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Rear, Technics SH-9020. enlarge.
Top, Technics SH-9020. enlarge.
Meter face, Technics SH-9020. enlarge.
The Technics SH-9020 seems like a goof, but it's actually a very accurate and precise wide-ranged meter that's very useful for measuring audio levels.
One thing it does is hold peaks forever. You can leave it running, and come back later and see the exact peak power used by your amplifier. It's so sensitive to even the shortest peak that I didn't realize I used so much power.
It's a masterpiece of analog design. It's accurate, fast and stable.
There's no overshoot; the needle moves up to the peak and stays there.
The Peak Hold setting works! You can set it, play the amp, and look or come back later and see what the peak power was. There's no auto reset for Peak Hold, it holds the peak and stays at that level for hours.
It uses a full-wave rectifier.
It either has an instantaneous peak attack, or a 200 mS attack in average mode.
Decay is either roughly VU, or infinite.
The front panel selects either of two loop-through line-level RCA inputs, or the back-panel speaker level (power) inputs.
Watts are measured as voltage, then displayed as power into your choice of 8Ω, 6Ω or 4Ω.
The +20 dB range switch is on front, and the 8Ω, 6Ω or 4Ω selection switch is on the back.
The SH-9020 is calibrated in dBu (0 dBu = 774.6 mV) for line levels, but it's not marked that way. A standard CD player or DAC has a 2 V maximum output, and will read +8.2 dBu peak.
Peak and Aveerage levels are calibrated for the RMS value of a sine wave; in other words, a sine wave will read the same in either the Peak or Average settings.
Serious meter movements inside the Technics SH-9020. enlarge.
Line-Level Inputs (Inputs 1 and 2)
The SH-9020 is calibrated in dBu, but it never tells you that.
A dBu is dB relative to the voltage which produces 1 mW into 600Ω, or 774.6 mV.
0 dB (sensitivity switch out, rarely used)
0 dB is +20 dBu or 7.746 V.
Full range reads -30 dBu to +30 dBu (24.5 mV to 24.5 V).
+ 20 dB (sensitivity switch in, normal setting)
0 dB is 0 dBu or 774.6 mV.
Line levels read directly in dBu from -50 dBu to +10 dBu (2.45 mV to 2.45 V).
A standard CD player or DAC has a 2 V maximum output and will read +8.2 dBu peak.
Speaker (Power) Input (Input 3)
The meter reads voltage, displayed as watts.
A watt is either 2.828 V into 8Ω, 2.4495 V into 6Ω or 2.000 V into 4Ω.
The 5dB markings correspond to 3.16 intervals, in other words, 316 mW, 3.16 W or 31.6 W, etc.
0 dB (sensitivity switch out, normal position)
0 dB is 100 watts power (+20 dBW or 28.28 V into 8 Ω).
The lower wattage scale reads correctly.
Add 20 from the dB reading to get dBW.
The dB scale reads power from -30 dBW to +30 dBW (1 mW to 1 kW, or 89.44 mV to 89.44 V into 8 Ω).
The 1 dB markings at the top refer to 125 W, 160 W, 200 W, 250 W, 316 W, 400 W, 500 W, 630 W, 800 W and 1,000 W.
+ 20 dB (sensitivity switch in, used only at quiet levels)
0 dB is 1 watt (0 dBW or 2.828 V into 8Ω).
The dB scale reads directly from -50 dBW to +10 dBW (10 µW to 10 W or 8.9 mV to 8.944 V into 8 Ω).
The wattage scales must be divided by 100. What reads as 100 W is really 1 W, full-scale 1,000 W is really 100 W and the lowest -50 dB reading isn't 1 mW; it's only 100 µW.
The 1 dB markings at the top are 1.25 W, 1.6 W, 2 W, 2.5 W, 3.16 W, 4 W, 5 W, 6.3 W, 8 W or 10 W.
120 VAC, 60 Hz.
Rated 12 W.
Actual power consumption is 7.6W (70 mA) at 120 VAC.
Made in Japan.
Corrugated cardboard box.
Two polystyrene foam ends.
19" rack mount, two RU (3.5") high.
Feet add a little height if use on a table.
2014: about $500 used.
These measurements were made with an exotic Rohde & Schwarz UPL laboratory generator.
I'll be darned, even at 30 years old every reading at every level is still accurate to within the width of the needle!
It's flat to within a fraction of a decibel (the width of the needle) across the entire 20 ~ 20,000 Hz range.
It's flat +0, -1 dB from 8 ~ 65,000 Hz in Average mode.
In Peak and Peak Hold modes, there is a +1 dB peak at 50 kHz. This makes its response ±1 dB from 8 ~ 93,000 Hz.
At lower levels (like -30 dB and below), the ultrasonic response falls off. This is marked on the top cover. Response to 20 kHz isn't affected.
-3 dB at 5 Hz.
-1 dB at 8 Hz.
Flat 20 ~ 40,000 Hz.
-1 dB at 65 kc.
-3 dB at 120 kc.
-5 dB at 160 kc.
-6 dB at 180 kc.
-10 dB at 250 kc.
-15 dB at 320 kc.
-20 dB at 360 kc.
-30 dB at 410 kc.
Peak and Peak Hold
-3 dB at 5 Hz.
-1 dB at 8 Hz.
Flat 20 ~ 14,000 Hz.
+0.2 dB at 20 kc.
+1 dB at 50 kc.
0 dB at 80 kc.
-1 dB at 93 kc.
-3 dB at 110 kc.
-5 dB at 130 kc.
-10 dB at 160 kc.
-20 dB at 260 kc.
-30 dB at 280 kc.
-40 dB at 295 kc.
-50 dB at 300 kc.
Peak and Peak Hold Attack
1 mS burst reads 100%
100 µS burst (one cycle at 10 kc) reads -0.5 dB.
50 µS burst (one cycle at 20 kc) reads -3 dB.
-12.5 dB after 500 mS
-25 dB after 1 second.
-40 dB after 2 seconds.
Peak Hold Decay
About -3 dB per hour in my nice sample of SH-9020, about -1.5 dB per hour in my beater sample. In my beater sample, the left channel decayed 50% more than the right.
This means it won't decay at all in an hour, and will decay about 15 dB overnight.
316 mS burst reads -0.5 dB.
100 mS burst reads -4.5 dB.
31.6 mS burst reads -10 dB.
10 mS burst reads -20 dB.
3 mS burst reads -30 dB.
1 mS burst reads -40 dB.
50 dB per second (50 dB in 1 second, 26 dB after 500 mS).
The SH-9020 runs cool.
It uses 7.8 W (70 mA) at 120 VAC regardless of what it reads.
The SH-9020 is far more accurate than other consumer meters. It's accurate and catches and holds any peak.
It also displays over a wider range.
Beware: the speaker grounds are grounded together. DO NOT USE THIS METER WITH BRIDGED SPEAKER OUTPUTS.
Likewise, do not reverse the polarity of the wires going to the meter. If you do, you'll short the speaker outputs to ground.
I use only AWG 24 wire to connect to my power amp. This way I hope the wire will fuse itself before I blow out something else if I do something stupid.
The Peak Hold resets either by moving the level to Peak or Average, or turning off the power.
When my used SH-9020 arrived in 2014, one of the feet had unscrewed, leaving a nut rattling around inside. Be sure to check the external screws and tighten them if needed when you get yours.
There is little to no real difference in audible power output between 60W and 100W and 250W. In each case, it's only one or two clicks of a volume control between each. Most people don't realize that amplifiers almost never have to put out their maximum power; most of the time at normal levels you're using one watt or less. You only get close to maximum when you play your system at deafening levels, and when you do, there isn't much difference between the different power levels.
The real difference is if you have it turned up so loud that you need 100W for a loud fortissimo passage. If so, the 60W amp would distort horribly while the 100W amp would be clean. If you're playing it this loud, turn down the volume one or two clicks and you're fine even with the 60W amp — and it will still be very loud.
This is why amp makers took off the power meters they used to feature back in this day: people quickly realized they never used more than a watt or two, even when played loud. With most of today's non-classical music, the peaks and dynamic extremes have been filtered out anyway, so no longer do we need high peak power for contemporary popular music,
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Dec 2014: beater right channel meter reads OK -20 dB,
0.5 dB low at -30dB scale and 1.5 dB low at -40dB scale