What power output you claim for your gear?

Discussion in 'Solid State' started by Blue Shadow, Apr 21, 2017.


What Power Output do you claim for you unit?

  1. I use the number my tech got when he benched my unit

    3 vote(s)
  2. I use the number my tech got when he benched the unit but state it is a bench test number

    4 vote(s)
  3. I use the highest number in the specs for my unit whatever I find

    0 vote(s)
  4. I use the 8 ohm spec for my unit

    51 vote(s)
  5. I use the 4 ohm spec for my unit

    9 vote(s)
  6. I've got a flea amp, proud to be under 3.5 watts of pure tube power

    2 vote(s)
Multiple votes are allowed.
  1. Blue Shadow

    Blue Shadow I gotta get me a new title

    SE PA
    Glenn in an ADS thread, now you know which Glenn, @GD70, made this statement about his amp:
    This triggered one of my pet peeves because it makes it difficult to compare amps. I asked whether this was a bench number or a specification. He responded that it was a bench number. Here is the response I moved from that ADS 910 crossover discussion to keep that thread clean.

    Well that is how Techs test stuff and it is one way we used to 'claim' power output. The FTC rule of Nov 1974 stated any 2-channel home amp would need to be preconditioned for 30min to 1 hour (IDK which) at 1/3rd power, the most demanding power output level for the common class A/B amps. Then the power output was taken. This spec must include ALL of the following:

    Power in Root Mean Square (RMS) watts
    Impedance of the load
    Frequency response of the power
    Maximum THD for this power
    How many channels were driven

    Such as this spec for Glenn's amp collected from the service manual data: 150wpc@8Ω, 20-20kHz, 0.003% THD, Both channels driven. (more anon)

    Because of these requirements, amps got rated more conservatively but the numbers were completely comparable JVC to Crown to Pioneer.

    Issues with this test were the need for better heat sinking to avoid thermal shutoff from the preconditioning and some amps did shut down during this test.
    The impedance of the load, some makers used both a 8Ω and 4Ω load and gave both numbers. Some companies didn't. With a big enough power supply many units would double down, without that some would have very similar power at 4 or 8 ohms. The lack of a 4Ω rating is not an indication that the amp can't handle 4Ω loads, one needs to check the back around the speaker connections to see if there were any ohm ratings for the speakers.
    Then you have the frequency response of the power. If you look at the bottom units early on, these were frequently rated at 40Hz to 20,000Hz, 20Hz requiring a lot more energy from the power supply.
    The choice of how many channels were driven, well if only one channel is driven the power supply can supply just that one and there is more for the one channel to get a higher number.

    Today's techs mostly use a single frequency and and a single channel. After the unit warms up they drive the amp to clipping and get a number. This is an indication of max power output at the frequency selected somewhere in the middle of the band, like 1,000Hz, where an amp has more oomph.

    Here is my issue with this overall. Without saying whether the watts number is the benched or rated number, the number posted can not be used to determine what power your amp has for comparison purposes. Just saying 210 is to me a meaningless number. Glenn has an amp rated at 150 wpc that was tested recently on the bench to produce 210 watts, a way that both numbers can be compared to other gear if the bench number is available.

    You can look at classicaudio's site for gear for sale where they bench the units and you can see that all amps far exceed their rated power level. Example Marantz 2270, 70wpc rated, 90 watt tested. Common on smaller units is 10% over. On bigger units that increases to 20% over, 20-30 or more watts higher than specification. Now for the good part, Glenn's amp at 60 over or 40% is very healthy based on info I have found for all sorts of different amps over the years...on the web.

    More on the issue of being able to compare numbers, the numbers, if not explained, don't mean crap because of the 10-40% difference between the specification and the bench power in RMS. Guys want the big number and go with that without stating the method of test for that number. This makes it difficult to compare an older benched unit to a more recent amplifier that has not been benched. I have an early 90s amp, 150wpc rated that was upped to 185 specification during its life, that also specified 300, then 330 into 4Ω. I can't really compare that to a 210 watt amp unless I know that was the bench number for this 210 watt amp. The early 90s amp has an output current of 50 amps per channel, something that was not mentioned in older amps. There are some speakers that do demand high current. Things keep changing.

    As to the specs for the JVC M-7050 amp, the THD is 0.0004% at 150 watts at 1kHz, 0.003% max between 20 and 20kHz and 0.03% max for 20 to 100kHz. With a 300µV/sec rise time, 120dB S/N. 0.003% IM distortion and a wide bandwidth it should be one heck of an amp. It is on my radar.

    Back to this thread then, how do you talk about the power your amp has?
    Last edited: Apr 21, 2017
    tcdriver likes this.
  2. FONSguy

    FONSguy Super Member

    Sterling, VA
    My tech (Crown authorized) went through my PSA2 and redid all the power supply capacitors and tweaked everything. I had brought his company over 300 jobs in the last few years so he was extra good to me. My PSA2 does 315 - R /313 - L into 8 ohms. All distortion specs were lower than advertised. Damping factor 1000+. I guess this is why folks love it for subs.
  3. Homer4beer

    Homer4beer AK Subscriber Subscriber

    Brisbane - Australia
    How does one bench test an amp? What equipment and method is used?
  4. SoCal Sam

    SoCal Sam Lunatic Member

    'scope, sine wave generator, and something to measure output in Volts which is converted to wpc Inject sine wave and push output to clipping. Must be repeated for a range of frequencies to get to true FTC rating. I am sure I am missing something.

    Not sure I would claim anything, However, I look for amps that double down watts when resistance is halved from 8 to 4 to 2 Ohm. Headroom is momentary output and while nice is not as important to me as having a true 4 Ohm watt rating that is double 8 Ohm.
    Homer4beer likes this.
  5. Drum

    Drum AK Subscriber Subscriber

    The only way to be consistent is to use the 8 ohm published number at 20-20,000 at rated thd. Once we start with the 1khz numbers at higher thd we get into car stereo type exaggerations - of course they take it a few steps further by going to 10% distortion and adding the two channels together.

    Of course there are some manufacturers that are more optimistic than others, but almost all under rate their equipment. No harm to under rate, but if you are caught over rating you can get in trouble for false advertising and you lose the consumers trust.

    On top that, the difference between 150 watts (manuf) and 180 watts (bench test) may seem like a healthy 30 watts, but that is deceptive. The first 30 watts can create a huge amount of sound, but the last 30 watts are hardly detectable to the human ear. People freak out when they look at my M504 meters and see that .1 watts is quite loud, and .01 watts (or less) is about where I am during the work day (office system).
    chef free and DRecovery like this.
  6. SoCal Sam

    SoCal Sam Lunatic Member

    If there is a sticker that says 1000W + 1000W, stay away!
    BilboBaggins, edwyun and stish like this.
  7. Chris Brown

    Chris Brown AK Subscriber Subscriber

    Northern California
    I run most of my amps bridged, which complicates stuff a bit. Yamaha doesn't actually list simple wattage output figures for their P2200 and P2201 amps while bridged, at least not that I know of. What they do have is this graph in the product manual:


    It specifies output, while bridged, across a range of speaker impedances. It's only at 1khz however. If they had a graph that was based on 20hz-20khz I would gladly use that instead. Generally if someone is looking for a basic single number I say ~700wpc at 8ohms which is lower than what is shown on the graph, and also corresponds with estimates from others who have owned these amps over the years.
    chef free likes this.
  8. avionic

    avionic " Black Knights " Subscriber

    Fort Dodge, Iowa
    None of the above..
    Hyperion likes this.
  9. sKiZo

    sKiZo Hates received: 8641 Subscriber

    Used the most sophisticated instrument in my arsenal, and the answer is ... just enough.

    Dave_1962 and Alobar like this.
  10. Hyperion

    Hyperion Roobarb & Custard Subscriber

    Hertfordshire, UK
    I have a reasonable idea what my amplifiers are rated at, but don't feel the need to go squawking it around unless someone asks, then I give the 8 Ohm figure, and move on with my life. :rolleyes:
    Last edited: Apr 21, 2017
  11. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Glen Burnie Md.
    After I recapped my SX-1010, and had replaced certain marginal transistors in the power supply and amplifiers with better alternatives, I burned it in for a couple days on a 4+4, 4 days plus 4 hours (52 hours) at approx 1/3 power into a 8ohm 200watt resistive load dropped into a 10 gallon bucket filled with motor oil. Shortly after that I took it in to get the tuner aligned. I asked him to do an FTC style test cycle while he had it in for alignment. The amp was hotsoaked for 1 hour @ 1/3 power, then run up to clipping at specified level on the manual. With both channels running and tested the Left checked in with 124 watts 20-20, 8ohms .09%THD(onset of clipping) with the Right checking in @ 125w. 1kHz single channel testing was 139W(L), and 141(R).

    Both my 939 and 737 have performed approximately as the 1010 did, after recapping and replacement of marginally operating transistors, and out of spec resistors.
    The 939 @ 81(L) 80R 20-20, and 85(L)1kHz single, 84(R)1kHz(R). 0.1%THD
    The 737 was closer to spec @ 40&41 20-20 and 44&451kHz Single. 0.3%THD

    The 1010 was about 24% over it's FTC Rating. The 939 a bit over 12%, with the 737 about 6% over. No big deal as I've got a little bit extra, but I still quote MFR ratings.
  12. Blue Shadow

    Blue Shadow I gotta get me a new title

    SE PA
    A couple things, some may like the performance of a combo that has x watts for some speaker. It is helpful to give good numbers when asked so that others with similar speakers can get that kind of watts to use.

    Since the car stereo 10% distortion figure was brought up, let's look at a diagram of some nice vintage amp showing THD vs. WPC.

    Amp Power v distortion.jpg

    This amp is rated at 80 wpc into 8Ω 20-20kHz 0.05% THD which it achieves from 1 watt to 80 or 90 depending on the frequency. Once at the max output of the amp with distortion climbing quickly it get to 90 wpc and if taken to 10% might go to 100 wpc. The slope on those car amps might not be as steep, but close allowing them to get higher power numbers quickly as the distortion gets to ear bleed levels.

    Other than the multiple power rating methods used before the FTC got involved the home stereo guys were kinda better controlled in going for the big number. Some companies showed 3 or 4 different ratings to allow the comparison. The FTC made it easier saying use this one...but it isn't one that is good for how the amps are used, with music. But it is what we have.
  13. Blue Shadow

    Blue Shadow I gotta get me a new title

    SE PA
    Good numbers and nice to see them explained because that helps put info together when using the classicaudio.com info on a sold SX-1010 that rated at 100 wpc did 0.02 THD @ 100 and when pushed to 1% THD, something that folks have said is about clipping, the number was 118 watts in each channel. They didn't post numbers for each channel separately, just the 1000Hz both channels at 1%. Your rebuild was more thorough, I'm sure, and that may explain why your numbers are better. But as mentioned those are the last 10 watts over 100 and those don't mean a much as the first ten when it comes to getting louder.

    The SX-939 is 75 wpc, did 0.015% THD at that and 91 wpc at 1% both driven at classicaudio...vs. your unit with a few watts less, showing unit to unit variation and the reason there was some extra left in the tank when specs were written for the entire production run, not just a sample tested and numbers maxed.

    The 737, looking for it did bring up their page on testing and an explanation of the FTC testing procedure.

    Here is a 737 they did test: 35wpc @ 0.03% and 45wpc at 1% both channels driven and according to your data, Larry, this is just past clipping.
  14. GD70

    GD70 AK Subscriber Subscriber

    Northern Westchester Co, NY
    Oops, did I open a can of worms here?
    You gents are far more knowledgeable than I am. When the tech told me what it put out before clipping, I was quite surprised. He had it running straight for several days after the repairs were completed to make sure no other problems popped up, then tested it for power output. How he actually measured it, I don't know.
    Last edited: Apr 21, 2017
    stish and 4-2-7 like this.
  15. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Glen Burnie Md.
    But really isn't the single channel 1kHz kind of like saying an engine will put out 450hp without giving the RPM's and the torque behind it? All these cars today with sub 4l engines most of them 4 bangers, putting out 300-450 hp, but at btwn 4500-5500 peak rpm turbo'ed and about 175ftlb's of torque? And for 3/4 of them you can't get the spec's from the brochures! They are lucky if the engine puts out 50 honest hp @ 1500rpm. I had a 1600 VW that put out 100hp @ 3500 rpm, but was so short geared in 1st and 2nd with a 4.10 final, I started in 2nd most of the time and short shifted to 3rd by 20mph. Take a stump puller like the old 300cid Ford 6 Cylinder. It made an honest 145-150hp @ 2K but with a FLAT Torque Band of 800rpm to 3000rpm with torque of 350ftlbs and ran out of steam by 3300rpm, if my memory is correct (it's slightly off here as I haven't had a ford 6 in 20 years.) The new Ford Eco6 couldn't get out of it's way without boost. There's a lot of times I want full power just off idle and nothing short of a Cummins or a Ford 7.3L or a Chevy (Isuzu) Diesel will do the job. But I can't afford a truck that is more expensive than my mortgage is. So I put up with a 4.3L V6 2002 Chevy S-10 with 195-200hp @4500rpm and 275ftlb's @ 2100rpm with a modified computer for towing corvette servo's in the trannie, and 3.73 gears. I wish the hell I still had my 91 Ford with the 6, 4spd auto and 3.73 or whatever the closest ford put in them. I could pull stumps all day with it. And no 4x4. (I don't want to get into that rant!)
  16. Alobar

    Alobar Pulling out of the Last Chance Texaco.. Subscriber

    SE Alaska
    Just get plenty for the task at hand, that way the numbers are not that important. My wife's Jeep Patriot has a 2.4L which is enough for her to go get groceries, but I wouldn't want to tow the boat with it.
    My amp is what I would call overpowered for my speakers and current listening habits by about 10 fold I guess, but the relation of watts and db makes it impossible to be precise. It is plenty in the extreme however, and I could never clip this beast with me in the same room.
    Last edited: Apr 21, 2017
  17. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Glen Burnie Md.
    I've got just about enough torque on hand. Pull an 18ft travel trailer with it. The only thing that sucks is long up hills and the gas mileage total. Otherwise it's a good combo. I get slightly better gas mileage on the flat's pulling with my 95 Jimmy(14) and 3.42 gears(vs 12.5 in the truck, Both get in the low 20's on highway with no trailer) No corvette servo's and no modified computer. It's worse on the hills, but total mpg avg's 2.4 mpg more. But in the hills it's 7 vs. 10 with the truck. I'm thinking about putting a crate motor small block(haven't decided on which one yet, gotta keep the cost reasonable) in the truck, the trannie will take it, and the gearing is about ideal for it. I'd have to either go Carb or redo the whole electronics setup on it.
  18. Ds2000

    Ds2000 All About every cool stereo component. Subscriber

    New York City
    Factory specs only here.
  19. sKiZo

    sKiZo Hates received: 8641 Subscriber

    I pull a 24 foot camper with my Ford Ranger with a 4 cylinder and the basic drivetrain ...

    Of course, it's only 500 pounds ... <G>
  20. OMGCat!

    OMGCat! AK Subscriber Subscriber

    San Diego, CA
    I just use factory specs at 8 ohms. I'm sure they would probably bench more but it really doesn't matter.
    My Yamaha PC2602 is rated at 240/8ohms but the manual says that it would be much higher if run through the FTC test. They just rated it at the WPC that it would do all day, every day and called it good. I just say 240wpc because it's in the book so good enough for me.
    GD70 likes this.

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