Kinter MA-170
When looking through low cost amplifiers I might use to practice my measurement process on, another good candidate was the Kinter MA-170. I picked up a couple of these when a local electronics store was going out of business. They were listing them at $20 each, but the sale price was 90% off - so $2.00... New ones are still available on Amazon for $12.95 in 2023.
The amp didn't come with a power supply, but says it nominally takes 12VDC and will run from 9V-14.4V.
Specs listed on Amazon are as follows:
Power output: 2 x 18 watts RMS
Speaker impedance: 4-8 ohms
Input impedance: 47k ohms
Frequency response: 20 Hz - 22 kHz
Back in 2014, some test results using an Audio Precision Analyzer were posted on the Parts Express Tech Talk forum by member "tyger23", so there is a sanity check for my results - although like the Lepy results, it won't be entirely clear whether discrepancies are due to the measurement process or unit-to-unit variation.
I'll start out with my version of the "dashboard. Wow, there is a lot of distortion - over 1% THD+N at 5W into 4 ohms! Even order distortion is about 20 dB higher than odd order distortion at this power level, so maybe it won't sound terrible. Channels matched better than the Lepy.
Now, we'll look at the frequency response. The Kinter doesn't have a tone defeat switch like the Lepy and with the tone controls at their center position, the frequency response is anything but flat (down about 10 dB at 20 Hz and 6 dB at 20 kHz). The Tech Talk review indicated that flat response should be with tone controls all the way clockwise, but in order to get reasonably flat response with my sample, I had to put the controls at about 3 o'clock. With that adjustment, we have very extended response from 10 Hz to 40 kHz +/- about 1 dB. The response doesn't vary much with impedance, which is a good thing. There is some strange low frequency modulation that shows up below 50 Hz. Changing sample rates or FFT size didn't seem to help.
Now, let's see how much power the Kinter MA-170 will actually produce. I'm betting against 18W RMS and the 100 W PMPO (whatever that is) printed on the back of the case. Sure enough, with the recommended 12V power supply we get about 5 watts per channel into 8 ohms and 6-7 WPC into 4 ohms. At least at 8 ohms we get under 1% THD+N. The distortion floor is so high, you don't really see the noise floor in this curve, which would drop in percentage with increasing signal. Power output and distortion levels appear similar to "tyger23's" as he measured at 4 ohms.
Looking at this, this amp should sound broken, but doesn't really until it runs out of power. Based on what we saw on the dashboard, the high distortion is mostly even order (until clipping), so maybe that is how an amp like this could be kind of acceptable in some situations. I don't have any idea how one would get 18W RMS x 2 out of this without cranking up the voltage and hoping it survives.
