there are no other comparable voltages for 8r0 and 4r0 test loads.
For the two sets of voltages +-12Vdc and +-30Vdc the pattern follows what I expect for all amplifiers, both discrete and chip.
As one demands more current the maximum output voltage drops.
I could guess from some of the non comparable results what type of performance one might get.
As it is I have stated what I can read from the results given.
The chip performs very well @ +12Vdc and slightly less well @ +-15Vdc.
The test results as shown are what I do for every amp I build.
I expect at least good current capability as the first basic pass or fail test.
There seems no point in "tuning" a proposed amp build if it can't deliver adequate current, relative to the proposed speaker impedance.
If you look back at some of my 3886 recommendations you will see that I propose the chip as a 60W to 68W into 8ohms capable amplifier.
I also propose that same chip on lower supply rails as a potentially good build with a target maximum output of ~40W into 4ohms speaker.
This reduced maximum output is specifically aimed at limiting the output current to what the chip is capable of passing very well.
It all fits with my assertion that all these National chipamps are current crippled.
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Maybe another way of interpreting the data is to look at comparable current results. If you want to build an amp that can supply 2 A into 2, 4 and 8 ohm, you would need a 55/2 V rail and need the rail voltage to stay above 31/2 V for 4 R or 18/2 V for 2 R.
are you talking about how STK based amplifiers always have undersized transformer as recomended in some STK app notes? just in this case you limiting current on chipamp?
you can look for other ways to test the current capability.
I use the relative output voltages as current demand changes.
A perfect PSU and amplifier would give 0dBV voltage change as current demand changes. -3dBV would indicate the same power into a half load impedance as into the rated load impedance. Most amplifiers give between -3dBV to -0dB. The closer to -0dBV the better the current capability.
Not that important anyway.
Even without measuring, like Enzo said, "the amplifier i just that thingie between Power Supply and Speaker".
A very close approximation is:
* measure idle rail(s) voltage, either single supply or end to end if split.
* calculate drop: ~10% for a very good supply to ~20% for a tight rated one.
* discount 4 or 5 Volts for inevitable transistor drop
That gives you available Vpp across the load.
Divide by 2.86 to get RMS voltage on the load.
* do the Math 🙂
thanks,
actually I am fumbling around trying to gather information to have somewhat safe PS voltages and speakers to have a deliberate distortion (2nd harmonics as shown in below link) without damage to speakers, where average music levels will be almost low distortion, but a little high level and music peaks will have some good harmonics which enthusiasts say sounds good. I do also like clean high power amp, but this is just to learn and have fun as a newbie. Adding to my indecision is transformer and speakers are not yet finalized. The amp build is almost finished. I do have 12-0-12V AC, 1.5 A transformer which I will test soon.
LINK : http://kit-amp.com/lm1875-testing
regards
Yes I understand that. just took a chance if any one saves such things. Just last year I deleted from my hard drive almost all the material (Amp, speakers, turntable articles, measurements etc., that I had saved since last 7/8 years. So I thought someone might have it.
regards.
Oh, that report carries some good measurements but conclusions are nonsense, completely blown out of proportion:
You can´t even HEAR -73dB second harmonic, even less find it "colors" the sound.
Try 3-5% as found in a SE Tube amp, low or no feedback, and we are talking 😉
Power Op Amps such as LM1875 are among the flattest most transparent cleanest devices created by Human minds, hardly the choice for an "effects box" 😉
OK understood.
probably having low sensitivity speaker which can tolerate some clipping can be used. That way I have to raise the volume to reach some distortion level.
probably having low sensitivity speaker which can tolerate some clipping can be used. That way I have to raise the volume to reach some distortion level.
