RIAA equalization.

[bob orbell]

Hi all, after posting problems about sibilance years ago, I have been reading much on the subject of the RIAA curve and found quite a lot of helpful papers by well known people, WAD designed the phono II and followed the RIAA specification, that is 3180uS 318uS and 75uS, then some bright spark said about adding a time constant at 3.18uS, a lot of us did it and a lot said it made playback to bright, I was one of those, now if you have a phono III it will have this 3.18 correction, but google and read (RIAA equalization - Wikipedia) and you will find that it is not nessasery, a paper by Stanley Lipshitz and Walter Jung said just that, I have removed this time constant from my phono III and it really does sound more natural, for those interested simply short (or remove and fit a link) R21-22 and try it, it is also stated that most pre amplifiers omit it, have a read, it is very interesting. Bob

[bikerhifinut]

Originally Posted by bob orbell

Hi all, after posting problems about sibilance years ago, I have been reading much on the subject of the RIAA curve and found quite a lot of helpful papers by well known people, WAD designed the phono II and followed the RIAA specification, that is 3180uS 318uS and 75uS, then some bright spark said about adding a time constant at 3.18uS, a lot of us did it and a lot said it made playback to bright, I was one of those, now if you have a phono III it will have this 3.18 correction, but google and read (RIAA equalization - Wikipedia) and you will find that it is not nessasery, a paper by Stanley Lipshitz and Walter Jung said just that, I have removed this time constant from my phono III and it really does sound more natural, for those interested simply short (or remove and fit a link) R21-22 and try it, it is also stated that most pre amplifiers omit it, have a read, it is very interesting. Bob

You're on the button Bob, it's a contentious one and I think its not applied during cutting, I may be wrong.
It's also worth playing around with capacitive loading on the input. Counter intuitively perhaps, adding capacitance can give an impression of excess brightness with some cartridges due to lowering the turnover frequency if I understood what I was told. Quite happy to be corrected on that aspect
I have been footering around with op amp based RIAA preamps of late from pure curiosity and none of my prototypes has had that correction.
By the way I have been pleasantly surprised with what you can get from a single op amp with the EQ wrapped around the feedback loop. I knocked up a reverse RIAA filter to see how close it is to the ideal curve. A project for the weekend I think.
AS a postscript, I haven't found my phono3S to be bright in any respect. But I also think its not quite right and suspect I need to redo a lot of solder joints as they look a bit dodgy especially around the valve bases. I reckon whoever built it (not me) used lead free solder...………… oh how I hate lead free solder it never looks a good "wet" joint.

A.

[bob orbell]

Thanks for the reply Andy, if you read the Wiki RIAA you will find some interesting points about cutting and playback and if you do put your 3S back in service, do as I have and short or remove R21-22 and let me know what you think. Bob

[bikerhifinut]

The basic phono3 as you say bob omits the 14.3k resistor and also the twiddly preset trimmer cap.
Looking at it and I haven't done any calcs, you'd need to tweak up C9a and c10a to get closer to the 220Pf of the basic Phono3. Or just take the thing out and bung a 220pF in place of the 180pF of C9/10.
I have been mulling this over for a while also Bob, and I did wonder about getting a Phono3 board and building it up knowing that I'd have decent "wet" solder joints as I am certain the issues I have had since day 1 with my Phono3 are down to bad soldering and crappy lead free solder, (LF instability and nasty low level noises).
I'd get what I need and wouldn't need to worry about the MC side of things as the basic Phono 3 would be ok, although for some bizarre reason phono3 doesn't have the extra RC filter on the HT in the shape of r29/30 1k.
Is that retro fittable on the phono3 PCB? otherwise its get a phono3S board and just wire link the 14.3k and omit the trimmer cap.
Andy.

[bob orbell]

Andy, with your regulated PSU you will get no LF instability or motorboating as the regulator will kill it, dead, if you have your PSU set to 250volts, forget the 1k resistor and the 100uF capacitor, instead fit 68uF to C13-14 and 10 or 20 to C15-16, the 3S board is a much nicer layout, if you don't want the low filters just fit .1uF 250v to C1-2, leave 3-4-5-6 empty, go for it. Bob

[Phil Y]

I also removed the 3.18 from mine a couple of years ago after reading the wiki page and some googling.

The difference wasn't huge but it was noticeable.

Phil.