cart measurement vs quoted spec

Axel,

Have you verified your measurement procedure with another cartridge?

If I had captured those numbers, they would seem to be suspect to me. I'm not saying that they are but I'd sure want to know that I can at least verify the results/technique with a different cartridge to be sure it's not a measurement error.

Dre

Axel,

I've done these measurements numerous times and have never seen this kind of a result, so that's why I'm cautious about condemning the cartridge at this point.

I think it would be very educational for you to test another cartridge so you can get a better handle on the likelihood of the measurements being reliable.

There are a few things that could possibly cause your numbers to be off that have nothing to do with the cartridge. The errors could also be cumulative. Again I'm not saying they are just that it deserves consideration.

- Please provide the model number of the O'scope you are using.

- Are you using the 10x probes?

- Have you verified the O'scope inputs track each other by tracing the same input signal?

- Where are you taking these measurements? (What output of your audio system are you using to feed your scope?) there is the possibility of additive and induced error...

- The area of resonance could also be possibly due to the tonearm resonance (or somewhere else in the system which is why it would be good to test another cartridge) on that note, does adding damping to your arm change your measurements?

- are you using a different amplitude settings on the O'scope to take amplitude measurements before you convert the output to dB? these amplitude settings can be off relative to higher settings which could contribute to an error in measurement.

- If this is a modern o-scope, are you using the cursors to take amplitude values OR are you using the measurement features to get amplitude values from the scope numerically? (I ask because these time based measurements can be misleading by containing more than the frequency of interest.)

- Are the gains settings for the phonostage set to the same level?

- Is the cartridge loading the same on both channels?

Depending on how you are gathering the numbers, there could be an entire spectrum of cumulative amplitude which is not exclusive to the frequency intended to be measured and this can also effect your results.

There are a number of variables that can stack up and add errors to the measured results. Some other thoughts are the crosstalk introduced by the system itself- this can be checked by sending the output of one cartridge channel into the both input (L&R) of the phonostage by using a Y-connector.

I hope this all makes sense,
Dre

Dan,

I'm just a little puzzled by the results and wanted to respond to Axel's request:

Has any one got some explanation for how such a major variation can be the case?!"

Hopefully, the information and my thoughts to his request is helpful to him.

Dre

Axel,

My attempt to help was more to do with your questions that you asked about your measurements and your results. Many of the questions I asked were because the translation of your posts were unclear to me. There are a number of things that still puzzle me that may be the cause of some of your measurement results. I'm not saying they are flawed but the results are puzzling nonetheless.

Thanks for the response on who did the measurements and what happened. Knowing that the measurements will not be redone any time soon or that another cartridge cannot be checked using the same measurement technique, it may not be helpful to continue discussions on the technical aspects of what may be contributing to the results you asked about in the original posting. This is simply because you are not currently able to double check anything or test any new procedures. I mistakenly thought that you wanted to run more tests and find out if the procedure was solid and you were confident with your results. Hopefully when you have a chance to try this again, you can post about it.

I do know what cartridge you are speaking of. If I had one, I'd be able to help you out by checking it out specifically. But I'm not sure those results would be helpful to you since it would be a physically different cartridge.

To answer your question to me about one of my suggestions. The reason for the Y-connector usage suggestion is because this test eliminates the cartridge inter-channel interaction completely. By doing so, the procedure will only be feeding the same signal into the phono inputs along with any subsequent amplification so you will know the contribution of error/offset of the electronics.

I know you said your consultant is away so you can probably answer this later if you choose to. How did you guys get differential measurements from the XLR output with a ground referenced scope? (did you use differential probes? 2 pairs of single ended scope probes (4 probes) in differential mode?)

I wish you much success in searching for what you are asking. I hope you can find the answers you seek.
Dre