Post by michaelw on Sept 2, 2018 18:45:28 GMT 12
colin; what model maggies does your father have ? some of the early ones, pre- 1.6 (1998) were not an easy speaker to drive. also tried the rm4/rm5 with disappointing results. the rm5 was sweet but lacked highs and bass, a consequence of phase inversion ? the rm4 didn't seem to like working into a standard 47k phono input. it was noisy and rolled off the bass. i preferred my cartridge (koetsu rosewood) straight into the rm5. or better yet, into an audio research or plinius preamp. 
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Post by Owen Y on Sept 2, 2018 21:43:25 GMT 12
[quote author=" colinf" source="/post/11403/thread" timestamp="1535869304Owen, what did you think of Roger's pre pre RM-4? How would you configure a hybrid pre-pre? For now my own pre pre uses a 417 valve with a SS highly regulated power supply, technically making it hybrid.[/quote]RM-4: It was a long time ago & all I know is that I did not feel attracted to have it  Hybrid pre-pre: I guess I meant really hybrid (or SS) phono stages generally - along the lines of the tube-MOSFET designs of Allen Wright's or Audio Research Corp's hybrid phono pres. Improved S/Noise.
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Post by Owen Y on Sept 2, 2018 21:47:21 GMT 12
Owen, what did you think of Roger's pre pre RM-4? How would you configure a hybrid pre-pre? RM-4: It was a long time ago & all I know is that I did not feel attracted to have it Hybrid pre-pre: A bit beyond my expertise but I guess I meant hybrid (or SS) phono stages generally - along the lines of the tube-MOSFET designs I've seen, of Allen Wright's or Audio Research Corp's hybrid phono pres. Improved S/Noise.
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Post by colinf on Sept 2, 2018 23:08:08 GMT 12
My father has MG2.5s with the 3/4 length ribbon tweeter. The RM-9 seems to drive them ok but he doesn’t listen at high enough volumes to worry about their voracious appetite for controlled power. I had some MG3.5s at one point and they needed a lot of nice power as well. It’s a reason I got into making hybrid amps in the first place, so I could drive them properly without having an enormous valve output stage. I made a 100w hybrid single ended Class A amp with 417 input valve, Hashimoto transformer coupled to the bootstrapped class A output stage to drive them, and that was almost enough power. They could have done with double that though. Since moving I only have a small hifi room and now the big class A is languishing in a bedroom cupboard :-0 I think most active MC pre preamps these days have a jfet input stage and valves for the rest of the circuit. But I always preferred the sonic clarity of a valve pre pre despite its noise. Sadly, memorable as the RM-4 was as an early attempt at that, it didn’t come off as being quite the step up in performance you'd expect. The best one I heard was Trevor Lees's two-tube, with a 6dj8 each channel and giant dual mono power supply. Some of those units are still being used and are in demand in Melbourne for those who know about them. (Not many!) The 6dj8 needed renewing about every 6 months to ensure the noise wasn’t too bad. I never got to hear the RM-5 properly in a system I know. It’s line stage was phase-inverting I believe, being a solitary 6dj8 common cathode circuit.
AMR-iFi R&D
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Post by colinf on Sept 3, 2018 4:40:07 GMT 12
Of the hybrid Audio Research Corp's preamps I liked the SP11. It used a jfet at the input of each of its gain stages for low noise, a hybrid jfet-6dj8 cascode with wideband frequency response and mosfet source follower for low output impedance. Each stage had its own opamp-based regulator, like the SP10. I see a theme emerging in high end preamps: jfets for low noise and maintenance-free input stages, valves for critical gain duty and mosfets for low output impedance. I think Audio Research inspired a lot of designers with their hybrids, including me. But ARC themselves later reverted to all-valve designs after their journey into hybrid territory. Here is the SP11 phono section. (Available on arcdb.com, the Audio Research Corp DataBase, not affiliated with ARC.) 
AMR-iFi R&D
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Post by Owen Y on Sept 3, 2018 9:02:04 GMT 12
Thanks colinf - I've looked at arcdb, esp when I had SP8s & a D70. Unfortunately in the end, I decided I didn't totally enjoy the sound of all that SS complexity in their PSUs (tube or hybrid signal ccts).
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