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Kind of surprising the distortion goes way out like that at 2 watts. I only have measurements done with TrueRTA of those amps; I might do them again with Multi-Insturment. At any rate, you can see the even order harmonic distortion component "supression" going on, which is happening in the...

And whom might that be????? :scared-eek:

H e l l o........anybody here??????? :eusa-whistle:

Yeah, be warned though; the program is not as user friendly as TrueRTA. :scared-eek:

That depends on the sound card / interface. Some interfaces can't take more than .2 volts and some can take considerably more; usually the maximum is about 1 volt. You should go by the input meters on Multi-Instrument Pro and avoid clipping. Also, make sure you are not clipping the output of...

This thread is getting to be a one-on-one dialogue.....where are the posts from other people? Aren't they interested at all in this stuff??? :scared-eek:

Yeah, those distortion components above the 7th shouldn't be there. Here is the 1 watt distortion spectra of my SET amp; the distortion components are basically gone after the 3rd harmonic, which is extremely clean.

The only thing that having the bias lower than usual would do is to make the amp clip at a lower wattage than otherwise. The bias voltage reading is independent of the AC line voltage (which was 117 VAC in the 1950s-60s rather than 120 VAC today). I think there's something else going on because...

I don't know. I have a USB interface in my shop (M-Audio Audiophile USB), and its noise is almost as low as my ASUS interface. Could be noise coming from your computer over the USB power?

Here's a plot I just did going from the output to the input of my sound card, which is in this case the Asus Xonar Essence STX; The distortion and noise floor are very low.

I think the high noise floor of your interface is obscuring most of the view of the distortion products. The Dynaco MkIV is a bit surprising because the sidebands on the sides of each distortion product is intermodulation distortion (IM). I know my Dynaco ST70 has very clean distortion...

No they would not in this instance. The only time this would be true is if there was a very strong second harmonic and a relatively strong 4th harmonic relative to the 3rd and 5th etc. And the odd harmonics would have to be basically gone by the 7th or so. Just the presence of even order...

It would appear to be a typical solid state amp which is only differential (push-pull) on its output stage. I would expect it to sound accordingly; not all that great under the right circumstances. BTW, either both these amps, or your interface is pretty noisy.

The peak at 19kHz appears in both graphs with different amps, so I would imagine it is something (a sub-harmonic of some clock maybe) coming either from your interface or computer.

Now place the top of the graph back at 0dB so the bottom has more resolution..... BTW, what amp is this; that could have something to do with the noise at 17kHz.

The amp appears to be very noisy which is obscuring the distortion spectra. You might also try lowering the resolution of the FFT: try 8024 or 4096, and set to "Hanning" for the FFT type.

There are certainly measurable differences between different DACs, but none which would be audible to most people. Of greater concern is the analog circuitry which follows the digital to analog conversion; the current to voltage conversion, filtering and output driver. However almost no...

Hard to tell what the cluster of noise (or oscillation) is in the 15-17kHz range. The amp under test seems to be a differential design, with quite a lot of global negative feedback. BTW, use the dBr setting on they "Y" axis as this automatically places the test tone at 0dB (full scale) which...

You should use the linear graph mode rather than the log representation as this lines up the harmonics on divisions which are easier to intrepret.

One thing I should make clear about that article I wrote: the RS meter is used to check sound pressure levels on dubbing stages, but it is not used to calibrate levels, and is not used to tune dubbing stage EQ for frequency response.