Phono3 3.18uS correction

[Richard]

For anyone wanting a bit more reading,
around 12 years ago, I built and used the Hagerman Inverse RIAA filter which included the 3.18 corner and used it to check and adjust Phono3S.
The resulting build always souded good to me and I built a second version in the simpler non-S case without bass roll off filter but still using the 3S pcb so as to get the extra decoupling caps and 3.18 corner.


The Hagerman info is here,

https://www.google.com/url?sa=t&rct=...8-U8nlGJhaD9sn


and I've attached the circuit gif of what I ended up with using 5751 valves with cathode bypass cap on the first stage.

[bob orbell]

More interesting reading from Richard, but what I dont' understand is if this 3.18uS time constant is added at cutting, which is 50.048Hz, way out of our hearing range, and is corrected at play back, why does it affect much lower frequencies in Phono III ? I still think this 3.18 corner has been implemented incorrectly. Bob

[Richard]

Originally Posted by bob orbell

More interesting reading from Richard, but what I dont' understand is if this 3.18uS time constant is added at cutting, which is 50.048Hz, way out of our hearing range, and is corrected at play back, why does it affect much lower frequencies in Phono III ? I still think this 3.18 corner has been implemented incorrectly. Bob

Hi Bob, If you mean the FAQ mod then yes it is slightly incorrect for Ecc83 as per my answer and link to Greg in post 18, read the update in that FAQ link,
http://www.world-designs.co.uk/forum...read.php?t=145
"To implement the mod for ECC83 by adding the 14k3 resistor the 180k should be reduced by a similar amount."

That update was added in 2009.

Whether or not it's a reason for the mod to sound wrong using Ecc83 to some folk like your good self I don't know. It was just something I noticed in doing the corner calculations; the mod as shown changes the 75uS corner as well as implementing the 3.18. (The mod works almost perfectly with 5751 valves though as they have a slightly different impedance.)

[bob orbell]

No Richard, I was not referring to your FAQ mod, I was / am referring to the 3.18uS addition in Phono III and II, it surely should not affect frequency's that we can hear, but it does and I would say it is affecting 7k upwards, as I see it, it has changed the 180k resistor to 194K300 . I may be wrong, but my ears tell me and others agree that removing it brings a more natural sound with almost no sibilance, very natural s sound from voice. Yours and other comments would be welcomed. Bob

[Richard]

Originally Posted by bob orbell

No Richard, I was not referring to your FAQ mod, I was / am referring to the 3.18uS addition in Phono III and II, it surely should not affect frequency's that we can hear, but it does and I would say it is affecting 7k upwards, as I see it, it has changed the 180k resistor to 194K300 . I may be wrong, but my ears tell me and others agree that removing it brings a more natural sound with almost no sibilance, very natural s sound from voice. Yours and other comments would be welcomed. Bob

Correct, you have explained it the other way around but are saying the same as me,
if you want to implement the 3.18 mod on Phono2/3 for Ecc83 you should change the 180K for 165K and use 15K with the cap. This is explained in the update posted back in 2009,
http://www.world-designs.co.uk/forum...read.php?t=145
<<To implement the mod for ECC83 by adding the 14k3 resistor the 180k should be reduced by a similar amount. The 14k3 value is not critical as it merely restores a little treble from around 50KHz upwards which was otherwise being allowed to roll off previously. Thus, readily available values of 165k and 15k metalfilms from RS will be fine>>
Whether that will make it sound acceptable to you I do not know.

[Greg.]

I think we have two schools of thought here.

Bob thinks the 3.18uS correction is not required per se; an argument which he seeks to support through his own listening and with this lift from Wikipedia.

https://en.wikipedia.org/wiki/RIAA_equalization

Richard agrees with the 3.18uS correction inclusion in the circuit but through listening and testing believes the standard circuit needs adjustment to make it more accurate in accordance with which valves are used.

It seems to me this is the question which remains unresolved. I for one would be interested in reading further discussion on this topic to see if we can get closer to a resolution.

[bob orbell]

Just a bit more on the subject, in the past, I have tried ALL the suggestions that Richard has suggested and only the removal of R21-22 replaced by jumpers sounds correct to me, and two of my chums agree. As a note, I have always used MC, but it should be the same for MM with input capacitance addition. Bob

[Richard]

Originally Posted by bob orbell

Just a bit more on the subject, in the past, I have tried ALL the suggestions that Richard has suggested and only the removal of R21-22 replaced by jumpers sounds correct to me, and two of my chums agree. As a note, I have always used MC, but it should be the same for MM with input capacitance addition. Bob

Good and fair comment from Bob.

For my part WD-wise I've only used Phono 3S with the 3.18 and have only tested it using the Hagerman inverse RIAA which includes the 3.18. (In the past I've had many phono stages and even built my own in the late 70's.)

I may be wrong but think Bob uses vinyl as his main source and don't know how much digital he listens to.

When I built Phono 3S it was after a return to vinyl from being CD-only during the 90's (I sold the LP12/Ittock at the time as our kids were toddlers and bought a Pioneer 91 CDp). The Linn with ATF5 and Pioneer CDp actually sounded very close on AB switching so I went the child-proof route!

After the return to vinyl in the 2000's I still continued with CD and now mainly stream digital but still enjoy vinyl which sounds good but warmer in the mids. Point being, my reference has become digital whereas Bob's may have always been vinyl (?).

Further, I've not compared with/without the 3.18 mod as I went straight to Phono 3S and didn't have the earlier versions 2 and 3. Phono 3S sounded great to me and checked out fine with the Hagerman. I used a Denon DL160 high OP moving coil into it and it was very similar to digital on many records. So don't listen to me, build and mod whatever pleases you. The WD phono amps are very good indeed and being able to tweak them a little is a bonus

[bob orbell]

To add on from Richards post, I use both CD and vinyl, my issue reared its head after changing my WAD Phono II for an all III set up, CD was still good but, vinyl produced a lot of very annoying sibilance, it became that bad I changed my cartridge for a new one, (same Ortofon) but after fitting and listening the sibilance was still there, I tried all of Richards suggestions but to no avail, after much reading on the subject of RIAA, it was decided to remove the 3.18 added resistors and the rest is now history, I also know others who posted similar issues, but I think a lot just gave up and moved on, pity, because this Phono is very good, save for the 3.18 time constant that I feel is implemented incorrectly. I wonder if Andy Groove could be contacted ? after all he designed the original, I think. Bob

[Richard]

Adding a bit to this,

The FAQ 3.18 mod,
http://www.world-designs.co.uk/forum...read.php?t=145
was developed and written up by NealG originally as far as I recall. The diagram went missing when NTL stopped my picture hosting.
I added the update on the bottom 2009 after building Phono 3S.

Nothing is cast in stone, the 3.18 mod itself is still debated, my maths may be wrong etc. Build the WD Phono and leave it there - it's great - unless you want to mod it for fun is my advice.

John Caswell developed the adjustable 3.18 Phono 3S version I think, maybe he will expand.

John certainly helped me in many ways including sorting the regulator drop out problem with PSU3 during my build and I incorporated and tested a 5V fixed LDO reg lifted by the existing diodes which I kept and it worked perfectly down to about 206V mains tested on a variac iirc.

John also gave me a full set of components to build the Hagerman inverse RIAA which I bird-nested into a box... and much friendly help as always