Recommandation for 1:6 1:8 SUT under $5K?

The math and physics say that even if the PH9 does have a gain of 55db, not 58db, then the LS28 linestage will still put out about 0.95V with NO SUT, which is STILL enough to drive the vast majority of amplifiers to full or near full output (which by the way is typically never needed lest one blow the speakers). If you or the OP insist upon inserting a SUT in the signal path, then go for it.  By the way, we have not heard from the OP in quite a while, even to report whether he ever tried the no SUT approach.  So I suspect no one is listening. The source I consulted originally to make my original calculation of 1.3V with no SUT said that the PH9 provides 58db of gain, not 55db, but it makes no difference really. And no, an LOMC cartridge would never overload a SUT.

I have no idea why or how it came to be that my text is underlined in the post above. It was not intentional.

 

How is the above pictured device a transimpedance amplifier with an adjustable input impedance from 300Ω to 40Ω?

 

I do agree with Lew that the OP should let us know what things sound like with the direct input into his phono.  Im many cases like this the gain is not the issue and noise is.  A small ratio SUT like a 1:4 will in theory net a 12dB improvement in S/N which can be substantial for an all tubed MC phono stage.

dave

'Resultant Impedance'

Ideally, you want independent control of GAIN (+db, x factor), and independent control of LOAD (impedance). Cost goes up.

Some MC cartridges are odd/difficult combinations of signal strength/coil impedance. OP's Hana Umami Blue and my AT33PTG/II are not difficult, but you have to pay attention to 'resultant' impedance if your SUT (like my Fidelity Research FRT-4) does not have separate controls.

 

My SUT has

PASS (bypass the internal transformers) (for typical MM or HOMC 'high enough for an MM input' signal strengths).

and 4 optional X Factors (4 different windings thru the passive transformers),

but the LOAD is 'resultant' of the x-factor. Some options for future cartridges is why I picked it. (luckily it also has 3 front selectable inputs so I just pick which tonearm I want to use).

It's lowest X Factor is 10.55

OP's cartridge is .4mv, 8 ohm coil: x 10.55 = 4.22mv, that should be great

except, the impedance is not separately selectable, it is a 'result' of X Factor Squared.

You divide your MM Phono Stage's impedance, (typical 47,000 ohms), by your x factor squared, to know what Impedance will be 'shown' to your cartridge.

'rule of thumb' is to show your cartridge 10x it's coil impedance, OP's coil is 8 ohms, thus we want to 'show it' around 80 ohms. mine is .3mv, 10 ohm coil, thus I want around 100 ohm load. (at least: avoid lower, higher is ok). 

x factor squared:10.55 x 10.55 = 111.

MM Phono stage 47,000 ohms, divided by x factor squared 111 = 423 ohms will be 'shown' to the cartridge, i.e. the 'RESULTANT IMPEDANCE' That's too high! It's not going to hurt anything, just closer to guidance should sound best.

It's an inverse relationship, as x factor goes up, the 'resultant' impedance goes down. my SUT's 4  options

100 ohm input = 10.55 x factor (+20db) = 423 ohms 'resultant' load

30 ohm input = 18.27 x factor (+25db) = 141 ohms 'resultant' load

10 ohm input = 20.68 x factor (+26db) = 110 ohms 'resultant' load

3 ohm input = 35.84 x factor (+31db) = 37 ohms 'resultant' load

My cartridge, .3mv

30 ohm input is x 18.27 = 5.48mv and will be 'shown' 141 ohms

10 ohm input x 20.68 x factor = 6.2mv and will be 'shown' 110 ohms

I hear the slight difference in gain but I could not describe any tonal change between those options.

 

 

@fa8362 @lewm  @elliottbnewcombjr @billstevenson @viridian @pindac 
Thank you all for the thoughtful input — I really appreciate it.

Something I didn’t emphasize enough in my first post is that the recording itself plays a huge role in what I’m hearing. For example, I have several of the new DGG “The Original Source Series” LPs, and they’re cut very hot. With those, even my Denon AU-S1 (1:13) or AU-340 (1:10) will push the ARC LS28SE into clipping on dynamic peaks. The only way I can play those records cleanly is without a SUT at all. But then, when I switch to something like Iron Maiden Live After Death, I have to turn the LS28SE volume up to around 70% for a realistic listening level, and in that case, the AU-S1 at 1:13 actually sounds glorious — open, transparent, and full of energy. I’m confident the clipping isn’t happening in the PH9 but rather in the LS28SE, because when I insert a pair of -6 dB Harrison Labs inline attenuators between the PH9 and LS28SE, the clipping disappears — though it also dulls the transparency and liveliness of the sound.

That tells me the gain structure is right on the edge — the PH9 (58 dB) plus LS28SE (12.5 dB SE) has just enough gain for quieter or conservatively cut records, but not much margin for hot ones. So I’m convinced a SUT around 1:4–1:6 would be the sweet spot: enough voltage boost for most material, but still keeping headroom for the “Original Source” LPs and other hot masters.

@billstevenson and @viridian — Bob’s Devices 1:5 is definitely on my short list. I like that it gives the flexibility of copper or silver windings and has a solid return policy. The Lundahl LL1931 (1:8) are also strong candidates, though I worry the 1:8 might still be a bit too much for those DGG pressings.

@elliottbnewcombjr — I agree, the Zesto Andros Allasso looks very clever. Being able to switch ratio and impedance independently is exactly what I’d need, since I’d likely vary settings between 1:4, 1:6, and 1:8 depending on the record. My only hesitation is sound quality transparency — they don’t specify the core material or wire type, and my experience with the AU-S1 has spoiled me a bit in terms of tonal purity and openness.

@pindac — thanks for mentioning Sculpture A. I know Zsolt’s work has an excellent reputation, and it’s a shame those units aren’t currently in production, but I’ll definitely try reaching out to him directly.

And just to clarify: I’ve never been a big fan of active head-amps for MC cartridges — I generally prefer a passive SUTas the first stage to preserve that sense of ease and dynamics.

So at this point I’m leaning toward either a Bob’s 1:5 or Zesto Andros Allasso.