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Old 27th January 2013, 11:04 PM   #71
SY is offline SY  United States
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Quote:
Originally Posted by popilin View Post

The only reference to noise, I could find is

The Sound of Silence: Lowest-Noise Riaa Phono-Amps: Designer's Guide - Burkhard Vogel - Google Libros

Which gives us for the ECC82, on a 20KHz bandwith, something like Vn ≈ 6.4μV RMS, well below the estimate of post#16.
Vogel's treatment of noise is quite good.

FWIW, Mullard's measurements of EF86 at 1.25mA anode current are about 2uV over 25Hz-10kHz (equivalent to 2.8uV over 25-20k). That's quite quiet for a pentode! As MJ points out, this is still somewhat higher than the RF-based equations predict, but still the same order of magnitude. If I remember correctly, Vogel ended up with a triode ENR equation which was roughly double that of the RF equation, i.e., something like 5/gm.

As a practical matter, I don't ever use phono stages with 20k output impedances, and I've never found the noise from a 50-100k pot in a tube line amp to be an issue. If you're concerned about it, use a transformer volume control.
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Old 27th January 2013, 11:48 PM   #72
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Quote:
Originally Posted by SY View Post
Vogel's treatment of noise is quite good.
Yes, right? I love it, unfortunately I can't read the whole thing, it's just a sample.

Quote:
Originally Posted by SY View Post
FWIW, Mullard's measurements of EF86 at 1.25mA anode current are about 2uV over 25Hz-10kHz (equivalent to 2.8uV over 25-20k). That's quite quiet for a pentode! As MJ points out, this is still somewhat higher than the RF-based equations predict, but still the same order of magnitude. If I remember correctly, Vogel ended up with a triode ENR equation which was roughly double that of the RF equation, i.e., something like 5/gm.
BTW. Morgan Jones third edition is one of my favorite books.
I have read that section several times, and predictions are astonishing.

I have seen something like 3/gm.

Quote:
Originally Posted by SY View Post
As a practical matter, I don't ever use phono stages with 20k output impedances, and I've never found the noise from a 50-100k pot in a tube line amp to be an issue. If you're concerned about it, use a transformer volume control.
Taking as a reference to Allen Wright, and your His Master's Noise, I would never do that, just said that to support my point, but keep it quiet.

I don't get along great with transformers, is also out of my budget.
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Old 27th January 2013, 11:56 PM   #73
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<snip>
I don't get along great with transformers, is also out of my budget.

As big fan of good transformers (my system typically has 4 in the path, and never less than 3 regardless of source) I do have to say a mediocre transformer will be worse than no transformer at all..
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Old 28th January 2013, 12:26 AM   #74
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As big fan of good transformers (my system typically has 4 in the path, and never less than 3 regardless of source) I do have to say a mediocre transformer will be worse than no transformer at all..
I agree with every word, and of memories to me left my last five transformers, more than 80 windings, handmade, during three months.

I hate transformers!
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Old 28th January 2013, 10:34 AM   #75
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For a full treatment of noise in tubes, including flicker noise, I would recommend chapter 8 of 'Amplifying Devices and Low Pass Amplifier Design' by E.M. Cherry and D.E. Hooper. Copies are expensive and hard to come by so I would recommend getting your local library to obtain a copy for you.

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Old 28th January 2013, 12:28 PM   #76
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Originally Posted by ruffrecords View Post
For a full treatment of noise in tubes, including flicker noise, I would recommend chapter 8 of 'Amplifying Devices and Low Pass Amplifier Design' by E.M. Cherry and D.E. Hooper. Copies are expensive and hard to come by so I would recommend getting your local library to obtain a copy for you.

Cheers

Ian
Hi Ian

The scope of our actions is often unexpected, maybe you never imagined that your posts and knowledge you helped me on the other side of the world, always with a clear and friendly style.

It is for this reason that you are among the superheroes of the forum, along with Wavebourn, SY, DF96, Salas and some other, who knows excuse my forgetfulness.

As well I have noted, noise is a rather complex issue, thank you very much for your advice.
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Old 28th January 2013, 01:52 PM   #77
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Quote:
Originally Posted by popilin View Post
Hi Ian

The scope of our actions is often unexpected, maybe you never imagined that your posts and knowledge you helped me on the other side of the world, always with a clear and friendly style.

It is for this reason that you are among the superheroes of the forum, along with Wavebourn, SY, DF96, Salas and some other, who knows excuse my forgetfulness.

As well I have noted, noise is a rather complex issue, thank you very much for your advice.
Thank you for the kind words. It is really nice to know that your efforts are appreciated.

Unfortunately there is very little information on tube noise in the audio band and even less in data sheets. One of the few tube data sheets I have found that does have this information is the E83F. It's Req at RF is 1000 ohms max but in the audio band up to 10KHz it is 30K. OK it is a pentode so partition noise is a big contributor but the difference is 15dB. It's data sheet is here:

E83F @ The National Valve Museum

Cheers

Ian
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Old 4th May 2014, 06:47 PM   #78
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70 khz phono response is possible but the RIAA Eq in the preamp will all but kill any trace of it
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Old 4th May 2014, 08:39 PM   #79
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Originally Posted by stocktrader200 View Post
70 khz phono response is possible but the RIAA Eq in the preamp will all but kill any trace of it
Rise time is inversely proportional to bandwidth, so a phono cartridge which can go up to 70 KHz must be pretty fast. IMHO.

With a properly designed EQ adding the missing 3.18 s time constant, you can go easily to 10 Hz - 50 KHz ( 0.1 dB), so I don't see the problem.
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Old 4th May 2014, 10:10 PM   #80
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RIAA curves place the sensitivity of a flat cartridge at least 40db down at 20 khz from 20hz.
You are correct that in having a mechanical structure that can resolve 50khz is a very good thing.
When youdid the volume pot noise tests, Did you leave the amplifier input impedance at normal value or short the amplifier input to ground?
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