohm rating of a speaker, the less resistance the amp will see in general, I understand that the impedance changes at different frequencies, but in general, a lower impedance speaker say 4 ohms vs 8 ohms will be a more difficult load for an amp.. The lower resistance of the load causes the current demand from the amp to increase. Just basics, don't tell me I even have that wrong.. Lol.

[fill35U 1,846]

Thanks, Jim! No need for apologies- just a sanity check.  

Makes sense to me now. 

 

There's a lot more to it than the "numbers game" of a speaker's nominal impedance or an amp's wattage rating...

[Ar9Jim 6,512]

Thanks, Jim! No need for apologies- just a sanity check.  

Makes sense to me now. 

 

There's a lot more to it than the "numbers game" of a speaker's nominal impedance or an amp's wattage rating...

I understand that the frequencies, that the impedance dips occur, have a huge impact on how difficult the load will be for an amp.. Like the Kappa 9s that are known for dips in impedance at frequencies that give some amps trouble. Agree much more than just nominal impedance involved but its a place of reference and it gave us something to talk about..

[Papajoe 221]

After scratching my head, I realized that the TFM-25 would be a great match. 225w@8 Ohms and 350W at 4 Ohms. Actually, that is the amp that he was using when I said "Why aren't you using your TFM-42"?  

Papajoe

 

• 

[Dav-Em 335]

It's not just the impedance, but rather when you have a huge electrical phase angle COUPLED with an impedance dip. That's when stuff gets interesting.

 

Look at any speaker test in Stereophile and they'll measure both impedance and phase angle. Across the full audio spectrum. In any of their tests, that data is usually presented as the first graph.

[Dav-Em 335]

I was finally able to find this article on phase angle.

 

 http://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase/page-2

[aslan7 954]

 

 

I was finally able to find this article on phase angle.

http://www.audioholics.com/loudspeaker-design/understanding-impedance-electrical-phase/page-2

 

 

Great article explaining that Davis.

Thank you!

[Papajoe 221]

Thanks Dav-Em. I read that article also and find it interesting stuff.

Papajoe

• 

[Papajoe 221]

This is where I need the input from the more electronically knowledgeable member than me.(Just a newbie).  Is there any way to limit the TFM-42 from putting out 600W@4 Ohms?  Can we lower the total input signal on the amp? Just not feeding enough input for the amp to reach 600 W?  Would that have any influence on the performance of the amp?  Of course, simply answer, keep the volume down.

Papajoe

[aslan7 954]

 

 

This is where I need the input from the more electronically knowledgeable member than me.(Just a newbie). Is there any way to limit the TFM-42 from putting out 600W@4 Ohms? Can we lower the total input signal on the amp? Just not feeding enough input for the amp to reach 600 W? Would that have any influence on the performance of the amp? Of course, simply answer, keep the volume down.

Papajoe

 

 

Now that's one you don't hear every day -- "I want less power out of my amplifier ".

 

Say it ain't so Papajoe! ;-)

 

[Belvedere2 232]

Wouldn't worry about that power output number. It's not like it's going to push that all the time. You just want the greater capability it has. I always look at such numbers like I'd look at torque ratings on engines. When you need that power its there. Better than trying to move a fully loaded truck up a hill with a four cylinder engine. Somethings gonna give. When your speakers demand output you want your amp to be able to comply. Without clipping or overheating.

[UncleMeat 1,173]

Loner_t bought several TFM-42's from NASA that had the gain pots modded to allow external adjustment (dual trim pot mounted to the back exterior). That mod to yours would allow gain adjustment similar to the TFM-35 and TFM-55 (non-"X" versions). Reducing the gain will limit the amount of maximum output of the amp.

[Papajoe 221]

Belvedere2-

I never would have believed that I would have ever, ever said that; but, those Thiel CS 3.6's, of my neighbor, have me asking that. (Shudder, Shudder)

 UncleMeat-

I was lucky enough to be one of the member who got in on that deal and still have that amp. In the back of my mind, I have been wondering if that would work in this case. I am glad that I asked that question. When I got that amp, I opened the case to see how those pots were used. I thought that they had been just placed in the input signal like the TFM-15s. But no, they are connected directly onto a circuit board in the amp. I guess that Carver added them specifically for NASA's needs. The amp just needs to be refurbished.

Papajoe

• 

[fill35U 1,846]

Is there any way to limit the TFM-42 from putting out 600W@4 Ohms?  Can we lower the total input signal on the amp? Just not feeding enough input for the amp to reach 600 W?

 

HARRIS LABS INLINE ATTENUATORS 

 

Also sold through Parts-Express.

 

Would that have any influence on the performance of the amp?

 

Might make the quiet passages just a tiny bit more or less noisy. 

 

Of course, simply answer, keep the volume down.

 

With great power...  

[fill35U 1,846]

Loner_t bought several TFM-42's from NASA that had the gain pots modded to allow external adjustment (dual trim pot mounted to the back exterior). That mod to yours would allow gain adjustment similar to the TFM-35 and TFM-55 (non-"X" versions). Reducing the gain will limit the amount of maximum output of the amp.

 

If those pots are a relocation of/addition to the RP2 pots on the amp boards, then they affect the output impedance of the amp. You could change the power seen by the speaker in much the same way by using rheostats(hefty ones!) at the output. But when you get into that territory of low damping factor, interaction with the speaker impedance can cause the "voice" of the system to change... kind of the point of the whole "TFM" circuit. 

 

A long time ago, when she was almost brand new, I added a volume pot to the *input* of my first TFM-45 (profile pic). Crude but effective, it's been very useful over the years.