Watts or Whatts..... What makes the difference

[a.wayne]

Hello Gents,

Wanted to run this by the forum and see what are the collective thoughts in regards to this and the differences between these 3 amplifiers. All 3 amplifiers are using BJT's all are A/AB bias 2 are rated into 2 ohms one is rated only into 4 ohm ..

Amplifier A is rated @ 300watts into 8 ohm is a mono bloc , with 20 output BJT , 70,000 uf and a 1.7 KVA trannie. rated into 2 ohm

Amplifier B is a stereo amplifier rated @ 200 watts into 8 ohm has 12 BJT channel, has 140,000 uf total and a 2.8 KVA trannie . rated into 2 ohm

Amplifier C is also a Stereo amplifier rated at 250 watts/ch and has 24 BJT /ch , 120,000 uf total and a 1.5 KVA trannie .. rated into 4 ohm


Now the test being conducted is into 4 ohms, Amp A and C is ran at 500 watts, Amp B is at 455. of course 1 ch of the stereo amplifiers are being used. While all 3 amplifiers are stable, measure very well and have no issues there is a noticeable difference in the heat being put into the dummy load.

Amplifier B is able to make the load turn cherry red , amp C get's it pretty hot , just not as hot as amp B and with Amp A there is very little heat compared to the others, the dummy load is much cooler.

The difference is very noticeable when listening also, Amp B easily powers the speakers the best, is effortless and has the best dynamics of the 3 with Amp A being the worst.

What is making the difference, design topology, PSU storage , tranny size, bias, amt of BJT, type of BJT's ?

Watts or Whatts...


Regards,

[mnemneth]

Hi there.
First off, let's be clear.

Assuming you are comparing like with like, a Watt is a Watt, there is NO difference.

The problem lies with how YOUR Watts are being measured.

There is massive difference between Watt(average, usually called Watts (RMS)) and Watts (music power) or the worst of the lot, Watts (PMPO, Peak Music Power Output).

Assuming your really ARE putting the same "kind" of Watts into your dummy load, the load MUST reach the same temperature! There can be NO difference!

How are you measuring the Wattage output of each amp?

Are you simply using the same input voltage and assuming the power out is correct?

If what you have posted is correct, then one or more of the amp manufacturers is being economical about the power rating of their product.

Sandy

[a.wayne]

Yes , the amt of power is as listed, ( we measured the voltage, meter/scope) the heat generated by amp B was tremendous vs the others the dummy load immediately got cherry red , not so on the others and not so on Amp A which just got it hot in that same time period.

I have experienced this in the past on custom made amplifiers with fully regulated PSU and would have thought the PSU was making the difference , but Amp A has a bigger PSU than Amp C, yet it does not respond the same way on the dummy load nor when listening .

I will add that Amp A has the least amt of heat sinks and does get hot faster than the others, but we never ran the full power test long enuff to push it into temperature deficit...

Ohh I believe Amp A has the highest bias amt also , i will try to confirm this..

[wakibaki]

Originally Posted by a.wayne

Yes , the amt of power is as listed,

You're pulling our plonkers, ain'tcha?

The facts as you relate them are inconsistent. You've either made a mistake, or you're dissembling.

w

[Speedskater]

Were all the amps tested at the same test tone frequency?
Did you always use the same dummy load configuration and the same speaker wires?
Did you measure both AC and DC voltages at the dummy load terminals?
Did you put the scope probe across the dummy load terminals? Did they all have sine waves?

[a.wayne]

Originally Posted by Speedskater

Were all the amps tested at the same test tone frequency?
Did you always use the same dummy load configuration and the same speaker wires?
Did you measure both AC and DC voltages at the dummy load terminals?
Did you put the scope probe across the dummy load terminals? Did they all have sine waves?

Hello Yes ..... to all, except DC voltage at dummy load .. why?

Originally Posted by wakibaki

You're pulling our plonkers, ain'tcha?

The facts as you relate them are inconsistent. You've either made a mistake, or you're dissembling.

w

I guess you don't do much testing ....


I have noticed this difference on others before , going back as far as 30 years ago, I'm not asking to be convinced or to convince anyone it does happen, it does , I'm asking to see what makes one amp "stronger " than another , if you have never tested before nor ever experienced such then you would never know of what i speak...

[AndrewT]

repeat your measurements using 16r0 cold dummy load. Then add another 16r0 dummy load in parallel and repeat the measurements again from cold.

Add an 8r0 to create an effective 4r0 loading and repeat the measuring.

Finally add a 4r0 to create a 2r0 load and repeat the measurements from cold.

If the amplifier or the loads get warm, you're taking too long to measure the output voltage.

Now compare the maximum unclipped output voltage for each of the loads from 16r0 down to 2r0 on one amplifier. Convert all the voltages to dBV and plot a graph.
Do the same for the other two amplifiers and superimpose their plot on the original graph.

You will see which are managing to drive high current into the load while maintaining output voltage.
The ones that can't do this well have been lying.

This is for short term continuous sinewave.

If you have the facilities you can use a 10% duty cycle sinewave test signal and repeat all the measurements. Again the plotted results of dBV vs Rload will tell much of the story.

BTW,
the 2ohm rated amplifiers should safely drive maximum power into 1r0 load. Worth checking this as well. Don't try this on the 4ohm amp unless you are very confident you won't damage it.

Another BTW,
the mains input voltage must be the same for all tests.

[wakibaki]

You're not measuring the power across the dummy load, otherwise it can't happen the way you describe. That's all she wrote.

w

[wakibaki]

Originally Posted by a.wayne

I guess you don't do much testing ....

Enough to know your test regime is faulty

w

[a.wayne]

Originally Posted by AndrewT

repeat your measurements using 16r0 cold dummy load. Then add another 16r0 dummy load in parallel and repeat the measurements again from cold.

Add an 8r0 to create an effective 4r0 loading and repeats the measuring.

Finally add a 4r0 to create a 2r0 load and repeat the measurements from cold.

If the amplifier or the loads get warm, you're taking too long to measure the output voltage.

Now compare the maximum unclipped output voltage for each of the loads from 16r0 down to 2r0 on one amplifier. Convert all the voltages to dBV and plot a graph.
Do the same for the other two amplifiers and superimpose their plot on the original graph.

You will see which are managing to drive high current into the load while maintaining output voltage.
The ones that can't do this well have been lying.

This is for short term continuous sinewave.

If you have the facilities you can use a 10% duty cycle sinewave test signal and repeat all the measurements. Again the plotted results of dBV vs Rload will tell much of the story.

BTW,
the 2ohm rated amplifiers should safely drive maximum power into 1r0 load. Worth checking this as well. Don't try this on the 4ohm amp unless you are very confident you won't damage it.

Andrew you have missed the point and all the amplifers have been tested at 1r ( speaker load ) they all drive it no issues. on the bench a 4 r load was used, the test does not have to be conducted the way you described , my question again is what makes one amp stronger than the other,
1. PSU?
2. Topology?
3. output stage
4. All 3

which would be of the utmost importance?

Originally Posted by wakibaki

You're not measuring the power across the dummy load, otherwise it can't happen the way you describe. That's all she wrote.

w

Waki.. read thru please .. we used a scope ....