Ljudoljus.net

Lite nyttiga länkar till olika papers/artiklar om Pin1 / SCIN-problemet:

Bill Whitlock, Jensen Transformers om CMRR och balanserade linjer:
http://svconline.com/mag/avinstall_cmrr ... index.html
http://svconline.com/mag/avinstall_cmrr ... index.html

Pin1/SCIN-artiklar av Jim Brown, Audio Systems Group
http://audiosystemsgroup.com/Pin_1_Revisited.pdf
http://audiosystemsgroup.com/Pin_1_Revisited_Part_2.pdf
http://audiosystemsgroup.com/Shield_Cur ... _Noise.pdf
http://audiosystemsgroup.com/SCIN-2.pdf
http://audiosystemsgroup.com/SurgeXPowerGround.pdf

AES48-standarden, kan laddas ner som "courtesy copy"
http://www.aes.org/publications/standar ... .cfm?ID=44

Jag stoppade huvet i elektronikverkstan i dag förmiddag och testade loss lite: (texten är på engelska för att den gick till Theatre-Sound också.)

I just got around to testing the Composer for Pin 1 problems, since I own a couple of them and that particular manufacturer always sparks off spirited discussion..

The measurement setup is as follows:

The unit is setup in engage mode, with unity gain, max treshhold, min
ratio, limiter bypassed, gate bypassed (both by turning the pot toward
disengage), time constants in auto, ie. as close to bypass as it goes
without deenergizing the bypass relay.

A 123 Fluke Scopemeter is placed across pins 2 and 3 on the output XLR and
set to AC Volts, auto range.

A Fostex TT15 tone generator (the small cigarette pack sized one) is set to 0dB level, (measured as 980 millivolts unloaded) and 1kHz frequency. Its output is placed between pin 1 of the input XLR and pin 1 of the output
XLR, via a 1 kiloOhm resistor to act as current limiter; since the DC
resistance between the two points is very close to nil and I have my doubts about the current drive capacity of the TT15. Measuring the output of the TT15 loaded vith the resistor shows around 962 millivolts, so there should be some current.

With the oscillator set to off, the Scopemeter shows a broadband noise
floor and a max value of around 2.2 millivolts. We are looking to the
output driver noise of the Composer, practically. Listening over the
measurement point is virtually silent, too.

With the oscillator set to on, there is no change. The noise floor does not
change its visual scope appearance, the peak value stays the same.
Listening to the output again reveals no trace of any foreign signal.

I would preliminary conclude that this means that the Composer is free of
Pin 1 problems. I do have two questions, though:

1. Does the setup seem sensible?

2. Does the current drive capacity of the interference source (the TT15
oscillator) affect the test setup? I would guess so, which is why I put
the resistor in place. Would I get different results if I placed
something with more current beef in the place of the TT15?