Watts; the worst measurement unit ever for amp output?

[tombowlus]

Interesting topic!

Our Technical Editor, Tom Lees, discussed this topic a bit in his Link Removed.

In this same issue, we tested the TC RH450 and the Orange TB500, which are two class-D heads which deliver the goods in very different - but yet in some ways rather equivalent - fashion. Tom discussed this comparison further in Link Removed

Tom continues to try to find ways to communicate to our readers that it's more than just one number (or even a handful of numbers) which defines how a given amp will perform for you on a gig. In BGM issue #11, Link Removed.

 

[acmebass]

Interesting topic!

Our Technical Editor, Tom Lees, discussed this topic a bit in his Link Removed.

In this same issue, we tested the TC RH450 and the Orange TB500, which are two class-D heads which deliver the goods in very different - but yet in some ways rather equivalent - fashion. Tom discussed this comparison further in Link Removed

Tom continues to try to find ways to communicate to our readers that it's more than just one number (or even a handful of numbers) which defines how a given amp will perform for you on a gig. In BGM issue #11, Link Removed.

You guys are doing a great job, Tom.

BTW, I had the pleasure of meeting your associate, Jordan Simms here in Denver several months back at the Denver Bass Bash. That kid is a great drummer, and a really nice young man.

Andy

 

[tombowlus]

You guys are doing a great job, Tom.

BTW, I had the pleasure of meeting your associate, Jordan Simms here in Denver several months back at the Denver Bass Bash. That kid is a great drummer, and a really nice young man.

Andy

Thanks! And yes, Jordan is a good dude, and has a ridiculous amount of musical talent.

 

[1958Bassman]

Try calling your company "Acme." Geez- you wouldn't believe some of the criticism I've gotten for that act of blandness. But catchy names and buzzwords give me gas.

A

Are you in Walla Walla, Washington, or Rancho Cucamonga?

 

[acmebass]

Are you in Walla Walla, Washington, or Rancho Cucamonga?

Haha.

 

[1958Bassman]

Hi Andy... yes this does appear to be a very odd decision.

My understanding is that they chose to use an output matching transformer to allow for driving very low impedance loads, down to 1 ohm or less. If this is indeed the driving factor behind the decision, then a matching transformer can increase the amplifier's efficiency and reduce the thermal load on the output stage at a time when the cost of quality silicon in that quantity (I'm pretty sure this was well past the germanium era) was very, very expensive. This is even more significant if bridging was an option. This also allowed the amp to deliver "rated power" into a much wider range of loads.

The historical perspective is easily forgotten once we remember how things were in "the good 'ol days". In fact, they weren't all that good when it comes to the availability of electronic parts even if cost was not factored in.

But it's not the really old Mac amps that have output transformers. I have a customer whose MC300 has the three output taps and that amp is fairly recent- it even has a 12VDC trigger, which I am using when they want to play music from the Zone 2 output of their AV receiver. I'll look when I go there later this week, but I don't think it's from any earlier than 1995.

 

[1958Bassman]

Its my Urban Legend understanding that GUITARISTS first overdrove their amps in live situations in order to attempt to achieve more volume, by overdriving the gain of the preamp since the master was already maxed.
And that, once guitarists (and likely bassist Entwistle) experienced overdrive and its inherent distortion effect, they found it pleasant and that this accidental effect began to shape rock composition during the Acid Rock era.
Course i was likely a few months old when The Who started overdriving Hiwatt amps so i must go by the stuff of legend...

Another way some people achieved a great distortion was by connecting amps in ways they were never intended, yet it worked. They, including me, didn't necessarily know what the heck they were doing, but it seemed like a good idea at the time. In my case, it was for guitar, but I took a little single-ended EL84 amp's output, soldered an RCA plug on the speaker wires and sent it into the input jack of an even older RCA phonograph amp that we weren't using. It was a push-pull 6V6GT amp and it was outstanding! I was absolutely clueless about this stuff at the time but I was also about 16, so.....

One of the first ways they got distortion was by using amps that just ran out of power for the volume they wanted/needed. The small amps weren't enough, so they started using old Bassman amps for guitar, so they could still be loud in a larger hall.

 

[1958Bassman]

What's difficult is to design an amp that overdrives in a desireable way, with no negative recovery artifacts, has desireable tonal composition under these conditions, and is also reliable. Indeed, this is a hard concept for many engineers to get their heads around.

Leave it to an engineer to bring reliability into the conversation.

 

[1958Bassman]

How speakers work, including back emf. I'm working on an improved version of this.

Invalid Link Removed

Thanks for this. Also, it has been approximately 37 years since I saw a reference to Bulk Modulus.

I might have to start a band with that name.

 

[1958Bassman]

2. Driving a fixed coil (of any type) with a current within or outside of a magnetic field causes electro-magnetic energy to be stored in the field and when the current is interrupted, a voltage will be impressed on the coil's terminals as the field collapses. The voltage = L x dI/dT, so the faster the switchoff of the current, and the larger the inductance, the larger impressed voltage.

Now this is going back to theory I haven't really thought about in many years, so pardon the rusty approach.

Nice explanation of an ignition coil. Just imagine how far we could get a speaker cone to move if.....

I think we could get it to go across the room, under the right conditions.

 

[agedhorse]

Thanks for this. Also, it has been approximately 37 years since I saw a reference to Bulk Modulus.

I don't even remember what that is... (similar time frame for me as well.)

 

[aborgman]

Nice explanation of an ignition coil.

Or why you need flyback diodes...

 

[agedhorse]

Or why you need flyback diodes...

and the speed of the diodes can be important as well (read on the LM391 application notes a good explaination IIRC)

(or was it the LM3886???)

 

[ThisBass]

The waveform of the Back EMF is an exact reflection of instantaneous VC velocity, dx/dt, if you will.

Yes it is and therefore back emf works like a differentiator.

Designers of servo-corrected systems will sometimes drop an extra turn or two into the gap, to provide an exact real-time picture of what the voice coil is doing, such that the servo circuits can can compare it to the input, and correct.

Which makes really sense. As far as I know those feedback loops are mainly used to prevent speakers from a X zero offset, and therefore in second instance to reduce 2nd harmonic distortion.

This signal would be EMF. The adjective "back" refers to the phase of the EMF generated by the voice coil, so to get geeky, one is Back EMF, and the other is just regular ol' EMF.
Andy

I don't agree that the adjective back refers purely to a phase. It can be mathematically figured on a time axis as a phase shifted signal, but with respect it is physical regarded more then a poor phase shifted voltage on a time axis.

 

[acmebass]

I don't agree that the adjective back refers purely to a phase.

Yeah,. A better choice of words would have been "polarity."

In a DC motor, of course, the EMF would be "back" at ya! It's certainly an antiquated term, in any case.

 

[megafiddle]

"Originally Posted by megafiddle
It has everything to do with watts.
Actual watts though, not published watts."

That's a different question, dude. If one of the manufacturers is misrepresenting his product,

that's relevant, of course, but any such accusations ought to be substantiated with data.

Again, I believe this is a solid state/tube issue.

A

But that was in fact the original question: "Watts; the worst measurement unit ever for amp output?"
Watts are the unit we are interested in. The problem is in the way it is measured. It doesn't correlate to the
way it is played. And that's been more than explained in this thread.

By "published watts", I am referring to the full undistorted output power that is commonly used for both tube
and solid state amps. I wasn't implying that they were by any means dishonest. I'm quite sure you could get
the same results if you measured the amps yourself.
And by "actual watts", I am referring to usable power, which under real life playing conditions, can be audibly
different, especially for solid state vs tube amps.

If you play the same note through two different amps, with the same spectral characteristics, and one is louder,
it's a safe bet that the actual power output was also greater. That's my point.

As I said, thanks for the link, but I read that piece, and while I don't want to slag another

Boulder boy, it's almost completely nonsense. He lost me at:

"As the Ohm number goes down, the need for power goes up proportionally. So the power needed to make an 8 Ohm speaker

produce sound in the room needs to double when the Ohms cut in half to 4 – and double again for 2 and so on. Lower Ohms,

higher power to achieve the same sound pressure."

That certainly was nonsense. I offered it for the little information that seems to be out there concerning the McIntosh.

.

 

[BawanaRik]

Like any other data much of it's value comes from the person interpreting it.

 

[BawanaRik]

Are you in Walla Walla, Washington, or Rancho Cucamonga?

Good thing you're not in Walla Walla Philippines!

 

[BawanaRik]

"We" is..who? in this case?

One of the things I find interesting about American English, or American, is our use of pronouns.

While your post reminds me of a punch line involving the Lone Ranger, pronoun use should be made as clear as possible. The use of "we" in the post you quoted is another fine example of what Paul Newman might consider a "Failure to communicate".

I do love that term and get a chuckle out of it..

I try to be as concise as possible when using pronouns.

 

[Major Softie]

One of the things I find interesting about American English, or American, is our use of pronouns.

While your post reminds me of a punch line involving the Lone Ranger, pronoun use should be made as clear as possible. The use of "we" in the post you quoted is another fine example of what Paul Newman might consider a "Failure to communicate".

Ah, but that was Strother Martin's line.