@lewm Long story. My new processor has a 4 way crossover. I decided to try bi amping the transformers. Roger suggested a crossover point at 500 Hz. I used the MA2s to drive the bass transformers and a Bricasti M25 to drive the treble transformers with a 150 watt 1 ohm resistor on each primary leg. The only parts of the original back plate left were the bias supply and the output junction box. It sounded fabulous at lower levels. At higher levels the M 25's protection would shut it off and worse the MA2s were clipping prematurely. The clipping burned out first one then the other bass transformer at $450 a pop. When the second one blew, knowing that the stock treble toroids do poorly below 300 Hz, I mounted up those Vanderveen 1:75 Toriods I bought a long time ago and ran them full range or rather down to 100 Hz where I crossed to my subwoofers and they sounded glorious! The only remaining problem was not enough gain. The stock toroid uses a ratio of 1:92. Nobody currently makes a 1:100 ESL step up transformer. I ordered four 1:50 Vanderveen toroids and strapped two for each channel. The primaries are wired in parallel with a series 1 ohm resistor on each leg and the secondaries in series with the junction as the center tap. Meeno had the factory (Trafco) make them for me without the usual center taps. The High end rolls off a little earlier, 14 kHz instead of 15 kHz, but I can not hear the difference. And the sound is pristine. Would it sound any better than what you are doing? I think so, but can't be sure and 4 of these transformers is $850.
The Shure V15 V with a Jico SAS/B stylus VS The Soundsmith Hyperion MR and Lyra Atlas SL
On a sentimental lark I purchased two Shure V15 V bodies and one SAS/B stylus. I was always a realistic about the Shure's potential. Was comparing it to $10k+ cartridges fair? Absolutely. The Shure was considered to be one of the best cartridges of the day. Why not compare it to a few of the best we have today?
The Shure has always been considered to be unfailingly neutral. Famous recording engineers have said it sounded most like their master tapes. I do not have an original stylus for the Shure and I can not say that the Jico performs as well.
My initial evaluation was quite positive. It worked wonderfully well in the Shroder CB. With a light mounting plate and small counterbalance weight a resonance point of 8 hz was easily achieved. There was nothing blatantly wrong with the sound. There was no mistracking at 1.2 grams. You can see pictures of all these styluses here https://imgur.com/gallery/stylus-photomicrographs-51n5VF9
After listening to a bunch of favorite evaluation records my impression was that the Shure sounded on the thin side, lacking in the utmost dynamic impact with just a touch of harshness. I listened to the Shure only for four weeks as my MC phono stage had taken a trip back to the factory. I was using the MM phono stage in the DEQX Pre 8, designed by Dynavector. I have used it with a step up transformer and know it performs well. I got my MC stage back last week and cycled through my other cartridges then back to the Shure. The Soundsmith and Lyra are much more alike than different. I could easily not be able to tell which one was playing. The Lyra is the slightest touch darker. The Shure is a great value....for $480 in today's money, but it can not hold a candle to the other cartridges. They are more dynamic, smoother and quieter. They are more like my high resolution digital files. Whether or not they are $10,000 better is a personal issue. Did the DEQX's phono stage contribute to this lopsided result? Only to a small degree if any. I do have two Shure bodies and they both sound exactly the same. The Shure may have done better with a stock stylus. I do not think the age of the bodies contributes to this result at all.
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You don’t need the one ohm resistor with the MA2. Its intrinsic output impedance is protective. Anyway you’ve corroborated my thesis that the passive crossover between bass and treble transformers in the stock configuration is an evil if using a tube amp especially. I’m glad you’re happy although sorry about the blown transformers. |
@lewm The 1 ohm resistors are for the Bricasti M 28 mono blocks I am trying out. Their output impedance is something like 0.02 ohms. The MA2s will not oscillate but they do not care for load impedances below 2 ohms either. They actually play loader with the 1 ohm resistors in place! Right now I am going back and forth between the amps deciding which ones I am going to keep. It was a circuitous path, but with a very happy if expensive ending. |
I’m sorry, but without the OEM passive crossover components, the inherent impedance of the speaker in the bass and midrange frequencies is very high, like 20 ohms and up (below 100Hz). I personally measured mine. Why would the MA2s ever have to look at a 1 or 2 ohm load? The reasoning behind using the 1 ohm resistors in series is to protect the toroidal audio transformer; they apparently do not like to look back at an amplifier with a very low output impedance, like your Bricasti or most other SS amplifiers. However, the MA2s have a high-ish output impedance which per se protects the toroid. So, yes, I understand why you use the 1 ohm resistors between the Bricasti and the transformer it drives, but they are not needed for the MA2, which anyway may be driving the bass transformer in parallel with the toroid. (Not sure how you have this stuff connected. I assume you are using a digital crossover that splits the frequencies between the bass and treble and super treble. I also assume the MA2 is operating only between around 100Hz and 5kHz, with the Bricasti taking over above 5kHz. Have you removed the OEM passive crossover components? If you have not, then I do see that the MA2s might have to deal with very low impedances, but I fervently hope not.) Meantime, I am driving my 845PXs full range (heavily modified by me as you know) with a single Atma-sphere MA240 (heavily modified by me). I doubt the speaker draws more than 40-50W at full volume. Yes, I should add subwoofers. |
@lewm That is correct, the impedance of the bass transformer is quite high, but that is after that fact. I am talking about driving the Vanderveen transformers almost full range except under 100 Hz. All the stock transformers are either blown or in the trash. The Vanderveens measured DC resistance is 0.3 ohms. The MA2s prefer by at least 6 dB driving the Vanderveens with the added resistors. They do not require them, but they do prefer them. Most transistor amps will detonate without the resistors. The Bricasti amps will just continually shut themselves off. The only cross over I am using now Lew is the one at 100 Hz for the subwoofers. With the subwoofers the Vanderveens have no problem driving the SLs full range. It is a beautiful thing. |
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