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A few quick Measurements of an Harman Kardon HK 3270RDS Stereo Receiver

LTig

Addicted to Fun and Learning
Joined
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#1
It happened to me that I got a Harman Kardon HK 3270RDS stereo receiver into my greedy measurements fingers. The service manual is dated as of 2004 so the unit should be some 15 years old, the owner however thought that it was older which could certainly be true: I found a price of € 450 in 2000-2002 here.

The receiver has some nice features:
  • preamp in and power amp out (bridged by external connection)
  • subwoofer out (but no highpass in the stereo outputs)
  • loudness control
  • balance and tone controls
A young colleague told me that one channel would be dead. On a visit to his home I opened the top lid and I could verify that the power amp should not be the cause: although one channel did not work when fed by the power amp input both channels hummed when I disconnected the cable between main board and power amp and touched it with my hand. My colleague found the service manual and mailed it to me, and after inspection of the mother board I offered to try to fix it. According to the schematics of the main board there is almost nothing between the power amp input and the connector to the power amp so it should be easy to find the cause.

Well, we found out soon enough that nothing was broken and the receiver worked without flaws (later my colleague found out that a cable was broken). So with some time left I did a few quick measurements of the preamplifier (I have no proper load yet for measuring the power amp). They were done in a hurry so excuse the different frequency scales please.

Specs are as follows:
  • Power at 0.08% THD (20 Hz to 20 kHz), both channels driven: 70W @ 8 Ohm and 95W @ 4 Ohm
  • THD @ 65W and 8 Ohm, CD input: <= 0.05% nominal at 20 Hz, 1 and 20 kHz
  • IMD @ 50W and 8 Ohm: <= 0.05% nominal
  • SNR @ 70W, CD input (shorted): >= 100 dB nominal
  • Input sensitivity is 200 mVRMS for all line level inputs
  • Power consumption 332W (confirms the power output)
  • Weight 11.2 kg
The service manual states that with 204 mVRMS for the CD input the preamp output should be 1.06 VRMS. Therefore I measured THD with a 1 kHz sinus at some 200 mVRMS and with volume set to max the preamp output was 1VRMS, using REW and my RME ADI-2 PRO fs both as DAC (to generate the sinus) and ADC (for measuring THD) with 192 kHz samplerate, 128k FFT size and 4 averages:

THD 1kHz CD in 204 mV rms pre out 1V rms 192 kHz 128 Kfft avg=4.png

Performance is dominated by hum and power supply noise.

Since most CD players emit 2VRMS a redid the test with a 2VRMS sinus and reduced the volume such that the preamp output was at 1VRMS as before:

THD 1kHz CD in 2V rms pre out 1V rms 192 kHz 128 Kfft avg=4.png

Unfortunately now harmonic distortion dominates (hum and noise are a bit lower though which is good).

REW offers a multitone test with 16 sinus signals:

Multitone-16F CD in 2V rms pre out 1V rms 192 kHz 128 Kfft avg=4.png

I think we have seen worse.

Finally measurement of IMD (CCIF: 19 + 20 kHz sinus):

IMD CCIF CD in 2V rms pre out 1V rms 192 kHz 128 Kfft avg=4.png


IMD is not that bad - we see also the power supply stuff to the left.

My colleague had to leave so I could not measure more. So far as I can see the receiver made a reasonable impression to me. No highend of course but nothing broken either.
 
Joined
Apr 12, 2019
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#3
Thanks for this LTig. I have an HK3375 which is a newer version but I expect performance is similar; the main difference is that the 3375 is rated at 75 Watts for 8 Ohms (with a marginally better .07% THD rating) and has a slightly updated faceplate. I bought it to replace a Sony GX-315 from the mid 90's that I got sick of repairing. Subjectively the HK sounded noticeably better than the Sony, like night and day. I know I know, not a blind test etc, but I think even when repaired with replacement output power transistors the Sony just sounded bad so I suspect there had to have been other issues with it. Objectively, it's been rock solid reliable over almost 17 years of daily use and I don't regret the purchase.

For reference, the 3375 was first released in 2002. The precursor was the HK3370 (physically identical to mine, rated 5W less power), released in 2000. So this puts the HK3270 that you reviewed around the 1998-99 timeframe, roughly 20 years old. It would be interesting to find out if the power supply spray was always there or if it has started to increase due to the age of the filter caps.
 
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