Ampeg SVT-7 Pro TEST

[KJung]

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.'"

+1 You are obviously 'independently testing' the manufacturer's specs, and I wouldn't 'run away from that'. However, if that is what you find on the bench test, and you believe your findings, then run with it and base your 'real world' review on this finding. Somehow, you need to educate or direct your reviewers to integrate what they report with your bench test results.

If you find amps significantly vary in what you define as 'real world performance' as measured on the bench versus published specs, then your 'real world performance' write-ups should reflect that fact. We all know that amps of the same wattage spec perform very differently.

The problem is, as you know, wattage testing results really don't correlate very well with real world performance, due to all the other voicing, limiting and power management stuff built into the amp that impact the performance of the unit as much or more than a couple hundred watts either way.

I continue to understand what you are trying to do, but not sure it is doable or, at least in its present form, that useful to the reader. IMO there.

 

[beans-on-toast]

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.

The resistance can change a little as the resistors heat up, enough to affect any calculations. It is a simple matter to test the resistance at the end of the process before the resistors have an opportunity to cool off.

Under laboratory conditions, I think that it is important to standardize all conditions so that the results are reproducible. This allows you to compare apples to apples. This won't happen from one manufacturer to the next. Real world results are going to vary because there are too many factors that change. Of course, the speaker cabinet that you use is going to make a big difference in the final performance of a rig.

 

[grendle]

First, one person took me to task for comparing to a QSC amp...... saying it couldn't even make full power on a 120V line due to current.

The one I was referring to was a smaller one, either the 1202, possibly the 1602..... amps in the same category of power with the 7PRO.

They have power outputs that are compatible with the 120V line, more so in the case of the 1202, and especially with the high efficiency amp topology (class G or H, I forget which).

So they were/it was indeed relevant.............

Well, I missed the test info, so I don't know what the line volts were DURING the test....

But, I will give you dollars to drachma that the manufacturer measured the power output WITH a known 120V line. I know I would, I always did, and have no problem with that.

If there is no standard, then there is no data, no numbers. There is only a "general impression", an "opinion" even.

The reason for using a 120V line is NOT because you expect users to have perfect power. No, it is so that there is some sort of standard which makes the test reproducible and get the same results in different labs.

I have no problem with measuring an amp with an unregulated line that may drop to whatever voltage..... But I DO have a very serious issue with taking the results as being "meaningful" in terms of the measured power vs manufacturer's claims . THEY ARE NOT.

Basically, the entire big mess is a bunch of hooey, very likely caused by BGM using a non-standard test method which came up (surprise) with a lower than claimed power output.

In effect, the test was bogus, at least in terms of "checking the claimed power".....because it was not done under conditions that can be compared to the test that backs up the manufacturer's claims.

As it happens, the 7PRO is particularly likely to draw down the line due to the voltage doubler which would have been used on 120V. That causes a somewhat more "peaky" current draw.

One might, with some justification, say that the "unregulated line" test fairly represents that worse draw combined with "typical" mains outlets...... But then nobody I know uses a sine wave when playing bass, so that more continuous draw "re-invalidates" the test, even if it was "short term"...

Using adjusted/regulated line voltage isn't perfect, most amps don't have a "PFC front end" in the power supply and so don't draw a perfect sine wave at any voltage. They typically have a nasty peaky draw, and the actual power supply voltage drop can be very severe due to "clipping the peaks" of the line waveform despite the mains voltage still measuring 120Vrms..

Anyhow, from my recollection of looking at the schematic and checking a few interesting circuit features, I saw nothing glaring that would make me think it couldn't put out rated power. Certainly nothing that would obviously cut power by some large amount..... I recall checking the amp current limit and seeing that it was plenty good, for instance. Didn't look at the power supply as hard, don't recall seeing any form of a current limit in it.....but I am sure there must be one.

I guess am going to pretty much blame the test method for this whole mess, unless I come up with strong info that shows a reason not to....... even though I think the test is well-intentioned, no doubt done quite competently, and has some decent logic behind it. Just a bad combo of unit and test method.

+1

As a Metrologist for almost 20 years, if you don't have a written specified test procedure from the mfr with the same equipment used in their testing, All bets are off. You should be able to get in the ball park with general testing methods which was seen ( closer than 10% of max rated power ). There are also the tolerances of the amp, the test equipment, and the uncertainties of the test method, (wich at 5-7% total would be consistant with what was seen). Personally I'd like to see the amp hooked up to a load and see what a dranetz PP1 measures.

One good point is the testers do show repeatability or least agreement with their equipment and methods for most of the manufacturers ratings that were tested.

On a personal note , I run a 1200w power amp. It's plenty loud, has far more power than I need , and will never be cranked to full volume. Do I care if its only pushing 1000 watts instead of the rated 1200? Not one bit.
When independent testing effects the sales of a mfr's product though, you had better have your ducks in a row with ISO, 17025, and NIST or you may be in for serious trouble.

 

[JGR]

Seems like some folks still want to muddle the waters... there is a clear answer.

I work in Test and Evaluation for the military as an independent evaluator for new systems. The methodology we use is also followed in commercial industry where I have also spent a great deal of time. It is based on simple, sound engineering.

For the sake of simplicity, you can break T&E down into Developmental Testing (DT) and Operational Testing (OT).

Developmental testing is done to determine if the initial product is meeting its specified requirements. It is done by trained, qualified personnel in a controlled environment. If a product does not meet it's requirements during this phase, changes are made until it does. This would equate to the manufacturer lab testing previously mentioned. Trying to replicate this is pointless and the wrong approach.

Operational Testing is done once DT has been successfully completed. OT is performed by representative personnel, in my case certain MOS soldiers, in TB's case, musicians such as yourselves, in an environment representative of how the product is going to be used. In my line of work, if the system doesn't pass this test, it will not go further - it FAILS. The same rigor should be applied to amps.

Requirements specifications are written to an operational mode summary mission profile which specifies typical shock, transport, vibe, temperature, etc. etc. that can be expected during operation. An amp is no different - it should be designed to meet its published specifications under a specified range of temperatures, voltages, minimum input signal, etc. IF IT DOES NOT, IT DOES NOT MEET THE REQUIREMENTS.

So, testing as BGM does is absolutely the correct approach, and manufacturers should be doing the same thing before they release a product to ensure it meets its published specs. There is no need for disclaimers - if one is needed, it is by the manufacturers saying their specs are under ideal circumstances and you will never reach said performance. Lab tests are only an initial part of the development, and shouldn't be used to verify and validate performance. If a manufacturer doesn't do this, they are remiss. Period.

 

[John D]

it should be designed to meet its published specifications under a specified range of temperatures, voltages, minimum input signal, etc. IF IT DOES NOT, IT DOES NOT MEET THE REQUIREMENTS.

I disagree that, "testing as BGM does is absolutely the correct approach", since they didn't prove or disprove that the amp met its specified output under, "a specified range of temperatures, voltages, minimum input signal, etc."

This is the only issue I have with BGM's testing or intentions. Other than that one point, I think yours is the best post in this entire thread. Still, to know what you are getting, you have to establish paramaters and test to them. IMO

 

[aborgman]

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?

At 1000W output the amp is drawing well over 1000W. A normal 15 amp 120V outlet can put out 1800W. So yes, you can certainly see some significant drop.

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.

The tests are fine - and very useful. You just have to expect that they're occasionally going to get answers different than a manufacturer due to test methodology.

The difference between this and the TC situation is that you can probably get the rated power out of the Ampeg under the right test conditions. You can never get the (formerly) claimed power from the TC no matter what the test conditions.

 

[aborgman]

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.... )

Heh... I've done that before on really "peaky" loads to keep the system from chasing and going into oscillation. I always considered it kind of a dirty fix though as a way to get around properly sizing the SMPS system to handle the worst case from the load.

 

[JGR]

I disagree that, "testing as BGM does is absolutely the correct approach", since they didn't prove or disprove that the amp met its specified output under, "a specified range of temperatures, voltages, minimum input signal, etc."

This is the only issue I have with BGM's testing or intentions. Other than that one point, I think yours is the best post in this entire thread. Still, to know what you are getting, you have to establish paramaters and test to them. IMO

I was implying that the manufacturer should verify and validate spec'd performance over a range of conditions that would be typical for the user, and would no doubt encompass whatever conditions BGM is testing under. That said, I suppose BGM could also post additional detail of their test conditions like the car mags do...

In the end, the onus is on the manufacturers to meet their published specs. Until BGM came along, there was nobody to keep them in check, and as such, we've already seen that some products have taken more liberties than others. I hope BGM continues to grow and manufacturers take notice - it will benefit the consumer in the end.

 

[John D]

I was implying that the manufacturer should verify and validate spec'd performance over a range of conditions that would be typical for the user, and would no doubt encompass whatever conditions BGM is testing under. That said, I suppose BGM could also post additional detail of their test conditions like the car mags do...

In the end, the onus is on the manufacturers to meet their published specs. Until BGM came along, there was nobody to keep them in check, and as such, we've already seen that some products have taken more liberties than others. I hope BGM continues to grow and manufacturers take notice - it will benefit the consumer in the end.

+1000

IMHO any further discussion is moot. You guys have fun.

 

[Jerrold Tiers]

The BGM test seems to have been confusing..... Whatever happened, people are DEFINITELY taking this as "Ampeg lied, BGM proved it and published it..... Good for BGM for exposing the lies and keeping manufacturers honest".

So if that isn't what BGM wanted, this would be a good time to say so..... TB has sort of said that, already.

But it shows the dangers of doing reviews in this way.

I would probably have called up Ampeg, and said "hey, I'm not getting what you say, what am I doing wrong". And I would have used my own judgment about what to report if the response was not what I think it should have been.

I don't regard that as being "in bed with the manufacturer", it's just common sense.

Maybe the unit for some reason doesn't put out. Or maybe it does and the test was flawed.... Others seem to get essentially full power, at least direct thru the power amp.... which adds to the idea that there is a test issue.... Would not be the first amplifier, or Ampeg unit, that has an odd feature or two that you need to know and use to get best performance.

1) We have "focused" on the power line issue.... but it may NOT be the real cause of the difference.

2) It is very possible to mess up with an amp having a lot of volume controls, and clip an earlier stage, or inadvertantly limit the output. I have done that myself, and not noticed, only to feel like a dummy later and have to re-do the test.

3) any amp with an unregulated supply AND a power-supply interactive limiter is going to look especially bad if mains voltage changes. Might not be the very best way to make the unit..............

Seems like some folks still want to muddle the waters... there is a clear answer.

So, testing as BGM does is absolutely the correct approach, and manufacturers should be doing the same thing before they release a product to ensure it meets its published specs. There is no need for disclaimers - if one is needed, it is by the manufacturers saying their specs are under ideal circumstances and you will never reach said performance. Lab tests are only an initial part of the development, and shouldn't be used to verify and validate performance. If a manufacturer doesn't do this, they are remiss. Period.

That is very definite, "my way or the highway", and it has its place. I think it is the WRONG approach here.

Assume for the moment that mains voltage is the culprit (we don't actually know that).

We KNOW that mains voltage affects amp power.... on about every amp made, with a very few exceptions.
I can make virtually any amp look bad by adjusting voltage or letting it drop.... and justify that by saying "well, power is often bad, and the amp should put out full power even if the line voltage is low".

That's probably unrealistic.... this isn't military gear. It's consumer electronics.

If the manufacturer states a certain result with certain basic and easily reproduced conditions, then if the unit does what they say, everyone told the truth.

It isn't hard to reproduce the test. And everyone understands that if you don't give it good power the amp won't put out as well.

Maybe some settings issue is the problem...... if you turn down the pre, nothing is going to put out full power.......

The tester normally would try to find out if the preamp CAN put out enough, and then decide if that setting is reasonable.... if it takes full mids with low and high at minimum, that's not reasonable.... obviously.

But if the master needs to be near full, or a clip light should be on, etc, that's OK, in my opinion, no issue.... You have to use some sense.....

I don't recall anything odd about the 7 PRO preamp that would cut output.....

 

[Hopkins]

Ive read through this whole thread, and about half of it might as well have been written in Latin. Now my head hurts

 

[Duke21]

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.

Well said.

 

[JGR]

The BGM test seems to have been confusing..... Whatever happened, people are DEFINITELY taking this as "Ampeg lied, BGM proved it and published it..... Good for BGM for exposing the lies and keeping manufacturers honest".

So if that isn't what BGM wanted, this would be a good time to say so..... TB has sort of said that, already.

But it shows the dangers of doing reviews in this way.

I would probably have called up Ampeg, and said "hey, I'm not getting what you say, what am I doing wrong". And I would have used my own judgment about what to report if the response was not what I think it should have been.

I don't regard that as being "in bed with the manufacturer", it's just common sense.

Maybe the unit for some reason doesn't put out. Or maybe it does and the test was flawed.... Others seem to get essentially full power, at least direct thru the power amp.... which adds to the idea that there is a test issue.... Would not be the first amplifier, or Ampeg unit, that has an odd feature or two that you need to know and use to get best performance.

1) We have "focused" on the power line issue.... but it may NOT be the real cause of the difference.

2) It is very possible to mess up with an amp having a lot of volume controls, and clip an earlier stage, or inadvertantly limit the output. I have done that myself, and not noticed, only to feel like a dummy later and have to re-do the test.

3) any amp with an unregulated supply AND a power-supply interactive limiter is going to look especially bad if mains voltage changes. Might not be the very best way to make the unit..............



That is very definite, "my way or the highway", and it has its place. I think it is the WRONG approach here.

Assume for the moment that mains voltage is the culprit (we don't actually know that).

We KNOW that mains voltage affects amp power.... on about every amp made, with a very few exceptions.
I can make virtually any amp look bad by adjusting voltage or letting it drop.... and justify that by saying "well, power is often bad, and the amp should put out full power even if the line voltage is low".

That's probably unrealistic.... this isn't military gear. It's consumer electronics.

If the manufacturer states a certain result with certain basic and easily reproduced conditions, then if the unit does what they say, everyone told the truth.

It isn't hard to reproduce the test. And everyone understands that if you don't give it good power the amp won't put out as well.

Maybe some settings issue is the problem...... if you turn down the pre, nothing is going to put out full power.......

The tester normally would try to find out if the preamp CAN put out enough, and then decide if that setting is reasonable.... if it takes full mids with low and high at minimum, that's not reasonable.... obviously.

But if the master needs to be near full, or a clip light should be on, etc, that's OK, in my opinion, no issue.... You have to use some sense.....

I don't recall anything odd about the 7 PRO preamp that would cut output.....

I'm pretty sure BGM runs their numbers by the manufacturers before they publish and allow them to comment if they wish.

I'll still maintain that a product should meet it's specified requirements in the environment that it is to be used, by the intended user, no getting around that.

The difference between military and consumer products is that the consumer products are intended to be used in environments which are much less demanding, and this is taken into account in the design requirements. The process for creating specifications, allocating to subsystem and component level, and verification and validation is no different. It's simply sound systems engineering. You aren't going to completely "sailor proof" it, but a manufacturer should be able to account for things within reason. In the case of the line voltage example, a conservative approach might be to make the unit capable of producing full power down to around 115 V which is on the low end of what folks typically encounter. A less conservative approach would be to verify during developmental testing, and validate during operational testing, that it meets its specs at 120 V - this should be a threshold requirement.

 

[svtb15]

Thats very interesting and explained well.

First, one person took me to task for comparing to a QSC amp...... saying it couldn't even make full power on a 120V line due to current.

The one I was referring to was a smaller one, either the 1202, possibly the 1602..... amps in the same category of power with the 7PRO.

They have power outputs that are compatible with the 120V line, more so in the case of the 1202, and especially with the high efficiency amp topology (class G or H, I forget which).

So they were/it was indeed relevant.............




Well, I missed the test info, so I don't know what the line volts were DURING the test....

But, I will give you dollars to drachma that the manufacturer measured the power output WITH a known 120V line. I know I would, I always did, and have no problem with that.

If there is no standard, then there is no data, no numbers. There is only a "general impression", an "opinion" even.

The reason for using a 120V line is NOT because you expect users to have perfect power. No, it is so that there is some sort of standard which makes the test reproducible and get the same results in different labs.

I have no problem with measuring an amp with an unregulated line that may drop to whatever voltage..... But I DO have a very serious issue with taking the results as being "meaningful" in terms of the measured power vs manufacturer's claims . THEY ARE NOT.

Basically, the entire big mess is a bunch of hooey, very likely caused by BGM using a non-standard test method which came up (surprise) with a lower than claimed power output.

In effect, the test was bogus, at least in terms of "checking the claimed power".....because it was not done under conditions that can be compared to the test that backs up the manufacturer's claims.

As it happens, the 7PRO is particularly likely to draw down the line due to the voltage doubler which would have been used on 120V. That causes a somewhat more "peaky" current draw.

One might, with some justification, say that the "unregulated line" test fairly represents that worse draw combined with "typical" mains outlets...... But then nobody I know uses a sine wave when playing bass, so that more continuous draw "re-invalidates" the test, even if it was "short term"...

Using adjusted/regulated line voltage isn't perfect, most amps don't have a "PFC front end" in the power supply and so don't draw a perfect sine wave at any voltage. They typically have a nasty peaky draw, and the actual power supply voltage drop can be very severe due to "clipping the peaks" of the line waveform despite the mains voltage still measuring 120Vrms..

Anyhow, from my recollection of looking at the schematic and checking a few interesting circuit features, I saw nothing glaring that would make me think it couldn't put out rated power. Certainly nothing that would obviously cut power by some large amount..... I recall checking the amp current limit and seeing that it was plenty good, for instance. Didn't look at the power supply as hard, don't recall seeing any form of a current limit in it.....but I am sure there must be one.

I guess am going to pretty much blame the test method for this whole mess, unless I come up with strong info that shows a reason not to....... even though I think the test is well-intentioned, no doubt done quite competently, and has some decent logic behind it. Just a bad combo of unit and test method.

 

[tombowlus]

+1 You are obviously 'independently testing' the manufacturer's specs, and I wouldn't 'run away from that'. However, if that is what you find on the bench test, and you believe your findings, then run with it and base your 'real world' review on this finding. Somehow, you need to educate or direct your reviewers to integrate what they report with your bench test results.

If you find amps significantly vary in what you define as 'real world performance' as measured on the bench versus published specs, then your 'real world performance' write-ups should reflect that fact. We all know that amps of the same wattage spec perform very differently.

I prefer to have our "real world" or "in hand" reviews to be based, instead, upon the reviewer's real world experiences with the amp. In most cases, the in-hand reviewer does not know the results of our on-bench analysis when they write up their reviews, and I prefer it that way.

 

[JimmyM]

I got no problem with BGM testing amps their way. I also have no problem with what Gustav is saying...anyone who knows me knows I'm all for honesty in specsmanship. What I DO have a very serious problem with is the idea that if BGM tests an amp and it doesn't come up to spec in their test, that we immediately need to form a TB lynch mob, impugn the integrity of the manufacturer even if they've never given us a reason to impugn them before, call them and their children liars, and browbeat everyone who isn't ready to lynch the manufacturer with them, all without the benefit of knowing the first thing about how an on-off switch works, let alone something as complicated as a class D amp.

Yes, I know I started one with TC on here exactly like that, but any idiot could read the results of BGM's test and know that something was hinky regardless of the raw number of the wattage. The HPF and compression circuits were the smoking guns. In the end, TC did the right thing, and we all benefitted from it. And I also congratulated Uffe when he had a baby And I was the first person who went over to TC's Facebook page and congratulated them publicly for doing the right thing.

But where is the smoking gun on the 7 Pro, or the GBE1200 for that matter? Questions should be asked, absolutely. But if the TC thing hadn't happened and I wasn't an Ampeg endorser, we wouldn't be having this conversation, absolutely 100% no doubt about it. This WILL happen again to another manufacturer, and I guarantee that the firestorm will not be nearly as vicious and malicious as this one was. And while me being involved may not have been the cause of all of it, it certainly was a tremendous driving factor, as there were a lot of TC fans who came into that thread specifically to play the "nanny nanny boo boo" game. And after the personal insults I took just because I supported my bros, anyone who wants to tell me different is full of crap.

So a limiter that may kick in a little too early in some circumstances to protect the amp when you're already operating it at such an insanely loud level is what's known as a "feature" to me, and I'd be darn glad to have it rather than toast an amp. Not that I'd ever need it in a million years. If you're at the point where you're pushing a 7 Pro that hard, you need something more powerful than a 7 Pro to play your stadium rock gig.

But that's neither here nor there. Specs should be accurate and right, but Ampeg (and Genz Benz for that matter) are great companies run by very honest and good people who don't believe in fudging numbers, and I believe that with all my heart. Honestly, no doubt in my mind that this controversy will prove to be one of lowest points that Talkbass members have sunken to. Half the bass playing community thinks Talkbass is full of mental patients who don't know squat and think they do, and quite honestly, we're not proving them wrong.

 

[tombowlus]

The BGM test seems to have been confusing..... Whatever happened, people are DEFINITELY taking this as "Ampeg lied, BGM proved it and published it..... Good for BGM for exposing the lies and keeping manufacturers honest".

So if that isn't what BGM wanted, this would be a good time to say so..... TB has sort of said that, already.

Well, I feel like we've already said that several times, but there have been a number of threads on this topic, and perhaps you have not read them all. To reiterate, here: A.) it is not our goal to prove or disprove a manufacturer's specific claims for output power, B.) our output power test is designed to be as representative as possible of what a player might reasonably expect to get out on a gig (with decent AC available), C.) we never said Ampeg "lied", D.) one of my first posts on this topic stated that if an amp can hit a burst of 914 watts and hold it long enough to complete the note that I am playing, and it doesn't have a super long recovery time, that is very impressive, and I can see where they might call that a 1,000 watt amp, E.) on our subjective scale (1-5) a 3 is entirely adequate, and the 7Pro got a 3.5 (above average) rating from Tom Lees for the "output power rating", F.) The average "on bench" score was 4.06, and the "in hand" scores were 4's across the board; this makes the 7Pro one of the highest scoring heads we have tested.

I would probably have called up Ampeg, and said "hey, I'm not getting what you say, what am I doing wrong". And I would have used my own judgment about what to report if the response was not what I think it should have been.

Well, we didn't phrase it that way, but we did say something along the lines of, "Here are the results of our bench testing. Do you see anything that strikes you as amiss?" And actually, the first time we tested the Rev A unit, we said something like, "Whoa! This amp isn't behaving quite the way we expected. Here are the results we are getting. Does this seem right to you?" And of course the net result of this conversation was the Rev C version of the 7Pro.

Maybe the unit for some reason doesn't put out. Or maybe it does and the test was flawed.... Others seem to get essentially full power, at least direct thru the power amp.... which adds to the idea that there is a test issue.... Would not be the first amplifier, or Ampeg unit, that has an odd feature or two that you need to know and use to get best performance.

Again, Ampeg was given multiple opportunities to look over our test results and had no issues with them. Tom Lees and Rob Riggs had a good bit of correspondence on the issue of testing this amp, and they compared notes on how they were each using their respective AP systems. We've also reviewed several other amps using these same procedures, and they've had a chance to look those results over every time, as well.

If the manufacturer states a certain result with certain basic and easily reproduced conditions, then if the unit does what they say, everyone told the truth.

It isn't hard to reproduce the test. And everyone understands that if you don't give it good power the amp won't put out as well.

Again, almost no bass player is going to gig out with regulated AC, so we don't test with regulated AC. But we do test with good power, and we monitor voltage during the testing, so if there is any voltage fluctuation from an external condition - like line voltage at the wall dropping on its own - we retest. We probably could replicate the conditions under which Ampeg did their test, but if it involves testing the output section only (by bypassing the preamp and the limiter) and/or involves using a regulated power supply, we'd rather not do that, as in our opinion, this is not representative of how the units will be used in the field.

Maybe some settings issue is the problem...... if you turn down the pre, nothing is going to put out full power.......

The tester normally would try to find out if the preamp CAN put out enough, and then decide if that setting is reasonable.... if it takes full mids with low and high at minimum, that's not reasonable.... obviously.

But if the master needs to be near full, or a clip light should be on, etc, that's OK, in my opinion, no issue.... You have to use some sense.....

Yup, we look at stuff like that, and again, we tweak all the gain controls to get the most output, and if the clip light flickers but the amp keeps putting out, that's cool by us, too.

 

[sincity]

"IIRC the 7PRO has, in the "C" version, a supply-voltage-responsive clip limiter. I think they had an opto in earlier versions. If my recollection is correct, the "cut-out" issues might be related to that....it can be tricky to get those limiters to work just right. And if you don't, you can get "issues" with long pulse lengths and other stuff that would cause a cut-out in a class-D amp, as has been reported in "some" units..... "some" maybe being the ones with the wrong ratio of resistor values due to tolerances.

"And most overcurrent limiters have some form of time-delay on them.... if you get a long pulse from the modulator, the output current in the pulse can get too high and trip the overcurrent detector. Then you wait for whatever time is inherent in the overcurrent shutdown circuit before output resumes.

"I'm not going to get into the really gory details of the design, I don't want to, and would have to go back and get another look at the schematic. And, I don't "give away Loud's store", it's theirs, not mine.

Tech Question:

Given the two different limiters between the REV A&B models and the new REV C models, how hard would it be to replace the limiter in the older models with the new limiter used in the REV C models??

Is this a big job for those of you who have worked on amps before?

 

[nutdog]

Just an observation from a TB spectator without a dog in the hunt:

The TC quasi-watt thread had about 1800 posts, primarily with people stating they were happy with the amp and then others repeatedly making veiled insults at the intelligence of those people for being happy with a product that came from liars. The thread ended with several gifs of dead horses.

That doesn't include the other posts that went into every other thread where TC was remotely mentioned. One thread still continues.

The TC marketing deception was revealed by BGM testing. One of the arguments that other manufacturers don't do the same thing that was repeatedly and continues to be made is that the micro VR exceeded the Ampeg specs in the BGM test.

Now that an Ampeg product doesn't match the advertised specs in the BGM test, the testing method is now under suspicion by some of the very people that touted the BGM micro VR test results as proof of Ampeg honesty.

The input from an ex-Ampeg engineer is interesting. The TBer test of the amp section is interesting.

But in the TC thread everyone wanted and expected an explanation from TC. I've seen Ampeg post on TB before. There is no reason not to expect Ampeg to provide an explanation. It may very well be all legit and reasonable. So they can clear it up.

But if they don't, it will never be completely clear.

 

[B-string]

Before I take my leave of this as I see it circling and going down the drain:

I am well educated (and that is all you will get on an internet forum) to engineering and to testing (empirical data analysis) and appreciate BGM's approach. Real world testing results are a refreshing approach for consumers.
BGM gives every chance for manufactures to dispute test results. If said manufacturer then does not respond, then the fault does not lye with BGM's result.
To imply that a "real world" test, undisputed by the manufacturer is false and flawed is ludicrous at best IMHO.

If test results pre-release do not represent current release specs then the manufacturer only need state this in an addendum to BGM's test results. Again IMHO
Lets stop wagging our fingers, did this unit need special test parameters to output it's rating? We don't know and to specify exact parameters in order to reach this result is fine for engineers. Not for a consumer outside his/her cubical who is out playing music not playing a test bench? Again IMHO for as little or as much as that is worth.

Stop being defensive JimmyM, you are well respected here by more than just the few who may want to get under your skin (maybe not so much for a little fun like I do?). If you were not held in such high regard, so many of us would not have come to your aid when you had the little noise problem.