sjc@angband.UUCP (Steve Correll) (01/05/85)
> My VHS HiFi deck is located about 20' away from my stereo components, > so in order to record FM simulcasts and play back through my stereo > system, I'll have rather long runs of cables carrying line-level > signals. Are there any problems which could arise from this-- > frequency response aberrations, increased noise or hum, etc. > Should I buy special cables, or will any rotgut $1.99 department store > cable do? > I'd use the highest quality connecting cables I can get, for two reasons: > 1) There's a lot of EMI/RFI out there and you don't want that stuff getting > into your signal lines - for better or worse most VCRs, like most line > level audio stuff, are high impedance (typically around 10K or so) and thus > are susceptable to hum, hash, and noise pickup. > 2) You want a cable that has low attenuation at video frequencies. Assuming the second posting refers to the first, I disagree. Connecting a cable to a VCR doesn't make it carry a video signal. The signal at the tape-output of an FM tuner or receiver is bandlimited to less than 19kHz. If the "source" impedance of the tape-output of your preamp or receiver is 600 ohms or so, 20 feet of cable is no problem. If the source impedance is several thousand ohms, then long cables could affect frequency response (roughly speaking, the source impedance forms the top half of a voltage divider, and the cable capacitance in parallel with the VCR input impedance forms the bottom half). High source impedance also makes the setup more susceptible to induced hum and noise. Ironically, the average mid-fi receiver which uses IC op amps is more likely to provide a low source impedance than an audiophile preamp which uses the minimum number of tubes with the minimum amount of negative feedback. Sometimes spec sheets specify the tape-output impedance; or your repair shop can determine it from the schematics; or you can load the output with a resistor, measure how much it changes when you remove the load, and use the voltage-divider model to calculate the answer. But I'd say the best approach is to try it both with 3 foot cables and with 20 foot cables. If you can't hear any difference, don't worry about it. If you hear a difference, low-capacitance cables may help (unfortunately, it's not clear that the capacitance of a cable is related to its price in the world of consumer audio). Better still, if you're handy with a soldering iron and a couple of op amps, you could put a buffer amp in a little box between the tape-output and the cables. -- --Steve Correll sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc
ed@mtxinu.UUCP (Ed Gould) (01/07/85)
> My VHS HiFi deck is located about 20' away from my stereo components, > so in order to record FM simulcasts and play back through my stereo > system, I'll have rather long runs of cables carrying line-level > signals. Are there any problems which could arise from this-- > frequency response aberrations, increased noise or hum, etc. > Should I buy special cables, or will any rotgut $1.99 department store > cable do? > I'd use the highest quality connecting cables I can get, for two reasons: > 1) There's a lot of EMI/RFI out there and you don't want that stuff getting > into your signal lines - for better or worse most VCRs, like most line > level audio stuff, are high impedance (typically around 10K or so) and thus > are susceptable to hum, hash, and noise pickup. > 2) You want a cable that has low attenuation at video frequencies. What I've done with my Beta HiFi is connect it close to my stereo gear (with 1.5 meter Monster Cables) and run a long (23 - 30 feet) coax from the RF output of the VCR to the TV. Running an extra 20' of RF cable isn't a problem, partly because it's all impedance matched at 75 ohms, and this keeps the audio leads short. -- Ed Gould {ucbvax,decvax}!mtxinu!ed
dmmartindale@watcgl.UUCP (Dave Martindale) (01/09/85)
In article <36@angband.UUCP> sjc@angband.UUCP (Steve Correll) writes: >Better still, if you're handy with a soldering >iron and a couple of op amps, you could put a buffer amp in a little box >between the tape-output and the cables. I've wanted to do this in the past. However, I'm not sufficiently familiar with analog circuitry to design a buffer amp whose quality is equal to that of semi-audiophile equipment. Can anyone point me at references?