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.
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JR.
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Re: Phono Transfer System Construction Information

Post by JR. » Tue Mar 02, 2021 5:13 pm

I am not sure I embrace the analogy...

The impedance transform "through" transformers is not the same thing as reflected energy in unterminated transmission lines... Both have "trans" in the spelling but the similarity ends there, IMO.

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billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Tue Mar 02, 2021 5:38 pm

mediatechnology wrote:
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.
BTW sorry for slightly de-railing things here. I don't doubt the stanton is unhappy at that load. There are a multitude of generators out there. I don't have a 681 but I have a range from 40mH to 700mH to mess about with so I will be kept amused for years. I'm just interested in flattening out the generator to get a better handle on the mechanical part. Attached is one of the more widely accepted theories about how a cartridge works. M is the mechanical response, E is the electrical and S the combined (actual output) and based on a simple model of a stanton 681. This would indicate that, if you don't load this cartridge down enough to damp the electrical response you will get a big lift about 10kHz. The problem I have with this theory is that, if MMs suffer from it why don't MCs? None of the literature that talks about resonant peaks in MM cartridges addresses that!

The other thing you can do is load the cartridge down to get an early roll off. This was first considered by Barney Oliver back when I was in short trousers and gets picked up and dropped again at regular intervals as it's one more thing for the punter to get wrong so will never make a commercial product leaving it for the odd basket case home experimenter. The nice thing about the PTS is that you can experiment with all this stuff as it's flexible enough to cope with whatever dumb thing the user wants to do.
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svr response.JPG

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Tue Mar 02, 2021 5:51 pm

Bill: It would appear that mechanical resonance is a "feature" used to extend/peak the response.
Is that fair to say?
Thanks for posting that.

JR: Comment about the difference in termination with R at the generator versus R on the secondary of the transformer.
It would seem that for an equal value of R the terminations at HF would be different.

The difference might explain why a similarly-loaded cart would sound different with an active input versus a transformer-coupled input.
One is terminated in pure resistance the other has a reflected termination.
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Re: Phono Transfer System Construction Information

Post by billshurv » Tue Mar 02, 2021 6:48 pm

That is certainly the theory. But as it makes no sense from an MC perspective and they use the same cantilevers as MM there must be something else going on. Note that in the paper I quoted the mechanical resonance was frigged to give the answer they wanted but since it then drove the design of an 'inverse resonance filter' to fix the output I think the point was somewhat missed. And he didn't do any tests with vinyl and a square wave test signal it was all theoretical.

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Re: Phono Transfer System Construction Information

Post by JR. » Tue Mar 02, 2021 7:13 pm

Square wave (rise time) response was not even a consideration back in the day... Frequency response was hard enough and they would take what they could get by hook or crook.

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Re: Phono Transfer System Construction Information

Post by Gold » Tue Mar 02, 2021 7:42 pm

My memory may be faulty but I think I was still using a Shure SE20 preamp when I tested the AT150MLX. That preamp was mounted on the back of the lathe under the tonearm. Not much more than a foot. I was also using RG59 coax cabling so I think I started with little cable capacitance.

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JP.
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Re: Phono Transfer System Construction Information

Post by JP. » Tue Mar 02, 2021 10:55 pm

150pF is ideal for the 150MLX according to what I believe is a fairly accurate test record.
46538C8D-AD70-40F4-A547-63A330A40CB5.jpeg

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Re: Phono Transfer System Construction Information

Post by billshurv » Wed Mar 03, 2021 4:29 am

Looks about right (0.5dB down at 20kHz) although that teeny dip in the midrange isn't explained by the generator electrical model. But I know that Fidelis have a lot of test records so the results should be accurate. A sweep up to 40kHz is really needed to tease out what is happening.

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Re: Phono Transfer System Construction Information

Post by JP. » Wed Mar 03, 2021 8:30 am

AT150MLX_47K_150pF_TRS-1005.png

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Wed Mar 03, 2021 9:45 am

JP. Is that last image a 150 pF or 0 pF load?
The header reads 150 but the .wav file has 0 pF in the path.
I'm guessing 0.

The distortion peak is bodacious.
Similar to what I heard with the '681 lightly loaded.
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