Designing a Phonostage with the S&B 10K LCR RIAA Module

[fdegrove]

Hi,

You may also ask yourself what result multiple 3db rolloffs at 20Hz daisychained have further up in the audio band.

Those roll-offs are still there whether the corner frequency is lowered or not.

Information that, if at all present, will be filtered out by the RIAA correction anyway.

"Should be filtered" would be have been a better way to put it.

Then, with all due respect, the best of your knowledge could use some improvement.

Let's just say I tried that path even down to DC as far as the coupling between the first two stages goes.
It taught me exactly what I suspected all along, too much LF garbage for comfort.

Not to mention the fact that the results were downright disastrous even to the point of being dangerous to the reet of the system..........

YMMV but I doubt it......

In short it's just plain disaster, something a little common sense or "knowledge" about TT systems can tell you straight away.

Cheers,

[ThorstenL]

Konnichiwa,

Originally posted by fdegrove
Those roll-offs are still there whether the corner frequency is lowered or not.

But what they do higher up is reduced if they are lowered below 20Hz, which is what i propose.

Originally posted by fdegrove
"Should be filtered" would be have been a better way to put it.

Sorry, but it is not so that they "should be filtered".

Originally posted by fdegrove
Let's just say I tried that path even down to DC as far as the coupling between the first two stages goes.
It taught me exactly what I suspected all along, too much LF garbage for comfort.

You should perhaps concentrate on your turntable setup first.

With a wide range of actual turntables which I have owned over time or had in the system (a number of eastern block belt drive tables, various Japanese "battelship" Direct Drive ones from Sansui, Kenwood and Technics, Systemdek IIX, Oracle Delphi and now the Acoustic Solid) plus a variety of tables with friends (VPI TNT, Linn LP-12, Garrad 301/401 and various EMT's come readily to mind) there is no problem with "LF garbage" using phonostages with extended LF cutoff.

Originally posted by fdegrove
Not to mention the fact that the results were downright disastrous even to the point of being dangerous to the reet of the system..........

I am not sure how you managed to attain such results, but it points to an extremely poor turntable or very poor setup of a good one.

Originally posted by fdegrove
YMMV but I doubt it......

Pretty much ANYONES milage will vary, assuming they use a competently set up "quality" turntable.

Originally posted by fdegrove
In short it's just plain disaster, something a little common sense or "knowledge" about TT systems can tell you straight away.

Actually, common knowledge and personal experience with many turntables tells me nothing of the like, as long as quality equipment is concerend.

Sayonara

[fdegrove]

Hi,

Pretty much ANYONES milage will vary, assuming they use a competently set up "quality" turntable.

O.K....
So you go tell the good folk over at Nothingham Analogue their 120 lbs spinner stinks, tell the guys at Air Tangent they don't have a clue what a tonearm should be designed like and last but not least you can have the pleasure to tell mister Jan Allaerts his masterpiece MCs stink as well.
All among the greatest of the planet and sure enough I stink at setting this stuff up regardless of the fact that I actually have designed just about anything bar cartridges in that department....
I can't even imagine the number of analogue systems I've set up...

No Sir, the problem is not the gear, not the rumble but just plain interaction of the vinyl, stylustip and tonearm that will give a very strong resonance at around 10 to 16 Hz and it won't just stop at those frequencies either.
No amount of setting up will get rid of that.
So yes, this tremendous energy that has no relation to the music should be kept out of the system as early as possible.

Besides, you never answered the question: what musical content is there to be found below say, 16Hz on a vinyl record anyway?
None?
Hmmmm.....Guess they left it out for a reason too, right?
Not to mention record eccentricities, warps etc....

Just put on a disc with a blank surface and crank up the volume, you'll know what you'll be amplifying when you let too much LF garbage through.....and that's on what most people would consider a decent system anyway.
Should no such record be available, just hook up a scope and watch your local tsunami at work....No, it's not supposed to be funny, I know....

Cheers,

[Eli Duttman]

Hmmm, the debate about EQ is interesting. I'll add my 2 cents.

I agree with Thorsten that keeping the original curve is best. AMOF, keeping the original curve is best even with inferior equip., as the IEC mod. simply does not get the job done. As always, keeping the baby while disposing of the bathwater is desireable. Disposing of infrasonic garbage (when present) while minimally impacting the audible band is the object. A 3 pole filter 3 dB. down at approx. 17 Hz. disposes of the trash. The "Catch 22" of the filter is phase distortion introduced into the audible band. Butterworth filters are poor performers in the phase shift department. At the end of the 1970s and into the early '80s, I used a Sansui 7070 receiver and BIC TT. The presence of infrasonic trash was manifested by the fluttering of the woofer cones. I acquired an audio bandpass unit that used Bessel function filters, which are purported to be good performers in the phasing department. The benefits were clear. Cone flutter was abolished and the overall sound improved. Infrasonic trash in addition to wasting power also causes IM distortion in the audible band. Obviously, superior equip. that doesn't produce the garbage to begin with is better.

Shifting gears, I EMailed Gary Pimm a link to this thread in the hope that he will comment. Thorsten's remark about setting the O/P impedance of the 1st gain block to 600 Ohms looks VERY interesting.

[ThorstenL]

Konnichiwa,

Originally posted by fdegrove
O.K....
So you go tell the good folk over at Nothingham Analogue their 120 lbs spinner stinks, tell the guys at Air Tangent they don't have a clue what a tonearm should be designed like and last but not least you can have the pleasure to tell mister Jan Allaerts his masterpiece MCs stink as well.

Maybe. Of the above I only know the NA Turntable. It is rather good. As for the rest, there is such thing as setup error and/or mismatch.

Originally posted by fdegrove
No Sir, the problem is not the gear, not the rumble but just plain interaction of the vinyl, stylustip and tonearm that will give a very strong resonance at around 10 to 16 Hz and it won't just stop at those frequencies either.

In a very poorely damped arm/cartridge combo such as evident with a sure V15 your VLF peak will be in the region of 10db (measured), using a pink noise track on LP and 1/6 octave weighting I found in my own turntable only one combo of cartridge and arm with more 3db boost overall and notable boost at 20Hz, that combo being an Ortofon SPU and RS-212 Arm. My other two combos (Denon DL-103/SME 3009 & Origin Live Silver 250/Goldring Elite) show less of an issue (that is across the Phonostage and Arm Cartridge, the Phonostage itself haveing very extended LF response)..

Originally posted by fdegrove
Besides, you never answered the question: what musical content is there to be found below say, 16Hz on a vinyl record anyway?

The issue is not per se musical content and more crucially, it is not what happens at 16Hz, but what your filter causes to happen higher up in the spectrum which leads (IMHO) to the audible problems.

In temrs of perception, taking out significant parts of the very low spectrum reduces in many recordings the "thereness" and/or acoustic sense of the actual recording space. What particular parts of what is recorded is of modest concern to me.

Originally posted by fdegrove
Not to mention record eccentricities, warps etc....

Record excentricities are at around 0.5Hz and will be already suppressed by around 40db if you use a Setup with an arm/cartridge resonance in the 8-16Hz region. Plus at 0.5Hz our 4Hz turnover will have added nearly another 20db of attenuation.

Originally posted by fdegrove
Just put on a disc with a blank surface and crank up the volume, you'll know what you'll be amplifying when you let too much LF garbage trough.....

I know very well what this is.

First, please use a record NOT with a blank surface but with a grove cut without modulation (any good test LP will have such sections). Inter Track unmodulated grooves may also be used sufficiently.

And at volumes that are near max with signal you can indeed see some cone flapping if the record is either very excentric or very warped. Using records that have no obvious problems leads to very little observable problems with VLF signals.

So, the bottom line is that while you may observe some issues, in practice and with quuality equipment they fail to be overly observable.

Sayonara

[fdegrove]

Hi,

In temrs of perception, taking out significant parts of the very low spectrum reduces in many recordings the "thereness" and/or acoustic sense of the actual recording space. What particular parts of what is recorded is of modest concern to me.

Sure....
I like my system to be as wideband as possible too for the same reasons but....
It seems to me someone has forgotten that when it comes to vinyl there's only there what's actually been put on the recording in the first place.

If you're talking about extending the LF response of a phono preamp by stretching the RIAA standards for playback maybe you should also consider that the inverse curve of that RIAA standard was used to cut the record in the first place....

Should extending the LF passband to as low as 4Hz not wreck havoc on your system then I can only surmise that somewhere along the line it must have been filtered out anyway.
In the meantime, all that has occurred is needless modulation of PS drawing energy that could have been left for what really matters, real music, not warps and resonances.

So that's another two cents worth of "knowledge",

[ThorstenL]

Konnichiwa,

Originally posted by fdegrove
It seems to me someone has forgotten that when it comes to vinyl there's only there what's actually been put on the recording in the first place.

Exactly.

Originally posted by fdegrove
If you're talking about extending the LF response of a phono preamp by stretching the RIAA standards for playback maybe you should also consider that the inverse curve of that RIAA standard was used to cut the record in the first place....

Yes, indeed. There is some rolloff in the cutting Amplifiers and low LF is blended mono, however usually the filters employed for cutting where not excessively steep and did not hack out anything below 20Hz untill quite late in the game (and even then they where often enough not applied). I see little benefit downgrading the reporduction to the lowest common denominator.

Originally posted by fdegrove
Should extending the LF passband to as low as 4Hz not wreck havoc on your system then I can only surmise that somewhere along the line it must have been filtered out anyway.

Correct. It is filtered out by the arm/cartridge resonance. I see little benefit from adding further to this to this fairly steep rolloff. The boost received at subsonic frequencies will partially offset attenuation during cutting, which can be seen when a well cut test LP with a pink noise track is replayed and analysed.

Originally posted by fdegrove
In the meantime, all that has occurred is needless modulation of PS drawing energy that could have been left for what really matters, real music, not warps and resonances.

Really. How interesting. All my powersupplies are loaded by class a stages, so I doubt they'll notice.

Originally posted by fdegrove
So that's another two cents worth of "knowledge",

Your "knowledge" seems curiously skewed. I do not dispute that what you describe is real to a certain degree. However the emphasis is on "to a certain degree". In relaity I find non of the problems you describe to be significant enough to warrant consideration, on the other hand using an excessively small value coupling capacitor (or worse a multipole filter) to roll off the "unwanted" LF content is very notable, to my ears at least.

Sayonara

[gingertube]

Is my face RED

Originally posted by gingertube:
together with the 3180us (50Hz) low pass. This means response is increasing (at 20 dB/decade) below 50Hz.

As KYW so kindly pointed out (YOU WHAT? Please retake EE101)this is pasture decore.

Response is flat below 50Hz and decreases at 6dB/Octave above 50Hz.

Sorry - brain was in idle.

Cheers,
Ian

[Gary P]

Originally posted by Kuei Yang Wang
You COULD use another trick.

The Mu-Follower output of your circuit has a low and fairly well defined impedance. The S&B Riaa contain Capacitors with 630V or more DC rating in all shunt path, so it will withstand quite a bit of DC offset, as long as no DC current flows.

Therefore, if your source can be made to have 600 Ohm net impedance you can couple the S&B RIAA (and ONLY the S&B one) directly and place the coupling cap AFTER the 600R RIAA, making it's value uncritical.

This is a nice simple way of dealing with the coupling issue that I hadn't thought of.

With the standing current high enough to handle driving the 600 ohm module the output impedance is going to be too low to use the MU output directly. The way it could work is to include a series terminating resistor between the MU output and the input of the S&B module. The value of the resistor would be selected to make the total impedance of the MU output + resistor = 600 ohms.

There are 2 ways to get the standing current of the stage up to the level needed to drive the 600 ohm input cleanly. One is to run the triode with the total current desired. The other is to add a resistor (or CCS) to ground from the MU output. The second variation gives the ability to choose the triode current independantly of the total stage current.

Another feature of using the CCS as a load is you will get full mu of the triode without having to bypass the cathode resistor. One less cap in the circuit is always a good thing in my book.

This coupling scheme could work nicely if you are not adverse to the series terminating resistor.

Gary

[Eli Duttman]

Gary,

Thanks for the feedback.

The 6DS4 nuvistor is a low current type. So, a secondary current sink is the route to follow. The 6DS4 runs at a voltage somewhat less than that used for the 6922. Finding a suitable N channel FET for the secondary sink shouldn't be too difficult.

Michael Percy carries 1 KOhm Vishay 1280G trim pots. With their bulk metal foil construction, the Vishay parts seem to be the right choice for dialing the 600 Ohm impedance in. An adverse sonic impact should not be observed.

FWIW, I'm thinking of using the same red LED for bias that is used in the Bottlehead Seduction.