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Watts; the worst measurement unit ever for amp output?

#181
1958Bassman said:
But engineers aren't the ones who come up with all of the catchy slogans, buzzwords, hyperbole and BS that grabs people by the schnoz and makes them pay more than they would ever conceive of, for something that usually isn't right for them, for reasons that are lost on the buyer.
:mad:
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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
 
#182
acmebass said:
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
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Well at least you started out with one built-in endorser:

162426066_wile-e-coyote-acme---this-might-hurt-round-stickers.jpg
 
#186
Leave it to the engineers lmao!
This was a real conversation i had with my dad, an electronic engineer;
"this amp was engineered to provide certain amounts of distortion at certain gain levels,". Dads response- "What? Thats crazy! Who engineers distortion INTO a circuit?? Circuits are supposed to eliminate harmonic distortion!".
"Dad, certain frequencies of distortion can please the human ear."
"What? Hogwash. Faulty circuits designed by faulty engineers!".

Understand, dad grew up in the 1940s and was NOT a fan of "the new music" lol.
Yeah, leave it to the engineers. Many engineers will never plug a bass
In and perform real world testing on their own circuit.
 
#187
Your dad is all right.
Every tube Push Pull amplifier eliminates Harmonic distortion (the even Harmonics).
Every feed back loop in every tube power amp reduces Harmonic distortion.
Every cathode resistor in an tube preamp reduces Harmonic distortion.

But indeed there are tons of designs in guitar preamps to produce distortion.
Whereas bass preamps very seldom produce those distorted sounds.
There are only a few bass preamps which are designed with drive stage.
Ampeg SVP preamp (SVT-II Pro) and Fender TBP-1 preamp have got a drive stage.

The 70s svt and v4b preamps was rather designed under proposition of minimized THD.
Preamps like that don't sound enjoyable in distorted modes.


Designing a enjoyable drive stage for distorted sounds is very tricky and a hard job to do.
It is very tricky on guitar preamps but probably more tricky on bass guitar preamps.
To provide a smooth balancing of even and odd Harmonics under the proportion of a direct "livelike" feel on the attack is more difficult as one might assume.
A very lot of designs are based on mixing of wet and dry which is necessary when the pure wet sound is a gas.
Enjoyable sounding designs don't need any mixing of dry and wet.

And sometimes the concept of a tube preamp is not fully understandable to me.
For example I don't see any sense if a tube driven compressor stage is placed behind a tube overdrive stage.
...so what
 
#188
acmebass said:
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."

Bull.

I don't know the guy, and have no idea if his amps are any good, but suffice to say I probably wouldn't drive very far to audition one.

There was a comment below the piece from a "Soundminded" which echoed some of my concerns about what the author asserted.

I think agedhorse's explanation makes more sense, and like me, he seems to be not convinced. Of course, I don't design amps anyway, I was just curious.

The other comments on the subject are interesting, and appreciated!

Andy
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PS audio sells a $799.99 power cable: draw your conclusions from that. :D

Seriously, his comments on amplifier design don't fill me with confidence that he could engineer a decent power amp, but I'd guess that the actual engineering work isn't done by him.

As an engineer with experience in the field myself, I'd put much much more stock in what Agedhorse has to say about it. ;)

As for OTs in solid state amplifiers, the only even marginally sensible reason to do that these days is if you feel you must have the same output power at multiple load impedances. We experimented with it when I was working in high end audio and found that the addition of an OT didn't impart very much tube-like behaviour to a SS amp unless it was driven to saturation and that still wasn't very convincing. There's more to it than just shoving a transformer in there, not the least of is the source impedance of the circuit driving the primary.

As for back-emf, yes it can be looked at as an impedance from the point of view of the amp outputs but the source impedance of the amplifier driving the speaker makes a difference in how much effect the back-emf has on the overall behaviour of the speaker. Higher source impedances ( i.e. low damping factor) can allow the back-emf to have sonic effects as the voltage created by that back-emf at the amplifier's terminals is higher if the amp's output impedance is higher. The higher the voltage is, the higher the impedance seen by the amp is at a particular frequency. This actually is a good example that highlights how we can't look at any of the Ohm's law factors in a vacuum when it comes to amp-speaker behaviour.

Assuming I have that correct, of course. Andy?
 
#189
Some weeks before I had a very interesting conversation on this OT topic.
A friend of mine who works in Germany as a custom amp designer for guitar amps did a series of experiments with different OT iron materials. He is convinced that the quality of iron material did change over the last decades of time, and therefore the performance and sound of an OT.


In particular he tried to find out a supplier for an iron material which is narrow or equal to the material which was used in the 60s of the last century. It is his believe that those vintage iron materials provide some non linearities in the characteristic line of an OT which are obsolete in materials of modern production eras.

Somewhere in England he was successful to find a supplier for those materials.
But it is clear that my friend did not gave me any address.
I'm sure that he has got some advantage on the market with such old style designed OTs.

It is very hard to explain the difference to a modern production OT by words, but one of my first audible impression I had was a kind of a smooth growling which reminds me a little bit on my 70s svt.
 
#190
ThisBass said:
Your dad is all right.
Every tube Push Pull amplifier eliminates Harmonic distortion (the even Harmonics).
Every feed back loop in every tube power amp reduces Harmonic distortion.
Every cathode resistor in an tube preamp reduces Harmonic distortion.

But indeed there are tons of designs in guitar preamps to produce distortion.
Whereas bass preamps very seldom produce those distorted sounds.
There are only a few bass preamps which are designed with drive stage.
Ampeg SVP preamp (SVT-II Pro) and Fender TBP-1 preamp have got a drive stage.

The 70s svt and v4b preamps was rather designed under proposition of minimized THD.
Preamps like that don't sound enjoyable in distorted modes.


Designing a enjoyable drive stage for distorted sounds is very tricky and a hard job to do.
It is very tricky on guitar preamps but probably more tricky on bass guitar preamps.
To provide a smooth balancing of even and odd Harmonics under the proportion of a direct "livelike" feel on the attack is more difficult as one might assume.
A very lot of designs are based on mixing of wet and dry which is necessary when the pure wet sound is a gas.
Enjoyable sounding designs don't need any mixing of dry and wet.

And sometimes the concept of a tube preamp is not fully understandable to me.
For example I don't see any sense if a tube driven compressor stage is placed behind a tube overdrive stage.
...so what
Click to expand...

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...
 
#191
Entwistle used:
three Hiwatt DR103 100-watt amps customized to the CP103 spec

Probably Hiwatt did the first preamp design with two cathode basis stages direct in series.
Turning the gain pot to max. position linked the gate input of the second tube stage via DC blocking C direct to the plate of the first tube stage.
The tone stack was placed behind this pseudo "drive" stage.

IMO an absolutely ingenious design.
 
#192
It's relatively easy (by comparison) to design a flat amp that has low distortion in the linear region. Almost trivial these days (not counting class D)

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.
 
#193
P Town said:
Since volts, amps, (and especially reactive) ohms are difficult for some people to visualize, I propose, (jokingly) that we convert these units into equivalent physical phenomena that people can more easily conceptualize.

Since power is work divided by time, and work is force times distance, (roughly), I propose we rate the output power of an amplifier in the equivalent of moving a mass, measured in stones, (6.35029 kilograms), a distance measured in furlongs, (291.168 meters) in a period of time measured in nanofortnights, (1.2096 milliseconds).

I hope this makes it easier for the average consumer to understand amplifier output power ratings.
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P Town said:
Yeah, I like "Cannon Power" as a unit of amp power.

We would have to agree to abbreviate it with: "CP" so it would not be confused with candle power, abbr:"cp".

Can anyone suggest some other units we could all agree on?

How about "elephant power" for very high powered amps, and "gopher power" for low powered amps. That way manufacturers/marketers would not have extremely large, or small numbers for amps that have a large difference in power rating when they are creating their marketing material.
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P Town said:
Vox has announced today that going forward their amps output power will be rated in Btu.

Quote: "The British thermal unit (BTU or Btu) is a traditional unit of energy equal to about 1055 joules. It is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. and we here at Vox believe that this best reflects how to measure Vox amplifier output power. God save the Queen."
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P Town said:
Come on guys, I'm just trying to have a little fun with the Btu reference. (just like some amplifier manufacturers do when they publish amp specifications).

Please don't try to cloud the issue with facts.

(Yes I neglected to include time). Please let me say that Vox does take time into account when calculating power ratings.

The formula looks like this: Btu/Jiffy.
Click to expand...

All of this is gold!! :D
 
#194
agedhorse said:
It's relatively easy (by comparison) to design a flat amp that has low distortion in the linear region. Almost trivial these days (not counting class D)

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.
Click to expand...

This strikes me as odd as overdrive/clipping behaviour is (not very) arguably the most important part of a power amp design. It's definitely what separates the boys from the men, so to speak. Given the dynamic nature of music, it's a very rare power amplifier that never enters its non-linear range.

Did you see my comments on back-emf earlier?
 
#195
Missed the back emf comments... Back emf is in fact energy that can be reflected or absorbed. The combination of source impedance (inverse if damping factor) an any distributed loads affect this. Back emf superimposes (sums) on the original signal (subject to reflection and absorption) and the result gets fed back along with the original signal. Generally it's a small contribution but it could be significant in some instances.

Where it can become a really big problem is in VI limiting circuits with substantial phase shift between V & I. In this case, the feedback loop is opened under limiting conditions and interrupting or clamping the drive signal (voltage) can result in a large inductive spike being generated due L x dI/dT. This can destroy an amp if mechanisms are not in place to absorb these spikes.
 

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