Ampeg SVT-7 Pro TEST

[B-string]

It seems unlikely that the caloric method would be used. So long as the resistance of the load doesn't vary a lot as it heats up during the test, it's a resistor with known resistance. Thus, the power dissipation can be inferred from a voltage measurement.

"Power" is unfortunately a confusing figure of merit for amplifiers. In most cases it's a shorthand for "average power delivered to a resistive load as computed from the voltage waveform."

Caloric not inferred.
Not a voltage measurement but a measurement of sustained output energy available.

Maybe a new standard to adopt? We had to use caloric load to certify AM and FM transmitters before shipment. Expensive equipment though.

 

[JimmyM]

And here I thought I was helping when I brought up tekdiver's wet load.

Um...

So anyway, this has all been very educational and fascinating. Rare do you get to see a new fangled amp so dissected as the 7 Pro. But it did teach me one thing...if you like an amp enough, you just plain don't care. I doubt these discussions affected sales at TC or Ampeg at all this week. OK, point taken.

 

[projectMalamute]

Conventional amps had unregulated power supplies. If the line voltage sagged to 80%, the output power would sag to 64%, give or take.

The SVT7 probably reaches a higher fraction of its rated power when plugged into iffy club wiring, because it has a regulated supply and is more efficient than class AB. But it also has to protect itself against over current if the line voltage gets too low.

But the Bowlus tests were at or over 120 volts and output was measured around 75%. Are we to believe that an SVT7 by itself on a circuit is causing a 20% drop in the mains voltage?

It is also interesting that all those other tests he has been doing with the same methodology for years were held in such high regard.

 

[B-string]

The point is Jimmy, if the caloric measurement was used, it would be a very impressive result (not to mention a very impressive test bench).

 

[someparts]

I nominate this for the nerdiest bass amp thread ever. Great stuff.

Guitards don't stand a chance in here, haha...

 

[Jerrold Tiers]

Dang JT it was me that went without coffee So basically your saying BGM's test method was flawed and to treat the manufactures claims for power output like EPA mileage claims? Seeing as how most bassists making $100 a night are not going to buy a $1200 line voltage regulator to get the manufacture's power output data?
Yes they are just numbers, but some amps tested (Ampeg branded and others) have tested above the rated claim. Are those that tested above also flawed and to be ignored? Meaning the flawed test produced an anomaly no one should expect to match.
I fully understand imperial data and repeat-ability but to suggest that a real world test should be dismissed is what I am gleaning. Because this unit that looks good on paper didn't perform as expected. We should all know that is what can happen once it leaves the lab.
I'll be better after the flux fumes clear......so don't take this as a personal attack, just some questions.

No..... Maybe yes, Or something............. I'm not sure what you are saying.

What I am saying is that if you want to get the same results that the manufacturer got, you need to test the same way.

If they test at a 120V line, which is what I would do, and what probably 99% of all the rest of the folks who are involved with this stuff would also do, THAT is the test.... If they test with settings at "x" "y" and "z", ditto.....

Basically, yes...... if you test some other way, expect a different answer.

To be very extreme, it is like complaining that a Lamborghini, or an old AMC Pacer, for that matter, doesn't meet it's typical specs when tested on a muddy dirt road. Just because there is a lot of muddy dirt road in the world doesn't make the Pacer or Lamborghini bad, it doesn't mean that the specs for the cars are a big lie (if those cars even HAVE any specs). It just means that the cars weren't made to go top speed in mud. Test them on a paved road and you get a different result.

I don't know HOW different the amp will be if tested under different conditions. YOU don't know how different it will be either.

Neither of us knows if it even has to do with line voltage AT ALL. But I'd bet it does to some degree, because IIRC the limiter is going to limit lower if supply voltage is low.... I recall it as responding to power supply volts. It won't act quite like an analog amp at low line volts.

It's possible that the line isn't the big issue, and some OTHER thing in the amp was not correctly dealt with, or some "standard" way of testing wasn't compatible with the amp. if the "standard" BGM method is without standardizing line voltage, maybe there is some OTHER stuff we don't know.

Maybe they always test with all gain knobs at 10:00 , or some other such setting.....and the 7PRO likes a different master setting. it's VERY possible that something like that is at fault.....

Or it can be, and probably IS, a combination of both.

I don't even KNOW how Loud tested the 7PRO..... I am assuming they did it the way I would.

To get any further with the issue of any internal reason, I'd have to check out a unit myself. It DOES seem like others have reported getting essentially full pop from the power amp, and said that it was harder to drive it sufficiently with the preamp....

I repeat there is no obvious reason why the amp wouldn't do spec power.... and it seems like it really DOES do it, or darn close in other tests.... so the next most likely thing is some test issue with the BGM test.

I've seen that before..... tested competitors and found gross differences, later finding that we didn't quite 'get it" when we made the first test, and rechecked with different settings to find all was well.

The BGM folks seem to be good people, trying to do right. Ditto for the PRESENT Loud people. Somewhere it sounds like there is a disconnect, and right now I am thinking it may be some issue with the BGM testing. I have no proof, it is purely my opinion, or more properly a "guess" based on reading through the large amount of info.

And I am NOT saying the BGM folks are messed up..... sounds like it may be a clash of "standard test method" with amplifier reality.....

Conventional amps had unregulated power supplies. If the line voltage sagged to 80%, the output power would sag to 64%, give or take.

The SVT7 probably reaches a higher fraction of its rated power when plugged into iffy club wiring, because it has a regulated supply and is more efficient than class AB. But it also has to protect itself against over current if the line voltage gets too low.

Ah, THIS I DO recall..... The 7PRO does NOT use a regulated main supply, so it will directly respond to low mains volts, just like every other amp except a very few that have some form of regulated supply. It has an SMPS, but that is purely used as an AC to DC converter, without any regulation. There are some pretty decent reasons to do that for high power, actually, so it isn't somehow "inferior".

For any techie wiremonger types that would "get it", there is a typical SMPS chip used in the 7PRO, BUT there is NO connection to the "COMP" terminal, and the feedback input is just tied to a fixed voltage. (if this means nothing to you, don't sweat it.... )

 

[tombowlus]

What I am saying is that if you want to get the same results that the manufacturer got, you need to test the same way.

This is very true.

And we try to be very upfront in saying that this is not our goal. Are tests are not designed to confirm or deny the manufacturer's specific tests or claims. Our tests are designed to tell a player what level of performance they might reasonably expect when they get this rig out on a gig.

I know it can cause some confusion, but again it goes towards our goal of making our bench tests as representative as possible of what a player may experience in the real world.

Jerrold is absolutely right in that if our goal was to independently check the manufacturer's claims, then we would definitely want to test in exactly the same fashion, using the same equipment and methodologies. But this isn't exactly our goal.

 

[Jerrold Tiers]

Along that line..... do you have in fact any 'standard" settings etc that might get in the way here?

Some amps like full master, some are fine with knobs on 12:00 or 2:00, that sort of thing.... And I recall some funny biz with the "FX MIX" control, like it was a subsidiary master..... I'd have to see the schematic again.... That might need to be at some particular setting.

 

[B-string]

Yes all we can do is speculate. I think maybe that is the spirit behind this thread? Not if ANYone is "pulling a fast one"?

It would seem if there was a major fault in the test performed that LOUD Ampeg would have spoken up? Maybe the shut down issue at that rev C addressed is the difference in results. The poweramp maybe capable but not under heavy stress or that stress causes a false protect? Pretty sure the spec sheet and ad copy was written before release of the unit (and we know how hard it is to get that changed).

 

[Duke21]

Reading this thread is like going to school, JT and the other veterans is giving us a master class tech lessons!

 

[JOE EDO]

Jerrod is a gem who been a mountian of "hands on knowlege" in these parts for years. TB Admins really should consider giving him his own dedicated fourm.

 

[Musicman20]

I assume this would mean that all amps, including the RH450, would need re-testing to match the manufacturers testing?

 

[f.c.geil]

To answer a few questions that were more or less directed this way:

1: I hadn't even thought of checking line voltage as a variable, but did a quick check after reading the overnight updates, and my line voltage is 115v, so it is at nominal power for the US, but not at expected "full" power. At least it's a true 60 Hz...

B: I calculate power dissipation through voltage drop, and not via caloric measurement.

Thirdly, and the best news: my friend is weakening on his refusal to allow me to use his amp, so there is still a chance that I'll be able to test it.

 

[4-string]

I assume this would mean that all amps, including the RH450, would need re-testing to match the manufacturers testing?

I don't think so. BGM's approach is perfectly valid IMO, but it is what it is, and should always be seen in context.

As far as the TC, that's a different story as TC designed the amps to have a max output of 236w to get the tone and feel they wanted. Also a perfectly valid approach, even though they could have handled the specs and documentation better.

The 7PRO and the TC both tested very well overall, and both BGM reviews were positive. No need to focus entirely on the bench test, even though I do see the point some are trying to make about published specs and accuracy.

The only amp I'd like to see re-tested is the GBE1200.

IMO.

 

[tombowlus]

Along that line..... do you have in fact any 'standard" settings etc that might get in the way here?

Some amps like full master, some are fine with knobs on 12:00 or 2:00, that sort of thing.... And I recall some funny biz with the "FX MIX" control, like it was a subsidiary master..... I'd have to see the schematic again.... That might need to be at some particular setting.

I believe Tom tries a variety of Gain and Master volume settings when he is trying to determine the max output. I'll ask him though, as we are meeting up for lunch today. It might be even easier if you two could talk directly, so if you like, hit me with your e-mail address in a PM, and I'll have Tom get in touch with you. Alternately, his BGM e-mail address is [email protected] but I know that our mail server just got switched over (along with our web page) to a new host, and I think Tom's BGM e-mail might not be up and functional yet.

 

[tombowlus]

I assume this would mean that all amps, including the RH450, would need re-testing to match the manufacturers testing?

If our goal was to double check or certify the manufacturer's own tests, then perhaps. But once again, that is not our goal. Our tests are designed to indicate what the head will do out in the field, not so much in the lab.

And in the case of the TC heads, their limiting setup guarantees that you will not get any more power out of those heads than we got, no matter how you test them (unless you disable the limiter).

 

[tombowlus]

I don't think so. BGM's approach is perfectly valid IMO, but it is what it is, and should always be seen in context.

As far as the TC, that's a different story as TC designed the amps to have a max output of 236w to get the tone and feel they wanted. Also a perfectly valid approach, even though they could have handled the specs and documentation better.

The 7PRO and the TC both tested very well overall, and both BGM reviews were positive. No need to focus entirely on the bench test, even though I do see the point some are trying to make about published specs and accuracy.

The only amp I'd like to see re-tested is the GBE1200.

IMO.

+1 Great post, which I should have read before I replied, LOL!

Regarding the GBE 1200, we did in fact retest it. The results were somewhat better than what we got with our earlier testing protocols, but still not quite to Genz-Benz's specs. But again, we perform a "gig test," and they perform a "lab test," so some variation is to be expected. We will be publishing new measurements for all issue #1 heads at some point. In all honesty, we've had too much content in each issue to leave any room for it, but sooner or later, we'll cram it in there.

 

[KJung]

This is very true.

And we try to be very upfront in saying that this is not our goal. Are tests are not designed to confirm or deny the manufacturer's specific tests or claims. Our tests are designed to tell a player what level of performance they might reasonably expect when they get this rig out on a gig.

I know it can cause some confusion, but again it goes towards our goal of making our bench tests as representative as possible of what a player may experience in the real world.

Jerrold is absolutely right in that if our goal was to independently check the manufacturer's claims, then we would definitely want to test in exactly the same fashion, using the same equipment and methodologies. But this isn't exactly our goal.

Unfortunately, when you publish your test results, there would be VERY few readers who would NOT think that you are are, in fact, 'independently checking a manufacturer's claim'. That is what you are doing IMO. By definition, if you get a different result than the manufacturer (even though that different result could be an artifact of a different test method, or just a 'learning curve' of being new to this whole thing) you are implicitly (and actually explicitly) stating that the manufacturers specs are NOT representative of 'expected performance in the real world'.

This would be fine, except that in EVERY case, your 'real world' review actually corresponds much closer to the manufacturers spec than the 'performance' measures you found in your bench test.

This results, as we all see, in all sort of confusion and drama, and IMO misinformation for the consumer. As you are seeing, test it one way, you get this answer, test it another way, you get that answer.

 

[tombowlus]

By definition, if you get a different result than the manufacturer (even though that different result could be an artifact of a different test method, or just a 'learning curve' of being new to this whole thing) you are implicitly (and actually explicitly) stating that the manufacturers specs are NOT representative of 'expected performance in the real world'.

If an amp is rated at 1200 watts, and can do that on a regulated power supply when tested in a specific fashion, but it can only get 800 watts when using an unregulated power supply tested in a manner that is designed to be more indicative of performance in the field, then I would agree that in that scenario, the manufacturer's specs are not "representative of 'expected performance in the real world.'"

 

[f.c.geil]

Perhaps there should be an explanation of test methods attached to amp tests, explaining that you are trying to show real world performance, and that the manufacturer may have used different methods to achieve their (possibly equally valid) results. Just a thought.

Perhaps I should fire up a generator, crank it up to 120 vac, see what numbers I get. Nah, that seems like too much work than it's worth.