xiaohan@engin.umich.edu (Xiaohan Wang) (01/16/91)
The other day I accidentally compared the headphone output of my CD player and the headphone output of my tuner/preamp Adcom GTP-400. To my great surprise, the output of the GTP-400 is a lot noisier than that of the CD player. Is this normal, or is it some kind of defects with my (4 month-old) GTP-400? I'm going to call Adcom. I'd also like to hear from other GTP-400 owners in the netland about their experience and comments. XH Wang
peter@apple.com (Peter Tapscott ) (01/18/91)
In article <8975@uwm.edu> you write: >The other day I accidentally compared the headphone output of my CD >player and the headphone output of my tuner/preamp Adcom GTP-400. >To my great surprise, the output of the GTP-400 is a lot noisier >than that of the CD player. Is this normal, or is it some kind of >defects with my (4 month-old) GTP-400? I'm going to call Adcom. >I'd also like to hear from other GTP-400 owners in the netland >about their experience and comments. > >XH Wang Have you been following the interconnect discussion in rec.audio? Perhaps that discussion should really be taking place in this forum, since disagreements so quickly digress into name calling in rec.audio. At any rate, the problem could be with your preamp or your interconnects. If you have a lot of equipment with transformers and line cords near your interconnect cable, using a better interconnect may help. This posting discusses interconnects; preamp problems will have to be covered by other postings. To summarize my assertions in rec.audio about interconnects: my current favorite interconnect is a twisted-pair shielded cable with the shield connected at the source end and insulated at the other end. The twisted pair are used to carry the signal and the return, while the shield carries no signal (only noise). I was suprised when I changed from some ~$20 coaxial cable to the twisted-pair shielded: the noise was significantly lower. (This was observed by listening with Stax headphones.) Interconnects like these can be made from parts from Old Colony. The cost is ~$15 for 4 connectors, and $1.25/foot for cable, so a 3-foot pair costs about $22.50. This seems a lot cheaper than Monster twisted-pair shielded interconnects. (I don't remember the price, but Monster has a number of lower priced shielded cables, but the twisted-pair shielded cables are significantly more expensive.) To support my observations, Seth Bradley posted this excerpt from a book noise reduction: ----------------------------------------------------------- In article <21293@versatc.versatec.COM> peter@versatc.UUCP writes: >Perhaps Seth should post his source of information on noise >reduction, or quote a couple lines? The book is "Noise Reduction Techniques in Electronic Systems", by Henry W. Ott. Published by John Wiley & Sons, 1976. Its an excellent reference for anyone who has to deal with noise and grounding issues in electronic applications. Here's a few pertinent quotes: "A coaxial cable grounded at one point provides a good degree of protection from capacitive pickup. But if a noise current flows in the shield, a noise voltage is produced. Its magnitude is equal to the shield current times the shield resistance. Since the shield is part of the signal path, this noise voltage appears as noise in series with the input signal. A double-shielded, or triaxial, cable with insulation between the two shields can eliminate the noise produced by the shield resisatnce. The noise current flows in the outer shield, and the signal current flows in the inner shield. The two currents (signal and noise), therefore, do not flow through a common impedance." "A shielded twisted pair has characteristics similar to a triaxial cable and is not as expensive or awkward. The signal current flows in the two inner conductors, and any noise currents flow in the shield. Common-res- istance coupling is eliminated. In addition, any shield current is coupled equally into both inner conductors by mutual inductance, and the voltages therefore cancel." "The shielded twisted pair provides the best shielding for low-frequency signals, in which magnetic pickup is the major problem." (low frequency is typically defined here as < 100KHz). -- Seth J. Bradley Address: sjb@dalek.iwarp.intel.com Or: dalek.UUCP!sjb -- |----------------------------------------------------------------------| | peter@versatc.VERSATEC.COM -OR- {ames|apple|sun}!versatc!peter| | Peter Tapscott - Xerox Engineering Systems, Versatec Products | | 2805 Bowers Avenue, Santa Clara, Calif (408)982-4235 |