Moving-Magnet Head Amp - without RIAA

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Battling to make any sense of this, care to explain? How can proper loading alone create a flat response?
I'm not surprised that it didn't make sense. My comment was entirely too brief.

I put "flat" in quotes because it's not flat in the sense that the original, pre-emphasized audio comes through flat.

What I meant was in reference to the fact that improper loading of a cartridge can effectively add another unwanted EQ, and that won't be corrected by the RIAA decoder. So, in that sense, this phono preamp is "flat."

Just as a reminder, vinyl involves several stages, two of which involve significant EQ. The rest of the stages should be flat, or else the EQ pairing doesn't restore the original.

You start with music that has the desired tones. In the old days, the mastering process included vinyl, but these days it cannot bake that process in because of CD and streaming audio. After mastering, but before the vinyl is cut, the RIAA encoding EQ is used. After that electronic process, we hope that cutting the record is as transparent as possible, and playback of the record is also as transparent as possible. After the audio has been recovered from the vinyl, RIAA decoding EQ is used. Often, the RIAA decoding EQ is implemented in analog circuits, but that requires expensive matching of capacitors and probably a bit more noise due to the complexities of the analog circuits. More recently, it's become popular to implement the RIAA decoding EQ in the digital realm, especially when converting vintage vinyl to digital for archival of music that is no longer available. When you move the RIAA decoding EQ from the analog domain to the digital domain, you need the phono preamp to be "flat" - not flat in the sense of comparing to the original audio, but flat in the sense of what was actually recorded in the grooves. Unfortunately, just moving the RIAA decoding EQ from analog to digital is not the whole story, because the phono preamp can still distort the audio if it has too much capacitance, too little capacitance, or if too much current is forced through the delicate cartridge windings and causes saturation. You can even burn out a cartridge with excessive current, so the preamp design has to be tailored to the job at hand - not just a microphone preamp circuit reused.

Anyway, there are many more details that could be discussed, but the executive summary is this: Apart from the RIAA encoding and decoding stages, all other parts of the vinyl signal chain should be "flat."

Of course, there are exceptions to this simplification, because clever people save money on parts by taking advantage of EQ in the cartridge preamp stage to implement part of the RIAA decoder stage. To be clear, my goal was to avoid any EQ at all in the cartridge preamp stage. Although I've developed my own digital RIAA decoding DSP, I wouldn't want to rewrite that to adjust for part of the EQ being done in the preamp. Besides, I cannot use my own DSP on every playback device, so I need a phono preamp that is "flat" so that a third-party RIAA decoder EQ can be used without incorrect results.

Does that make any more sense?
 
I'm not hearing too much treble because the cartridge is properly loaded, and the intermediate result is "flat" such that the subsequent digital RIAA restores everything to normal.
Battling to make any sense of this, care to explain? How can proper loading alone create a flat response?
I should also point out "the subsequent digital RIAA" - in other words, I'm not trying to say that "proper loading alone create a flat response." The system I've designed relies on subsequent stages to restore the audio to the original response.

I'm merely treating the cartridge as a pure transducer - from physical groove to electrical signal - such that the transducer stage should be as flat as possible. If it's not flat, then the subsequent digital RIAA decoding process will not produce the correct results. There would either be too much EQ or too little EQ if the transducer and preamp are not flat.
 
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I still don't understand what you are saying. A MM cart loaded with 47K and recommended capacitance is what the the manufacturer considers "flat". Using a low noise FET buffer into a soundcard with a good mic pre-amp and DSP eq has little or no disadvantage with respect to noise. Please elaborate.
 
I still don't understand what you are saying. A MM cart loaded with 47K and recommended capacitance is what the the manufacturer considers "flat". Using a low noise FET buffer into a soundcard with a good mic pre-amp and DSP eq has little or no disadvantage with respect to noise. Please elaborate.
The phono preamp circuit that I adapted from Doug Self's "Small Signal Audio Design" has the required 47 kΩ and 330 pF load. I checked the Ortofon documentation to confirm the optimum resistive and capacitive loads for their cartridges that I own.

Doug simply recommends the NE5534 (or any of a few other op-amps) for reasons outlined in his book (like low noise). Another chapter features discrete transistor circuits, but those happen to be BJT instead of FET.

It seems like we're saying the same thing: That it's fine to move the RIAA EQ into DSP. I'm just pointing out that the phono preamp does not include an analog RIAA EQ - and I'm calling that "flat" because there's no RIAA decoding.
 
You have stated just obvious stuff which does not explain post #119 at all. Is the end result sounding unexpectedly dull?
No, the end result of the circuit I've built does not sound dull. When I listen, I use the RIAA EQ in my DSP, between the ADC and the DAC. The only problem is a little hum, presumably from the compact power supply I'm using.

If my statements are all just obvious stuff, then I don't quite understand why explanations are needed.

I'm confused because some of the comments in this thread talk about adding parts of the RIAA filter to the analog circuits, and that doesn't make any sense to me. My DSP is performing the exact RIAA EQ, so any attempt to mess around with "the 2nd RIAA pole" in the analog circuit will be redundant to the DSP.
 
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