300b lovers

Lynn,

I appreciate your candid views about the efficacy of DACs at varying price points. I was in the Spatial room when you heaped praise on the Mola Mola dac in the Songer/Whammerdyne room, a far less expensive DAC than the Lampi DAC in your room.  I read an owner's report that a Topping DE90 SE DAC for $900 was, to his ears, pretty much the same as the sound of his DCS Bartok DAC that cost ~12X as much.  My audio pal with nice gear has been is a rabid needle-dropper and he bought this same $900 Topping DAC and now honestly admits that his fealty to only analogue music is over as what he hears with this modestly-price DAC is pretty much the same as he hearing with his $15K analogue rig.

DAC technology, top to bottom, is really fantastic these days.  One of the happiest days of my audio life was getting a SOTA Sapphire vacuum TT in the mid 80's and another very happy day was the day I sold the TT to a local guy a few years ago, no shipping required.  Once I got an Ayre QB-9 DAC in my system, it was game over for my TT rig.  

Love ’em or hate ’em, DACs have gone a long way in the last thirty years, and continue to evolve pretty quickly. The internals of the AKM and ESS converters run at 90 MHz, with stupendous processing power. It’s what makes 4K TV and digicams possible.

That kind of speed makes up for many sins, and lets the noise-shaping algorithms operate much, much better than earliest days of SACD and single-bit MASH converters running at 2.8 MHz. In a lot of ways, it makes the endless upsampling discussions on the forums moot, since the internals are upsampling everything to 90 MHz anyway. Might as well let the chip do it, rather than play games in Roon. (Although converting PCM to high-rate DSD forces the chip to use different algorithms, which will definitely sound different.)

It is a consciously retro decision to use antique Eighties-vintage Philips TDA1541A converters, or late-Nineties Burr-Brown PCM-63 or PCM-1704 converters. Those are true once-through flash converters, with no signal processing or noise-shaping involved. But the least significant bits are kind of marginal, since it took R2R to the limit of what can be done with laser trimming and ultra precise fabrication. Nowadays, speed and good algorithms are the answer.

Which leaves the current-to-voltage converter as the last domain of audio tweakery. Op-amps are way, way better than the 1979-vintage 5532/5534 from Philips/Signetics, but you still find these antiques in consumer DACs. That’s probably where tuning happens in modern DACs, since there is little left elsewhere in the design.

And if you want to "sweeten" things, do it in the power amp or speaker. Much easier to tweak. I think making records sound like ultra-quiet, ultra-precise digital, or making CDs smoothed-out and "analog", is taking away from the strengths of each medium. LPs sound like LPs, and PCM sounds like PCM.

PCM to DSD256 is fair game, though, so why not? It’s what my Marantz SA-KI SACD player does to incoming PCM (it has S/PDIF and Toslink inputs), and an interesting "alternate view" of PCM sources.

lynn_olson

74 posts

07-04-2023 at 02:08am 

Well, enough of the rant on DACs. Addressing the question in the post by lewinskyh01, what does a really good tube linestage bring to the table if the DAC can directly drive the power amps?

A sense of ease, dynamic impact, and sometimes more vivid tone colors. How? Partly better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables. On paper, op-amps can do an amazing job driving a cable, in practice, not so much. If the preamp passes a quality threshold, yes, it can improve the signal compared to a direct connection to a DAC. Found that out the hard way with first Amity amp.

Great! Thank you for the answer. Would building such a device, passing said quality threshold, be super expensive? This device wouldn't need volume control nor the capability to handle multiple sources. Maybe the device increases gain by a given amount and then listening level gets adjusted down through software volume control.

I agree it's an endless rabbit hole going down into the audibility of DACs vs upstream network settings vs software. And bleeding edge DACs bleed out their value soon after their peak in fame. Yet some more professional-oriented devices (such as Merging Horus/Hapi, Prism Titan, Lynx Hilo) are worth the same today as they were 7-8 years ago (nominal prices are higher due to inflation, price of Cu, etc) and still are the company's reference product. I like to stay among these, which of course are the ones capable of doing 8-ways.

My gut feeling has been there is something else good preamps achieve, and your post helps put this into more specific words. I'm not aware of any commercially-available product that does this and I'm intrigued to explore and maybe DIY. The idea of introducing a tube-driven class A stage to achieve "better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables" is appealing. How would you recommend I learn about this?

The idea of introducing a tube-driven class A stage to achieve "better cable drive, partly signal conditioning, scraping off RFI and noise induced in the cables" is appealing. How would you recommend I learn about this?

@lewinskih01 You might want to study how balanced lines work. Properly done, balanced lines are the best cable drive available to audio. RFI and noise are rejected due to the low impedance aspect of balanced lines (in the old days the studio line inputs were 600 Ohms; these days its more like 1-2KOhms); weak signals induced in the cable are swamped by the low impedance. In addition the input that is being driven has a high Common Mode Rejection Ratio, which is to say that signals common to both the inverted and non-inverted inputs (such as noise and RFI) get rejection.

In a true balanced line system ground is ignored to eliminate ground loops. If using tubes this is usually done using an an output transformer which can float with respect to ground. Its also possible to direct couple using a Circlotron output, for which Atma-Sphere has several patents.

If you are supporting the balanced line standards (AES48 is one of the standards; the other is the low impedance aspect) these two methods are the only ways to do it.

@atmasphere - If the input of the next component is balanced and not referenced to ground (e.g. transformer coupled), I don't understand why it is necessary to decouple the output in the source component from any ground reference to achieve the full benefits of balanced connections. Can you please help me understand. Thanks.