Re: [Harp-L] Watts Up With That?



I agree with Greg. The difference between 40 and 50 watts isn't enough to
hear. Speaker efficiency makes a bigger difference.

On Thu, Dec 3, 2009 at 11:48 PM, Greg Heumann <greg@xxxxxxxxxxx> wrote:

> Rick - it is a fair question and you did a good job of explaining the
> issue. Expecting that all amp manufacturers are suddenly going to begin
> publishing power specs based upon a standard you propose on HARP-L (even if
> we all demand it) however, is pretty unrealistic.  If you want to make it
> happen you need to form an amplifier industry association, encourage all the
> amp makers to join it, succeed at getting them to, and put this on the
> agenda. Examples of such organizations are IEEE (engineering), the RIAA
> (recording), CTIA (cell phones.) In a previous career I had to work with
> CTIA. Getting anything done is like pushing on a rope. Get yourself a staff,
> a large budget and plenty of time to spend.
>
> In the mean time, we have  among us on this list a handful of well
> established, respected amp builders. And they all make amps that are loud
> enough for just about any situation. At which point, who cares about watts?
> It is, as you point out, not a very good way to compare amps anyway. The
> present "typical" ranges (5W, 15W, 30W, 50W) are close enough to know
> whether two amps are in the same ball park.
>
> /Greg
>
> http://www.blowsmeaway.com
> http://www.bluestateband.net
> http://cdbaby.com/cd/bluestate
>
>
>  From: Rick Davis <bluesharpamps@xxxxxxxxx>
>> Date: December 3, 2009 9:00:28 AM PST
>> To: Harp- L <Harp-L@xxxxxxxxxx>
>> Subject: [Harp-L] Watts Up With That?
>>
>>
>> I’ve been thinkin’ about watts lately… the wattage ratings that harp amp
>> makers claim for their amps. There is no standard method of measuring amp
>> power being used at all. Sometimes it seems the numbers are related more
>> to
>> marketing than to real engineering.
>>
>> There is a rule of thumb used by some amp makers that goes like this: a
>> certain kind of power tube has the potential to produce X watts of power.
>> So, if they use 6L6 tubes they claim 20 to 25 watts per tube; if they use
>> 6V6 they claim 9 to 12 watts per tube.
>>
>> But the amp circuit design has a LOT to do with the amp getting to that
>> potential. For example, a cathode biased amp has a tough time getting
>> beyond
>> 25 clean watts in a 2x6L6 amps, while a fixed biased amp may get all the
>> way
>> to 50 watts. (For now, don’t worry about the technical mumbo jumbo. Just
>> agree with me that amp watt ratings can be fuzzy.)
>>
>> You might notice I wrote the phrase “clean watts” in the previous
>> paragraph.
>> Why would a Chicago Style blues harp player want a clean amp? Well, you
>> don’t, but the amount of power an amp can generate before clipping (the
>> amp
>> starts running out of power) is an important measure of its performance.
>> Hi-fi buffs will recognize this spec from their favorite stereo: 100 watts
>> RMS per channel @ 8 ohms with .1% of total harmonic distortion.
>>
>> That last part about percent of distortion is the missing piece in harp
>> amp
>> power ratings. Tube amps are capable of producing power beyond their clean
>> power rating, and the distortion in tube amps can be a lovely sound, while
>> in solid state and digital equipment it can be very harsh sounding.
>>
>> So then… To what point do we drive a tube amp when testing for power
>> output?
>> Should we dime the amp all the way to get ultimate peak power? There are
>> several problems with that: Tone sometimes degrades considerably at that
>> level, and nobody ever plays that loud anyway because they get feedback
>> before getting there. (My 5-watt 1970 Fender Champ is excused from both of
>> these rules.)
>>
>> What power rating will make sense to amp shoppers? How can we make the
>> system more honest and meaningful? My proposition is this: All harp amps
>> makers should publish a clean RMS rating as well as their best estimation
>> of
>> real usable power, NOT maximum theoretical power.
>>
>> The clean signal should be derived by driving the amp into an appropriate
>> dummy speaker load and measuring on a scope the electromotive power output
>> in volts. Crank the amp until the sine wave just begins to visibly deform,
>> back it off to clean, and use Ohms Law to calculate watts at that exact
>> point.
>>
>> All amp makers should publish this spec, and all consumers should demand
>> it.
>> If you take your amp to a tech and it does not produce the level of clean
>> power specified by the manufacturer, you should return it for repair or
>> refund.
>>
>
>
>
>
>
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