As far as I can tell, “CR type” and “NFB” are typiically used interchangeably for “passive” and “active”, respectively. That’s why I find it helpful to define terms, and also why I tend to assume others on this forum might know stuff I don’t.
Phono Stage - The great analog tragedy
In the world of analog playback, there is an interesting observation. There has been tremendous innovation in the field of
Turntable - Direct, Idler, Belt
Cartridge - MM, MC, MI
Tonearm - Gimbal, Unipivot, Linear Tracking
For all of the above designs we find some of the best reference components designed in the 50s, 60s, 70s and 80s. Most of the modern products are inspired from these extraordinary products of the past. But when it comes to phono stage, there is hardly any "reference component" from that era. They just standardized RIAA curve for sanity and left it. Manufacturers made large preamps and amps and allocated a puny 5% space for a small phono circuit even in their reference models, like a necessary evil. They didn’t bother about making it better.
The result? It came down to the modern designers post 2000 after vinyl resurgence to come up with serious phono stages for high end systems. Unfortunately they don’t have any past reference grade designs to copy or get inspired from. Effectively, just like DACs, reference phono stages is also an evolving concept, and we don’t have too many choices when we want a really good one which is high-res and natural sounding. Very few in the world have figured out a proper high end design so far. And most of the decent ones have been designed in the past couple of decades. The best of the breed are probably yet to come.
It is a tragedy that our legendary audio engineers from the golden era didn’t focus on the most sensitive and impactful component, "the phono stage"
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So I am trying to define some terms. The only meaning of "CR" as applied to a phono stage is to indicate that the RIAA filter is effected with capacitors and resistors. To say that the phono stage incorporates NFB or does not incorporate NFB is another matter entirely. With or without NFB, a CR stage uses capacitors and resistors to effect an RIAA filter. |
@larryi in those days there were many high quality MM carts and MC carts from EMT and Ortofon. But they relied on SUTs for the MC gain. Those SUTs by Cotter, Jorgen Schou, Fidelity Research were all masterpieces that even today is held as reference. But as we know, the MM stage is the heart of the phonostage which provides the big dynamic range and resolution. That they didn’t bother to engineer to the same level |
As I put it in my original post, “The founder of Leben has indicated that his inspiration for his phono pre (i have one) was the HK Citation IV, which apparently featured CR-type RIAA equalization (no negative feedback).” So I made clear that I was talking about the use of nfb, or lack thereof. This is consistent with the description on the Leben website: “There are two major types of RIAA phono equalization systems, one is NFB(Negative Feedback) type and the other is CR type. A representative preamplifier equipped with NFB type equalizer is the MARANTZ Model: 7. The Leben discussion is consistent with the discussion of the topic all over the place, including, for example, on the Allnic Audio website: “There are four de-emphasis methods that can be applied at playback: A. Active filters (Negative feedback types): Different quantities of negative feedback are applied, with deeper feedback to the high frequencies and shallower to the low frequencies. The benefits of this method are improved signal to noise ratios, low cost and consistent operation. Some of the shortfalls are looser bass reproduction and possibly a pinched and compressed high frequency playback due to excess feedback ratios. B. Passive filters (CR type): The frequencies are filtered to fit the RIAA specification by varying the amount of attenuation at different frequencies through a complex capacitor-resistor network. This technique results in no voltage overload, purer reproduction (because there is no feedback), and more accurate RIAA compensation. However, there are problems because the system provides no gain, and insertion loss and impedance matching issues arise. C. Hybrid filters (use of both CR and negative feedback types): In this method, both types of filters applied separately; an active filter is applied to the low frequencies and a passive filter to the high frequencies. Unfortunately, both the advantages and disadvantages of each of these two types of filters, already discussed, affect the playback system at the same time. D. LCR filters, which are used in the Allnic’s H-7000V : Two pieces of a linear reactor (a kind of choke coil) comprise the main part of these filters, assisted by precise CR filters, in order to lower impedances and insertion loss. In vacuum tube circuits, active and passive filters usually are operated on one hundred plus kilo ohms of impedance. An LCR RIAA filter’s impedance is a constant 600 ohms. Furthermore, an LCR RIAA filter’s series resistance is less than 13 ohms (as a comparative, some famous ones are 31 ohms). The lower the impedance, the more dynamic is the sound reproduction, with better bass response and speed. But LCR RIAA units have drawbacks as well. These drawbacks are high cost and the difficulty of impedance matching; the latter has been the primary hindrance to the commercialization of this superb method in the construction of phono stage amplifiers. However, Allnic Audio manufactures a high quality LCR RIAA unit and has developed a 600 ohms impedance matching method.” But hey, what do they know?
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