Phono Transfer System Construction Information

Construction information for DIY projects, including the MS Mid Side Matrix, Elliptic Equalizer, Mastering Console, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
Gold
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Re: Phono Transfer System Construction Information

Post by Gold » Mon Mar 01, 2021 4:07 pm

JR. wrote:
Mon Mar 01, 2021 1:58 pm

MM carts are sensitive to termination capacitance. High and low capacitance cables, and length, should be considered when going for a target termination.

I used to sell a kit 4 station dip switch and PCB with 24pF, 47pf, 100pF and 200pf polystyrene caps to cover a wide range of terminations.

There used to be frequency response test records, but I don't know how many playings it takes to compromise their HF accuracy. I don't think I'd look for one of them in the used vinyl bin.

In my judgement termination (capacitance) was not well appreciated back in the day, and may be responsible for mixed results from similar gear.

JR

I've had exactly zero luck flattening out cartridge response by adding capacitance. To me cartridge resonance sounds like band pass filter. Fixing it with a filter or shelving response of a capacitor doesn't work IME. I have no idea how to test cartridges for the shape of the resonance but my ears tell me it's a bell curve.

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Mon Mar 01, 2021 5:09 pm

JR. wrote:
Mon Mar 01, 2021 1:58 pm

hi Bill...

MM carts are sensitive to termination capacitance. High and low capacitance cables, and length, should be considered when going for a target termination.
Well I'm trying out a theory with this build. Attached is a VNA sweep of the cartridge I am using that Hans Polak did for me with a stab at an equivalent model. This allows me to load the generator for flat frequency response to 'try' and get an idea of the contributions of the mechanical side of the cartridge. Loads of theories have been postulated but never satisfactorily measured. I'm going to give it a try and see what I learn. I suspect I will find most people have 2-3x the actual required capacitance loading their MMs, but I'd be just as happy to find I've been completely wrong all along.

There used to be frequency response test records, but I don't know how many playings it takes to compromise their HF accuracy. I don't think I'd look for one of them in the used vinyl bin.
I've got a CH precision test record with an accurate pink noise channel on it. Most test records you can pick up are wrong in many ways. I have a mad idea to try and make cal files for some of the widely used ones. Hey I can have a dream to get me through the dull tedium of my life :)
In my judgement termination (capacitance) was not well appreciated back in the day, and may be responsible for mixed results from similar gear.
I'd go further. Phono stage manufacturers IMO generally are clueless on MM, maybe as they want people to upgrade and spend more for MC.

Also not sure most punters actually cared even back then! (Grado users are of course Smug as their cartridges are very insensitive to C).
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AT150MLX-2.png

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JR.
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Re: Phono Transfer System Construction Information

Post by JR. » Tue Mar 02, 2021 9:26 am

billshurv wrote:
Mon Mar 01, 2021 5:09 pm


I'd go further. Phono stage manufacturers IMO generally are clueless on MM, maybe as they want people to upgrade and spend more for MC.
I'm inclined to get a little defensive about this, as I have designed both types. Indeed MM cartridges cover entry level all the way up to relatively high end, so there are dramatic differences between those users.
Also not sure most punters actually cared even back then! (Grado users are of course Smug as their cartridges are very insensitive to C).
In my experience termination capacitance was not even an after thought for most users back in the day.

For the record I do not claim any magical performance improvement from getting this correct, but as usual better is always better. 8-)

JR
Cancel the "cancel culture", do not support mob hatred.

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JR.
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Re: Phono Transfer System Construction Information

Post by JR. » Tue Mar 02, 2021 10:15 am

billshurv wrote:
Mon Mar 01, 2021 5:09 pm

I've got a CH precision test record with an accurate pink noise channel on it. Most test records you can pick up are wrong in many ways. I have a mad idea to try and make cal files for some of the widely used ones. Hey I can have a dream to get me through the dull tedium of my life :)
If you have a test record that you trust it seems easy enough to empirically compare different terminations for best result.

JR
Cancel the "cancel culture", do not support mob hatred.

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Tue Mar 02, 2021 11:45 am

JR. wrote:
Tue Mar 02, 2021 9:26 am
billshurv wrote:
Mon Mar 01, 2021 5:09 pm


I'd go further. Phono stage manufacturers IMO generally are clueless on MM, maybe as they want people to upgrade and spend more for MC.
I'm inclined to get a little defensive about this, as I have designed both types. Indeed MM cartridges cover entry level all the way up to relatively high end, so there are dramatic differences between those users.
This is why I said 'generally'. And in the last 15-20 years it has gotten a lot worse. I would never accuse your designs of falling into that trap.
If you have a test record that you trust it seems easy enough to empirically compare different terminations for best result.
If all I wanted was a flat response yes. But I want to try and settle a long running debate on a fundamental point of cartridge operation. Is there a HF peaking response due to the cantilever in the audio band?

Gold
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Re: Phono Transfer System Construction Information

Post by Gold » Tue Mar 02, 2021 1:02 pm

Bill,

I'm not sure what those graphs are showing could you explain them a little?

I have an AT150MLX. I got it because it was described as a Shure V15 replacement. I hope I am not poking the bear when I say I found it painfully bright. I tried taming it with added capacitance but no luck. It was like, not enough, not enough, whoops too much. That said I don't find cartridge resonance is easily tamed with more sophisticated EQ either. The Neumann PUE74 has a seven band graphic EQ and although it can flatten out general response I've never found it to tame resonance. I've tried to tame the resonance of the DL103 I use. I can hear it's around 10K. No minimum phase EQ I tried sounded like it was the inverse of the resonance. I think there is more going on. Perhaps a small delay due to the inductance?

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JR.
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Re: Phono Transfer System Construction Information

Post by JR. » Tue Mar 02, 2021 1:28 pm

billshurv wrote:
Tue Mar 02, 2021 11:45 am
JR. wrote:
Tue Mar 02, 2021 9:26 am
billshurv wrote:
Mon Mar 01, 2021 5:09 pm


I'd go further. Phono stage manufacturers IMO generally are clueless on MM, maybe as they want people to upgrade and spend more for MC.
I'm inclined to get a little defensive about this, as I have designed both types. Indeed MM cartridges cover entry level all the way up to relatively high end, so there are dramatic differences between those users.
This is why I said 'generally'. And in the last 15-20 years it has gotten a lot worse. I would never accuse your designs of falling into that trap.
Curiously old time phono preamps were quite crude also...

I pretty much stuck a fork in my preamp design pursuits last century.

I need to stop talking before I insult modern vinyl aficionados.
If you have a test record that you trust it seems easy enough to empirically compare different terminations for best result.
If all I wanted was a flat response yes. But I want to try and settle a long running debate on a fundamental point of cartridge operation. Is there a HF peaking response due to the cantilever in the audio band?
I vaguely recall a CD4 vinyl system where audio content was encoded above the top audio octave, I suspect the very HF response of the mechanical system was well inspected, but not sure where too look for discussion of that technology.

JR
Cancel the "cancel culture", do not support mob hatred.

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Tue Mar 02, 2021 4:12 pm

Gold wrote:
Tue Mar 02, 2021 1:02 pm
Bill,

I'm not sure what those graphs are showing could you explain them a little?
Top left is the inductance sweep. next to that is the equivalent model. Top right you can ignore as that is simulating current mode operation. Bottom is the frequency response of the generator based on the equivalent model. Or half the cartridge. This infers that the AT150 is happiest with a very low loading. But until I get some sweeps I can't tell what the overall frequency reponse is. Currently I'm loaded a total of 100pF and it's sounding neutral to me in my system. But I could get a horrible shock when I measure it.

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Tue Mar 02, 2021 4:15 pm

JR. wrote:
Tue Mar 02, 2021 1:28 pm

Curiously old time phono preamps were quite crude also...
But these days a lot of them have a fixed 250pF loading which is REALLY crude.
I need to stop talking before I insult modern vinyl aficionados.
no chance of that with me as I know I am polishing a turd.

I vaguely recall a CD4 vinyl system where audio content was encoded above the top audio octave, I suspect the very HF response of the mechanical system was well inspected, but not sure where too look for discussion of that technology.

JR
The AT150MLx that Gold has will play CD4 (so will pick up over 40kHz.) and yes its one of the reasons I don't buy the audio band mechanical peaking iun anything made since about 1955!

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Tue Mar 02, 2021 4:52 pm

My Stanton 681, with only a cable Cload (maybe 120 pF) makes a cymbal crash sound like trash can lids.

I'm using the DL-103/MC preamp now and would have to look at the uninstalled MM preamp's jumpers but I recall adding 150 or 200 pF to tame it.
C-Loading the '681 sounds like what I would expect it to.

The DL-103 loaded in 1KΩ sounds screechy to me.
With 100Ω load I get the appeal of the '103.

If it's not a mechanical resonance at some frequency than what else would it be?

I have a theory about MC carts loaded by transformer reflected secondary load.

An MC loaded by a resistor sees that load without delays.
An MC loaded by a transformer's reflected secondary load see's the load after it's undergone the round trip phase delay of the transformer reflected back from the secondary.

An MC loaded by a resistor is like an RF transmitter feeding a dummy load: The load dissipates the energy. It's all forward and incident.
An MC loaded by a transformer is like an RF transmitter feeding a transmission line and antenna: It has a VSWR. The load is reflected.

In RF you don't want reflected energy - with an MC cart you depend on the reflected load to terminate the generator.

RF may be a bad analogy but having a load resistor on the secondary of a transformer may not be the same as directly loading the MC generator even if the resistive component is equivalent.

Food for thought...
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