Tubo, A lot in your posting there. I will just take various issues up one at a time.
You said "both methods are capable of excellent performances (both sonically and technically) if correctly implemented and neither is inherently better or inferior to the other."
I guess I would at the most basic level disagree with that, pretty much just from the idea that two completely different highly technical processes could end up with exactly the same analog result. Over and over again in audio, it is found that there are sonic differences, and people can hear those differences, and sometimes it's not subtle. Please, no offense, but to say that something is the same because it looks the same on a scope, or that there is no measurable difference is what I call "engineering arrogance". And I can talk about it that way, because I am an engineer and was taught that arrogance just like every other engineer. Hearing is tremendously more sophisticated than any measuring instrument, because the ear integrates and evaluates information from both the frequency and time domain with all kinds of emotion and meaning thrown in.
It's like saying "these two amps both have 0.2% harmonic distortion, so they must sound the same." Again, no offense, but that is engineering arrogance.
It's not just me who is amazed by the Eico tuner. Over the last few years, trying to figure this out, I have collected some quotes from postings on news groups. Here's some of them. Keep in mind that most of these are about stock unrestored units with the ceramic caps still in circuit. Most of these from AK.
“When I first got my ST-97, I was shocked how good it sounded. I let go all my SS tuners right after I got the EICO (those ones mentioned in my previous post). It even beat the McIntosh MR74 in stock form. “
“I've had tube tuners from almost all the major brands at the time. (Sherwood TOTL S2100II (FM same as S3000V). FM-100B, Scott 350B, EICO ST-97). The EICO is the best. “
“I bought mine for $90 cad. The old gentlemen did some restoring work on it. It sounds amazing. Better than most of the SS tuners that I had (Pioneer TX-9100, TX-9500II, TX-7800; Luxman T-117, T-530, Sony ST-5130). Much better than Sherwood S2100II (FM same as S3000V). Very close to Fisher FM-100B (ST-97 has better low end while FM-100B has edge in high end).
The only one bettered it in my setup was my fully upgraded McIntosh MR74.”
“I neglected to mention the part where this tuner blows away my Adcom GFT-1A, and I think that's a very respectable one, to say the least. I've owned it since new in 1985-86 and use it daily. The Eico really grabs those signals, very impressive for such a "cheap" tuner. Definately a sleeper.
“
“One issue with the Eico are ceramic caps in the audio chain. Ceramic series capacitors are very bad news in an audio frequency application.”
“I got the 2 new 8.2mH coils today and installed them in the ST97...wow what
a nice sounding tuner..now I know what Jim Showker was talking
about.....nice bottom end, nice stereo separation...I'm not a huge fan of FM
radio , but this sound is amazing.... Thanks, I'm shocked how good it sounds...”
As I indicated earlier, the sampling bad, analog good argument, is not something that I agree with. However I will state unequivocably that sampling done at a 38khz rate is not going to be good.
As far as the Eico MPX circuit using a sampling techniques, I am somewhat mystified by those statements. Maybe that language was as much motivated by marketing as it was engineering, I don't know. They promoted their decoder in advertising by saying it provided the best of both techniques. Compromise appeals to a lot of people.
The same ring demodulator circuit is used in SSB communications equipment to demodulate a SSB signal and it is not called sampling.
It is essentially a balanced detector giving a smoother signal, in the same way that a full wave or bridge rectifier gives a smoother DC output.
An audible analog signal will result. In the ingenious balanced Eico circuit, the two out of phase 38 khz signals are nulled out when they go to the L-R amp, thus doing away with that problem with no filtering required. The audible L-R components are in phase and combine to go to the L-R amp. Notice that there is no smoothing capacitor as would be required for a sampling technique.
To me, this circuit demonstrates the same kind of brilliance as the Scott chopper circuit. I think they did apply for a patent.
I guess you could call it sampling, due to the very nature of detecting an AM modulated signal. It probably would have been better to use a higher frequency than 38khz.
If one insists on calling it sampling, this circuit, by double sampling two out of phase signals, with a balanced pair of two out of phase 38khz signals, and then the audible components of this sampling being combined in phase... this effectively doubles that sampling rate to 76 Khz, which, from that point of view, may be the key to the improved sonic qualities. In the same way that a full wave rectifier will give 120hz DC ripple from 60 hz AC.
I think all that I am saying here is pretty much the same thing as the paragraph you quoted from the Eico manual. Remember, the word "sampling" was a new electronics term in '61 and did not have the precise meaning it does today. One could say that a bridge rectifier "samples" the + and - components of the AC line and routes them to the appropriate connection of a power supply.
I think this circuit, that derives the L-R signal, is the key to the improved performance of the Eico decoder.
I'm certainly not the expert here. This whole quest for me has been to find out
why the Eico MPX sounds so much better. I had to learn all about MPX decoding to even have this conversation.
Interesting what you say about the warm up affecting separation. Maybe I have skirted this issue entirely with my own preferences, by not running these units with the cover (cage) on. The separation just seems so solid and unaffected by the control anyway. Tube gear just runs so hot, that I practically always run it with no cabinet. I like the look of tubes, anyway.
I would suggest to you that you actually hear the Eico MPX decoder and then you might look at it differently. Of course that's not so easy to do.
