Thanks all for the extra notes here. As regards the input voltage and current at the input of op-amp phono stages. You might have hit on something. Elsewhere on this forum recently, I have asked about a noise/interference sound on the DIRECT output of a Technics SL1500c turntable. What was crazily odd that this noise was being produced even with the turntable unpowered from the mains supply. I tested with 3x different phono-preamps with the same noise result but all of the designs had direct coupled op-amps so I can only imagine the very low voltage might have been the source of the crackling but then again something must have been wrong with the Technics switch-over from internal to direct sourcing. Perhaps a leakage back to the built-in preamps output? I was going to introduce a small series capacitor but forgot to do the experiment and cannot do it now as the turntable has been sent back to the shop from where it was bought. I will report what they find and say what result they got when doing their test usage. Thanks again
personally i don't like the idea of decoupling cap between cartridge and pre amp input. i was getting only worst results from such cap. all my phono pre are DC coupled to my cartridges. any cap at this position will form another filter and if i try to move it out of audible range, cap itself becomes useless (at best).
I thought (in good humor) that Bob's standards for audio capacitors were a wee bit over the top. After he'd been "retired" by National, and I think it was before he'd died. Paul Rako and others were trying to Saran Wrap his cubicle, like Jim Williams' Linear Tech cubicle and move it to the Mountain View CA Computer Museum. It was hopeless. After Bob's cubicle was declared Off Limits, I still managed to take some 35 mm photos.
An EE who worked for me before National had a similar office, but, like Bob, he knew exactly where everything was. The solution was simple - every 3 or 4 years we'd give him a new office and leave the old one intact.
Bob was an asset to National. His presentations and books were always loved by analog and audio EEs. Definitely not a management type. His and Jim Williams' design persistence and excellence were known worldwide. They were gifted teachers. We miss them both. I gave our teenage grandchildren signed copies of Bob's How to Drive into Accidents and How Not To.
I have a PCB based on the TI design:
https://github.com/profdc9/PhonoPreAmp
and I use this in conjunction with a home-built preamplifier:
https://github.com/profdc9/PrettyGoodPreamplifier
They both use the LM4562 and sound just fine. I have them both in the same box running off of the same +/-12 VAC transformer.
https://github.com/profdc9/PhonoPreAmp
and I use this in conjunction with a home-built preamplifier:
https://github.com/profdc9/PrettyGoodPreamplifier
They both use the LM4562 and sound just fine. I have them both in the same box running off of the same +/-12 VAC transformer.
Just another late observation - the LM4562 is about the most RFI sensitive opamp out there, which makes it a poor choice for an input that cannot be heavily RF filtered (1nF to ground isn't friendly to a MM phono stage input!), not counting the high current noise. Try putting a mobile phone near the phono cable to see if this is a problem?
That circuit is too simple. The Oamp's feedback circuit is just two identical resistors, 3320 Ohms and 150 Ohms, on both levels, so it's natural that the sound isn't good.
That makes no sense at all. Low impedance feedback will keep noise down, and is inherently linear. The RIAA is all in the passive network between the stages.