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Old 26th May 2015, 06:40 AM   #1
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Default Power at 8ohm, 4 and 2....

Can anyone explain to me why it is a good thing to have amp A over amp B?

Amp A

8ohm -200w
4ohm - 400w

Amp B

8ohm - 200w
4ohm - 320w

In other words the wattage doubling down as ohms do?

Thanks!
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Old 26th May 2015, 07:11 AM   #2
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Amp A looks to have a regulated supply - so its power supply's not sagging under heavier load. A stiffer power supply is generally regarded as a good thing to have.
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Old 26th May 2015, 08:27 AM   #3
DF96 is online now DF96  England
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If the figures are for sustained sine wave drive, then it may be that on occasional musical peaks that amp B (with an unregulated supply) can go to higher power than amp A. It all depends on whether you want to listen to real music or manufactured music with no dynamic range. The bare power figures don't give enough information on their own for someone to make an informed choice.
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Old 26th May 2015, 12:52 PM   #4
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well .... not so many amplifiers i ve seen in the Cheap pro area with regulated power supply so i don't think that this is the issue here ...

Since we don't know the models and so on the all thing is hypothetical ...

In reality though you can have double the Watt in 4 ohm load given :
--- that power supply will manage
---Number of outputs will manage both current and thermals
---VI limiter will allow that

In cheap pro amps this will never happen or it may happen on resistive tests , In reality and with a speaker as a load VI limiter will not allow that much power like double the wattage in Ohm

To the OP i could trust more the second amplifier since its spec looks like a number that has been measured not calculated ...Probably the limiter doesn't allow double the Wattage on 4 Ohm due to the above limitations ..

Kind regards
Sakis
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Old 26th May 2015, 02:17 PM   #5
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Quote:
Originally Posted by zenpmd View Post
Can anyone explain to me why it is a good thing to have amp A over amp B?

Amp A

8ohm -200w
4ohm - 400w

Amp B

8ohm - 200w
4ohm - 320w

In other words the wattage doubling down as ohms do?

Thanks!
In answer to your actual question. If both amps are being measured in the same manner then amplifier A will have better output power into lower impedance.

Due to the fact they are likely not being measured in the same manner there are other things you can look at. Do either of the amplifiers give a 2ohm rating? Are the measurements with "both channels driven" this is a much better indicator of the power supply size? What are the THD numbers at the rated power outputs?
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Old 26th May 2015, 02:28 PM   #6
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In answer to your actual question. If both amps are being measured in the same manner then amplifier A will have better output power into lower impedance.

If they tell the truth ...which in most cases they don't .....also measured ??? i don't think so ...i think this is coming only form the specs so amp B probably says the truth ...
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Old 26th May 2015, 02:40 PM   #7
wwenze is offline wwenze  Singapore
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Just a design decision... of how much current and voltage the parts can output.

I pick whichever gives me better performance at 1W. The difference between 1W and 10W is just 10dB. Same goes for 10W vs 100W. 320W vs 400W is negligible in terms of SPL.

Add: Overall, amp A has more capacity, because if we assume that both amps are limited by voltage at 8 ohm, then at 4 ohm, amp A is still limited by voltage but amp B is limited by current. If you go further down to 2 ohm, you may squeeze even more power out of amp A, but most likely you'll get less power from amp B.
Just as it is good to have additional current capacity, having additional voltage capacity is also good for sound. However both amps have the same max output voltage (since power into 8 ohm is the same) so I grab the one with more current capacity.

This is before we consider another limiting factor of power, which is heat (or cooling). Some amps have a 8ohm/4ohm switch that reduces supply voltage when 4ohm is selected.

Last edited by wwenze; 26th May 2015 at 02:49 PM.
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Old 26th May 2015, 02:42 PM   #8
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by east electronics View Post
If they tell the truth ...which in most cases they don't ...
More meaningful would be to find out 1) what is the rail voltage? 2)what is the VA capability of the transformer? 3) how much capacitance? and 4) how many output transistors in parallel?. The answers to those qustions will see right through the lies. Back in the day, we used to judge amplifiers by weight.
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Old 26th May 2015, 02:45 PM   #9
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Originally Posted by wwenze View Post
Just a design decision... of how much current and voltage the parts can output.

I pick whichever gives me better performance at 1W. The difference between 1W and 10W is just 10dB. Same goes for 10W vs 100W. 320W vs 400W is negligible in terms of SPL.
In a production amplifier its a cost issue. Massive power supplies and extra output transistors are expensive.
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Old 27th May 2015, 05:48 AM   #10
djk is offline djk
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"Amp A looks to have a regulated supply "

Uhh...amp A is understating its 8Ω power.

Which sounds better?

A listening test is in order here.
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