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ARSCLIST  January 2010

ARSCLIST January 2010

Subject:

Re: Max length on audio cables?

From:

Tom Fine <[log in to unmask]>

Reply-To:

Association for Recorded Sound Discussion List <[log in to unmask]>

Date:

Wed, 20 Jan 2010 15:44:27 -0500

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (113 lines)

For what it's worth, I was always taught -- and this was universal, every person I ever knew who was 
a professional audio person told me the same thing -- phono cartridges want the shortest cable 
length possible to the preamp, and they need proper loading to accurately reproduce the mechanical 
energy generated by the groove moving against the needle. If the cartridge's response is rolled off 
by cable capacitance or improper loading, the preamp has no hope of reproducing the RIAA (or other) 
curve correctly.

In theory, it's a Good Thing to have this new generation of turntables with a preamp built right in, 
with very short cable lengths from the cartridge to its R/C load and the preamp input. Whether it's 
executed properly is up to the manufacturers (ie a good-quality preamp that can handle a range of 
cartridge output levels and is well-shielded from turntable motor noise and motor power supply 
noise). Reviews I've read indicate some do it better than others.

Many Ye Olde Broadcast Turntables had the preamp built into the turntable base/cabinet, thus keeping 
low-level unblanced runs from the cartridge as short as possible.

-- Tom Fine

----- Original Message ----- 
From: "Richard L. Hess" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 20, 2010 1:44 PM
Subject: Re: [ARSCLIST] Max length on audio cables?


> Hi, Don,
>
> Thank you for the commentary - further thoughts inline, below.
>
> At 03:08 AM 2010-01-20, Don Cox wrote:
>>On 17/01/2010, Richard L. Hess wrote:
>> > Jan,
>> >
>> >
>> > Higher impedance circuits, and especially unbalanced ones, should be
>> > kept short -- typically in the neighbourhood of 3 m or less.
>> >
>> > Phono cartridge connections and Nakamichi cassette machine unbalanced
>> > outputs are especially sensitive to cable loading.
>> >
>>I think this is a problem with most consumer and "hi fi" equipment using
>>unbalanced connectors, and accounts for much of the subjective
>>description found in magazines.
>
> Indeed, this is very much the problem that you defined. With any inductive source, the inductive 
> reactance increases with frequency, so phono cartridges and tape heads are a huge challenge with 
> interconnection. But, since these are low-level devices and the head-to-preamp connection and 
> interface is hopefully well-engineered and the preamp is more-or-less tightly coupled to the 
> transducer, this is not where the surprise comes in.
>
> The Nakamichi Dragon--for all its wonderfulness--has an output level control as the last element 
> in the circuit--almost.
>
> The high side of the 10 k ohm audio-taper pot is fed directly from the output of an IC operational 
> amplifier (essentially a zero-ohm source impedance) and the low side of the pot is grounded. The 
> wiper is fed through a 2,200 ohm resistor to the output jack with some transistors shunting that 
> lead to ground to dim and mute the output to avoid propagating transients and noise under certain 
> operating modes (I have not deciphered the logic driving these transistors--they do not affect the 
> operating output impedance)
>
> In the normal operating modes, then the MINIMUM output impedance is 2,200 ohms (the resistor) and 
> that is with the pot full up (or less-usefully, off). The worst case source impedance is when the 
> pot is at - 6 dB (half level). In that case, the wiper is electrically centered so the wiper's 
> output impedance is 5,000/2 or 2,500 ohms, added to the 2,200 ohm fixed resistor, or 4,700 ohms.
>
> 500 pF of capacitance at 20 kHz provides a capacitive reactance of
> 1/(2*pi*f*c) or about 16,000 ohms. So, even with that small amount of capacitance across the 
> output, we see a loss of at least 1.1 dB at 20 kHz and a maximum loss at -6 dB output of 2.2 dB at 
> 20 kHz.
>
> I think looking into this for many consumer pieces of equipment we will see the interaction 
> between source parameters, cable parameters, and input parameters. This is a major part of the 
> reason why different combinations of equipment sound different. I suspect, if properly analyzed, 
> the mystique would go away.
>
>
>>A buffer amp with high input impedance and low output impedance can
>>help.
>
> Very much so -- for the Dragons, I have installed Aphex 124A balancing units close to the machine. 
> http://www.aphex.com/124A.htm
> These are often available on eBay for about $100 each, used. I like their sound (or lack of 
> colouration), their interface, and their internal power supplies. They are easy to use and to 
> manage.
>
> I would not use a transformer-equipped box on the Dragon as we don't really know how the 
> transformer will react being fed a signal at up to 4,700 ohms source impedance.
>
>> > You might be better off leaving the A-D converters in the control
>> > room and running digital signals to the computers (AES/EBU either on
>> > 110 ohm twisted pair or 75 ohm coax). If I were re-building my
>> > transfer suite, I would consider MADI and local converters for each
>> > machine. While it is more expensive than wires and patchbays, the
>> > price differential is narrowing.
>> >
>>Or one could run digital on optical cables.
>
> I have not researched it in depth, but I think if you're going to do this, you are best off 
> running single mode glass fibre and not the inexpensive multimode plastic fibre if you want utmost 
> performance. Apparently eye patterns and jitter suffer on the multimode plastic fibre.
>
> This was just something I've filed away without any research except hearing some papers presented 
> at an AES a while ago.
>
> Cheers,
>
> Richard
>
> Richard L. Hess                   email: [log in to unmask]
> Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
> Detailed contact information: http://www.richardhess.com/tape/contact.htm
> Quality tape transfers -- even from hard-to-play tapes. 

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