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agedhorse

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Posts posted by agedhorse

  1. 19 minutes ago, Bill Fitzmaurice said:

    Where it comes into play with respect to speakers has to do with the potential for damaging the amp. With sufficient phase shift between current and voltage the current and voltage can both be at a maximum. Combine that with low impedance and the result can be magic smoke.

    Current and voltage will be simultaneously at the maximum into a resistive load where the phase shift is zero degrees. 
     

    Where phase shift gets tricky and particularly dangerous is where it’s leading (capacitive) which is difficult to compensate for. 
     

    With highly reactive loads it’s possible to have the highest currents where the voltage is not the maximum. This has to be accounted for in VI protective limiters and SOA calculations for linear amps. For class D amps this is not as difficult.

  2. VA is apparent power which is different than watts which is real power. Real power does work, apparent power x power factor = real power. 
     

    Real power is the apparent power x the cosine of the phase angle. When the load is resistive, voltage and current are in phase and the cosine of zero degrees is 1, so VA = watts.  
     

    Since a speaker or resistive plus reactive, both electrically as well as mechanically, the phase angle is generally mostly inductive and his the current lags the voltage. The cosine of this lagging phase shift is less than 1, therefore the real power is less than the apparent power. By how much depends on how reactive. 
     

    This is all basic electrical engineering stuff, something every amplifier designer should know inside and out. It’s also something that a speaker designer should have at least a basic working knowledge of. 

    • Like 2
  3. 26 minutes ago, Salt on your Bass? said:

    Thanks for the update! Do you know if they'll be available to test and buy, or just on display only? Not meaning to be a pedant! ✌️

    Good question, I don’t have these details but expect that they won’t be set up to sell amps for another month or so. They seem to be pretty overwhelmed with the opening itself and all the work associated with launching such an endeavor. I could be wrong however, but that’s my best guess from where I am sitting. 
     

    This was just forwarded to me:  https://www.guitarworld.com/news/gibson-garage-london-preview


     

     

    • Like 1
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  4. 1 hour ago, Bill Fitzmaurice said:

    The issue with respect to speakers is that impedance isn't a constant figure, it varies with frequency. Volts x amps= watts, but since amps vary with impedance which varies with frequency power also varies across the spectrum. Even if you have the gear required to simultaneously measure both voltage and current across the audio bandwidth the result looks like this, a 2.83v signal into an 8 ohm speaker. That's nominally 1 watt, but as the chart shows there are only four frequencies out of fifteen thousand where it's actually 1 watt.

     

     

    Driver power 2.83v 8 ohms.jpg

    This reinforces my earlier comment about nominal impedance for the discussion of power being close enough, for this LF driver, if you take the average between 40 Hz to 1kHz, it’s close enough to 1W for most purposes. For power purposes, the area under the curve method is the most convenient way to visualize this for most people.
     

    Amp designers however, need to be aware of the data in this plot because it affects the absolute current through the components for a given voltage and frequency. This affects how protection circuits work as well as the demands places on the active devices themselves. 

  5. 14 hours ago, ebenezer said:

    Strange to think, this amp I believe uses the same ice 700 power module as the aguilar ag700 and the gentler magellen and yet this only developed 280 Watts at 8 ohms, whereas the others are 350-400 Watts at 8 ohms....please explain?

    Because it doesn't use an ICEPower power module. 

     

    The ICEPower module has become the industry standard because of the higher performance and reliability compared to virtually everything else on the market. That's why it's capable of 400 watts into 8 ohms, 800 watts into 2 or 4 ohms.

  6. 38 minutes ago, Stub Mandrel said:

     

    Absolutely, the example I gave used VA for the input power of an amp with an SMPSU, the power factor for an SMPSU can range from 0.5 to 0.99, so the VA rating has the potential to be significantly misleading.

    But my beef was solely with the assertion "Volts multiplied by amperes is the very definition of watts." which is demonstrably wrong.

    You and Bill are experts and sticklers for accuracy; people reading that the two of you consider VA = Watts are likely to assume that this is a fact, regardless of any context.

    Yes, I understand. I was explaining why the simplification is made with regards to the audio output power.

     

    The PF of most SMPS used in the audio amps I work with is around .9, which makes watts and VA within ~10%. That's plenty close enough for audio work, nothing precision about audio.

    • Like 1
  7. A quick update - Boogie gear is in the UK and will be on display for the opening of the Gibson Garage in London this Saturday.

     

    Dealers throughout Europe will have Boogie products in their stores in April, be sure to let them know what models you would like to see.

     

    Also, for anyone that’s able to visit the garage, I would love to hear your impressions as I won’t be able to visit. Please message me or comment on this thread.

    • Like 5
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  8. For audio output power, the VA term is simplified to watts because the amp is modeled as a close to ideal voltage source and for practical purposes it’s easy to measure RMS voltage, square it and divided by the nominal impedance (simplified to resistance) to calculate power. 
     

     

    • Like 1
  9. On 15/02/2024 at 00:43, Beedster said:

    Thanks @agedhorse, I assume an off the shelf 7-pin to 5-pin cable's not going to do the job then?

    I kind of doubt it. I don't know which pins are dropped as to how the adapter is wired. Since I can't find any docs on the original 7 pin wiring diagram, I would be just guessing and there's no need to guess wrong here.

     

    All I can find is this information on the 4 button footswitch and 5 pin DIN wiring:

    image.thumb.png.7e642024954981c8e3fb054f485eb24c.png

     

     

    • Like 2
  10. 3 hours ago, Beedster said:

    Thanks Pete, I'm not sure, I guess it depends on how it's connected, @agedhorse @sandy_r any thoughts? 

     

    There is one pin that's connected to circuit ground and 4 pins that are pull-down pins connected to the opto-isolators for each function. The footswitch circuit works by connecting each of the function pins to ground which will switch the function. A QUALIFIED tech will be able to identify the correct pins and not damage anything.

    • Thanks 1
  11. On the Presonus boards they use 2 separate inputs (mic and line). By the spec sheet for the Studio Live 16, the input clip point with the trim control at unity is +12dBu and rotating it counter-clockwise from unity increases the input clip point by 15dB to +27dBu which is 17 Volts RMS and 48 Volts P-P. I believe this is an error in the manual because it exceeds the power supply rails.

     

    This is complicated a little bit because the signal block diagram doesn't match the console silk screen values, but even using the -6dB from unity headroom yields +18dBu which is 14dB of headroom on a +4 nominal signal. +18dBu is 6V RMS and 17V P-P

     

    Note that it's important not to throw numbers around without understanding the units. Peak, P-P and RMS are all differentfro the same signal.

     

    I don't see how you can overdrive the input if you are using the board properly.

     

    image.thumb.png.582993eac191748aa92663145b372256.png

     

    image.png.627a1e9f4ee069a02ab7fde6601e6e8c.png

     

    image.thumb.png.18662472f9531242367462c05f64a84d.png

    • Like 1
  12. 3 hours ago, tauzero said:

     

    When the standard says "1/8 non-clipped output power", is that 1/8 of the measured maximum non-clipped output power or 1/8 of the claimed maximum output power?

    Non-clipped output power in rms metrics. 

  13. 8 hours ago, Chienmortbb said:

    @agedhorse Thank you for posting that snippet of the Standard. It is now close to 15 years since I retired, and with retirement I lost my access to the Standards Library at work. I should also confess that whilst Audio was the driver that led to my career in Electronics, I spent just about all my working life designing and testing Video products. While having the basic grounding, I don't have the earned experience that you have.

     

    In case anyone wants to see the whole standard, it is 425 Swiss francs or approx £400.

    The video world moved way too fast for my comfort level, you could be qualified one year and completely unqualified to design new products the next year as the technology changed and the big player drove the market. It's hard to have a 40 year career in the video business as a designer/engineer IME based on friends of mine who followed this path.

    • Like 1
  14. To respond to the message I received calling me a liar, here is where the test conditions for normal conditions are defined in the IEC 62368 regulations (for the EU). The input power to be labeled is defined to be the input power under these normal conditions (or greater if the manufacturer chooses a more stringent duty cycle because of the application). For example, for the amps I design for bass and electric guitar, I typically use more than double the minimum required under the regulations but for acoustic guitar it will be a little less than double:

     

    image.thumb.png.9eadfeddd4c2826bced1779f8828d7b8.png

     

    Also, may I ask why there's so much rudeness here? For those interested in learning, I'm providing information that most players clearly don't understand or haven't been exposed to. For those of you who don't want to learn, why challenge the facts is such a manner? 

     

     

    • Like 11
  15. 9 hours ago, MOSCOWBASS said:

    24th Feb 2024, Gibson Garage opening in London... according to email I got. Hopefully Mesa bass amps available too.

    Our hope is that the Mesa showroom will also be complete by that date, but I don't know the details. There are containers of Mesa products that have already been shipped, so we are all hopeful that this date remains correct.

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  16. First of all, these additional discussions can be valuable for those who are open to learning. that’s why some of us put in the effort to explain things the way we do. 
     

    Of course the additional information are going to be frustrating for someone who is struggling with the facts yet continues to post incorrect information as though they know what they are talking about. Clearly I poked that bear here, sorry for that.

     

    The term RMS power is defined by industry convention to be power based on rms voltage and current, it is a descriptor which is well understood and accepted by the industry. It’s also been accepted by all of the regulatory agencies (safety and EMC) for audio equipment testing.

     

    Hopefully this isn’t going to be controversial as well.

    • Like 7
  17. On 22/01/2024 at 14:44, sandy_r said:

     

    Bill, welcome to the OP: 800W Amp - 200W speaker (i guess you missed that, no worries)

     

    So - possibility of overdriven speaker - 600W excess drive over rating - severe clipping - in most other universes, effectively a square wave 

     

    Not a Robert 'Strawman' Moog in sight

     

     

    Actually, Bill’s correct on this. This example has nothing to do with clipping (in this universe anyway)

  18. On 22/01/2024 at 12:26, Bill Fitzmaurice said:

    +1. By the same token I do this loudspeaker stuff every day as part of my design work. 😉

    Yes, and so do I Bill, but you already know this. ;)

    • Like 1
  19. 6 minutes ago, Lfalex v1.1 said:

    Quite apart from judicious use of the master volume control, some sort of compression and possibly an HPF (or something that acts like one) can be a worthwhile addition.

     

    Tames nasty peaks, and prevents unwanted low frequencies that the cab can't reproduce  from making it past the HPF.

    A HPF can certainly help by reducing the level where the cabinet is most vulnerable to mechanical damage.

     

    A compressor might also help, but too much compression increases the average thermal power which may place the cabinet at risk due to increased  thermal power. With compression, a little can go a long way. 

    • Like 1
  20. 7 hours ago, sandy_r said:

     

    Well, we'll obviously have to agree to differ on that then - interestingly we don't disagree on the bottom line that the amp can be used carefully (ie. "less than 200W.") with that speaker, as long as the system is operated below clipping

     

    You are obviously very welcome to have your own opinion on why the guideline value of "1/8 max. Power" (which i showed in a photoclip) was chosen by the regulating bodies to be at that level

     

    Have a nice day 😊

     

     

     

    You may disagree with my comments about the 1/8-rated power designation for labeling, but it’s fact not opinion. Its part of every global safety regulation and in order to legally place the CE mark under the CB scheme regulations, the power consumption that’s on the label must be the minimum of 1/8-rated audio power or higher IF the manufacturer intends for the amp to be used at higher average duty cycles. Every product that complies with CB scheme (IEC 60065 or 62368 with national differences) is required to be marked in this way.

     

    I do this regulatory stuff every day as part of my design work.

    • Like 5
  21. On 17/01/2024 at 19:11, sandy_r said:

     

    the clue is on the backplate: the manufacturer is stating that the effective operating power drawn by the amp (including the PSU) is typically 200W av. just before onset of clipping (ie. less than 200W will be output to the speaker) Whether this is a meaningful measure is another matter

     

    TC_BH800.png.16c716824f024f9b2dcafc4c9bc1c17c.png

     

    So, if your speaker rating is valid, then technically your setup is ok as long as you keep the max drive level in the clean output region (personally, i'd feel happier with a higher-rated speaker, to avoid ...Oops!)

     

    This is why you have to be careful using Drive/Fuzz effects, 'cause it can mask the fact that a speaker is being overdriven - and, in the case of the BH800, there's up to another 600W where that came from, just ready & waiting to to weld the speaker coil to the magnet pole

     

    As others have said, proceed with caution!

     

     

    No, that is not what it means.

     

    That is the power that is drawn by the amp at 1/8-rated audio power in rms metrics, into the minimum rated load. It's a minimum labeling requirement by the global safety regulations (assuming that it does comply with IEC 62368-1. The actual amount drawn can't exceed 200 watts but may in fact be less to account for any duty cycle additions beyond 12.5% that the manufacturer wishes to address.

     

    It's fairly easy to take that power consumption number and calculate the approximate rated audio power...

     

    Since the average efficiency of a SMPS + class D amplifier is 85%, take 800 watts RMS, multiply it by 0.125 and divide the result by 85% and this number must be less than 200W.    (800 x .125)/.85 = 118W which is less than 200W.

     

    Now is this amp a good idea for a 200 watt/4 ohm speaker? It's perfectly fine as long as you don't have an accident, have a lapse in good judgement or have unrealistic expectations of the speaker's capabilities. It's one reason why we see blown speakers, nobody's perfect.

     

     

     

    • Like 5
  22. I haven’t heard this, my understanding is that Mesa gear will be there for the opening.  
     

    I’m not directly involved with the marketing side, especially international marketing, so things may have changed related to the construction or the phasing in of the brands owned beyond Gibson branded products themselves.  I will ask and see if I can get updated info. 

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