SUT - electrical theory and practical experience

@o_holter 

I tested a SUT with the Io and did not like it - sounded good at first but then I noted that it subtracted from the purity, the sound became more hi-fi, for lack of a better word. But that was with a mid level SUT years ago and things could be different now.

When you delve into the waters of the external SUT there are a lot of considerations beyond the obvious.  One "gotcha" many people run into is dynamically overloading the input of the phono.  It is important to remember that the numbers thrown about for phono are all typically referenced to 5cm/sec @ 1kHz so your atlas will put out 0.56mV @ 1kHz with a 5cm/sec signal.  The important thing to remember is that the same signal level @ 8kHz will be 12dB hotter for a 2.24mV level (20cm/sec).  Now toss in a bit of cushion in the form of a 12dB of headroom and you might see a nearly 9mV dynamic peak from that cart.  Now consider what happens when you put this 0.56mV signal into a 1:20 SUT and the nominal 1kHz level is in the 10mV range and the dynamic HF peaks are in the 160mV range.  That 160mV @ ~8kHz will pretty much momentarily eat the input of any phono for lunch.  The good news is this is just a quick transient overload so it isn't a constant nagging problem but one that only pops up occasionally.  The bad news is since this overload happens dynamically it is elusive and by the time your brain senses something is amiss, it is gone.  

Now back to the situation where you move to the Atlas Lambda which basically cuts the output in 1/2.  If you add anything more than a 1:2 SUT you have to dig a little deeper into the available overload margin to make sure you don't start tickling the HF input limit with your peaks.  This overload situation happens in the very first stage so any gain adjustment beyond bypassing an active stage entirely does not change the situation.  Just because a switch allows you to get 12dB less gain doesn't also mean you now have 12dB more input headroom.  With the current trend of higher output cartridges like the Atlas being paired with the typical 1:20+ SUT intended for LOMC's I see this type dynamic overload happening al lot.  

A good example of this is comparing an EMT TSD15 (24Ω 1mV) to a denon 103 (40Ω 0.3mV)  From an impedance standpoint the same SUT can handle either but if you use the typical 1:20 on the 103 you end up at the 5mV "traditional" MM spec.  but use that same 1:20 with the EMT and you end up with a hot mess because the phono stage input is not happy with the quarter of a volt peaks it is being fed.  This results in a situation where the denon owner loves his SUT and the EMT owner curses the same device.  Drop the ratio of the SUT for the EMT to 1:7 and more often than not you will have a happy camper.  

dave

Hi @intactaudio ,

I have a DIY phonostage based on EAR 834p schematic + EMT TSD 15 + SUT Sun Audio SAT1000 Tamura.

https://www2.big.or.jp/~sunaudio/assem/sat1000_e.html

I use 20 Ohm input (26dB, 1:20). The phonostage has overload points - (1% THD+N) for the 834P were 69.2mV at 1kHz, 260mV at 20kHz, and 7.85mV

I tried 40 Ohm input. But it sounds less good, thinner and less musical.

Before this I used Altec 4722 SUT with Ortofon Jubilee cartage. But I don’t like this SUT with EMT TSD 15.

I tried a modern Houfe T890 SUT and Jensen JT44 SUT. But both are very low resolution and dynamic compared to Altec. I also had Tamura SUT-83TWIN. Bot Tamura transformers are the best.

Alex.

The EAR 834p is a Phonostage I have been encountering for many years.

I have been demonstrated it when it was first released and was listening to it in use on system using other EAR Amplification in the late 90's on regular occasion. 

At various events and Bake Off's I have attended throughout the past 10 years the Model has been demonstrated in both Original Build and the Clone DIY Version.

The Phon' in my assessment has a very noticeable richness and bloom at the lowest frequencies.

I find it hard to think of any SUT that will reduce this presentation to a condition where it is difficult to detect. From experiences encountered, a Head Amp' might be the most successful in reducing the perception of richness.

A better description of what was wrong with the SQ for your tastes, that encouraged the changes of a SUT, might help with understanding what your ideal presentation could sound like.

When my Bespoke Built Phon' was being built and I was experiencing it at different stages of Design, Topology and Circuitry, I rejected the prototype on more than one occasion, due to the detectable Richness and Bass Bloom that was being perceived. It took a careful organisation of the Topology and Circuit to use Boutique Cap's and Resistors, that were selected through component rolling to tame the ECC 83's. I use this with SUT's or occasionally a Head Amp with Ortofon Cart's.

The point I was trying to make when I pointed out that transimpedance phono stages generally are just voltage driven stages with a current to voltage converter added on to the front end is that they are subject to foibles just like voltage input phono stages. As Atmasphere pointed out in another thread, a current driven stage ought theoretically to present zero input impedance, but that is impossible as there would then be no signal at the output of the converter. So they all have a finite input impedance ranging from ~2 to ~20 ohms, based only on research I’ve done on my own. That’s a fly in the ointment of perfection. Because of differences in actual input impedance ( and probably in current gain and maybe distortion of the input devices, either an op amp or transistors), different transimpedance stages seem to act differently and sound a bit different dependent upon the internal R of the cartridge. This is evident to me based on my communication with Mijostyn. He uses a Lino and I use a BMC MCCI. And each of us has experimented with a few different LOMCs. We’ve reported somewhat different results, depending on cartridge. So there’s nothing perfect about current drive or stages that use it, though they can be very competitive with the best voltage driven stage.

@alexberger 

I use 20 Ohm input (26dB, 1:20). The phonostage has overload points - (1% THD+N) for the 834P were 69.2mV at 1kHz, 260mV at 20kHz, and 7.85mV

you seem to have a frequency number missing from the above since you have three voltages listed and only two frequencies.  

dave