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iant

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About iant

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  • Birthday 07/01/1953

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    Balwyn Melb
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    Australia
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    Ian

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  1. You're dealing with two opamps with vastly different GBW bandwidths,8Mhz vs 55Mhz.Any difference soundwise could easily be attributed to incipient instability in the 55Mhz device(LM4562). This opamp is going to need very careful layout and decoupling and forget about using sockets or it's going to be quite unhappy.At the very least you'll need a CRO to check for stability. https://www.analog.com/media/en/technical-documentation/application-notes/AN-202.pdf
  2. William Thakker in Germany has good stocks of these.Have you checked his Ebay store- free postage on the Super OM20.
  3. Audio Technica quote their compliance at 100hz instead of the more customary 10hz.An approximate rule of thumb is to double the 100hz dynamic compliance figure to give a comparable result at 10hz ie. 14cu.This would result in a resonant freq of approx 12hz in the G707.
  4. Digikey.com have a good range of larger caps that may meet your criteria including examples from EPCOS,KEMET & Nichicon.I've found their service excellent with fresh stock and prompt delivery within a few days.
  5. According to the service manual at Vinyl Engine this is a 0.047uf "noise canceller" or spark quench capacitor. An X2/Y2 rated equivalent currently available is the Panasonic ECQU2A473ML available at RS Components etc.
  6. "On "modern" 78s like the Elvis one in the picture, the bass is almost too much " That's because ceramic/crystal cartridges already have inbuilt equalisation ie a flat response curve and do not require further bass boost/treble cut from the RIAA preamp.They also have typically 200-500mv output which will grossly overload a typical mm input.Fed into a normal line input via a 500k-1m series resistor they'll sound quite reasonable,maybe not hifi but acceptable.
  7. One omission indicative of less than stellar design is the absence of a bleeder resistor at the output cap.Lack of this resistor (usually about 100k)will cause disconcerting clicks as the preamp is switched in/out of circuit and the output cap charges/discharges to load.
  8. Different ball game with valves,much greater headroom on offer passive eq is a viable proposition. No personal experience of the complicated maths calculations required however I'd be quite tempted to try another of Thorsten's little masterpieces.
  9. Active RIAA eq with opamps uses the time honoured method of wrapping the eq filters around the series feedback network.As used in countless phono preamps. And for good reason as Doug Self describes in his book Electronics For Vinyl "The notion of a completely passive RIAA stage is a daft idea where the noise and overload performance is inevitably compromised"
  10. Having built both active and passive phono eq's the active version wins subjectively every time.Cleaner,more dynamic and much less inclined to clip on heavy passages when driven with a high output MM cartridge.
  11. To quote the estimable Mr Loesch "Any passive EQ solution introduce noise and headroom penalties and while in Valve circuits we have loads of headroom and often circuit resistances dominating the noise, with Op-Amp Phonostages we typically have a +/-12V supply, which limits output swing severely, typhically to less than 20V P-P which is around +20dbu. Using a passive EQ wedged between two Op-Amp's produces a humungous headroom penalty, even just having the 75uS HF eq between two stages drops some headroom. Apart from the noise and headroom issues another key factor in favour of the single stage active RIAA when using Op-Amp's is that the open loop gain falls with a first order funcion above a fairly low (usually below 100Hz) frequency. This means also the available feedback to correct amplifier non-linearity drops by 20db every time we go up a decade in frequency. So if we have a "flat" amplifier with 40db gain (as we might use in a passive EQ Phono Stage) we have for an Op-Amp with 120db open loop gain and a 10Hz corner frequency (a fairly common construct) at 100Hz a feedback factor of 60db, at 1KHz 40db and at 10KHz 20db. Worse, at 100KHz we are right out of negative feedback. So, between 100Hz and 10KHz the feedback factors changes by some 40db!!! This means distortion will rise strongly towards higher audio frequency and if any supersonic noise is present (groove noise, needle resonance in MC's, RFI/EMI) things will really go haywire, also the distortion profile will vary with frequency and so on".
  12. Schematics available here.It's using the less desirable passive RIAA arrangement which has noise and headroom penalties when using opamps (ref.Thorsten Loesch Analogue Addicts preamplifier 2006) https://www.muffsy.com/schematics.html
  13. Sadly suffering with advanced prostate cancer. * SL* - Aggressive Prostate Cancer (2002) - - Stage 4 PrC (2016) - - Hospice Care (2018) - http://www.linkwitzlab.com/about_me.htm
  14. And yet another industry guru Thorsten Loesch loves silver mica especially the Soshins,go figure.Best advice is try 'em all and decide which YOU prefer.
  15. Very good low mass arm,another classic like the Grace.
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