Where to start - sibilance on analogue replay

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mac72

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Reading OL specs there phono leads are 50pf per metre so with the 150pf of your PS all should be good at 200pf.

For valves, if you've not got any suitable spares give Robin a PM, he will have a couple spare he may post to you as loaners to experiment with. 
Yes , should be fine with peak around 15kHz  , 

 

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Hi gents

Finally got a chance to have a check / adjust of my setup yesterday and today (best-laid plans and all that). So, to recap (save you re-reading my "war & peace" first post, but be aware I'm creating another one)...

  • I'm finding excessive sibilance on LP replay. Trying to work out why, given that the cartridge alignment / setup looked OK on initial measurement.
  • It's a 3-motor Voyd with Origin Live Onyx arm and Goldring 1042 MM, into a Tube Technology M.A.C. phono stage. The arm is the 9.5" version so uses the same geometry as Rega.
  • Phono stage does not have adjustable capacitance for MM, specs quote it as 150pF (plus tonearm cable - I have the OL upgrade cable fitted so not sure if that's different to the 50pF John mentioned). I have also noticed that I have different valves fitted to those described in the specs, which is different again to what's printed on the actual board inside (12AT7 / 12AX7 vs 12AU7 / 12AT7 vs 12AX7 / 12AX7, respectively). The valves are the ones fitted when I bought it (Second hand) so no idea if it was supplied like this from the factory or a previous owner changed them. Photos shown below.
  • The quoted input sensitivity for the phono stage is an (unbelievable?) 0.8mA for MM and (also unbelievable?) 0.08mA for MC - see the spec sheet that I downloaded from the website (Tube Tech stopped production many years ago I believe, but the website is still active).

I adjusted the VTF and, heeding the advice I was given here, re-checked it by bringing the weighing scales down to the heigh of the platter + LP. I did this twice, once to align with a thicker (180g) LP and again slightly lower to align with a thinner pressing. Before doing this I used the supplied 5g weight to calibrate the scales (of course this assumes the weight itself is accurate!) The difference in VTF was small - 1.93g at the lower height vs 1.97g at the upper height. I found an old set of the Ortofon balance scales and checked the weight with these against the electronic scales, it seems that the scales are fairly accurate, as far as my knackered old eyes can see. It looks like the Ortofon is recording 2g at the upper height, not sure I could discern the difference between 1.97 and 2 on those balance scales...

I checked (with a ruler, so not 100% accurate) the pivot to spindle distance and it's 223mm I think, which is within the 1mm tolerance that Origin Live quote so I believe the armboard has been drilled accurately. The cartridge overhang is approximately 18mm.

I reduced the side bias by moving the clamped ball back close to the pivot. It's now about 8.5mm from the centre of the upright as far as I can tell. I also re-checked the cartridge's zenith and it seems to be aligned correctly (sighting the cantilever along the lines of the gauge, not using the cartridge body).

The VTA is set so that the armtube is parallel with the platter. 

I should have mentioned before that the LP I noticed the big problems with is Texas - The Conversation. Perhaps this is just a particularly cr*p production / pressing (no comments on musical taste, thank you!)  :D  but although there may be a slight improvement I can still hear the sibilance quite obviously. Just for clarity, and in case I've been using the wrong term, by that I mean that the vocal sound "S" (as-in "Speak") sounds distorted and exaggerated as if you're trying to hiss like a snake, the "Sh" ("Shove") sound can also sound shrill. Crash cymbals also sound, well, too "crashy"! I can hear this effect on other LPs too although not to the same extent. A recent 180g pressing of David Bowie "Let's Dance" has a slight tendency towards this effect, and a few older LPs have also exhibited it. I'm not unconvinced that I can also now detect a tiny bit of mistracking distortion on some louder passages, during "Ricochet" for example.

I'm going to experiment some more with that side bias as I can say that the imaging is not good, and from what I understand, getting the bias correct does make a significant difference to this. My digital setup runs rings around LP in this regard at the moment.

I've still not tried swapping the stylus over with the one from my other turntable yet, which I will do, but for the moment I'm going to persevere with the current one while I seem to be making small improvements. If anyone can think of any other possible reason for the problems, please let me know!

I need to get this right because in the not-too-distant future I need to repeat the exercise with John's OL Encounter! Best make sure I know what I'm doing....  o_O

Thank god for Ikea Groggys! Not too clear from the photo but the centre point on the measuring platform is near-as-damnit the same height as the HFN test LP:

IMG_7456 (1).jpg

Readout in this position

IMG_7458 (1).jpg

Double-check with the Ortofon balance scales - again not too clear (excuse my awful photography with an iPhone) - the stylus appears to be on or almost on the 2.0g mark:

IMG_7459 (1).jpg

Checking again at the slightly lower LP height:

IMG_7462 (1).jpg

Side bias adjusted to give 8.5mm distance from the upright part of the bias hanger to the centre of the clamped ball:

IMG_7464 (1).jpg

IMG_7457 (1).jpg

 

Jules_S

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More photos:

Alignment at the outer null point - front-on

IMG_7466.jpg

and from the side:

IMG_7468.jpg

Alignment at the inner null point - now that I'm looking at it close-up on  the computer, the cartridge doesn't seem to align properly?

IMG_7470.jpg

and from the side again, inner null point:

IMG_7469.jpg

Viewed from above:

IMG_7471.jpg

from the front:

IMG_7472.jpg

Arm appears level playing a 180g LP, by eye

IMG_7473.jpg

 
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Lurch

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@Jules_S Looking at the penultimate pic, you have too little bias, the gap between the verticle part of the bias arm and edge of the ball is only 2.5mm, with a vtf of 2gm this should be 6 - 8mm, (10mm max). 

Ignore centre lines of bar and ball, the gap should be along the horizontal part of the bar only. (where 6mm is, on the ruler in photo, as this is the closest point to the yoke that the ball will go). 

I'm assuming the vtf wheel on the Onyx is the same as other OL arms 1 full turn = 1mm? Your sibilance could in part be due to Cable burn-in in which case to reduce it at, drop the back of the arm slightly say an 1/8th - 1/3rd of a turn. Keep a note of this and then once you have another 20-30 hrs on the arm it can be returned to horizontal to see what changes if any have occurred. 

 
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Lurch

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And yes definitely slightly misaligned, it needs a slight tweak anti-clockwise. 

 

Jules_S

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@Jules_S Looking at the penultimate pic, you have to little bias, the gap between the verticle part of the bias arm and edge of the ball is only 2.5mm, with a vtf of 2gm this should be 6 - 8mm, (10mm max). 

Ignore centre lines of bar and ball, the gap should be along the horizontal part of the bar only. (where 6mm is, on the ruler in photo, as this is the closest point to the yoke that the ball will go). 

I'm assuming the vtf wheel on the Onyx is the same as other OL arms to turn = 1mm? Your sibilance could in part be due to Cable burn-in in which case to reduce it at, drop the back of the arm slightly say an 1/8th - 1/3rd of a turn. Keep a note of this and then once you have another 20-30 hrs on the arm it can be returned to horizontal to see what changes if any have occurred. 
Ah, so I have misunderstood your earlier post about the bias adjustment, apologies. That might also explain why I noticed that bit of mistracking then. I'll put the bias back up again, bearing in mind it was a lot further than that to begin with. Somewhere in the middle might be the happy medium I'm looking for!

VTA (I assume that's what you meant?) isn't so easy to adjust on the Onyx as the more expensive OL arms. To do it I have to undo the clamp nut beneath the armboard, turn the top VTA wheel then re-clamp. Which is why I'm loath to adjust it if I can avoid it as it's a PITA!

 
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mac72

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You should really investigate what valves should be used in which position as it might be your biggest issue , I'm not going to comment on cable burn-in as it would lead to another pointless discussion  9_9

 
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Jules_S

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Sorry, I forgot to post the spec sheet for the phono and the photos of the internals. Note the slightly odd sensitivity for MM and MC? Have I misunderstood what is meant by that?

Screenshot 2020-05-05 at 21.35.12.png

Board is marked 12AX7 in all four valve locations:

IMG_7060.jpg

I have these:

IMG_7067.jpg

IMG_7069.jpg

 

mac72

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Do you have a meter , you could check cathode resistor values , no voltage measurement involved st this  time 

 
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Jules_S

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Do you have a meter , you could check cathode resistor values , no voltage measurement involved st this  time 
Sorry but no, and even if I had the meter I wouldn't have the faintest idea what to do with it. I am totally non-electronic from a practical sense, although I can cope with understanding some basics in theory. I appreciate your suggestions though and perhaps once we can get out and about again, I might get someone to check it over for me.

 
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mac72

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Sorry but no, and even if I had the meter I wouldn't have the faintest idea what to do with it. I am totally non-electronic from a practical sense, although I can cope with understanding some basics in theory. I appreciate your suggestions though and perhaps once we can get out and about again, I might get someone to check it over for me.
You should either contact manufacturer or ask someone to check the circuit , if you can borrow a meter you can easily check yourself 

for now can you check colour codes on resistors : R8,  R21, R10, R15  on right channel 

 

rabski

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R9 is more likely to be the cathode resistor on the bottom half in SRPP as it's bypassed by C4. Either way, it's not going to tell you much because it will depend on the HT voltage and plate resistor values. Just the cathode resistor value is close to meaningless without the rest of the circuit. The resistor value could easily be the same for many small double triodes, depending on the rest of the circuit.

Simple answer is get someone who knows what they're doing to look at it. Other simple answer is put four 12AX7s in it, as per the board, Unless someone has done something insane, you won't break it by doing that.

Either way, get the cartridge alignment right, as that's far, far more likely to cause sibilance if it's out.

 

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Jules, for bias initially set the ball on the arm roughly 5mm out,  (gap between ball and yoke) then adjust out further as you tweak. With a vtf range of 1.7 - 2. 0g, you shouldn't need to move the ball to more than 10mm from the base of its arm. 

Another thing to consider (as discussed in a recent thread) is the discrepancy in vtf caused by the distance above a record, digital scales weighing pans are. This discrepancy can be around 0.4g as the centre of gravity of the cart & arm system (cart an arm must always be considered together as a system) has changed, potentially in your case from a reading of 2.0g to an actual of 1.6g, hence the sibilance from to low a vtf. 

If possible move the scales off of the platter and onto the plinth, and then raise it up on whatever you can find, such that the weighing pan the stylus sits on is at record height, this will then give you an accurate vtf as it will be set at record surface height. 

You may have to repeat the above vtf procedure as the possible additional downforce needed will change level of the arm to a nose down stance. 

As before if you need any further help/guidance give me a ring. 
Good point re. weight on scales versus weight on a record. I'd often wondered about this, but I'd always thought the stylus travelling further downwards would result in a higher tracking force i.e. 2.0g in scales would be 2.4g on a record....?

 
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mac72

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R9 is more likely to be the cathode resistor on the bottom half in SRPP as it's bypassed by C4. Either way, it's not going to tell you much because it will depend on the HT voltage and plate resistor values. Just the cathode resistor value is close to meaningless without the rest of the circuit. The resistor value could easily be the same for many small double triodes, depending on the rest of the circuit.

Simple answer is get someone who knows what they're doing to look at it. Other simple answer is put four 12AX7s in it, as per the board, Unless someone has done something insane, you won't break it by doing that.

Either way, get the cartridge alignment right, as that's far, far more likely to cause sibilance if it's out.
You're right about R9  but for Ecc81/Ecc82 vs Ecc83 there could be a fair bit of difference  in cathode resistor value irrespectively plate voltage we're talking about 470R-3k  vs several kohm  more difficult to say a difference between Ecc82 and Ecc81 but as Rabski says get someone to check this  

 

rabski

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You're right about R9  but for Ecc81/Ecc82 vs Ecc83 there could be a fair bit of difference  in cathode resistor value irrespectively plate voltage we're talking about 470R-3k  vs several kohm  more difficult to say a difference between Ecc82 and Ecc81 but as Rabski says get someone to check this  
Could be indeed, but doesn't have to be. Without the whole circuit you're wandering around a dark room without even a match. You need the circuit, to see how it's actually configured, and you need cathode and plate resistor values and plate voltage. Without all those it's no more than a vague guess.

 

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R9 is more likely to be the cathode resistor on the bottom half in SRPP as it's bypassed by C4. Either way, it's not going to tell you much because it will depend on the HT voltage and plate resistor values. Just the cathode resistor value is close to meaningless without the rest of the circuit. The resistor value could easily be the same for many small double triodes, depending on the rest of the circuit.
Oooo I love it when you talk dirty  xD

Thanks to all who have posted so far. I've just re-adjusted the bias again, so that as-per John's earlier post there is now a greater distance between the left edge of the ball and the beginning of the horizontal part of the support. Currently set at 6mm and seeing how that goes.

I will try slightly moving the cart in the headshell tomorrow when the light is better and I'm not so tired, to try and improve the alignment on the inner null point. I'm assuming that in doing so it will actually make things slightly worse at the outer one, so I'm looking for the best compromise between them?

Any thoughts on the quoted input sensitivity? I would have expected,, as-per @mac72 earlier post, that for MM this would be in the order for a few mV. As the 1042 has a fairly high output could there be a problem here? I should note that when playing LP I am turning the volume on the amp up significantly versus CD - generally it's around 10 (background) - 45 (very, very loud) on CD, but for LP the rough equivalent is 45 to 80 (for ref the volume goes to 99...)

 

rabski

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The input sensitivity is the minimum. Basically, the minimum input at which it will work. Above this is fine within reason. Also bear in mind these are figures quoted at a specific frequency (usually 1kHz), so they're only really useful to figure out if your cartridge has enough output to meet the minimum. The overload is quoted as 500mV as David points out. That looks rather high to me, but you're not going to overload it on the MM setting. The volume will quite often be lower for a phono stage than a CD. The specs quote 1V output for .8mV input. A CD player will output anything around 3V RMS, some significantly more. The ratio of input to output on the phono stage will not be 100%, so if .8mV input is 1V output, that doesn't mean 1.6mV is going to be 2V. Basically, the chances are that it will need more gain to match the CD, but that doesn't mean anything is wrong.

 

mac72

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As per advice above it shouldn’t cause a problem , when you mentioned earlier input sensitivity I thought it’s for rated output which usually is 2.5V also there is massive overload margin .

Get your alignment sorted it should sort sibilance -check what happens , if still distorting you need to look at phono stage valves , if you have more Ecc83/12ax7 try them on all positions . Checking colour code on cathode resistors won’t cost anything , if suspected valve has very low resistor I’d say most likely it’s Ecc83  otherwise get someone to check your stage .If you’re ready to live without stage for a few days post it to me and I could check circuit and test it , I won’t charge you for a return postage , no need to send valves as I have quite few.Another option is to borrow another stage to check , obviously get your alignment sorted first.

 

Jules_S

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Ah, I understand. I thought that the quoted sensitivity was the maximum input level, and so anything over that was too much. I get it now, thank you for the clarification.

I don't have any spare valves to hand to swap out unfortunately, I'm stuck with what I have. To be honest I asked about them as I was more confused as to why the spec sheet and the PCB don't tie up, and which one is more likely to be correct (if there's such a thing). The fact that I have different valves to either of these points of reference I put down to a previous owner probably trying some tube-rolling for themselves. The 12AT7s don't appear to have any branding on them (no doubt someone will know by the style of font used!) whereas the 12AX7s are clearly Mullards (are they any good, by the way?)

As long as I'm not going to damage the phono with a too-stong input signal (which I now know is OK - and I understand the meaning of "Overload" too!) and the tubes that are installed aren't causing any instability that's going to cause issues, I'll live with what I have for the time being.

More tweakery with the alignment to come later today. It's slow progress because I have a tendency to be a bit ham-fisted, which is the last thing I wish to be when mucking around with such delicate things. When I eventually move to MC I shall be a bucket of nerves....