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Re: Phono Transfer System Construction Information

Posted: Sun Jun 23, 2019 11:59 am
by JR.
Gold wrote:
Fri Jun 21, 2019 12:58 pm
I've never had any luck flattening out cartridge response via termination. Most of the time the problem with cartridges sounds like a resonant peak. I've never tried to measure it. Terminating an MM cart with capacitance forms an LPF, right? How could that possibly work?
I never tried or promised to make one flat with my old termination selector kit, only to approximate the design termination the manufacturer expected. A remarkable number of people playing vinyl back in the day were completely ignorant of things like cable capacitance, etc.

Getting anywhere near to proper termination for them was pure chance. :lol:

JR

Re: Phono Transfer System Construction Information

Posted: Sun Jun 23, 2019 1:46 pm
by Gold
JR. wrote:
Sun Jun 23, 2019 11:59 am
I never tried or promised to make one flat with my old termination selector kit, only to approximate the design termination the manufacturer expected. A remarkable number of people playing vinyl back in the day were completely ignorant of things like cable capacitance, etc.
I'm not sure many manufacturers recommendations are based in practical experience. I say this because I have followed manufacturers recommendations on quite a few cartridges along with altering the values. I've never been able to flatten out or audibly improve performance by altering termination values. I can change the sound but it just never actually improves performance. For example with a bright cartridge like an AT150MLX, typically by the time you add enough capacitance to get it anywhere near flat frequency response it sounds like a current starved TL072. This is done by ear while simultaneously cutting and playing back a lacquer.

Re: Phono Transfer System Construction Information

Posted: Sun Jun 23, 2019 3:51 pm
by billshurv
The 150 likes low capacitance. Adding it will not help flatten things out. When I get this new preamp built that will be the first cartridge I experiment with to try and tally generator specs with end to end performance.

If you look at the bottom graph you can see that the generator flattens out with lower loading, although 47k||150pF isn't too shabby. Tonearm wiring can be 50pF so as long as the preamp is under 100pF in your case it SHOULD be relatively flat unless there are funny mechanical effects (which is what I am looking for). All for fun of course :)

Re: Phono Transfer System Construction Information

Posted: Sun Jun 23, 2019 7:00 pm
by JR.
Gold wrote:
Sun Jun 23, 2019 1:46 pm
JR. wrote:
Sun Jun 23, 2019 11:59 am
I never tried or promised to make one flat with my old termination selector kit, only to approximate the design termination the manufacturer expected. A remarkable number of people playing vinyl back in the day were completely ignorant of things like cable capacitance, etc.
I'm not sure many manufacturers recommendations are based in practical experience. I say this because I have followed manufacturers recommendations on quite a few cartridges along with altering the values. I've never been able to flatten out or audibly improve performance by altering termination values. I can change the sound but it just never actually improves performance.
I've only had passing experience dealing with cartridge manufacturers and that was when I traded Shure some of my kit surround sound decoder delay lines in exchange for some V15s(?)... We were both happy with the trade... but they probably made out better trading me around $3 material content for $15-$20 worth of parts. :lol:

Years later at Peavey I recall talking with a senior ex-Shure microphone design engineer, when I took the opportunity to pick his brain about microphone termination philosophy. It was not very revealing but electromechanical transducer designs are apparently a basket of competing compromises.

I am glad phono carts are obsolete (or probably should be).

I expect microphones to be with us for a while longer, but I expect us to go full circle back to the bad old days when microphones (transmitters) were designed with their own dedicated preamps to linearize and flatten the transfer functions. Imagine what we can do with cheap DSP?
For example with a bright cartridge like an AT150MLX, typically by the time you add enough capacitance to get it anywhere near flat frequency response it sounds like a current starved TL072.
I am not sure i recognize that technical characterization. :lol:
This is done by ear while simultaneously cutting and playing back a lacquer.
Luckily no wiggle room for errors in that process... :lol:

JR

PS: I apologize in advance to all that I may have offended with these comments.

Re: Phono Transfer System Construction Information

Posted: Mon Jun 24, 2019 9:45 am
by mediatechnology
This test is pretty revealing.
You can eyeball the resonant frequency and Q pretty well.
I want to perform this on a DL-103.

viewtopic.php?f=6&t=423&p=8873#p8873
mediatechnology wrote:
Tue Sep 29, 2015 3:45 pm
Great stuff Wayne :)
Thank you!
Looks like NJM2068 on paper looks slightly better on paper (test gear?) than OPA2134 including the important 4kHz region. I sorta expected OPA2134 to do better in that region.
The NJM2068 was just a little bit better.
Were you trying to say the OPA2134 sounded quieter though it measured slightly worse? This is entirely possible and I've used this phenomena to cheat ... I mean present figures which more truly reflect the excellent user experience with my designs :D .
The OPA2134 originally measured worse than it actually was so it sounded almost as quiet as the NJM2068. But it turned out to measure really close so what I heard correlated to what I later measured. (Thanks to the benefit of shielding.)
I can't really A/B but I suspect the NJM2068 may still come in a tad quieter audibly based on its midrange advantage.
Do you have Inductance and Resistance for your 681EE? I make Stanton 680/1 (their previous top model) 910mH & 1k3
Stanton 681 927 mH 1.25K for another 681 found in the same box. (Am I lucky or what?)
The one item we haven't added in this investigation is the effect of the optimum load capacitance. In the 1975 Boston Audio Society article I sent you as part of my MCamp.doc, you can clearly see the effect of this on V15 III which demands a very high capacitance.
Well maybe we have....

I had a chance to check it with both 47 K and various capacitance.

This is 47K Ohm, 100pF added, approximately 100 pF cable, tonearm capacitance unknown. Total Cload approximately 200 pF.
Stanton 681 CBS STR-112 Group 1A.

Image
Stanton 681EE 200pF CLoad 47K Rload 1kHz 5cms Square Wave Lateral Modulation. Left channel is top trace.
I'm tempted to resurrect my spreadsheet based on that NI application note on MM noise :ugeek:
Let me scan what I have in the original Audio Handbook. It's completely different than the modern TI version and spread over two sections.

Re: Phono Transfer System Construction Information

Posted: Wed Jun 26, 2019 12:44 pm
by mediatechnology
mediatechnology wrote:
Wed Jun 26, 2019 12:40 pm
I decided to check the DL-103 square wave response with terminations of 100Ω (the recommended minimum) and 1000Ω (used by Denon for response measurements.

As I expected there was a difference in level but not much change in wave shape.

Image
DL-103 Square Wave Response with 100Ω Termination, CBS STR-112. Preamp response Flat

Image
DL-103 Square Wave Response with 1000Ω Termination, CBS STR-112. Preamp response Flat

Compare to the moving magnet (moving iron) Stanton 681:

Image
Stanton 681EE 200pF CLoad 47K Rload 1kHz 5cms Square Wave Lateral Modulation. Left channel is top trace.

op amp substitutions

Posted: Wed Jul 24, 2019 4:03 am
by billshurv
NJM2114 are out of stock at the moment at mouser. Can't decide if to be patient of just bung 5532s in on the phono switcher...

It does appear that the 2114 is EoL and production will end december this year.

Re: Phono Transfer System Construction Information

Posted: Wed Jul 24, 2019 4:43 am
by mediatechnology
An NE5532 or OPA2134 both work very well in the switcher.
If they weren't EMI-susceptable and often noisy due to process the LME49720 would also be a good choice.

The NJM2114 was my "go to" turbo 5532 and NJM unfortunately discontinued it and a bunch of other linear.
Fortunately for all of us they kept two legacy op amps: The NJM5532 and NJM2068.

Re: Phono Transfer System Construction Information

Posted: Wed Jul 24, 2019 6:00 pm
by billshurv
Hmm Mouser have really changed their discount structure on some things. 10 of your preferred resistors costs less than 1! Spares are always handy. I'm sure it never used to be quite that extreme.

Re: Phono Transfer System Construction Information

Posted: Wed Jul 24, 2019 8:47 pm
by mediatechnology
I was buying a few values of 1% I don't stock and noticed the same thing.

I would always buy a few extra and if you choose to ratio-match a few such as input bias resistors (MC and MM preamps) and collector loads (MC preamp).
Isn't totally necessary but doesn't hurt either.