Ortofon ST-70 Moving Coil Transformer Review

[amirm]

How to change version A or B is clearly in the manual I see online.

You are taking turns to be who can be more obnoxious?

There is nothing in the manual beyond the spec I posted and how to change the jumper. Nothing in there explains how to get this frequency response:

Further, the config B says "recommended" impedance is less than 10 ohm.

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.

 

[amirm]

I would have spend a little more time finding out what is wrong when seeing so much deviation from spec.

No such investigation should be necessary as no user has this kind of instrumentation. They need to provide full frequency response graph as jensen provides: https://www.jensen-transformers.com/wp-content/uploads/2014/08/PI-XX.pdf

If they had provided a proper set of measurements, then I would know how to correlate mine with theirs. And buyers would know, kind of, how it would impact their situation.

So don't go defending nonsense. It is not my job to find information that they should have provided.

 

[Bland_username42069]

Could one use a step up transformer to bring a MM cart to line level and equalise it in a DAC? Is there any disadvantage to this rather than using op amps or Jfets? (I’m not very technically minded so this is probably a stupid question)

 

[amirm]

Also what was the input impedance of the AP555 with this measurement, as 47k is the rated load?

You haven't read the review, have you.

 

[amirm]

Could one use a step up transformer to bring a MM cart to line level and equalise it in a DAC? Is there any disadvantage to this rather than using op amps or Jfets? (I’m not very technically minded so this is probably a stupid question)

You wouldn't know what to correct for, especially if the transformer is so impedance sensitive.

 

[amirm]

I would have at least try to change the source impedance to find out the effect and if it explains the large deviation seen.

Which was done. See the bloody graph for heaven's sake.

 

[Hayabusa]

You haven't read the review, have you.

read the review missed that, sorry

 

[Hayabusa]

Come back when you can actually bring some knowledge to the conversation

Just try a source impedance that is lower!
the change from 600 to 20 is huge so the change from 20 to 2 will most probably also be.
Just try it! (please...)
It could maybe reveal the device was in mode B? (did you check the what mode it was in?)

 

[Sokel]

Taken from their Moving Coil transformer apps, here's the doc of a random one as we don't have the exact model :

https://www.lundahltransformers.com/wp-content/uploads/datasheets/1678.pdf

It states:

Moving coil input - Lundahl Transformers

Moving coil input transformers Moving coil cartridges are low voltage devices. Typical output levels are below1 mV, and often as low as 0.1 mV. In order to generate 12.5W on an 8 ohm loudspeaker, a 0.1V signal must be amplifier 100000 times (or 100 dB). In particular for tube amplifier devices...

www.lundahltransformers.com

 

[stefanovesa]

in addition the manual is very puzzling: < 10 Ohm could fall in the 5-50 Ohm range .... I'm scratching my head.

 

[Hayabusa]

in addition the manual is very puzzling: < 10 Ohm could fall in the 5-50 Ohm range .... I'm scratching my head.

indeed, we can already see that this can not be correct: so switch on your own mind in go in detective mode: find out how it really is

 

[peniku8]

Thanks to the member and for your testing Amir, but geez... $1500 for this!?

Pics;

View attachment 461645

View attachment 461646


JSmith

For that price and those internals I'd expect a cnc machined titanium housing, not stamped sheet metal. Gotta justify that cost somehow, if the (hand) assembly time is already down to 5-10 minutes per unit.

 

[French Meloman]

You are taking turns to be who can be more obnoxious?

There is nothing in the manual beyond the spec I posted and how to change the jumper. Nothing in there explains how to get this frequency response:

Further, the config B says "recommended" impedance is less than 10 ohm.

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.

Hello, In light of this explanation, I understand that configuration A or B boils down to a gain choice in which the cell's impedance matters little. In this case, Ortofon should have simply included a gain control and not forced the user into an unpleasant and complicated disassembly. Your review is therefore perfectly valid to demonstrate that this device has a frequency response that is completely out of specifications on a major criterion that makes the product nearly unusable. As a result, I give it a headless panther, especially since the selling price is ridiculously high.

 

[Sokel]

For that price and those internals I'd expect a cnc machined titanium housing, not stamped sheet metal. Gotta justify that cost somehow, if the (hand) assembly time is already down to 5-10 minutes per unit.

Given that the transformer's lowest price start from $90 and can go up to $1100 each...

MovingCoil

(of course it will be lower for companies but not much)

 

[Hayabusa]

Hello, In light of this explanation, I understand that configuration A or B boils down to a gain choice in which the cell's impedance matters little. In this case, Ortofon should have simply included a gain control and not forced the user into an unpleasant and complicated disassembly. Your review is therefore perfectly valid to demonstrate that this device has a frequency response that is completely out of specifications on a major criterion that makes the product nearly unusable. As a result, I give it a headless panther, especially since the selling price is ridiculously high.

We still don't know which configuration is tested...
My estimation is the device was in B mode and will show an approximate input impedance lower than 10 ohm.
This would explain the low gain measured with a 20 ohm source.
Lets see if the truth will come out, I am really curious now.

 

[Ropeburn]

For that price and those internals I'd expect a cnc machined titanium housing, not stamped sheet metal. Gotta justify that cost somehow, if the (hand) assembly time is already down to 5-10 minutes per unit.

I'd also expect the jacks to be in proper order, not in/out grouped together instead of left/right, just because it makes the board layout easier in relation to the transformers or whatever was the reason. Lazy design you would let a cheap box get away with, but not this money for which you can get two or three terrific MC preamps or a single luxury one...

...making this whole thing obsolete.

I don't get it. What's the purpose even? Why not use an MC capable preamp in the first place instead of this expensive detour? What am I missing here?

 

[Soniclife]

Why not use an MC capable preamp in the first place instead of this expensive detour? What am I missing here?

These sort of things are popular with people who like valves, which are too high noise for low output MC. Also popular with people who just like to make things complicated, and worse.

 

[SIY]

Sigh. I've talked about this again and again. An MC transformer CANNOT be universal. The performance is CRITICALLY dependent on source and load impedances (note "impedances," not "resistances"). For literally a few pennies in parts, it can be optimized for a particular cartridge and load, and performance can be excellent, but this is almost never done. This transformer could be shown to have excellent performance had this been done, or if source and load impedance for testing had been at the design values (assuming those are given, which is NOT a safe assumption).

The biggest advantage of a step up transformer was apparently not tested here- common mode rejection. With my preamp and cartridge, wiring to the transformer done balanced, I used to freak people out by turning up the volume, then touching the cartridge pins. And... almost no hum from that!

 

[sceptical1]

When I can get the Fidler Spartan 20 for $670, an entire phono preamp with mc for half the price of a load critical sut why should anyone care about this thing. Bespoke RC compensation to optimize the cartridge, I don't think so without test equipment.

 

[TNT]

I assume you mean input

He means to mimic the source.

Of course ;-)

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