Crown Straight Line Two
SL-2 and PSL-2 Stereo Preamplifiers
Made in USA (1981-1995)
Crown Straight Line Two SL-2 Preamplifier. bigger.
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The Crown SL-2 packs exceptional audio performance and a lot of features into just one rack space. Add this to excellent design and construction quality and you'll see why they routinely sell for $500 today - even though they are 35 years old. Crown made these superb preamplifiers in Elkhart, Indiana, USA from 1981~1995.
The SL2 has two tape loops, a fixed external processor loop (EPL), a precision phono preamp with calibrated gain, 1% resistors and 2.5% capacitors, tone controls, a stereo-mono-reverse-mute control, a rumble filter and indicator, and all these can be bypassed one-by-one, giving rise to the STRAIGHT LINE TWO model name. There's also a superb switchable Loudness contour that's the best I've heard, boosting the extreme deep bass and not muddying up the midbass.
The earlier Straight Line One was a very primitive preamplifier that took up two rack spaces and wasn't much more than a selector and volume control.
This STRAIGHT LINE TWO lives up to it's name, with actual measured performance of both the ancient samples I've tested of 0.00005% THD (that's four zeros!) and +0, -0.4dB response from 4 Hz ~ 110 kHz!
The SL-2, seen here, was made from 1981~1985 and the PSL-2 was made from 1987~1995. The PSL-2 is the same, except that the AUX 1 input is labeled "C.D." and AUX 2 is simply called "AUX."
The SL-2 came in silver as seen here, as well as with a black face with the same silver aluminum knobs. Early models used the shiny turned aluminum knobs with deeply engraved index lines as seen here. Later models used matte aluminium knobs with just tiny engraved index arrows on the front of each knob. The PSL-2 only came with the black face and matte silver aluminum knobs with the small engraved arrows. The knobs are extremely solid, and believe it or not, are push-on knobs with very solid metal outsides and plastic innards.
While all are rack mountable, some have handles on the sides as shown here, and some don't. The handles are most common on the earlier SL-2 and less common on the newest PSL-2, but they come both ways and the handles come in either color.
Like all Crown products, these preamplifiers are very durable. The first sample I bought arrived flopping around in a box shipped 3,000 miles with no packing material or padding and mostly worked, except for some of the front panel LEDs. No worries, even though the seller made no efforts to correct this, eBay's Money-Back Guarantee gave me a full refund so I got rid of it and bought another. Service information and most of the parts are readily available and most of these should run forever. It runs on common TL082, TL084 and NE5532 op amps on ±18V supplies for greater than 10 V RMS output.
There are two tape loops, but no front-panel EPL switch so you must use jumpers as shown above to connect the PROCESSOR LOOP output to its input — or you won't get any output!
Measured from the AUX 1 input driven from the 5Ω source impedance of the R&S UPL at 1 V to the MAIN 1 output, terminated by the 200kΩ load of the UPL. The SL-2 is set to level 28 (unity gain).
Frequency response, AUX 1 in to MAIN 1 out.
Frequency response, second sample, 22 µF output coupling capacitors bypassed.
Infrasonic frequency response, second sample, 22 µF output coupling capacitors bypassed.
Ultrasonic frequency response, second sample. 22 µF output coupling capacitors were bypassed and 560Ω build-out resistors bypassed with 91Ω resistors, making the effective output source impedance about 86Ω.
AUX 1 in to MAIN 1 out, Tone at zero.
Tone at zero, second sample.
Treble -5, -4, -3, -2, -1, +1, +2, +3, +4, +5.
Bass -5, -4, -3, -2, -1, 0, +1, +2, +3, +4, +5.
Loudness 50 + Filter
Filter response, first sample.
Filter response, second sample, 22 µF output capacitors bypassed.
AUX 1 in to MAIN 1 out — but with Grado SR80e 32Ω headphones plugged into the Monitor jack. The 22 uF output coupling capacitors were loaded by these headphones, along with the 22Ω series build-out resisters, to attenuate the low frequencies. Shorting across these capacitors restores straight-line performance — or use 600Ω headphones.
THD at 1 kHz.
THD at 1 kHz, second sample.
THD from 1V to 10V output at 1 kHz, second sample.
THD at 100 mV
THD at 1V
THD at 10V
Channel tracking. + (up) Image moves left, - (down): image moves to right.
Channel tracking, second sample. + (up) Image moves left, - (down): image moves to right.
Channel tracking, second sample, after I calibrated it for ±0 at 0 dB gain at level 28. While the image is 3dB to the left at full gain where no one ever listens, I restored the balance to ±0.8 dB from -48 dB to +12 dB gain where we actually use a preamp.
Phono to Tape 1 Out response, deviation from RIAA.
It uses very high precision components in the phono preamp for much more accurate RIAA phono response than other consumer phono preamps. It's flat to ±0.2 dB from 7 Hz to well over 20 kHz!
Phono to Tape 1 Out response, deviation from RIAA.
Shorten turn-on delay, now 8.2s
11 pounds (5 kg)
1/8 A fuse
Well balanced channels, full featured and quiet.
$479 1981 = $1,250
Headphone output has no turn on delay
Easy-glide, well tracking level control
Heater power cord, heavy duty switched outlets
14.2 watts at 116v cold
7 second delay rated
18 v supplies
Tape outs hard wired; not buffered
EPL fed from hard wired input selector
Detectors at three stages peak hold overload protection indicator. Detects phono overload even if only sent to tape out for instance.
TL072 TL074 and NE5532
Gain: vary either up or down rotation direction to get to stop, then measured counterclockwise
20.065/19.864 dB 0
Wide range and well tracked
Loudness good compensation with dt880
Loudness good at really soft levels, not good for general use
Mono shorts to perfect balance, balance control ignored except as input mixer
Tone delta gain: -0.0461/+0.0708 dB
Noise -104.8 dBV A -102 dB 22k
OVLD at 10.45v at 0.005% with tone active
THD Same with 1V in for 100mV out or 100mV in for 100mV out
Low cut Filter is harsh, but perfect for vocal classical.
Feed Stax from main 2
Put Expander in EPL, program or headphone EQ in tape 1 and 2.
Toggle switches would have been better. Push buttons too much work, too slow and can't see their positions - but they feel nice.
Semi-generic bass control. Not useful. Better than most, but not as good as Apt or Adcom.
Great treble control, perfect for correcting things that are too brilliant.
SECOND SL-1 17 Oct 2017 010741 different dull knobs lacking indices
WORK 21 OCT 2017 about 5 PM:
Now gain is:
17.015/20.407 00 bal -4
Rumble light on at (full wave detection):
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October 2017, April 2015