If you have any questions about this amp, please ask, I used to have one and designed and built my own version from scratch. This amp has an interesting background in that it was designed using an input/output null distortion analysis to be the "world's most perfect amplifier". It actually has a "linearity adjustment" designed to optimize it into your particular speakers.
The proof of the puding...
This is my favorite test,that i use for so long...with it you can see all distortions ( invented or yet indiscovered)...it was amazing to do this test in some very expensive comercial amps.. hehehehe!
You can do the test even with music signals...and with a speaker load...in real conditions of operation!!
In a nutshell...if the input is equal to the output the amp desapear from the equation...as it is tottaly transparent...so time to look at the source and speaker!!
So simple and so true!!
But i wonder who is searching the truth in audio...just a fews!!
Cheers
This is my favorite test,that i use for so long...with it you can see all distortions ( invented or yet indiscovered)...it was amazing to do this test in some very expensive comercial amps.. hehehehe!
You can do the test even with music signals...and with a speaker load...in real conditions of operation!!
In a nutshell...if the input is equal to the output the amp desapear from the equation...as it is tottaly transparent...so time to look at the source and speaker!!
So simple and so true!!
But i wonder who is searching the truth in audio...just a fews!!
Cheers
Nice to agreed with you...
Well can you tell me where is that thread?? please!!I'm curious!!
Yes with this test we can even state that amp X is 2 times better (or worst) that amplifier Y...a designer dream...
I' remember the entangling of the Hi-Fi news /stereo revue crew...when they compare using the nulling test the hafler and a very expensive Audio Research...and some letters from David Hafler to Martin Coloms..
Many years have passed and the most powerfull tool in acessing amps linearity....is not only forgotten...but sometimes deliberately
ignored!!
With this test the breaking in of cables...the vibration coumponds..the suporting cones...ETC...will have no future!!So no wonder!!
Hoping hear from you!!
Well can you tell me where is that thread?? please!!I'm curious!!
Yes with this test we can even state that amp X is 2 times better (or worst) that amplifier Y...a designer dream...
I' remember the entangling of the Hi-Fi news /stereo revue crew...when they compare using the nulling test the hafler and a very expensive Audio Research...and some letters from David Hafler to Martin Coloms..
Many years have passed and the most powerfull tool in acessing amps linearity....is not only forgotten...but sometimes deliberately
ignored!!
With this test the breaking in of cables...the vibration coumponds..the suporting cones...ETC...will have no future!!So no wonder!!
Hoping hear from you!!
The above post is correct, the XL-280 is closer to some of Erno Borbely's Hitachi MOSFET designs (and, in fact, I seem to remember Borbely helped out on the XL-280 design?) than the DH-220. It does have one more pair of output devices per channel as well.
I can vouch that it does much better in the "null difference" test than the DH-220 did.
I can vouch that it does much better in the "null difference" test than the DH-220 did.
xl-280 excilinear adjustment
The Xl-280, starting from the speaker terminal, has a 47k resistor in series to the negative input of the differential pair. In parallel with this resistor is a 3.3k resistor is inseries with a 10pf capacitor to compensate the feedback loop.
From the differential pair input there is a 270 ohm resistor in series with two parallel high frequency compensation capacitors in parallel to ground. One is 330pf fixed, and the other 120pf variable. That 120pf capacitor is the excilinear (null) adjustment.
There is also a 2.2k resistor in series with a 1000uf NP electrolytic in parallel with a 0.1uf poly film capacitor to ground to set the gain and low frequency cut off.
Please let me know if you have more questions!
The Xl-280, starting from the speaker terminal, has a 47k resistor in series to the negative input of the differential pair. In parallel with this resistor is a 3.3k resistor is inseries with a 10pf capacitor to compensate the feedback loop.
From the differential pair input there is a 270 ohm resistor in series with two parallel high frequency compensation capacitors in parallel to ground. One is 330pf fixed, and the other 120pf variable. That 120pf capacitor is the excilinear (null) adjustment.
There is also a 2.2k resistor in series with a 1000uf NP electrolytic in parallel with a 0.1uf poly film capacitor to ground to set the gain and low frequency cut off.
Please let me know if you have more questions!
The adjustment gives you a lower null (in the high frequencies) but I can't say that I could hear the difference? At any setting of the capacitor, the XL-280 has a much better null than most amplifiers. I think in part because the frequency response is -0.1db from 1hz to 500khz! So the XL-280 has very little phase shift below 20khz.
It is a good design. In 1987 I think it was one of the best amplifiers you could buy on the null test (that's what Hafler claimed at least). It is the best I have measured.
I liked it so much I later built a "super XL-280" based on my own design with several improvements and slightly more power. It didn't do any better on the null test, however. In fact, I couldn't get my amplifier to do quite as good as the XL-280 but still better than most amps.
It is a good design. In 1987 I think it was one of the best amplifiers you could buy on the null test (that's what Hafler claimed at least). It is the best I have measured.
I liked it so much I later built a "super XL-280" based on my own design with several improvements and slightly more power. It didn't do any better on the null test, however. In fact, I couldn't get my amplifier to do quite as good as the XL-280 but still better than most amps.
The improvements...
So the "improvements"!!!
For to have an idea of the amp perfomance when we are designing news amps...and for comparation of comercial designs..the null test tell all.
If we can find a similar test for the loudspeaker...it will help a lot in the porsuit of good sound!
Anyone??
So the "improvements"!!!
For to have an idea of the amp perfomance when we are designing news amps...and for comparation of comercial designs..the null test tell all.
If we can find a similar test for the loudspeaker...it will help a lot in the porsuit of good sound!
Anyone??
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