Show me your dummy load(s)!

[Alan0354]

Have to look that up, but remember that maximum power dissipation in the amp doesn't happen at full output, but somewhat less.

Yes, I saw the analysis on DIYaudio before, I just forgot........old mind keep leaking. It is something that you have to write an excel file to step through the output voltages with given rail voltage.

I am almost sure that even my new chassis cannot take the maximum dissipation of my 120W amp continuously.

One thing people never even talk about, the speakers, can they even handle the published power handling. I played guitar, we blow big speakers with much lower power amps. Look at all the JBLs that advertised for over 100W per 12", they blow and blow with amps less than 100W. Those little hifi speakers advertise 100W or more on a 6" woofers?!!! I bet the cone will pop out and fall in your lap if you run 50W 60Hz for a few seconds.

 

[rottalpha]

Yes, I saw the analysis on DIYaudio before, I just forgot........old mind keep leaking. It is something that you have to write an excel file to step through the output voltages with given rail voltage.

I am almost sure that even my new chassis cannot take the maximum dissipation of my 120W amp continuously.

One thing people never even talk about, the speakers, can they even handle the published power handling. I played guitar, we blow big speakers with much lower power amps. Look at all the JBLs that advertised for 100W per 12", they blow and blow with amps less than 100W. Those little hifi speakers advertise 100W or more on a 6" woofers?!!! I bet the cone will pop out and fall in your lap if you run 50W 60Hz for a few seconds.

Wasn't it that at least in the case of class A, idling or full power, the heat dissipation is about the same??

 

[ConradH]

I think that's correct, or close to it, on class A.

Speaker power ratings have always been a mystery to me. Some drivers are rated for a hundred watts or more. Efficiency is low, so most of that has to be dissipated as heat. How in the world even a medium large voice coil could dissipate 100 watts and not catch fire within a minute or two is beyond me. They just can't be talking about continuous power.

 

[Binkman]

the master... "conrad" speaks truth. I think a whoever designed the 'gain' or volume without 'idiot' limiters was how you sold a new amp. hot shot surfer with power amp and pooph! buy a new one. Now lets say a service amp without audio scaled much higher in amps and v's or compare the auditorium service amps with audio and getting repaired or serviced. To me it's public open or closed in room listening. E.g. I can't crank a modest marshall amp (valvestate vs 100) just a tad and wake the dead in a decent 24x30 room. not even 10:00 am on the vol pot.

Interesting as a 'time period' was mentioned.. how long can a system last perhaps cranked? lol meaning saturation? probably has to do with how saturated the owner is without vol. knob 'training wheels'.

 

[Alan0354]

Wasn't it that at least in the case of class A, idling or full power, the heat dissipation is about the same??

Yes, I edited post #39 later to include the class A using Krell as example. That's the reason the big Krells are so big and heavy. That KSA250 is like 150lbs!!! This is a review and picture of the KSA250:http://www.stereophile.com/solidpoweramps/191krell/index.html#YUROubhyqiqtQh9I.97

I almost bought one, one was on ebay for $1850, it was a very good price. BUT after finding out it draws 12A idle and 150lbs, I passed. I got the Nakamichi PA-7 that was designed by Nelson Pass, that is almost the same as his Threshold S300 Stasis amp. Even the PA-7 is no light weight, it must be like 70lbs. with huge heatsink. Nelson Pass tell people to adjust the idle current so it's not too hot that you can put you hands on it for a while, I adjusted to 700mA idle current and it heated up the living room. I had to back down to 350mA as the service manual suggested.

 

[Alan0354]

the master... "conrad" speaks truth. I think a whoever designed the 'gain' or volume without 'idiot' limiters was how you sold a new amp. hot shot surfer with power amp and pooph! buy a new one. Now lets say a service amp without audio scaled much higher in amps and v's or compare the auditorium service amps with audio and getting repaired or serviced. To me it's public open or closed in room listening. E.g. I can't crank a modest marshall amp (valvestate vs 100) just a tad and wake the dead in a decent 24x30 room. not even 10:00 am on the vol pot.

Interesting as a 'time period' was mentioned.. how long can a system last perhaps cranked? lol meaning saturation? probably has to do with how saturated the owner is without vol. knob 'training wheels'.

For guitar, I think you can crank it up all the way and strum chords all day long without worry about burning. I looked on the scope, even with severe clipping, the signal level falls off big time after the initial attack. No where close to constant output. Based on result, I never blew an amp. I had a 100W Marshall Plexi triple stack, a Fender Twin and Marshall JCM900. Never burn one performing yet.( long time ago). I think the one instrument that can burn amp is the organ. If you hold one chord, that is like signal generator going and going at constant amplitude.

People don't realize how loud is 10W or 20W. Get a Fender Deluxe and crank it up, it's only 20W, people will realize how loud is 20W. Both guitar amp I designed are only 30W or so each. I use 6L6, but I lower the +B to 390V to keep the power down and I designed in power scaling so I can reduce the output power down to below 5W.

 

[DrumminDaddy]

The oil barrel was wild!

Hehe..."caution, amplifier waste."

Saw a similar deal on YouTube.

 

[whoaru99]

I think that's correct, or close to it, on class A.

Speaker power ratings have always been a mystery to me. Some drivers are rated for a hundred watts or more. Efficiency is low, so most of that has to be dissipated as heat. How in the world even a medium large voice coil could dissipate 100 watts and not catch fire within a minute or two is beyond me. They just can't be talking about continuous power.

I thought straight, old school Class A was typ. 20-25% efficient. So, to have 100W output capability you're dissipating 400-500W.

About voice coils, yeah, some can apparently handle quite alot. Granted, they're sound reinforcement drivers, but the JBL 2241s I have I believe are rated 600W continuous (i think JBL defines continuous as for 8 hours). They have a whole white paper on their power rating methods. I think it's largely based on some EIA (or is it IEC?) standard.

 

[Binkman]

Alan0354 LOL.. I know what you're saying. I guess I'm reflecting on power vrs fried chicken amps. output transistors come in low med and high and reflecting on how many threads in the last month alone are transistor related. (and or fried condition.)

 

[Alan0354]

I thought straight, old school Class A was typ. 20-25% efficient. So, to have 100W output capability you're dissipating 400-500W.

About voice coils, yeah, some can apparently handle quite alot. Granted, they're sound reinforcement drivers, but the JBL 2241s I have I believe are rated 600W continuous (i think JBL defines continuous as for 8 hours). They have a whole white paper on their power rating methods. I think it's largely based on some EIA (or is it IEC?) standard.

All I know is my JBL K120 blew in my Twin within the first year. I had only one JBL parallel with one original Twin cheap speaker, both were 8ohm. I did not play that loud. The JBL voice coil deformed and rubbed the frame. I had to recone it, I found out there were so many blown JBL that needed to be recone the tech even had stocked stacks of voice coil ready to be used. JBL since went of out style in the 70s. They were rated like 200W per speaker, can't even handle 50W. Celestion is a whole lot better even though they were not rated as high power. I am using Warehouse Speakers in my amps. They sound really good and reasonable priced.

I cannot ever trust JBL nor all the other people. They now belong to the antique, nobody use JBL in musical instruments.

 

[whoaru99]

I cannot ever trust JBL nor all the other people. They now belong to the antique, nobody use JBL in musical instruments.

They are very well documented in their power rating methodology. It can't be categorically dismissed unless you've made an apples to apples comparison in the power, duration, and signal content. It all factors into the rating.

Deviating from the test method used for the ratings negates any other conclusion drawn about the ratings. You know that.

 

[miniman82]

100w audio load recepie: power resistors salvaged from a Sony TV, old military case, fan cooling from a computer power supply, aluminum diamond plate. The resistors are 4-ohm/20w in series, but with forced cooling they handle a lot more. I've pushed 130w through it recently without I'll effect, makes a nice heater when you hook it up to a Mac amplifier. lol

Total cost: maybe $6 worth of diamond plate?

 

[Alan0354]

They are very well documented in their power rating methodology. It can't be categorically dismissed unless you've made an apples to apples comparison in the power, duration, and signal content. It all factors into the rating.

Deviating from the test method used for the ratings negates any other conclusion drawn about the ratings. You know that.

All I know is they blow, everybody blew theirs. The way they do their rating is not good. That's the bottom line, they blew so bad that's why they belong in the history in the last 30 years already. If their advertized rating is anything close to the real life, they should had stood up to a Fender Twin with only one speaker. I doubt they can last 30 minutes of the full on Twin Reverb.

Those K or D120 might be able to last a little more if you run just say 60Hz sine wave. The voice coil is 4" wide with paper voice coil form running in a very narrow gap. If you run one low frequency, it might hold up, but if you over drive with clipping with a power chord, the voice coil just jump and bent out of shape. The diameter is so large it doesn't take much to get out of shape and start rubbing the frame and destroyed. It was such a bad design even a novice can see it.

I am talking as a working musician in the real world that see all the bad JBLs back it the 70s. Funny when I went to the tech, he had a big bucketful of bad JBL 4" voice coil cut out he even gave me a few to take home. You look at one and you'll know exactly what I mean and why it failed, how easy it bent out of shape.

More importantly, they don't sound good for the rock over drive distortion. They might be popular for the 60s surf music like the Ventures and Beach Boys with crystal clear guitar sound with reverb, but when the hard rock music came in style, JBL just did not cut it. The middle aluminum dome was the problem. It's more a full range speaker than guitar speaker. When over drived, it sounded more scratchy. You want the Celestion Green Back type of speakers for rock. By mid 90s, JBL was non existence.

 

[sc2dave]

I'm new here and VERY AUDIO IGNORANT. How ,why do you place loads? Do you place them on unused terminals?

 

[Alan0354]

I'm new here and VERY AUDIO IGNORANT. How ,why do you place loads? Do you place them on unused terminals?

Load are for few different purpose, people use it to test whether the amp can actually drive the load at rated power like we have been talking about here. For me, I use it to test distortion. Power amp distortion (THD) increase with decrease load resistance. So we test the THD with a given load. That's how manufacturers spec the THD of amps. They usually rate amps with say 8 ohm load. Better ones rate amps at 4ohm or even 2ohm load. Dummy load is also used to test stability. You need to make sure the amp is stable with load.

For solid state amps, you usually don't require load for the amp to function. Don't even thing about not using load for tube amps as you can burn the output transformer and the power tubes.

 

[whoaru99]

All I know is they blow, .

Exactly my point.

 

[whoaru99]

If their advertized rating is anything close to the real life, they should had stood up to a Fender Twin with only one speaker. I doubt they can last 30 minutes of the full on Twin Reverb.

I'd suspect you're correct on this, considering the rating for D130 is only 25 watts based on the literature I just looked at. Rather than a poor speaker design, it sounds like misapplication to me.

 

[whoaru99]

The diameter is so large it doesn't take much to get out of shape and start rubbing the frame and destroyed. It was such a bad design even a novice can see it.

It was actually a brilliant design and execution for the time. Quite an accomplishment, really.

 

[rottalpha]

Load are for few different purpose, people use it to test whether the amp can actually drive the load at rated power like we have been talking about here. For me, I use it to test distortion. Power amp distortion (THD) increase with decrease load resistance. So we test the THD with a given load. That's how manufacturers spec the THD of amps. They usually rate amps with say 8 ohm load. Better ones rate amps at 4ohm or even 2ohm load. Dummy load is also used to test stability. You need to make sure the amp is stable with load.

For solid state amps, you usually don't require load for the amp to function. Don't even thing about not using load for tube amps as you can burn the output transformer and the power tubes.

Looking at THD under load goes without saying....but first you need the load and the equipment.

I know, this is a subject for a different discussion....but does anyone here currently have of the Panasonic VP-77XX audio analyzers in their possession, or acess to one?

 

[miniman82]

No but I have an HP 334A, is that good enough?