[sgrossklass]

I've just done a bit of recording from LP and looked at the result. Consistently among various LPs there's a fairly narrow (about 300 Hz) but fairly deep (about 7 dB) dip at around 9.45 kHz followed by what appears to be a broad slight peak (and preceded by a slightly rolled-off response). What is that? Mechanical resonances of the stylus/cartridge (Ortofon OMP10)? If so, is this by design? Also, the frequency response appears to be rolled off by about 6 dB per octave starting at 7 kHz or so. Is that the effect of too high an input capacitance?

 

[studeb]

You are recording froma phone stage eq'd source right? Like not from the TT straight.

 

[memepool]

Quote:

Originally Posted by sgrossklass What is that? Mechanical resonances of the stylus/cartridge (Ortofon OMP10)? If so, is this by design? Also, the frequency response appears to be rolled off by about 6 dB per octave starting at 7 kHz or so. Is that the effect of too high an input capacitance?

It could be resonances in the arm or cartridge. Mechanical resonances in the deck itself usually emanate from the bearing and would commonly be at the other end of the range, ie sub-bass.
You don't mention what deck/arm you are running?

 

[sgrossklass]

The setup used for recording is as stated in the 3rd line of my sig - Technics SL-BD20 with OMP10 cartridge on the stock tonearm (T4P), run into the phono stage of an Onkyo TX-SV636 (ProLogic A/V receiver of 1997 vintage), then via TAPE1 out to the computer with a reflashed Aureon Sky which then recorded in 88.2 kHz 16 bit via Audacity 1.2.4 which was also used for FFT analysis. Tonearm resonances would typically be in the 100s of Hz, wouldn't they? As for chassis resonances, there appears to be some kind of hump well below 20 Hz, but the FFT resolution no longer is very good at this point.

 

[Garbz]

What did you test this with, your ears and music? It's worth mentioning lots of older records experience this lack of treble. Also very few cartridges are perfectly flat, unlike their digital counterparts.

The phonostage's filter could also play a part although a sudden notch at 9khz is unlikely.

 

[bigshot]

I would try another cartridge. It's a lot more likely to be the cartridge than the phono preamp.

See ya
Steve

 

[studeb]

i read your eq thread were you say that the your Onkyo is rolled off on the high end, that could explian the high end roll off.
What source material are you using? Test tone LP White noise? Pink?
Another better cart would be good to try.
Tonearm/Cart resonances can be anywhere from 8Hz to several hundred depends on the combo. You could try wrapping the arm with some rubber to tame it if you think that it is a problem.
Your original description is confusing. You say there is a 6db/oct rollof @ 7k, then @ 9.45k there is a 300hz wide 7db dip, then the roll off continues?
Lastly what is the loading on the cart?

 

[sgrossklass]

Umm... this already *is* a better cartridge (upgraded from the stock one, which was a bit of a pain to get off so I'd be reluctant to try that again). I had 3 different (non-test) LPs there, and I also did analysis of surface noise on one. The phenomena were consistently there.
Quote:

You say there is a 6db/oct rollof @ 7k, then @ 9.45k there is a 300hz wide 7db dip, then the roll off continues?

Yup, pretty much that.
Loading is 47kOhm with unknown capacitance (at least I didn't find that anywhere on the schematic of the amp). (I guess I should take a look at a DIY phono pre.) The cable currently is a 1 m long Skytronic one of fairly good quality, I used to have a slightly shorter one of only slightly less quality there but that one always is such a pain to get off again (far too tight) that I may just buy another, shorter cable of the other good kind for the record player, should it turn out that the present one still has too much capacitance.

Now, I still have some recordings taken way back with the old cartridge and, I think, the same amp (with the old stock cable), and while it's difficult to judge rolloff, there are no notches there. The new cartridge itself also sounds quite a bit different, it emits noticeably more high-frequency noise when playing.

 

[Garbz]

capacitance won't cause problems like that. Not unless they are way off, and given that there's a very sufficient latitude for error here I doubt that the cartridge would be incorrectly loaded. Mine is loaded with 50pf, i also tried with 150pf. Very subtle difference but no frequencies were suddenly pulled way out of whack.

I'd be more inclined to look at how the cartridge is set up, perfectly aligned and all?

 

[lini]

Garbz: There's not so much one can do (wrong) with T4P/P-Mount cartridges in terms of alignment. But input capacity being way off could be a possibility - as some of the particularly CE handicapped phono inputs are well in the 1000+ pF range... Nevertheless, that 9.something kHz dip really puzzles me.

Greetings from Hannover!

Manfred / lini

 

[Garbz]

Oh sorry didn't realise that it was a Pmount. Back to loading.

The cartidge is 450mH, so to generate a filter that operates at 9.4khz you'd only need 650pf in capacitance. Ideally if it is infact loaded with 650pf then you'd want a 27k load and not a 47k. But I have the feeling that this would potentially cause a spike in the response not a dip...