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Old 17th April 2007, 04:15 PM   #11
Clipped is offline Clipped  Thailand
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i used the same subs for both amps just wired differently.

two, 4ohm per coil, dvc subs.

so thats 2 & 2=1 ohm (parralled)
and 8 & 8=4 ohm (series + parrallel)
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Old 17th April 2007, 04:38 PM   #12
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Quote:
Originally posted by Clipped
one amp has a 1 ohm load, the other has a 4 ohm load to maximize the rated power for each...

i know better than to stick the same ohm speaker per amp.

the 250 and 2150 both use the same outputs and fets and the boards are almost identical except for small differences in the powersupply section....(originally they used the same fets, but i had to change the fets in the 2150 to weaker ones in the 2150)

i havent thoroughly checked the components in the opamp paths, because i sold the 250 a while back.

the 250 has +-22 volt rails and the 2150 has +-36 volt rails

eventhough they should put out around the same power at the optimum ohm, the 2150 is louder.

the 250 has more current but less voltage
the 2150 has less current but more voltage

the 2150 is louder....and the difference is quite distinguishable.

the 250 plays the lows better
the 2150 plays quick drum beats tighter.

there must be an explanation for this...

or could it be that, the 250 requires a better current source?

this is quite a surprise to me , because i always thought the 250 was louder...but it isnt.

come to think of it, i bet its a trade off for a specific range of frequencies for each amp...lower frequency bass requires higher current.

maybe an analogy between torque and horsepower could clarify things?

Well, if you use different speakers there's the issue of different speaker sensitivities. You're still comparing apples with pliers.

If those two amps have the same gain, and the speakers the same sensitivity, they will sound equally loud. Period.
The sensitivity takes into account how many volts you need across that 4 or 8 or 2 ohms to sound at a certain level with a specified input level.
Now, if the speaker is low-ohmic and the amp cannot deliver the required current, it will clip. But that's another issue than sounding more or less loud.

If the amps have the same gain, and one speaker has 6dB less sensitivity, it will sound half as loud.
If one amp has 3dB less gain but the speaker has 3dB more sensitivity, they would still sound the same loudness-wise.
I think you get the point I'm trying to make?

Jan Didden
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Old 17th April 2007, 05:06 PM   #13
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Are both amps and speaker systems running the same crossovers and supplying the same frequency response?

For example, if one amp is running just sub-woofers and one is running full-range, the full-range system will sound louder and the sub-only will sound quiet – albeit with more/similar bass.

There are a lot of variables when running two different amps and two different speaker systems.

Also remember that power amps and their power supplies tend to be less efficient running low-Z loads. If you measure two amps delivering 250WRMS, one into 1-ohm and one into 4-ohms, the amp running 1-ohm will typically consume much more current from the 12V source.

It seems as if two amps delivering the exact same power into different loads would require the exact same input power, but efficiency falls quickly as the load drops. Once you’re in the 20-to-100+ amp range at 12V, your cable, power transformer, and device losses become significant. Class-D is an exception, of course.
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Old 17th April 2007, 05:34 PM   #14
Clipped is offline Clipped  Thailand
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janeman, i used the same subs for each amp just wired differently.

these two amps do not sound the same, the one with 36v rails is louder...im not imagining this

Dcpreamp, i think we have the same idea regarding efficiency.
the amps are (were) setup the same way.


i dont believe it either.

i think ill just blame it on my charging system, not able to keep up voltage AND amperage at the same time.

but i think we could all agree that the more efficient amp will be louder?
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Old 17th April 2007, 10:00 PM   #15
luka is offline luka  Slovenia
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Hi

There is one more thing. Let say that two amps drive same speaker each. One has supply voltage let say +/-30 and other one has +/-70. Same output power, but sound will be "louder" with the one with higher supply voltage as it has more power (voltage) reserve. I could be way off, but I think that there can be difference in sound you hear, even if scope says it is not.
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Old 18th April 2007, 10:17 AM   #16
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The rail voltage is unimportant. However it is possible in real life that the lower rail voltage is driving a lower impedance so rail sag is more.
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Old 18th April 2007, 11:24 AM   #17
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Quote:
Originally posted by Clipped
janeman, i used the same subs for each amp just wired differently.

these two amps do not sound the same, the one with 36v rails is louder...im not imagining this

Dcpreamp, i think we have the same idea regarding efficiency.
the amps are (were) setup the same way.


i dont believe it either.

i think ill just blame it on my charging system, not able to keep up voltage AND amperage at the same time.

but i think we could all agree that the more efficient amp will be louder?

What do you mean by more efficient amp?

Jan Didden
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Old 18th April 2007, 11:49 AM   #18
AndrewT is offline AndrewT  Scotland
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Where do I start?
So many here are confused.

Let's start by converting those power figures into volts and amps.
800W into 1r0 = 28.28Vpk and 28.28Apk into that 1r0 load.
600W into 4r0 = 49Vpk and 12.2Apk into that 4r0 load.
Note, that both Vpk are above Vrail so this confirms that the amplifiers are in bridged mode.

Next, an amplifier's performance deteriorates as the load resistance/impedance reduces.
A solid state amplifier can work into ANY resistive load that is equal to or HIGHER than the minimum resistance/impedance.
Both these amps will work into an 8ohm reactive load and both will perform as well as expected for a CAR type amp working into a high impedance load.

Both amps will work into a 4ohm reactive load. The performance of the 2150 (4ohm capable) will probably deteriorate more than the 250 (1ohm capable). The 250 will work into a 2ohm load and performance will deteriorate a bit more. And when asked to work into a 1ohm load the performance is going to be at it's lowest. By performance I mean any combination of the following: lower/higher distortion, lower higher damping factor, poorer/better control of the driver, poorer/better current delivery on transients, more/less sag on the supply rails and probably quite a few other characteristics I have forgotten about.

Now let's go back to the Vpk delivered by these amps.
To get from input signal to output signal the amplifiers need voltage gain. Both these amps are probably set for a different gain. That will affect apparent volume. To take account of this the gain for the two amps should be set so that an identical input signal takes each amp to it's maximum output voltage. Lets say 1Vac at input, then the 250 should be set to 20 times (=+26db) and the 2150 should be set to 36.7 times (=30.8db).
Now, set up the same speaker with the alternative impedance connections: parallel parallel for 1ohm and series parallel for 4ohms.
Try listening to those combinations. Then measure the maximum undistorted sinewave output voltage for each amplifier. How do the the measurements compare to the specifications? How do the supply rails voltages hold up when delivering power? Your answers may be in the results.

Finally. run the 4//4 from one amp and the other 4//4 from a second amp. That is an effective load of 2ohms (reactive) on both amps but select an amplifier that is 1ohm capable to get acceptable performance from your amp/speaker combination.
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Old 18th April 2007, 09:01 PM   #19
Eva is offline Eva  Spain
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Quote:
Originally posted by Clipped
i used the same subs for both amps just wired differently.

two, 4ohm per coil, dvc subs.

so thats 2 & 2=1 ohm (parralled)
and 8 & 8=4 ohm (series + parrallel)

Double voice coil speakers have different T/S parameters depending on whether the coils are wired in series or parallel. Enclosure requirements are different too, and frequency response is not the same.
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Old 18th April 2007, 09:10 PM   #20
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The 250 should produce more power but running into a low impedance load, it's going to be less efficient.

To have an audible difference between the amps, there has to be a 'significant' difference in power. To make such a difference, I'd think the rail voltage on the 250 was dropping significantly. It's was likely drawing more current from the charging system which would have made it more difficult to maintain regulated the rail voltage.

You mentioned that it did better on the lows. This could have been due to the one or two impedance peaks. The peaks would have lightened the load and therefore allowed the rail voltage to remain higher. At higher frequencies, the load impedance would have been closer to 1 ohm which would have caused the rail voltage to drop.
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