300b lovers

@donsachs 

not being an EE myself I may have this wrong, but isn’t IT a long established superior way of coupling? Nobu Shishido’s Wavac EC300b with its superb Tango transformers is a prime example of the technique, isn’t it?

@donsachs ​​​​@lynn_olson 

It was great to meet you both at PAF and thanks to each of you for taking time to talk to me. That was the main reason I went there (and yes, Lynn, the lines at SeaTac were awful flying out). My given name is Jonathan and I know you were talking to a lot of different folks up there so you might not remember me. Don, you gave me information about a cable company and a semi-affordable DAC that wasn't as expensive as the top LampizatOr tiers. 

I posted most of my thoughts of the Blackbird (I suggested to David Whitt that you might come up with different names due to Raven Audio's avian naming for their tube amps) in the Spatial Audio Circle at Audiocircle but I was impressed with everything in both Spatial rooms and I spent significant time listening to both the Blackbird/Raven combo and Cloud's updated Valhalla amp with the X4 Ultras and both were impressive. 

I thought the Songer speakers were impressive as well although there are so many components in a room that, if you are unfamiliar with the speakers/amps/cables etc it is hard to attribute something you really like to one thing.

Since this was my first audio show, I asked a guy in the Seattle HiFi/Modwright room how things work because it seems to me the speaker is like the lead singer in a band, getting most of the credit and the spotlight and not always deservedly. He told me that they try to get synergy and sell the equipment as a unit rather than just sell individual components and I thought that probably makes sense.

I also saw certain kinds of music being played in most rooms, usually female vocals with sparse arrangements in order to show off the dynamics and quiet background. Some rooms had the music playing too loud to really make any opinions about anything other than "it's hurting my ears."

One of the things I liked about the Spatial rooms is that they were willing to play any kind of music and not always modern/hi rez stuff and they played at what I would call reference volumes which Goldilocks would say was "just right."

Anyhow, because of both of your willingness to share time and experience there and here, I really had a worthwhile time and learned a bunch. Thanks.  

@antigrunge2 Yes, IT is known as an excellent way of coupling, but it is expensive for very good ITs, and also they take far more physical space than your typical coupling cap.  So most vintage tube amps use RC coupling due to cost and size considerations.   Bad ITs don't sound very good, they can oscillate, or have very poor frequency response.  Done correctly with top shelf ITs and with a plan for the layout, then IT coupling walks all over RC coupling.   Medium ground is LC coupling with a high quality anode choke and good capacitor.  Also, there are circuits and tubes that are very difficult loads for ITs, so it is process of using the right method for the right circuit.  It is not one size fits all....  But in the right spot, I prefer IT coupling....

IT coupling dates back to the 1920’s Atwater Kent and radios of that vintage. Like field coil loudspeakers, it is the oldest form of coupling of all. But transformers have always been labor-intensive and expensive (going right to the beginning of electronic amplification), so when coupling caps became practical in the late Twenties, ITs mostly went away, although Western Electric and high-end radio builders used them as late as the end of the Thirties.

What pretty much ended them in all applications was the universal use of global loop feedback, with the landmark Williamson of 1948. You can wrap feedback around one set of coupling caps and an output transformer, but two transformers are out of the question. So IT coupling was moribund until zero-feedback amps saw a comeback in the early Nineties.

In the mid-Twenties, the only signal source was AM radio. Electrical phono pickups were just coming on the market, and movie sound was brand-new and experimental. By the mid-Thirties, movie sound was universal, with a bandwidth topping out at 8 kHz. Electrical phonographs could reach 8 kHz, but users often used "scratch" filters to soften the sound of noisy shellac 78’s. AM radio reception could go higher, but people often used the narrowband setting to get rid of interfering whistles from adjacent stations. The only truly wideband source was the Armstrong "Yankee Network" of FM stations in the 42~50 MHz band, which was limited to a few stations in the Northeast. These were the only FM stations in the world, and could be received by the high-end radios of the day.

It was only in the postwar years that wideband (30 Hz ~ 15 kHz) sources became widespread, with LP records in 1948, pre-recorded tapes in the mid-Fifties, FM broadcasting in the postwar 88~108 MHz band, and 70mm movies with magnetic soundtracks in surround sound. By then, all amplifiers were medium to high feedback designs, and used RC coupling throughout.

Modern wideband transformers were in studio use from the early Fifties, and the triode designs of the early Nineties opened the market for more unusual products, such as interstage transformers. True, it’s a 1920’s technology, but they didn’t have modern bandwidths back then ... the recording technology was unforeseen and decades in the future. What we hear now, with our ultra-wide band, ultra-low distortion sources, is a brand new sound, running through new-tech devices.

I hope you don't mind me going a tangent, but delving into modern and old technologies and taking advantage of such knowledgeable folks sharing with an open mind I wanted to humbly ask what function does a preamp fulfill in the context of a single digital source (DAC) driving a good SET? 

Here's why I'm asking: time ago I got into DIY speakers and adopted software-based FIR crossovers and 4-way active stereo, driving amps directly from a multiway DAC. AMT tweeters are driven from a 45 Yamamoto SET (hopefully not considered "junk" here 😊, combo sounds great to me), mids by KT88, midbass and subs by class D. My system sounds better now than it did before with branded speakers with passive xo, but I do wonder if I'm missing something driving amps from a DAC...I did love my Lamm LL2 preamp but I decided to optimize for digital sound reproduction with multiway so a stereo preamp didn't fit anymore.

In the context of not needing more than a digital source, the DAC producing enough gain such that using a digital volume control works well, and gain matching among amps being already solved, what would the advantage of using an interface between DAC and amps? 

Thank you in advance!