SRA/VTA adjustment and tube distortion

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Wolfgang
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SRA/VTA adjustment and tube distortion

Post by Wolfgang » Sun Oct 28, 2018 4:13 pm

Finally I could find the time to adjust my tonearms "dynamically" with a spectrum analyzer for smallest amount of IMD. I have used before the USB microscope method as explained in Stereophile/Absolute Sound but as the results have shown it was less accurate compared to the test record/spectrum analyzer method.
Even 0,1% difference made a huge impact on the sound. I was kind of shocked because I thought that my system was already well adjusted.
I still don't understand how the difference between 0,38% and 0,29% IMD can have such an impact on the sound. But it's the same dramatic result with my SME 309/Dynavector Karat and with the Origin Live Conqueror/Shelter 501. So I guess my experience is real.

Now I have a big problem: If this little amount of IMD makes such a difference in SQ how will be the effect of more IMD coming from my tube based phono pre/buffer? And how would harmonic distortion mix up with the tiny bit of IMD coming from the cartridge? Even if it's mostly harmonic distortion which is present below clipping levels in case of tubes, wouldn't even small amounts of IMD from the cartridge have a big presence in the sound if it is combined with harmonic distortion? Wouldn't it be a lot better to use only solid state amplification for the phono section?
Is there any theory about this topic, any scientific explanation, test, comparison?

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Nick
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Re: SRA/VTA adjustment and tube distortion

Post by Nick » Sun Oct 28, 2018 4:30 pm

I have a strong belief that distortion matters, but masking also happens where lots of 2nd will mask a little 3rd and so on, but if you can get less distortion without making any other compromise then I find it sounds better. You should be able to get a valve phono stage down to around 0.05% without much problem.
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RhythMick
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Re: SRA/VTA adjustment and tube distortion

Post by RhythMick » Sun Oct 28, 2018 7:06 pm

If you go from 0.38% to 0.29%, isn't that a 25% improvement?

Wolfgang
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Re: SRA/VTA adjustment and tube distortion

Post by Wolfgang » Mon Oct 29, 2018 4:16 am

RhythMick wrote:
Sun Oct 28, 2018 7:06 pm
If you go from 0.38% to 0.29%, isn't that a 25% improvement?
I think it depends on were you start adjusting/measuring. It is between 14% and 20%...still a lot of improvement.

Nick,
how would you measure the IMD of the phono stage? With the test track and subtract the cartridge distortion or with a test signal (4k/60Hz) from the signal generator? Would the RIAA in this case distort the measurement ? I use at the moment the TS phono stage with passive RIAA between 6C45pi and 12AX7. I really wouldn't know how to improve any IMD in this circuit and where to start. Also interesting that no phono pre I have looked at today has any information about THD/IMD.

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Nick
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Re: SRA/VTA adjustment and tube distortion

Post by Nick » Mon Oct 29, 2018 8:51 am

IMD is not a separate distortion, its just a result of non linear behaviour and a two frequency test signal. Its easy to measure IMD with a phono if you have the kit, just feed a IMD test signal from a generator (a record IMD would be too high) either though a built in RIAA filter or a external inverse RIAA, the the output to a analyser set to measure IMD.

I would question if IMD is the symptom or the cause in the case of your cartridge. You are setting up SRA, and using the level of IMD to adjust that, but is it the SRA being better that you are hearing (through what ever other effect that is much harder to measure than IMD), or the difference in IMD you are hearing. I dont know the answer to that.

The simple way to reduce distortion is to use CD.
Resistance isn't futile it's V / I.

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pre65
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Re: SRA/VTA adjustment and tube distortion

Post by pre65 » Mon Oct 29, 2018 9:23 am

Nick wrote:
Mon Oct 29, 2018 8:51 am
The simple way to reduce distortion is to use CD.
:)
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Wolfgang
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Re: SRA/VTA adjustment and tube distortion

Post by Wolfgang » Mon Oct 29, 2018 5:05 pm

Nick wrote:
Mon Oct 29, 2018 8:51 am
The simple way to reduce distortion is to use CD.
I totally agree. But then there are many old first releases on vinyl the SQ of which have never been reached by later releases on CD or vinyl. Remixes seem to be even worse in most cases. I bought all Genesis albums 4 times already (twice on CD, twice on vinyl) and the worn out LPs from the first release still sound best regarding the balance of the sound mix. A re-release on 180g Vinyl from Musical Surroundings for almost $200 sounds shockingly bad.
Nick wrote:
Mon Oct 29, 2018 8:51 am
I would question if IMD is the symptom or the cause in the case of your cartridge. You are setting up SRA, and using the level of IMD to adjust that, but is it the SRA being better that you are hearing (through what ever other effect that is much harder to measure than IMD), or the difference in IMD you are hearing. I dont know the answer to that.
Next to optical adjustment of the SRA to use a test record with a spectrum analyzer is the only other way to my knowledge- at least theoretically and considering what the SRA is and how it effects the sound -in order to make sure that the stylus follows the same path in exactly the same angle as the groove was originally cut. Whatever is the reason for it I can only say that it sounds much better when it has been adjusted to lowest IMD.

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Nick
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Re: SRA/VTA adjustment and tube distortion

Post by Nick » Mon Oct 29, 2018 5:29 pm

I totally agree.
I was just suggesting that obsessing too much about distortion was not necessarly the best thing to do WRT vinyl.
Next to optical adjustment of the SRA to use a test record with a spectrum analyzer is the only other way to my knowledge- at least theoretically and considering what the SRA is and how it effects the sound -in order to make sure that the stylus follows the same path in exactly the same angle as the groove was originally cut. Whatever is the reason for it I can only say that it sounds much better when it has been adjusted to lowest IMD.
I was not suggesting that getting SRA right was not important or that using IMD to do that was not a good method. I was just questioning if the assumption that reducing IMD in the system in and of itself was a goal that followed from the SRA adjustment.
Resistance isn't futile it's V / I.

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