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.
This is a 3-step amplification NF equalizer based on 12AX7, which applies NFB from the 3rd stage cathode to the 1st stage cathode.(so-called "K-K type").
The advantage of the NFB type is that it does not require a high gain level and is not very sensitive to tube quality. However, the impedance of NFB at high frequency range becomes very low and results in a negative effect - the sound becomes hard and dry.
The NFB type is usually used as it is an easier way to attain a good signal-to-noise ratio.
As for the CR type, a masterpiece preamplifier equipped with the CR type equalizer is the vintage Harman-Kardon Model: "Citation IV".”
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?