Allnic OTL/OCL Phono vs Allnic DHT

No transformer ought to be better than even a very good transformer or a very good capacitor, so your observations don’t surprise me. I’d like to find out more about the OTL unit.

The idea of an OTL/OCL phono stage intrigued me, so I looked up this Allnic product.  At $45,000 retail, you are not apt to find too many, except dealers, who have compared it to their DHT phono stage, which also costs well into the 5-figure range.  Anyway, to do away with both a transformer and capacitor for coupling, the unit must use some sort of servo mechanism to cancel DC offset at its output.  This has been done before, a few times, with OTL tube amplifiers. The servo itself then can become an issue, either for coloring the sound or for developing faults in its operation.  However, I have faith that Mr Park can get around such problems.

I've always wanted to try Allnic products based purely on aesthetics.   

If they sound nearly as good as they look... JACKPOT!! 

I am interested too. never heard the sound of OTL phono amps. 

You can't have heard it before, because to my fairly extensive knowledge, this is the first such product (OTL/OCL phono stage).  However, OTL tube amplifiers have been around since the 1950s (Futterman) and have always been a minority species, my favorite for driving any high impedance speaker but particularly for ESLs.  In fact, I have been using OTL tube amps to drive ESLs since the mid1970s.  Tube OTL headphone amplifiers are also not new; the first one I heard was designed and marketed by Futterman in the 60s. This is easier to do because the typical headphone has a very high input impedance compared to any speaker.

It's a bit ironic to have a phono stage that uses SUTs to step up gain and then sports an OTL/OCL output as a major asset. But I like Allnic too.

never heard the sound of OTL phono amps. 

@joeycastillo nearly all phono sections are OTL; OTL stands for 'Output TransformerLess'.

Since we have been making preamps with direct-coupled outputs (so OCL and OTL) for decades now, we had considered doing a phono stage as a stand-alone but kept running into the issue of doing the direct coupled output.

That requires an additional tube and a servo circuit. We patented a method of doing this balanced; when its done single-ended you usually have to have some kind of timer or protection circuit to be active until the output has warmed up and stabilized properly. David Berning made a very interesting preamp using this technique about 40 year ago called the TF-10. 

The tricky bit is making sure the servo does not affect the sound of the unit, for example if the opamp for the servo gets changed out for another. The design should be immune to that sort of thing.  

$48K is a bargain compared to the SS  Vitus MP-P201@64K

AND you get the tube magic that SS SOTA cant replicate.  

https://jaguaraudio.com/product/mp-p201-mk-iii-phono-preamplifier-by-vitus-audio/

Might as well drop another couple grand for vintage Euro glass for the Allnic too, just cuz.

Ralph, As phono stages go, OCL is more unusual than OTL, of course. I thought that was salient to my point. As the owner of an MP1, I know about the OCL/OTL linestage section, but the built in phono is capacitor coupled to the linestage, at least in my unit.

Here are some additional resources that may be useful-

From the Allnic H-10,000 OTL/OCL manual:

“Some circuit experts might be concerned about DC potential in the music signal in an OTL/OCL design.  However, the chance of this problem occurring can be essentially and reliably 100% mitigated. To do this, Allnic uses a “floating power supply circuit”, a design that deals with the issue by not creating any DC potential in the first place, or such a small potential that it is harmless.”

My personal experience with these units:  the H-10,000 requires less user attention for tube maintenance, more stable circuit and more robust to different environments.  

For the more advanced Allnic circuits I recommend this read:

https://www.kevalinaudio.com/circuit-balance-review-recommendations

For Manuals:

https://www.kevalinaudio.com/copy-of-current-legacy-allnic-manuals

For Reviews:

https://www.kevalinaudio.com/allnicreviewcurrentlist

“Some circuit experts might be concerned about DC potential in the music signal in an OTL/OCL design.  However, the chance of this problem occurring can be essentially and reliably 100% mitigated. To do this, Allnic uses a “floating power supply circuit”, a design that deals with the issue by not creating any DC potential in the first place, or such a small potential that it is harmless.”

That's an interesting turn of phrase ("floating power supply circuit").  Usually you would design the unit so as to have as little DC offset as practicable at the output, then cancel (or greatly reduce) that small DC offset with a servo circuit. Perhaps Atma-sphere can comment on whether the Allnic circuit might be unique. I think Allnic may be saying they treat the power supply as in a circlotron, a la the Atma-sphere products. Semantics.

To do this, Allnic uses a “floating power supply circuit”, a design that deals with the issue by not creating any DC potential in the first place, or such a small potential that it is harmless.”

@kevalinaudio We have two patents concerning a method of using a Circlotron circuit for this purpose as @lewm  suggested. It indeed is

a “floating power supply circuit”, a design that deals with the issue by not creating any DC potential in the first place, or such a small potential that it is harmless.”

During warmup, the Circlotron circuit can produce small DC offsets less than 1 Volt. Once warmed up the DC Offset is typically less than a milliVolt. Its plug and play since no adjustment is required. 

However its pretty obvious such a circuit is not used here. 

On reading the documents at the links you provided, it appears an SEPP circuit is used. The SEPP is a push-pull circuit of the 'totem pole' variety not unlike what you see in Futterman OTLs. They are often used in headphone power amps. 

Was wondering how or even if the floating PS as used by Atmasphere in the circlotron could be implemented in a SE output.

Regardless of the design wizardry Allnic employed in the OTL/OCL phonostage, I find it to be noticeably quieter than the DHT — and far easier to live with in terms of maintenance, operation, and day-to-day running. Cartridge loading flexibility is effortless, and the noise floor is effectively nonexistent.

With the older DHT 8000, I often battled microphonics and an occasional quirk where the soundstage would lean subtly to one side. Achieving a rock-solid, dead-centre image could be frustrating, requiring constant fussing with tubes and fine adjustments. The H10,000 OTL series has been the complete opposite: it simply warms up and is ready to make music, no drama, no fiddling.

What really stands out is the leap in performance: transparency, microdetail retrieval, tonal accuracy, soundstage precision, and dynamic range all surpass the DHT 8000 — which I had always regarded as an exceptionally musical phono stage in its own right. The H10,000 series feels several levels higher on the ladder.

Bass is no longer a touch overripe; instead, it extends deeper with greater control. Vocals have gained refinement without losing body and presence, while the highs are sweeter, more polished, and free of any edge — delivering a presentation that’s both revealing and inviting.

For much less money, though I don’t know the current retail price, the Atmasphere MP1 will give you similar results. Two differences: the MP1 does not use a SUT to achieve high phono gain, and the Allnic affords 4 pairs of phono inputs vs one pair on the MP1. Important also, the MP1 is fully balanced with an OCL/OTL linestage built in

@lewm      As Phantom audio is an Atma-sphere dealer, I'm sure he can test your hypothesis for himself. I, for one, would love to hear the unbiased results of such a comparison.

I’ve lived with both the Atma-Sphere MP-1 and MP-3, each with the built-in phono stage, and honestly, they’re both great in their own way. The MP-1 has that beautiful transparency and dynamic punch Atma-Sphere is known for — it really lets the music breathe. But for my own taste, the Allnic just speaks to me more. It’s got this gorgeous tonality, real weight to the notes, and a richness that makes me want to keep listening for hours.

The H-10,000 especially is a joy to live with — super quiet, really flexible, and easy to integrate into my system. The built-in SUT is a nice touch, even if you don’t need it, because it avoids extra cables and the colouration they can bring. Being silver-wired, it’s very open and detailed, but it never sounds thin; it’s still full-bodied and musical.

Just to be clear, I’m only talking about how the Allnic DHT phono compares to the OTL here — I’m not trying to make it an Atma-Sphere vs. Allnic battle.