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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 3rd Aug 2020, 6:41 pm   #121
john.north
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Default Re: Very low noise op amp recommendations?

I have a PW Winton amp with toroidal transformer and fet output transistors which I built in 1979. It’s pre stages were tlo72s.It has been in continuous use with sme3009 arm connoisseur bd1 deck and Nagaoka MP110 cartridge, and Telefunken 710s. I had slight hiss with the volume control at about 11 o’clock.
A few weeks ago I replaced the first stage with a surface mount OPA1642 dual jfet and stage 2 and 3 with OPA2134. I Can now turn it up to about 2 o’clock before I hear any hiss. This set up sounds just as good as a new Denon PMA600NE with Dali spektor2s.
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Old 3rd Aug 2020, 9:56 pm   #122
bikerhifinut
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Default Re: Very low noise op amp recommendations?

First lash up in use. NE5532A. DIY thread for pics as Its more relevant there.

A.
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Old 8th Aug 2020, 1:09 am   #123
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Default Re: Very low noise op amp recommendations?

Quote:
Originally Posted by Craig Sawyers View Post
Peter Baxandall published an excellent letter to follow up on Stanley Lipschitz's seminal paper on RIAA networks.
Thanks much, Craig, for posting that Baxandall letter, which I had yet to find on the web. The Lipschitz article to which it responds is more readily available, for example at: https://pearl-hifi.com/06_Lit_Archiv..._RIAA_JAES.pdf.

Baxandall had provided a brief synopsis of that letter, and his NE5534-based circuit, circuit, in Talbot-Smith (1), but it is good to now have the full version. It is classic Baxandall in the way that it was written. It was not the first time that he had provided what was effectively a technical paper in letter form rather than as an article or a paper. Previously he had done the same in respect of what became known as the “Baxandall diode”, in the letters section of Wireless World (WW) 1969 September.

I had not been aware of his 1967 RIAA stage work, but I can now see that his contribution to Amos (2) was probably a distillation of this. Therein he provided a qualitative assessment of the relative noise performance of the various circuits. Judging by his articles in WW 1968 November and December, noise might have been a specialty of his in his “day job” at the time, which seems to have been RF-oriented. Possibly Baxandall was the first to flag the T6 issue with series feedback circuits, neglect of which was seen by Lipschitz as a common source of RIAA curve errors.


Cheers,


(1) M. Talbot-Smith, editor; “Audio Engineers Reference Book”, 2nd edition; Focal Press, 1999; ISBN 0 240 51528 5. See section 2.8, “Power amplifiers, control units and preamplifiers” by P.J. Baxandall. I assume that this section was largely unchanged from that in the 1st edition, 1994.
(2) S.W. Amos, editor; ,”Radio, TV and Audio Technical Reference Book”, Newnes-Butterworths, 1977; ISBN 0 408 00259 X. See section 14, “High-Fidelity Amplifiers”, by P.J. Baxandall.
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Old 8th Aug 2020, 5:16 am   #124
Radio Wrangler
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Default Re: Very low noise op amp recommendations?

While we're dissecting the accuracy of the RIAA replay equalisation, it would seem appropriate to question the accuracy of equalisation at the cutting stage.

Has anyone analysed those networks?

Of course it's probably academic because the signal will have been twiddled at the mixing stage to suit the studio's speakers as well as the hearing and tastes of the operator.

If we are trying to re-create the original sound, the devil's advocate's question would be 'Which one?'

Trying for pragmatism, I use a reasonably accurate (not quite perfectly accurate) circuit by Baxandall and don't worry about it. Then I allow myself to twiddle frequency response to my own taste. I might disagree with the mixing and cutting people, my speakers are definitely different to theirs and my hearing and tastes probably are as well. I'm not sure which sound I'm trying to re-create. I'm just listening to the music, to the performance. A flat-stereo rendition of a three-dimensional experience.

What I am punctilious about is in never saying that my setup is right or better than others.

Small variations in frequency response do seem to be audible. It's difficult to put your finger on just what difference you're hearing, but a quick flick test between two alternatives can show up as a perceived difference. But instead of leaping in saying this one is right and that one is wrong. I'm damned if I know. It's quite possible to perceive a difference and still be unsure which one you prefer. It's unlikely to come down to right and wrong. Both will be wrong, but different sorts of wrong.

All subjects seem bottomless and infinite in extent if infinitesimal differences are pursued. The art lies in knowing when to stop.

To quote Dan Rowan and Dick Martin, 'If it feels good, do it!'

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Old 8th Aug 2020, 7:06 am   #125
Ted Kendall
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Default Re: Very low noise op amp recommendations?

How do you set up the cutting EQ? Easy! You make a test cut and check the frequency response as played on the lathe's pickup, tweaking the adjustments for best response.

How do you set up the lathe's pickup for flat response? Easy! You play a test disc and tweak the replay EQ for best response.

How do you make a test disc? You cut the best guess and then calibrate it by Buchmann-Meyer effect in a light box, iterating for best response.

How do you calibrate a light box? Easy!....
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Old 8th Aug 2020, 7:21 am   #126
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Default Re: Very low noise op amp recommendations?

Ouroboros!

David
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Old 8th Aug 2020, 8:07 am   #127
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Default Re: Very low noise op amp recommendations?

"There's a hole in my bucket, dear Lisa, dear Lisa..."
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Old 8th Aug 2020, 12:24 pm   #128
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Default Re: Very low noise op amp recommendations?

RIAA issues aside, the cutting engineer often makes adjustments to the signal fed to the lathe to compensate for weaknesses in the format related to out-of-phase bass, very low bass, very high treble, dynamics etc, and the poorer response at the slower inner grooves. Whereas with a CD, such "mastering" in this sense is much less an issue if at all.

Often the vinyl sound we hear is a more processed sound designed to compensate for, and disguise the limitations of the format.
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Old 8th Aug 2020, 10:37 pm   #129
Ted Kendall
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Default Re: Very low noise op amp recommendations?

Very true. Actually the calibration process is not quite recursive, as the graticule in the light box is a straightforward ruler, in effect, but it is long and convoluted. It's still nice to know that you can get one part of the chain exactly right, though.
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