Cartridge alignment with Oscilloscope

[dimkasta]

I m openning this thread to describe the little things I know (or think I know) so that we can discuss it a bit further.

First of all, since the cartridge signal is probably too low (especially on MC ones) I m measuring the signal on the phono output (which also gives us RIAAed signal).

We really need a record that includes frequency tracks on both stereo channels (together and independently) (need your proposal here... already have the HiFi news one but it only has separate noise tracks)

It s also nice to have a 2 channel oscilloscope so that we can see both signals at once and use the math/fft functions of the scope.

On the first screenshot, I have the two signals on top of each other. The difference is almost 1v, which is rather substantial. Probably due to bad azimouth (unfortunately the SL1200 MK2 shell does not offer azimouth adjustment... I should get a Jelco or something)
The purple line show the difference between the two channels (math A-B)



Unfortunately the HiFi news record does not have separate channel tracks with frequencies. Only noise which makes it difficult to get a measure of the crosstalk (or am I missing something?).

The second screenshot shows FFT of the left channel. We see some small spikes on the right of the 300Hz signal, probably showing some distortion? I need your help here on how to better understand what we can see in an FFT graph.



Measuring the frequency is very easy using the relevant measure options of the scope. For me both channels had a small deviation from the 300Hz of the disk (around 320Hz on both channels) which points rather to a deviation on how the disk was cut, or a deviation in the phono RIAA.

I really need to learn how to work on triggers and acquiring technics so that I manage to see the frequency responses using the ferquency sweep tracks.

Waiting for your comments, additions, advice, curses, whatever...

[merlin el mago]

Interesting thread, a lot of to learn, suscribed!!!!

[grufti]

Originally Posted by dimkasta

Measuring the frequency is very easy using the relevant measure options of the scope. For me both channels had a small deviation from the 300Hz of the disk (around 320Hz on both channels) which points rather to a deviation on how the disk was cut, or a deviation in the phono RIAA.

The phono RIAA filter does not change the frequency of the signal. It only changes the level of the signal.

Your observed difference is either the result of of the disk being cut at that frequency and/or your turntable running fast. I assume that it's both of those: the frequency on the record could easily be 315Hz and the remaining difference could be the contribution of your turntable.

[dimkasta]

Ah... nice pointer thanks

[ungie]

I have always found it curious that, despite all of the audiophile turntable setup tools, jigs, and gizmos, we are STILL waiting for a proper test LP. I think I remember one that was put out by Bruel&Kjaer in the 70s that did have tones in stereo and each channel, but I have never seen one in the flesh. This will be step one in making alignment work well with an oscilloscope.

[grufti]

The old Cardas Frequency Sweep and Burn-In Record No. 1 had test tones in stereo and in each channel. You could try and find a used one. The new one Cardas Frequency Sweep and Burn-In Record No. 2 no longer has them [weird].

Analogue Productions has more recently produced what they call "The Ultimate Analogue Test LP" and that one has stereo tones plus right and left and some other useful signals. It is currently available, but it isn't cheap. I bought it anyway.

[jackinnj]

thanks for starting this thread!

[sakellogg]

Originally Posted by merlin el mago

Interesting thread, a lot of to learn, suscribed!!!!

me too.

could the 1v come from anti skate?
i guess I'm asking if the A.S. was off would it show up like that.....or how would it look?

also what if the R&L side of your phono pre isn't matched? like right side 20db of gain and left is 21, or whatever.
should you adjust for that at the cart? will that mess up lps?

[ashok]

I have some Denon test discs from the early 80's. They had sweep tones and I think 1 khz etc. Will check when I get back home next week. If my memory is correct it was a 3 disc set. I could be wrong. Will know for sure next week.

[ashok]

One Japanese audio magazine had an article on tone arm damping with frequency plots of the low end of the freq scale. Plotted to show the effect of different damping schemes. I had the articles for many years but can't find them now though some other material is still there.

Should be possible to do similar tests nowadys with the storage scopes I guess.
The Denon test discs should have a low freq sweep for this test.

Does anyone have a set up that can run such tests ?