Yes, but as they do not require current limiting to prevent self destruction, more than one designer (!) has chosen to do implement very basic, text book-ish design with output powe transistors directly connected to the rails, single drive stage and a minimum of feedback and regulation. Since I have seen these design choises implemented in a number of different products from different brands, I guess that either "great minds think alike" (designers intentionally realized the simple design that COULD be chosen), or they followed an implementation suggested by Hitachi (the manufacturer). It does not matter which way, as they all (that I saw) had the same basic design, thereby also behaved in a similar way.
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Class D, power consumption, power output and creative figures
- Thread starter andruca
- Start date
- Feb 12, 2006
- 61,038
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- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
Right, it depends entirely on the circuit as I said. The circuit topology you mention can be implemented using a wide range of lateral FETs and the results are similar because the basic circuit topology is similar. There are many ways to skin this cat.
Now these devices absolutely do require current limiting, in this family it is provided on the die. It can just as easily be added as external parts with identical results. Without this current limiting, the devices will fail upon short circuit.
There are some big advantages to this family of devices and some equally big disadvantages. I can think of several manufacturers who had disastrous results due to parasitic oscillation causing "spontaneous combustion".
As I said, I have a lot of experience with this family of devices, and a handful of successful commercial products out there, tens of thousands of these devices still working day after day is a variety of circuits. I happen to like a couple variants on this topology, but not because of that specific device (which is no longer available... I got rid of the last bin I had to a tech here on the forum a few years back. There are newer, more robust versions of this device out there that when used in the same circuits sound pretty darn close without the challenges the original devices bring to the table.
What do you mean? Typically, I have seen a "fast" glass fuse on the power rail plus an inductor on the output to prevent oscillation. That is all that's needed. The negative temperature factor takes care of thermal runaway problems, too low load impedance etc.
This, and if doesn't get the tone I want at the volume I need, it's not the amp for me.
Yes, I own (and love) a BG250-115.
As a technical kind of person (but not an electrical engineer), I can kind of understand what TC Electronic was aiming for when it introduced Active Power Management into its RH and Blacksmith heads. These heads sound pretty darned good to me, so I am also a little bemused at the vitriol that gets flung at TCE every few months because of what a lot of users now think of as deception (and what TCE themselves probably agree was a mistake).
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The OP does identify the BG250 as an example of watt-fudging. So, I think it is only fair to point out that BG combo's and BH heads do not use APM.
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So... just my $0.02.
As a technical kind of person (but not an electrical engineer), I can kind of understand what TC Electronic was aiming for when it introduced Active Power Management into its RH and Blacksmith heads. These heads sound pretty darned good to me, so I am also a little bemused at the vitriol that gets flung at TCE every few months because of what a lot of users now think of as deception (and what TCE themselves probably agree was a mistake).
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The OP does identify the BG250 as an example of watt-fudging. So, I think it is only fair to point out that BG combo's and BH heads do not use APM.
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So... just my $0.02.
- Feb 12, 2006
- 61,038
- 5
- 220,968
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
A typical fast fuse is maybe ten times too slow to protect a semiconductor device without the circuit (or device) having some form of current limiting incorporated. In the case of lateral FETs, there are gate drive shunt Zener diodes that prevent the device from conducting destructive current when the source is shorted to ground. Gate to Source voltage is proportional to source current. This is the basis for Hitachi's protection circuit that you don't realize exists.
The inductor in series with the output provides lagging high frequency isolation, which helps insure closed loop stability. My comment had nothing to do with this, I specifically stated parasitic oscillations, which would be due to interactions between circuit elements, often due to unintentional cross-coupling of a signal into a place that it doesn't belong (usually due to layout). Since the impedances can be high as well as the voltage gain at high frequencies, FETs are usually much less forgiving in this manner compared to bipolar devices.
The negative temperature coefficient of the device helps but is not a solution by itself. Many amp companies and designers have proven this with their failures. There are other enhancements needed to make a stable, reliable MOSFET amp.
I have designed both MOSFET and bipolar amps, bipolar are much easier to work with, make unconditionally stable and reliable.
Fortunately in that metalcore band I sub from time to time they are really careful with volume. OTOH I have 2 other 200+BPM HC bands with 2 guitars and the loudest drummer I've ever played with and the TNT keeps up (needless to say with the DDT speaker compression engaging very frequently) as long as I'm not too far from the amp. In fact the first time I had a hard time with just one TNT was at a theater, with a ska-punk band (not too loud but too many instruments, keyboards, horn section) and mostly because I had to stand some 3m away from the amp, that's when I decided to get a second TNT. This is so I don't have to lug around my huge cabs (a couple 4x10, 1x15, 2x15, now all sold except for the 2x15) as they didn't sound as spot on to my ear and were obviously much more of a hassle to transport so they stayed at the rehearsal place for most part of the last 3 years maybe.
BTW ported cabs are more efficient on the lowend than sealed, don't know where you got the oposite information ;-)
I think you are (in a slightly condescending tone - bonus points for claiming "that you don't realize exists" about something I am not discussing!) constantly trying to steer the discussion off on a tangent. How one otherwise CAN design these circuits might be of a limited interest to some reader here, but does not change the fact that there must have been hundreds of thousands of amps produced in the 80s, using the simplified design I refer to. Many of them are still in service thirty years later...
I am trying to bring supportive information to the readers of the thread, I have said nothing controversial or factually wrong, but you still try to invalidate, question or reduce my contribution. I find it unnecessary and somewhat immature, especially from a professional.
Well, I have explained that some Trace Elliot amps sound the way they do partially due to the output design and devices used. If you think the thread would benefit from an in-depth discussion of chosing the right parameters for HexFET designs, I let you have the stage without further ado.
Thanks everybody for all the great technical information, I just ended catching up with the reading as was forced to frequently go google stuff I didn't have a clue about (don't have an electronics background at all, even have an electronics engineer brother, but he's centered his career in automation, not that much into audio).
My point is still the same, the lack of a standard to compare amps' output, once many manufacturers started deciding by themselves that the RMS way was not fair (or "over-designed"/underrating) for an instrument amp (the home audio industry abandoned RMS LONG before with their PMPOs and all that b/s). I don't care if there comes a new standard, even only for bass amps (being that bass is one of the most power demanding applications), IDK, if someone developed the POT W standard (measured as the maximum peak obtained while playing "Portrait of Tracy" with EQ set flat) and everybody used it, well, it would be fair to us comsumers and would serve us for comparing. As someone said, probably many bass amp manufacturers (probably the most deceiving) would have to go out of business. But even that would be somewhat fair, I don't trust companies that deliver a technological product but are ruled by the finance or marketing depts., sorry, I only trust engineers deciding on both tech product development and specs' measuring and publishing. Is it better that everybody claims whatever they want so that nothing can be compared? Sounds to me like the wrong kind of competition industrial capitalism loves to praise.
My point is still the same, the lack of a standard to compare amps' output, once many manufacturers started deciding by themselves that the RMS way was not fair (or "over-designed"/underrating) for an instrument amp (the home audio industry abandoned RMS LONG before with their PMPOs and all that b/s). I don't care if there comes a new standard, even only for bass amps (being that bass is one of the most power demanding applications), IDK, if someone developed the POT W standard (measured as the maximum peak obtained while playing "Portrait of Tracy" with EQ set flat) and everybody used it, well, it would be fair to us comsumers and would serve us for comparing. As someone said, probably many bass amp manufacturers (probably the most deceiving) would have to go out of business. But even that would be somewhat fair, I don't trust companies that deliver a technological product but are ruled by the finance or marketing depts., sorry, I only trust engineers deciding on both tech product development and specs' measuring and publishing. Is it better that everybody claims whatever they want so that nothing can be compared? Sounds to me like the wrong kind of competition industrial capitalism loves to praise.
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I think it is very good of you to start chasing facts and educate yourself when you have encountered something you feel you do not understand or that seems "fishy". There is a number of bass amp manufacturers that supply valid (and probably fairly accurate) data, but many have chosen their own criteria, making it hard to compare different brands.
This now extra confusing, as so many use the same output circuits, albeit with their own implementations.
Bass Gear Magazine is a great help, as they measure the amps in a standardized way.
It has been said before here, but I repeat it; the maximum output of an amp might exceed the rating on the back panel label. It is nothing fishy or strange, but based on the fact that musical signals only call for maximum signal amplitude for a fraction of the time, even when playing heavily compressed, droning bass signals.
In the PA business, a crest factor of 1/8 is typically used and I do not think any buyers feel LabGruppen, QSC, Powersoft etc are cheating.
- Feb 12, 2006
- 61,038
- 5
- 220,968
- Disclosures
- Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
You are attributing results to things that are not correct. I'm trying not to be condescending, but you keep arguing factually incorrect things... how can I help that?
For example you insist that there is no current limiting in that design, but you are ignoring the gate shunt Zener that IS the current limiting circuit which is built into some devices or added externally depending on the device.
Also, the devices are Lateral MOSFETs, not HEXFETs which are a totally unrelated device unsuited to linear operation. The Lateral device is very unique, which is why it is used in these designs.
The Trace amps you are talking about have a particular voicing, and lower feedback designs can sound louder at the expense of tightness, just one of the tradeoffs that are made in the design process.
Since one of the companies I worked for owned Trace at one time, I studied the historic evolution of the designs over the years to understand where they came from, why they were likened/disliked, and what lessons could be learned from their evolutionary path which was ultimately not viable.
Sir Alexander, you may or may not know most Americans use the word "you" not meaning YOU, but meaning anyone, someone, most people, etc. I can't speak on behalf of Andy, but I would guess he was not stating that you personally don't understand or know about the internal limiting; he's thorough and not derailing the thread any more than it was already derailed. He does us a great service and spends a lot of time providing us with accurate information.
Edit: never mind, I see he already responded. As you were. Please take it outside if it's going to get violent.
It's not the lows that get you heard in a mix, especially not a metal mix, so sealed cabs are more likely to get you heard since there's less amp energy spent pumping lows that mostly just make a dense mix even muddier when it comes to metal.
Consider also that all things being equal you need 3000w to double the volume of a 300w amp, so it's no marvel that a 600w or even 900w class D into modern smaller/lighter cabs might not sound any louder than a 300w into the typical old-school relatively giant cabs. Even the difference between a 600w Class D and 300w Class D into the same cab(s) may not be readily discernable.
I think many people expect 600w to sound "twice as loud" as a 300w amp, then incorrectly blame the topology or the ratings if it doesn't. Factor harmonic distortion, such as with tube amps, plus many other factors (including external factors such as guitarists getting louder/thicker with larger amps and down-tuning, and so too drummers taking up more sonic space with double-kick) and ...?!?!
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I'm aware that "twice" is some 10db more (more than 8x the power), also have appreciated the fact that so many metal heads still swear by their sealed 8x10 ampeg fridges (no one would tell those aren't low enough although their low end response dies around 60hz IIRC). That's exactly the reason why I prefer not so low tuned cabs, for me the chest thumping zone is indeed around 80-100hz. I think that's why I squeeze my combos in a more efficient way, instead of wasting available power in useless sub low. That might be the reason why most of the times I manage to get away with them with enough headroom. I definitely prefer the FOH system dealing with sublow (and also shake the stage floor).
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In my opinion, if it were possible to compare sealed vs. ported with all other aspects being equal, you would see the low end of ported shifted around more than more efficient. That would be relative to the entire cab's efficiency. You would see a hump, then a rapid decline in the ported cab, and a gradual degradation of lower frequencies in the sealed cab. I've seen several arguments against sealed cabs here and all were based on misinformation about generalities of the pros and cons. Sealed vs ported is a trade off. No perpetual energy involved. This is a pretty good comparison: Sealed vs. Ported Enclosures | Eminence Speaker
Thinking about this, the original question/complaint of the OP. First I should say I don't really have any pigs in this race, but I am curious. All of the amps and most cabs I've taken a serious look at I've been able to track down the information to my own satisfaction. I know there are some amp and cab manufacturers that blatantly inflate the specs (the B word coming to mind). Those types of companies are not anything most of us involved in this thread would even consider, with a few exceptions where the wattage claim is known false and ignored. I don't think we are talking about that, boutique stuff or other extremes (very cheap, very expensive, etc.). So, I would like to ask for a few specific examples of some manufacturers or models of amps, class D or not, that have false, misleading or unlabeled wattage claims. Suspected false cab claims welcome as well. I'm not out to challenge anyone, just seeking the truth behind the advertisements.
like i said, i don't know the science behind it like you and some of the other experts here. And I don't doubt for a minute that you are correct, but let me ask this- why is it that that GK seems to make those cabs (and the speakers in them) seem to come alive so much more than the ampegs? You mention EQ, and I'm sure that's a factor, but is there something more? i know enough to know that GK and ampeg voice their eqs differently, but I try my best to get a relatively flatish, even tone from every amp I play - no one frequency too severely boosted or cut, just little tweaks to try to even out the sound.
Yeah a GK amp has a more scooped sound baked in...more bottom and less mids. Ampeg has less bottom and more mids baked in. Setting the EQ's flat does not mean they are both equal due to their baked in EQ curves. The taper on the volume controls are different as well, so setting both to 'halfway' does not mean both are equal volume.
yeah i definitely know that noon doesn't mean flat on either one of those makes of amp. based on research here and my own ears I've tried to account for the baked in sound and adjust accordingly - and then tweak from there.
