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Ortofon ST-70 Moving Coil Transformer Review

If you want to extract the very best from your moving coil cartridge, you really should consider a good step-up transformer. Let’s take a look at a beautiful Ortofon ST-70 moving coil transformer I recently supplied for one of my customers.

You may have read me raving on about just how much I love my golden age Fidelity Research XF-1 step-up transformers and what they do for the sound of a good vinyl system. Well, the Ortofon ST-70, whilst not quite at that level, is a very good option for those wanting to take their vinyl rigs to the next level with a really good transformer. This article is about the Ortofon ST-70, about step-up transformers or SUTs in general and why you would choose one. Let’s go.

Fidelity Research XF-1
The Fidelity Research XF-1 is right up there at the top of the list of moving coil transformers. There are three variants, selected based on the impedance of your cartridge. This one is my XF-1L, which suits cartridges with impedances of 3 Ohms or less, generally the highest performance and most sought after MC carts. The lack of switches, taps and the hard-wired cable combine to make this an end-game transformer.

Why a Step-Up Transformer?

I’ve written an FAQ about this and a my review of the Fidelity Research XF-1 from back in 2015. Transformers are a little bit of audio magic from the golden era that can take your vinyl playback to the next level, given the right starting points. Old technology, maximum performance, like vinyl. Let me explain.

Basically, transformers ‘transform’ AC voltages, from low to high and vice versa. You need to transform the voltage from a moving coil cartridge because it is so incredibly tiny, sometimes below 0.2mV. Such small signals must be amplified hundreds of times before being sent to an amplifier and this needs to be done with extraordinary precision, hence the high cost of really good phono preamplifiers.

The tiny output signals from moving coil cartridges can be amplified by conventional means, with active electronics. Alternatively, part of that job can be handled by a transformer. The advantages of using a transformer are that they are essentially noiseless, passive devices, adding no hash, hum or hiss of their own. Nor do they add any colouration, being essentially just long coils of wire, wound onto metal cores. The disadvantages are none, other than the expense involved in making good ones.

This signal boosting can be done entirely with active electronics, but it takes very, very good active electronics to even come close to the level of transparency and low noise achievable with a good transformer. And by very, very good, we mean very, very expensive. So don’t expect your Cambridge Audio or Rega phono preamplifier to be in the same sonic universe as a transformer, it’s simply not possible.

It’s best to hand some of the heavy lifting over to a transformer and for this reason, many of the very best moving coil-based vinyl playback systems, and some of the best hi-fi equipment, use transformers. For an MC playback system, you’ll need the transformer and a really good MM phono preamp to partner it with. Both are expensive, so transformers are less common and generally reserved for use in better systems.

Features

The Ortofon ST-70 sits just above the middle of Ortofon’s range of step-up transformers and with an RRP of around $1799 AUD, it’s not cheap. But, when you compare what this can deliver in terms of added realism, midrange magic and micro-resolution across the spectrum, a step-up transformer like this is a no-brainer if you can afford one.

The Ortofon ST-70 is built with the right ingredients, including a pair of Swedish Lundahl transformers in mu-metal shielded boxes. This is a good way to do it and leads to low noise and excellent isolation. The ST-70 also features switchable taps to allow for two cartridge impedance ranges: a ‘medium’ range of 5 – 50 Ohms and a ‘low’ impedance <10 Ohm setting. This adjustability makes the Ortofon ST-70 a versatile moving coil transformer, certainly more so than the XF-1 for example where you have to buy the XF-1L, XF-1M or XF-1H, depending on what you need.

That being said there is no actual magic here and these wide impedance match ranges are ‘suggestions’. Medium impedance would not ordinarily take in a range from 5 – 50 Ohms and they likely specified this so that owners of Denon DL-103 carts with their 40 Ohm impedances were catered for. Ideally this transformer would be used in low impedance configuration B, with carts rated at 5 – 10 Ohms.

Ortofon ST-70
Simple, quality packaging

Specifications

Configuration A:
Recommended cartridge impedance 5-50 Ω
Gain 24 dB at 1 kHz
Frequency response 10 Hz – 100 kHz ± 1 dB
Recommended load 47 KΩ // 200 pF

Configuration B:
Recommended cartridge impedance < 10 Ω
Gain 30 dB at 1 kHz
Frequency response 10 Hz – 80 kHz ± 1 dB
Recommended load 47 kΩ / 200 pF

Dimensions and weight
Dimensions: 58 mm(W) x 135 mm(H) x 150 mm(D)
Weight: 1.233 kg

Ortofon ST-70
It looks like an FR XF-1, but the ST-70 doesn’t have the same build quality. It’s well-made, no doubt, but weighs about half as much as an XF-1.

Pros

I’m not a retailer and I’m not selling SUTs, I’m not sponsored by Ortofon and I have no advertisers, so it doesn’t bother me if you use one or not. But I do love helping people get the most from their systems and their vinyl especially. So, why use a SUT? That’s easy, there are only gains to be had: better realism, micro-dynamics, fluidity, lower noise, wider frequency response, no parts to wear out and on it goes. Sonically, once you’ve heard a decent SUT in a good system, you simply CAN NEVER GO BACK. I mean this, I’ve tried.

The added punch, reduced noise and ‘glare’, extra ‘in-the-roomness’ and liquid-smooth texture that you can only get with a SUT make them the MC phono preamplifier of choice for discerning listeners. The problem is, they just aren’t a part of mainstream vinyldom these days, so most people no almost nothing about them!

Hi-fi retailers with shelves filled with active gain stages are going to tell you something very different. They don’t have an Ortofon ST-70 to sell you and they can’t supply you with one either because they don’t keep stock. * Heck, I bet nobody in the store has ever even seen one. I custom ordered this one from Ortofon Australia. There were none in the country, it took three months to arrive and was a ‘special import’ item.

* Amusingly, this is despite several Australian online retailers continuing to advertise that they have ST-70s in stock available for shipment. They do not!

Ortofon ST-70
Inside we see a high-quality glass fibre PCB, almost zero wiring, board-mounted RCA connectors and twin Lundahl transformers.

Cons

Cost is the most obvious con. A SUT only replaces a moving coil gain stage. As mentioned, you’ll still need a good moving magnet phono preamp to partner with any SUT and this puts many people off, understandably so. Most people don’t like the idea of spending a few hundred dollars on an active gain stage, so nearly $2000 on a transformer and another couple on a good MM phono preamp puts most people WAY beyond where they want to be. A SUT isn’t an entry-level, background music purchase.

Another issue is a lack of access to good advice about transformers. Transformers have to be well-matched to their cartridges and most have little understanding of step-up transformers or cartridge-transformer matching. Actually, most have never even seen a SUT as I mentioned, let alone used or owned one. Ask many retailers about transformers or transformer-cartridge matching and they’ll likely look at you with a puzzled expression and wander off. This is a problem.

A classic example comes from the very customer I supplied this Ortofon ST-70 to. He asked a couple of retailers who said they stocked the ST-70 about the advantages of transformers and why someone would choose one and was met with basically a wall of silence and lack of knowledge. Not only did these retailers not actually stock it, but he was given technically incorrect information. This is the current reality, even with the great vinyl resurgence.

We are still actually a long way from the golden era and many are just getting into vinyl, with little experience using equipment like transformers. My customer and I had several productive pre-purchase conversations. I answered a lot of questions and even loaned him one of my own transformers to try before he asked me to order this Ortofon ST-70 for him. Keep all this in mind when thinking about purchasing a transformer.

Ortofon ST-70
Construction quality is high and you’ll note the jumpers, here configured for my customer’s Ortofon Cadenza Red moving coil cartridge.

SUT Sound Quality

My apologies but I haven’t listened to this Ortofon ST-70 so it’s not a full review in that sense and I’ve not included a sound quality component for this reason. I supplied this ST-70 new to my customer David, and he probably wouldn’t have been happy with me plugging it in and using it before he did!

David tells me it sounds fantastic though, better than the moving coil gain stage in his beautiful Accuphase E-600 class-A integrated amplifier and that the ST-70 improved his Ortofon Cadenza Red and every aspect of his vinyl playback. He also said that he wasn’t easily able to put the improvements into words. This is to be expected from someone who doesn’t write about audio and it also describes the sorts of incremental improvements one can expect when adding a transformer like this to an already very good system.

Transformers add an elusive ‘magic’ to the sound that’s very difficult to obtain any other way. Many chase the magic with ever more expensive cartridges but the amplification chain has to be right and the fewer transistors, tubes, capacitors and power supplies there are in the way, the better. Transformers deliver this, partly because of excellent matching between the cartridge and the rest of the system.

The fact that the Ortofon ST-70 improved a $15k Accuphase amplifier/phono preamplifier at all tells us something about what a good transformer can do for an already very serious system. Imagine what a transformer could do for you!

The Bottom Line

Transformers aren’t for everyone, so should you buy a SUT like this Ortofon ST-70? If you love vinyl and want to get the most out of it, if you own a $500+AUD low output MC cartridge with an impedance or DC resistance of 50 Ohms or less, ideally 10 Ohms or less, and want the very best from it, and if you can afford one, then absolutely yes. You will need the best moving magnet phono preamp and ancillary equipment you can afford though, so don’t go partnering the ST-70 with a cheap phono preamp or turntable.

There are alternatives to transformers. Some very good fully active phono preamplifiers exist, but they are very expensive. Many high-end phono preamps like my Cayin Phono 1 use transformers internally for the MC gain stage because it gives the best results. That should tell you something.

A SUT like the ST-70, XF-1 or similar is a serious purchase and an investment not to be taken lightly. You’ll need the best accompanying components and the right advice, so seek this out, but get these aspects right and you will never look back.

Ortofon ST-70

$1799 AUD
8.6

Chassis/Build Quality

8.5/10

Features

7.5/10

Scalability

9.5/10

Bang-Per-Buck

9.0/10

Pros

  • Solid build with excellent parts
  • Fantastic sound quality according to my customer
  • Selectable impedance to suit wide range of carts
  • Small, quiet and completely passive

Cons

  • Expensive when compared with golden age SUTs

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