GBE1200 Power Ratings...

[will33]

But is it what it says it is?

Sorry, had to. I really only read the last page of this.

 

[alexclaber]

The impression I'm getting is that due to Genz designing their amps for tube-like clipping characteristics the THD distortion is higher at only 50% power, but is predominantly even-order distortion. When analysing power for a given distortion the analysis equipment doesn't distinguish between good and bad sounding distortion so once 1% THD distortion is measured that is set as full power despite a user not hearing that as sounding like 1% of more typical nasty distortion and being able to turn the amp up much higher before clipping becomes a problem.

Therefore the Genz Benz is likely to not only meet its specs but also to sound even louder than specified because of the additional even-order distortion increasing the apparent loudness, just like a good tube amp.

The line sag issue is also pretty irrelevant in the real world because of the dynamic nature of bass playing - you are unlikely to draw even 1/8 power (once averaged over time) even when the amp is hitting the limiters regularly, so the load on the wall is much lower than during any lab based testing.

Alex

 

[tombowlus]

The impression I'm getting is that due to Genz designing their amps for tube-like clipping characteristics the THD distortion is higher at only 50% power, but is predominantly even-order distortion. When analysing power for a given distortion the analysis equipment doesn't distinguish between good and bad sounding distortion so once 1% THD distortion is measured that is set as full power despite a user not hearing that as sounding like 1% of more typical nasty distortion and being able to turn the amp up much higher before clipping becomes a problem.

Therefore the Genz Benz is likely to not only meet its specs but also to sound even louder than specified because of the additional even-order distortion increasing the apparent loudness, just like a good tube amp.

The line sag issue is also pretty irrelevant in the real world because of the dynamic nature of bass playing - you are unlikely to draw even 1/8 power (once averaged over time) even when the amp is hitting the limiters regularly, so the load on the wall is much lower than during any lab based testing.

Alex

+1 Alex. I agree with you across the board.

 

[seamonkey]

I always throw caution out when the discussion turns towards even/odd harmonics. I don't think any power section would want to purposely produce any distortion. Saying it's OK because the distortion it produces will "sound" good is subjective. This shouldn't be an excuse. Although these are heads so I don't think you can rule out what the integrated pre-amp section adds. Whatever the pre-amp adds would trump what the power section does except for the extreme conditions.

For anyone interested. What is even, what is odd and what sounds good? These Articles explain it well:

Blackstone has a good write up on even/odd harmonics and what sounds good and bad. He even has an applet to play with.
Invalid Link Removed
Quote:
"Do we want to add even harmonics? Let's take on that controversial issue. Even sounds better, right? Tubes produce even, transistors produce odd, right? Wrong! Wrong! ..."

Universal Audio has an article:
[Invalid or Expired Link Removed]
Quote: "...absence of even harmonics has often been (wrongly) attributed to solid-state technology."

 

[seamonkey]

There is no rat, just different manners of testing.

Trust your ears.

Tom.

Also trust the tests. They will be a good indicator of how the amp will perform in the real world. Given one amp and personal knowledge of how it performs on the tests, you can use that to gauge how another would sound and perform. Use the tests to know what models you want to go out and try. Buy from a store that gives you a good long tryout period where you can try it at a few different venues in real world situations.

 

[Kindness]

Also trust the tests.

Trust tests as much as you trust testers. Trust your interpretation of the test results as well as you understand the underlying subject matter.

 

[detracti]

I for one just hope that bass gear magazine is not influenced to change their approach one tiny bit. It is awesome to have a truly consistent testing methodology applied across the board. I think it is also equally important to put those results into context, as has been stated.

We all already know that manufacturer's numbers can be inconsistent from one another. We all learn this with our ears, and experiences over time.

Case in point, numbers on the GBE 1200 moved me to post a question on the boogie board regarding why the Titan V-12 can't do 1200 watts into 2 ohms too.

In light of the bass gear results, the answer I got back makes all the sense in the world:

"when they were building the amp they were going to allow it to push more wattage at 2 ohms but it was pulling more than 20A from the wall, and was enough to blow fuses and flip breakers. So I don't know if they'll revise the V12 with more power."

Link to the thread (I'm TB Player there)
http://forum.grailtone.com/viewtopic.php?t=23606

 

[svtb15]

You sort of answered your own question that was in your first sentence with your second sentence..

You are right that is it subjective,
But don't forget, it is what is desired of the end result.

I have an electrical engineering background from decades ago, but have no clue to amp design.. But I think it would be impossible by the simple laws of physics to create and amp that has Zero distortion in any form.

Like i have always maintained in many threads , my test bed amp is a vintech preamp with a crown MT amp... even it has distortion in some form...
If you want fast, clean and big, there are not many amps on TB that can match that rig, if any at all.It is studio quality, hands down... But that is not my desired end result right now.
IMVEO

I don't think any power section would want to purposely produce any distortion. Saying it's OK because the distortion it produces will "sound" good is subjective.

 

[Coelho]

I still can't read the magazine, get the weird error I pasted on page 8...

 

[Vic]

I for one just hope that bass gear magazine is not influenced to change their approach one tiny bit.

I disagree with this as stated, and I work for the mag.

I would "adjust" your comment to say "...one tiny bit unless it truly made sense to do so after carefully reviewing all the feedback as objectively as possible."

Trust me, Tom's got some great technical folks on staff, and they're taking ALL this in. IF an adjustment, either in the written analysis, or the test methods, needs to take place. It will.

Our goal is to do the best job for everybody. I know you can't always totally please everyone, but to slam the door on the potential for improvement by being closed minded to input from qualified folks, well, that would just be foolish.

 

[detracti]

I disagree with this as stated, and I work for the mag.

... but to slam the door on the potential for improvement by being closed minded to input from qualified folks, well, that would just be foolish.

Excuse me!?

No, I don't think I'll adjust anything. The moment you start pandering to manufacturers, you've it.

Or maybe you're misunderstanding what I meant.

 

[Eublet]

Excuse me!?

No, I don't think I'll adjust anything. The moment you start pandering to manufacturers, you've it.

Or maybe you're misunderstanding what I meant.

It's not pandering. It's adjusting testing mechanisms to allow room for variables that were not previously considered relevant, or that were not even known by the testers to be considered in the first place. It's the basis of science. Test and retest.

 

[heath_r_91]

I think they should do one of those tests on the Ampeg SVT-4PRO just to see how the test varies from the manufacturer information.

 

[Fretlessboy]

This thread is strange.

I guess the only comment I have is what about those of us who don't work for Genz Benz or who aren't endorsees associated with the company (nor associated with the magazine), nor associated with any other company (i.e., just TBers who have no interest in reporting anything but what we hear) who saw the review and thought 'THAT's why these things sound different than the spec's suggest'

So with the above being stated. Should endorsers and anyone affiliated with any company in any way not post experiences and or opinions/reviews on TB about gear?

That IN NO WAY means that, for example, the 1200 doesn't sound great and isn't 'loud enough' for many situations. However, there is a rat in the soup here IMO

And where is the rat in which you speak of? I will not derail this thread because I believe tests are important... And lab findings are great things.

 

[fdeck]

This is going to get technical because the comments being made are technical in nature and I want to be as unambiguous as possible in my answers so that they do not get misconstrued. I will try to formulate my responses so that those of you interested in learning a little about amplifier design can do so along the way. I will try to hit on comments and questions brought up in this thread as well.

Bring it on! And thanks for the education. You're an engineer's engineer, and I have no doubt that your designs perform as advertised.

Limiter Operation:A limiter circuit can be very difficult to make work well, in that it does not suck the life out of the dynamics but still allows for graceful transition into the overload region of the power amp. Our limiting circuit does much more than limit the output signal. It emulates reasonably closely how a tube power amplifier overloads, the distortion characteristics, it increases the area under the output voltage curve (hence increases the true delivered power), and along with the power amp design, helps prevent sticking and chattering under saturation conditions. The limiter should be switched in when making any maximum power measurement, as it was intended to be used when the amp is being driven hard. When a maximum power measurement is being made, the limiter action must be known and factored into the true clipping point of the amp. The only reliable way to do so is to measure the saturation voltage of the output transistor to the supply rail. For this to be done, the operating characteristics of the output stage (including average CE saturation voltage) must be known. I was never asked for this data.

I learned a similar lesson the hard way, when testing an amp with a built in limiter. By habit, I had always used the hard clipping threshold, which is easy to see on a scope, as a guide for where to set the output level for a power measurement. But a good limiter doesn't willingly reveal the clipping threshold, save perhaps with a tone burst test. In the end, I was forced to conclude that without further guidance from the designer, I could not hang a definite number on the output power.

AC Line Voltage... Any testing lab that works with high powered amplifiers will be equipped with a high capacity 20 amp (minimum) branch circuit and a suitable autotransformer (Variac) to adjust terminal voltage under load.

Mental note... I will get a Variac.

Output Power versus Frequency:The review gave a maximum output power versus frequency. This is an absolutely inaccurate statement. Maximum power is based on the clipping point of the amplifier and has NOTHING to do with the frequency response of the preamplifier. The ONLY thing this test tells you is how the output power relates to the preamp frequency response relative to one data point that is not defined! Power amp output power is flat all the way across the spectrum.

Good point. My habit is to bypass the preamp when testing the power amp.

Reactive Power: Ok, here’s where things start to get technical. It’s easy, almost trivial, to design an amp that will deliver impressive NUMERICAL specs into a resistive load. The gorilla in the room is that your speakers ARE NOT RESISTIVE!!! They are reactive, meaning that there is a phase shift between the voltage applied and the current delivered through the load. It also means that there is energy storage present in both the capacitive and inductive elements. For example, the speaker stores energy in both the mechanical position of the diaphragm and in the magnetic field. The power amplifier must be able to deliver the current phase shifted from the voltage, and must be able to dissipate energy as the reactive components release energy. This is done as heat in a linear amplifier such as the GBE-1200. Something interesting about reactive loads… they appear to disobey Ohm’s law too! You can have current flow with zero applied voltage. Investigating the vector math behind the complex version of the Ohm’s law equation shows that the Ohm’s law that most people are familiar with is simplified down and all the phase angles are simplified to zero which applies ONLY to resistive loads.

AFAIK, a speaker is modeled as the coil resistance in series with all of the reactive stuff. My speaker has a 5-Ohm coil. For practical purposes, can I assume that testing with a 5-Ohm resistive load is sufficient to ensure that the same amp can drive 5 Ohms plus an additional complex impedance?

Sub-Nominal Loads:Take a close look at a REAL impedance curve and you will see that the true impedance of a speaker system varies greatly. Unfortunately for an amp designer, there exist areas where the impedance dips below the ”nominal rated impedance”, so a 2 ohm load may in fact be 1.6-1.8 ohms over a significant part of the real world bandwidth. Again, this must be factored into the power amp design as well as the power supply. This drop of 10-20% in impedance requires an additional 10-20% output current as well as thermal headroom in the output stage. The GBE-1200’s output stage can source or sink over 30 amps. This is enough to deliver close to 1800 watts into 2 ohms, meaning the amp is voltage limited rather than current limited. That’s a good thing. Combine this with reactive loads and the reasons for the large power transformer output stage and heatsink are obvious.

I suspect that failure to consider sub-nominal loads was what killed one of my DIY power amps.

 

[fdeck]

I still can't read the magazine, get the weird error I pasted on page 8...

Is your computer plugged into 120 Volts?

 

[svtb15]

I say this becasue it is heading this way from past experience....

The one thing that bothers me with these type of threads is that when some folks make accusations ,if right or wrong... Then the manufacturer then tries to verbally correct those mistakes that another witter may have made..
The manufacturer gets written up in a BS CUP violation, and either gets their post deleted, edited, or or they are banned from the site ..

That is a problem here... And as we all know that exact scenario has happened a few times.
In fact i woulld be supized if my post is not deleted fpr saying that.. but **** it!

And the CUP in not carried out in an equal and just way from what i have seen in the past. But instead seems to be slanted in some shape or form most of the time. Sure TB will boast about fairness and rules are rules.. but in the real world it is not and it is slanted..
I think the manufactures should be able to speak about their product in any way they wish when there are issues that come up like this, especially if they are cool enough to actually be in here on a daily basis to offer help and answer questions..
Just my two cents .

 

[willsellout]

I say this becasue it is heading this way from past experience....

The one thing that bothers me with these type of threads is that when some folks make accusations ,if right or wrong... Then the manufacturer then tries to verbally correct those mistakes that another witter may have made..
The manufacturer gets written up in a BS CUP violation, and either gets their post deleted, edited, or or they are banned from the site ..

That is a problem here... And as we all know that exact scenario has happened a few times.
In fact i woulld be supized if my post is not deleted fpr saying that.. but **** it!

And the CUP in not carried out in an equal and just way from what i have seen in the past. But instead seems to be slanted in some shape or form most of the time. Sure TB will boast about fairness and rules are rules.. but in the real world it is not and it is slanted..
I think the manufactures should be able to speak about their product in any way they wish when there are issues that come up like this, especially if they are cool enough to actually be in here on a daily basis to offer help and answer questions..
Just my two cents .

+1 on everything.

 

[Fretlessboy]

+2

I say this becasue it is heading this way from past experience....

The one thing that bothers me with these type of threads is that when some folks make accusations ,if right or wrong... Then the manufacturer then tries to verbally correct those mistakes that another witter may have made..
The manufacturer gets written up in a BS CUP violation, and either gets their post deleted, edited, or or they are banned from the site ..

That is a problem here... And as we all know that exact scenario has happened a few times.
In fact i woulld be supized if my post is not deleted fpr saying that.. but **** it!

And the CUP in not carried out in an equal and just way from what i have seen in the past. But instead seems to be slanted in some shape or form most of the time. Sure TB will boast about fairness and rules are rules.. but in the real world it is not and it is slanted..
I think the manufactures should be able to speak about their product in any way they wish when there are issues that come up like this, especially if they are cool enough to actually be in here on a daily basis to offer help and answer questions..
Just my two cents .

 

[detracti]

It's not pandering. It's adjusting testing mechanisms to allow room for variables that were not previously considered relevant, or that were not even known by the testers to be considered in the first place. It's the basis of science. Test and retest.

Ok, yeah. If that is what they mean, sounds good.

Looking forward to seeing more gear reviewed.

Thanks y'all for doing the Mesa cab. They don't publish full specs, so its great to see that.