Ortofon ST-70 Moving Coil Transformer Review

[Davey]

Curiously, in the screenshot of the ST70, there are 4 resistors on board but no capacitors I can see.

Unless the zobel network is encapsualted in the metal case for the transformer?

I see two shunt resistors. But those should be adequate because a capacitor is not really needed. You need that additional shunt on the transformer secondary so when the recommended 47k load is attached the response is flat with no peaking.

 

[Timcognito]

BOAT "break out another thousand"

VINYL "very intensive neurosis you love"

Leveling the Turntable
Turntable Dampening
Tracking Force Adjustment
Balance the Tonearm
Set Tracking Force
Anti-Skate Adjustment
Vertical Tracking Angle Adjustment
Azimuth Adjustment
Table Speed Adjustment
RIAA Curve
MC, MM, MI Cartridge Choice
Preamp Settings
Step Up Transformer Matching
Record Cleaning and Storage

 

[rongon]

I see two shunt resistors. But those should be adequate because a capacitor is not really needed. You need that additional shunt on the transformer secondary so when the recommended 47k load is attached the response is flat with no peaking.

Thanks...
Are you thinking there should be a parallel R across the primary, and another parallel R across the secondary?

 

[SIY]

Thanks...
Are you thinking there should be a parallel R across the primary, and another parallel R across the secondary?

No to both. The secondary needs to be loaded with the cables and termination going to the chosen preamp, then a Zobel across the secondary. No resistor across the primary.

 

[sceptical1]

I see two shunt resistors. But those should be adequate because a capacitor is not really needed. You need that additional shunt on the transformer secondary so when the recommended 47k load is attached the response is flat with no peaking.

Those are jumpers not resistors. Easy installation vs wire links.

 

[markstein]

BOAT "break out another thousand"

VINYL "very intensive neurosis you love"

Leveling the Turntable
Turntable Dampening
Tracking Force Adjustment
Balance the Tonearm
Set Tracking Force
Anti-Skate Adjustment
Vertical Tracking Angle Adjustment
Azimuth Adjustment
Table Speed Adjustment
RIAA Curve
MC, MM, MI Cartridge Choice
Preamp Settings
Step Up Transformer Matching
Record Cleaning and Storage

Love it! ;-)

 

[Davey]

Thanks...
Are you thinking there should be a parallel R across the primary, and another parallel R across the secondary?

No, just on the secondary.
This is standard practice and would also be done with line-level transformers when optimizing to a specific load.

Nothing wrong with using a Zobel. As an example, the Jensen MC transformer specifies a 13k/100pF shunt

https://www.jensen-transformers.com/wp-content/uploads/2014/10/jt-34k-dx.pdf

The internal photo of this unit shows no capacitors, that I can see. (Maybe they're on the underside of the board.)
Also the resistors are enigmatic. The color code (one black band) indicates zero ohm resistors.

There are recommended shunt resistances noted here for the Lundahl transfomers:

SUT Calculations

Fine tune your speakers with the Energos MKI for the ultmate listening experience!

www.erhard-audio.com

 

[Davey]

Those are jumpers not resistors. Easy installation vs wire links.

Yes indeed. I noticed that. Thank you.

 

[audio_tony]

@Davey @sceptical1 There are resistors? There are 4, labelled RCA1, RA2, RA3, RCA4. My slight colour blindness prevents me from identifying the values.

There are of course jumpers as well.

 

[Billy Budapest]

Not a step up transformer, but a microphone preamp and then an ADC, or something similar, and then RIAA EQ applied through software.

There is a company that markets such a solution:

CHANNEL D - Pure Vinyl

They recommend this unit:

https://www.amazon.com/gp/aw/d/B0C5JRTS3Y/ref=dp_ob_neva_mobile

 

[MRC01]

Yes, vinyl can be an expensive hobby. But it doesn't have to be that expensive. Back in the day, I used one of these for my low output MC. I built a box, power supply and wiring for it. It had excellent performance for a fraction of the cost, and DIP switch configurable for gain, impedance & capacitance, with balanced and unbalanced outputs, to drive just about any cartridge on the planet, MM or MC. No need for transformer units, cleaner, simpler and cheaper.

 

[JDS]

How would you spin an LP in an iphone?!?

On the other hand, I have an app on my iPhone that uses the accelerometers in the iPhone to measure speed and (supposedly wow) if you spin the iPhone on your turntable.

 

[Davey]

@Davey @sceptical1 There are resistors? There are 4, labelled RCA1, RA2, RA3, RCA4. My slight colour blindness prevents me from identifying the values.

There are of course jumpers as well.

View attachment 461772

Those labels are for the jacks, not the resistors.

It's water-under-the-bridge at this point.
Amir has sent the unit back to the owner so no further testing/investigation is possible.
And jackers will now take over the thread.

The review now has 58 voters, 38 which rate the unit "poor".

 

[Soniclife]

The review now has 58 voters, 38 which rate the unit "poor".

I think this is a case where the poll should rate the review, not the DUT.

 

[JDS]

On the other hand, I have an app on my iPhone that uses the accelerometers in the iPhone to measure speed and (supposedly wow) if you spin the iPhone on your turntable.

Also: if you want to test a different SUT, I would be happy to have you test my Rothwell MCX.

 

[Balle Clorin]

As best I can tell, all the source impedance does is cause more losses, not change the frequency response. Come back when you can actually bring some knowledge to the conversation.

Not a perfect measurement set her either, but source resistance do affect the SUT frequency response in my measurements with varying source resistance ,

The measurements I have done of my SUTs reveal that they are only fully linear when the source resistance is optimal for the tap.

deviating from this makes then either peak of roll off. I do not believe any SUT can be perfect for 3-40 ohm range,

With an improved set up I get not the same result,but still show differences with different source resistance..

An example is my Denon AU-320 with 3 ohm and 40 ohm taps . With cartridges with these resistances, SUT are very linear 20-close to 100khz, but not with a 10 or 20 ohm cartridge,
I will post a figure when I find it
Edit: Here the 3 and 40 ohm taps run with optimal source resistance

The frequency response is only valid for the conditions the test was done at..

And here with other source resistance, and trying to compensate Zobel RC network etc RS is source resistance

Doing SUT measurements is not easy,,,,,,is not definitely not plug and play , if you want the result to be correct,

 

[Chester]

Some of the rudeness in this thread is quite shocking. If you have suggestions of how to improve the tests, there is a way to say it. Someone has still taken the time and effort to run tests and write a review for us, regardless of whether or not you agree with the approach.

 

[JeremyFife]

Thanks for an interesting review of an unusual component. Always good to see something new, and I always learn from the comments from more experienced members.

Didn't vote as I have no frame of reference for this. It's not cheap though, and the benefits of MC cartridges seem debatable anyway ...

 

[SIY]

If you have suggestions of how to improve the tests, there is a way to say it.

I have, repeatedly, for years. Like the incorrect testing of MM phono preamps, there's just no sign that the criticisms (which have included data and analysis) have had any effect. Amir wants to test black boxes, which is understandable, but phono stuff just doesn't work that way.

 

[audio_tony]

Those labels are for the jacks, not the resistors.

Me: DUH! RCA - I should have realised!

But the fact remains there are two resistors there but no capacitors which doesn't make a great deal of sense.

Even more odd is that one resistor appears to align with an input jack, and the other an output jack.