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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: OP-AMPS FOR PHONO PREAMP posted by Dan on May 15, 1999 at 20:10:11:
Hi there,A few years back (before permanently switching to valves) I designed what I considered the "ultimate" Solid State Phono-Pre.
This was optimised for using the OPA-627 or (better) the OPA-637.
Extreme RIAA accuracy to what is actually cut on the record (and which deviates notably from the published spec). It included a RIAA EQ network designed to account for the loading of the output of the Op-Amp by the RIAA Network (most active NFB Eq-ed RIAA Amp's do not take this into account, causing severe distortion in the Treble due to excessive loading of the Output).
There was also a MC "headamp" using a single J-Fet. The whole design had only one (Film) Capacitor in the Signalpath (and the two polystyren RIAA EQ ones of course) for Moving Magnet Cartridges and two for Moving Coil.
Together with powering the Pre from a pair of 12V Lead Acid Batteries, this RIAA Pre managed to beat the stuffing out of quite a few expensive Phono-Stages (both Valve and Solid State)....
I used this unit for a good while as part of a passive Controll Unit for Line-Sources.
Most people would think the OPA-627 too noisy for this application, yet the reverse is true. With the Source-Impedance presented by most Moving Magnet Catrtridges, the OPA-627 has a noise-advantage over both the AD797 and the NE5534.
The AD797 will be less noisy (not much though) with High Output Moving Coil Cartridges. But both the NE5534 and the AD797 require a large Value DC Blocking Capacitor directly in the Input (due to the comparably high input leakage current). This usually requires a large Value Electrolytic Capacitor which is operated without the DC bias required for even modest linearity and as a result such circuits often show pretty bad distortion behavoir as the hysteresis distortion within the 'lytic Capacitor causes a THD of easily 0.1% and more at the frequency extremes.
The Design was supposed to be included into the Analogue Addicts Web-Site, but this has never happend. If you are interested I can e-mail you the Files (essentially a web-page).
If there is interest to host this in the Asylum FAQ Pages, let me know....
Later Thorsten
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Follow Ups
- Re: OP-AMPS FOR PHONO PREAMP - Thorsten 09:27:51 05/17/99 (0)
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