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Review and Measurements of vintage Yamaha AX-396 integrated amplifier

pma

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Review and Measurements of vintage Yamaha AX-396 integrated amplifier

This review shows measurements of Yamaha AX-396 integrated amplifier, ser. no. Y399871TV, made in Malaysia.

I bought this amplifier in the year 2002 and have been using it shortly. Then it was sleeping in my stock and 5 years ago I gave it to my son, who has been using it till nowadays.

Description

AX-396 is a 2-channel, integrated amplifier. It has 5 linear inputs (150mV/47k) and 1 phono RIAA input (2.5mV/47k). It has 2 link level outputs (150mV/1.6k) (tape and MD). It has headphone output. It has 2 pairs of speaker outputs A, B. And it has 3 switched AC outlets to connect 3 audio units with total power consumption 100W max.

Front view of the Yamaha AX-396
Yamaha_front.jpg


Rear view of the Yamaha AX-396
Yamaha_rear.jpg


It is a class II unit with rated power consumption of 150W/230V.

There is an impedance selector switch on the rear panel to select minimum speaker impedance at A or B output terminals, it has 2 positions – 4 ohm minimum and 6 ohm minimum. I have moved the switch to 4 ohm position, as my tests will be performed with 4 ohm load.

The amplifier has tone controls and loudness control, both may be bypassed by pushing “CD/DVD direct” button at the front panel and using the CD/DVD input at the rear panel. The “direct” path has considerably lower noise and better S/N, about 15dB, as will be shown later. That's the reason why it was used for measurements.
The amplifier is working and is in quite a good shape, the only serious issue is that the rotary input selector works very badly and one has to turn it many times round and round before it is willing to jump to the next input. As I was measuring in the direct mode, I left the selector just at the CD/DVD position.

Measurements (direct mode, if not stated otherwise)

THD and THD+N at 1kHz, 5W/4ohm
ax396_1k_5W_4R_SW4.png

Yamaha AX-396 distortion 1kHz/5W/4ohm. THD = 0.005%, SINAD(A) = 83.9dB. We can see quite a lot of higher order harmonics and PSU mains lines are about -90dB below base frequency, which is not excellent, however it is acceptable. Maybe new PSU filter capacitors might improve this.

THD vs. output voltage at 100Hz, 1kHz and 15kHz, 4ohm load
ax396_thd_ampl_4R.png

Yamaha AX-396 THD vs. output voltage. We can see that maximum output voltage below clipping is about 20V in all 3 cases, which makes 100W/4ohm output power and it is more than specified by the manufacturer, regardless the age of the unit. Very good. Rated power, according to the user manual, is 95W/4ohm/0.7% THD as DIN specs, so the test result is better. I would only appreciate if THD was going a bit lower between 1W and 5W, we have a forest of higher order harmonics even at low power like 1-2W. This gets better if the impedance selector is switched to 6 ohm position, however I did not want to risk damage of the unit.

THD vs. frequency at 5W/4ohm
ax396_thd_freq_5W_SW4.png

Yamaha AX-396 THD vs. frequency at 5W/4ohm. Distortion is quite flat with frequency and I appreciate it.

19+20kHz CCIF IMD measurement
ax396_ccif.png

Yamaha AX-396 CCIF 19+20kHz IMD at 11.2Wpeak/4ohm. IMD = 0.0047% and this is really not bad at all.

Multitone distortion
ax396_multi_4R.png

This is good!

Output noise in direct mode
ax396_noise_direct.png

Yamaha AX-396 output noise A weighted. It is -81.6dBV(A) and this is very good, the only pain is the PSU ripple throughput. S/N to full power (100W) is 107.6dB(A).

Output noise of complete amplifier, direct mode switched off
ax396_noise.png

Yamaha AX-396 output noise A weighted, direct off. It is -65.9dBV(A) and this is much much worse than in the direct mode. S/N to full power (100W) is 91.9dB(A), nothing to call home about. My recommendation is to use direct mode only.

Maximum input voltage in CD direct mode
Maximum input voltage is 2.6Vrms. Above this level, internal clipping + distortion occurs. Most players would be OK, but never forget about this limit.

Maximum power at 20 kHz
ax396_4R_maxpower_20kHz.png

AX-396 keeps its ability to yield 100W/4ohm even at 20 kHz. This is very good.

Square wave response, 4Vp-p output, 4 ohm
ax396_10kHz_sq_risetime.png

Response to 10 kHz square is aperiodic, with rise time of 3.20 us. This makes -3dB frequency roll off at 109 kHz, so bandwidth is sufficient.

Measurement to complex load, 4ohm//(33uF+0.44ohm)
ax396_complexload.png

ax396_complexload_dist.png

An attempt was made to measure distortion vs. frequency at 4.6Vrms output voltage, which would be 5W at 50Hz, to the complex load described in this thread
https://www.audiosciencereview.com/...ad-for-power-amplifier-torture-testing.10298/

The attempt was not successful and the amplifier protection triggered the unit off at 3.4kHz frequency, where the load impedance is 1.275 ohm and -53°, which indicates to mostly capacitive impedance. The amplifier has only one output pair of 2SA1695/2SC4468 devices,
https://www.semicon.sanken-ele.co.jp/sk_content/2sa1695_ds_en.pdf
which is insufficient for 100W/4ohm amplifier loaded with a complex load like the one used. It is just at the edge for the purely resistive load, however that's how consumer electronics has always been designed. On the other hand, the protection circuit worked well and saved the amplifier. For the same reason, I surrendered to perform a square wave test into the complex load.

Conclusion

The Yamaha AX-396 made a respectable test-bench result, regarding its age and the fact it was a consumer electronics product, priced about $400. I would appreciate if it had lower distortion in 1 – 5W range and less high order harmonics in the spectrum even at low power. It was able to work well with 4ohm resistive load, however it failed to drive my “torture” complex load, triggering the unit of at 4.6Vrms output voltage and 3400 Hz frequency, where the impedance was rather capacitive, 1.275ohm/-53°. Still, for usual use, this amplifier might still be considered, taking into account its output power and low noise in the “direct” mode. I would not use it with direct mode switched off, dynamic range falls of -15dB.

I have this unit here now, so in case you are interested in some kind of a meaningful measurement that I did not do, please let me know.

I will do some listening now.
 

solderdude

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What does it do with your complex load ?
Squarewave response with capacitive load ?
I can hear March Audio ask
 
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pma

pma

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What does it do with your complex load ?
Squarewave response with capacitive load ?
I can hear March Audio ask

Please re-read the post #1, there are 2 plots and the answer
An attempt was made to measure distortion vs. frequency at 4.6Vrms output voltage, which would be 5W at 50Hz, to the complex load described in this thread
https://www.audiosciencereview.com/...ad-for-power-amplifier-torture-testing.10298/

The attempt was not successful and the amplifier protection triggered the unit off at 3.4kHz frequency, where the load impedance is 1.275 ohm and -53°, which indicates to mostly capacitive impedance. The amplifier has only one output pair of 2SA1695/2SC4468 devices,
https://www.semicon.sanken-ele.co.jp/sk_content/2sa1695_ds_en.pdf
which is insufficient for 100W/4ohm amplifier loaded with a complex load like the one used. It is just at the edge for the purely resistive load, however that's how consumer electronics has always been designed. On the other hand, the protection circuit worked well and saved the amplifier. For the same reason, I surrendered to perform a square wave test into the complex load.
 

solderdude

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Must have missed it the first time I glanced through it. :facepalm:
It is quite logical amps like these can't pass this test though.
Not many probably can.

Do you have a squarewave plot with the complex load (small amplitude) or the pure capacitive one ?
 
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pma

pma

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Do you have a squarewave plot with the complex load (small amplitude) or the pure capacitive one ?

OK, you persuaded me :). This is a 1kHz square response into my "torture" complex load described in other thread. But I am not going higher neither with amplitude nor with repetition frequency, based on sound I am hearing from the amp :D. Ooops, this was with 1:10 probe and scope probe selector set to 1:1, so the swing was 12.6Vp-p!! This explains the sound.:D

ax396_complex_sq.jpg
 
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pma

pma

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I made a listening test yesterday and the resulting sound was not that transparent as I am used to with my amp that has similar output power
http://pmacura.cz/powersym_en.htm

The sound of Yamaha was a bit dull and not tight enough compared to the POWERSYM. So I have started a 2nd round of measurements. Yesterday's results were from Left channel. Now, when I measure Right channel, I have found something is going terribly wrong in the R channel.

Though the usual ASR test at 5W/4ohm/1kHz is a bit better than with the L channel and SINAD is a bit higher, see
ax396_1k_5W_4R_R.png


another measurement, that of THD vs. frequency shows that something very wrong is happening at high frequencies

1st run
ax396_thd_freq_5W_R.png


2nd run
ax396_thd_freq_5W_R2.png


Both to purely resistive 4ohm load. It seems I will have to engage my oscilloscope(s) again. Any ideas, @restorer-john and @solderdude ?

Edit: my oscilloscope has shown no stability issues. It looks like output relay contact issue or A/B speaker switch contact issue. When it "works" properly, the results are very good, re this consumer audio unit.
ax396_R_1k_67W_4R.png


10kHz 87W
ax396_R_10k_87W_4R.png
 
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solderdude

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Maybe a feedback miller C acting strange ?
An electrolytic in the feedback path to ground ?

Did you listen to it before running it through tests ?

I once had an old Technics SU-7200 and could actually tell it apart from my other amplifiers.
This I found strange and started measuring it.
Turned out the actual 'middle position' of the tone control wasn't the electrical middle position.
Once I set the tone control to 'measured flat' (so slightly offset from the middle position) the differences were gone again.
 
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pma

pma

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Did you listen to it before running it through tests ?

Yes I did, as described in the post above yours, I started to measure R channel based on the listening test (less transparent, bit dull compared to my usual experience with my POWERSYM amp).

The issue continues and is best seen as LF noise rise in the 20kHz HD plots. Scope image has no oscillations, but slight LF modulation of amplitude of peaks is visible. How about cross-conduction current through output devices at 20kHz?

ax396_R_20k_25W_4R.png


ax396_R_20k_83W_4R.png


Edit: see noise bottom and 2nd harmonic jumping up and down in the video

http://pmacura.cz/yamaha20k.MP4
 
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restorer-john

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Run the tests on the speakers "B" relay, and also, try running the unit the 8/6 ohm switch (secondary txf tap voltage change). Otherwise, if nothing changes, we have a problem to chase down.
 
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pma

pma

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Run the tests on the speakers "B" relay,

We are reading our thoughts at the distance :). Yes that's what I have done and the issue was in the "A" path binding posts. It is wrong even if used for monitoring into 22k impedance. Path "B" is OK, solved.

ax396_R_20k_83W_4R_repair.png


ax396_thd_freq_56W_R_repair.png


The R channel has now a bit lower distortion than L channel, especially between 1W and 20W. Good!
ax396_thd_ampl_1kHz_4R_R.png
 
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lopchu

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Nice review, thanks a lot! I have the same unit at home. It was replaced by a NAD 3020 but still serves as a backup and a living room amp.

Just out of curiosity, would you know the headphone out impedance and the power at 300 Ohm? (if not, no worries!)
 
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pma

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Nice review, thanks a lot! I have the same unit at home. It was replaced by a NAD 3020 but still serves as a backup and a living room amp.

Just out of curiosity, would you know the headphone out impedance and the power at 300 Ohm? (if not, no worries!)

Thank you.
Headphone output impedance is about 600 ohm. The amplifier is able to send clean 8.33 Vrms into 300 ohm load, that makes 0.23W/300ohm. Nice, isn't it?
 

lopchu

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Thanks for these measurements!

230mW sounds nice indeed. But 600 Ohm output impedance is way to high, isn't it? I mean my Sennheiser HD 650 have 300 Ohm. That's quite a mismatch and wouldn't almost all headphones be above a value calculated by the 1/8th rule?

Anyway, nobody would buy the amp for the headphone out. So it doesn't really matter probably.
 
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pma

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These amps have the headphone output connected directly from speaker output via a series resistor. So you have some 24Vrms output + 600 ohm resistor. With 600 ohm headphones, you get up to some 12V. Frequency response flatness will of course depend on headphones impedance frequency plot. It is often not that bad, as shown in another thread.
 
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pma

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I have some more measurements. First, there are THD(1kHz), CCIF IMD 13+14kHz, CCIF IMD 19+20kHz, DIN IMD 250Hz+8kHz, SMPTE IMD 60Hz+7kHz, all into 4ohm load, output voltage (rms) vs. frequency. Please take into account that same output Vrms for different plot does not mean same voltage swing in the test. Simple calculation of power, P = V^2/R is possible only for THD, where we have a single frequency signal.

ax396_ccif_thd_imd.png


Then there is another measurement, now the obligatory THD 5W/4ohm/1kHz, but taken with cold amplifier and warmed up amplifier. The distortion number is similar, however harmonic profile differs quite significantly. This shows that idle current thermal stabilisation is not very good. This is quite usual in commercial consumer amplifiers.
ax396_1k_5W_4R_R2.png


ax396_1k_5W_4R_R3.png
 

miero

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Do you know why SMPTE IMD shows an earlier rise of distortion?
 
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pma

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Do you know why SMPTE IMD shows an earlier rise of distortion?

I think it is because 60Hz test component is close to residual 50Hz mains line throughput and intermodulations and it might affect the resulting IMD of the SMPTE 60Hz+7kHz test. I will check it when I test another amp. 60Hz also probably worsens the 50/100Hz PSU ripple.
 
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