Input sensitivities of older equalizers

[murat]

Hi,

I recently bought an old Technics SH-8017 equalizer. The specs I found here:

http://www.vintagetechnics.com/equalizers.htm

says:

s/n ratio: 107

THD at Rated Output, %: 0.005.

What is the typical rated output for this (or similar) units?

What is a typical rms input voltage before increasing the distortion? Thanks,

Murat

[Frank Berry]

These old ones typically operate at a level of -10dB.
As the various frequency bands are boosted, you'll lose some headroom.
I expect that the equalizer is probably good for a couple of volts output before clipping.

[murat]

These old ones typically operate at a level of -10dB.

Frank, does this mean that the equalizer will reduce the signal 10 dB if there is no boost or cut? My observation is, if I turn the equalizer on and off while all the pots are in the middle position I don't observe any change in the sound level. Thanks.

Murat

[Frank Berry]

No. The normal operating level is -10dB.
With all boost/cut controls set to 0, the equalizer should have unity gain. The output level should closely match the input level.

[PRR]

> does this mean that the equalizer will reduce the signal 10 dB if there is no boost or cut?

No. That would be annoying. It is, as you observe, unity-gain (roughly, +/- EQ).

Frank's "-10dB" is shorthand for "10dB below 1 Volt" or 0.316V. This has been the general level of Hi-Fi gear since the late 1960s, and codified by Dolby chips which referenced 0.316V.

Speech/music at nominal maximum level in a tape recorder, measured with a slow mechanical meter like a VU meter, will read about 0.316 Volts. And since all the line-level in/out in a Hi-Fi is unity-gain, that's the expected level at the EQ jacks.

Peak levels will be 10dB-20dB higher than 0.316V. In soft analog tape we didn't worry too much about that, but CD players have hard clipping. They are (often) specced to deliver 2V sine RMS at maximum digital level. This is 16dB above the 0.316V meter reference, a very nice headroom.

> What is the typical rated output for this (or similar) units?

Older gear will make much more than 0.3V on peaks, several volts. A lot of gear your vintage used chips running on +/-12V or more, and can deliver maybe 6V RMS without gross midrange distortion. Slew distortion may be an issue; however one reason the 0.316V/2V levels were picked is that quite tame chips (like 4558) can make over a volt over most of the audio band, and don't trash-up the sound too bad. (But for $89 original list price, don't expect perfection, especially pushing over 2V through it.)

0.005% THD for $89 does suggest chips, and not the worst ones on the market. 0.005% is surely measured mid-band, and may be much higher at 20KHz, though probably below 0.1% for a volt of output.

> What is a typical rms input voltage before increasing the distortion?

Same as the output, minus whatever EQ you put on it.

> Input sensitivities

Noise level of chips and cheap discrete amps is about 2uV. Sloppy design and EQ-section loss will increase this 10dB-20dB. I'd expect 10uV to 30uV of output noise with all sliders flat. The rated dynamic range 107dB (conditions unspecified) might be 10uV noise, 2V nominal signal, 30uV noise, 6V gross overload, or any similar ratio, or might just be a made-up number.