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Old 2nd December 2011, 06:21 AM   #18641
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Quote:
Originally Posted by Steve Eddy View Post
Seems easy enough to avoid using cables made from unrolled capacitors.

se
The cable capacitance is not the reason (in case that you do not drive 100 Feet )
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Old 2nd December 2011, 06:28 AM   #18642
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Pavel,

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it is more than 30 dB, even for recorded symphonies. Much more.
Crest factor is the peak to average ratio.

30dB peak to average is generally not found during orchestral crescendo's (when the level is loudest), but at lower levels.

I checked quite a few recordings even completely uncompressed ones and I have yet to see 20dB Crest factor at very high levels on classical (telarc's 1812 excluded of course). With most current pop music I am struggling to see a 10dB Crest factor. I think the worst I saw so far was around 3dB...

I personally feel that 20dB Headroom over 85dB suffices normally (this goes back to my days as recording engineer in East Germany), a bit more of course does no harm, just like having a big powerful motor in your car does no harm.

This means a pair of "average" 87dB/W/m efficient speakers at 3-4m listening distance needs at least 200 clean Watt's.

For a pair of 97dB/W/m efficient speakers like a pair of Tannoy Monitor Reds or the Crescendo Grande I designed for DIYHiFisupply around 20 Watt suffice.

With something like my 104dB/W/m Magnificats around 4 Watt suffice.

I would say being 3dB short (halve the listed power) is no big deal either, but being 10dB short (one tenth the listed power) is a big deal...

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Old 2nd December 2011, 06:35 AM   #18643
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Quote:
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The cable capacitance is not the reason (in case that you do not drive 100 Feet )
Then what is the reason? Inductance? Resistance? Dark matter?

se
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Old 2nd December 2011, 06:38 AM   #18644
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Quote:
Originally Posted by ThorstenL View Post
30dB peak to average is generally not found during orchestral crescendo's (when the level is loudest), but at lower levels.

I checked quite a few recordings even completely uncompressed ones and I have yet to see 20dB Crest factor at very high levels on classical (telarc's 1812 excluded of course). With most current pop music I am struggling to see a 10dB Crest factor. I think the worst I saw so far was around 3dB...

I personally feel that 20dB Headroom over 85dB suffices normally (this goes back to my days as recording engineer in East Germany), a bit more of course does no harm, just like having a big powerful motor in your car does no harm.

This means a pair of "average" 87dB/W/m efficient speakers at 3-4m listening distance needs at least 200 clean Watt's.
Thanks for the clarification, Thorsten. 200W of needed clean power for 87dB/W/m speaker corresponds to my real life experience.
My screenshot is Telarc, Berlioz, Symphonie Fantastique.
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Last edited by PMA; 2nd December 2011 at 06:42 AM.
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Old 2nd December 2011, 06:43 AM   #18645
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Then what is the reason? Inductance? Resistance? Dark matter?

se
Whatever else. You can easily make a test with 100 pF capacitor vs. 1,5 m of link cable.
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Old 2nd December 2011, 06:51 AM   #18646
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Whatever else. You can easily make a test with 100 pF capacitor vs. 1,5 m of link cable.
Why make a test with 100pF of capacitance when you say capacitance isn't the problem?

You said that an unbuffered opamp output "...will never drive the cable well." Drive the cable in what respect exactly? What aspect of a typical cable is difficult to drive save for its capacitance?

se
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Old 2nd December 2011, 08:19 AM   #18647
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About 25 or more years ago, with the introduction of quiet dual jfets from Toshiba and others, I tried to interest Deane Jensen in using them. I did this as repayment of a favor that he did for me in about 1978-79, giving me an Apple compatible cassette with a useful filter design program for my Apple 2 computer. This really saved my socks in making difficult head bump correction filters for my first master recorder for Mobile Fidelity.
I offered him my input, but he rejected it, until a year or so later when my technician who knew him better, was approached by Deane about using jfets. He ended his life relatively soon after.
Parasound was using a Jensen type topology for their preamp that they produced, before my time, and THEY had substituted jfets on the input with great success. This was about 1989 or so, when they did this.

All else being equal, and with source impedances over 100 ohms, jfets are almost always a winner, transformer or no.

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Old 2nd December 2011, 09:37 AM   #18648
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All else being equal, and with source impedances over 100 ohms, jfets are almost always a winner, transformer or no.
I've built the classic Demrow/Cohen preamp with FET's instead of LM394's and it was wonderful. That's why I was surprised that George Massenburg is so down on FET's, possibly just to be different?
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Old 2nd December 2011, 09:44 AM   #18649
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I never knew there was anything about it there? I had a standing sample request for them with Paul for years.

I figured the LSJ74 was just like one of them yellow submarines, or it must've been one of them "Unidentified Flying Cupcakes". Or a pigment of me imagination.
They sent 10 right away, even with a new datasheet that looked like they were ready for a rollout. Even Google now turns up mostly only our conversations. How would anyone else even know to ask for samples?
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Old 2nd December 2011, 09:57 AM   #18650
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I asked for samples of LSK170 and LSJ74, never received any answer. I was prepared to buy hundreds (at least) of both.
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