Hachidori Fukami Tape/Phono Preamplifier
- Thread starter Zeotrope
- Start date
Just came across this thread and have a few thoughts.
First off - have known Jonathan for many years. Worked with him on a few projects. He LOVES to experiment and brings novel approaches to all his endeavors. Lives in Japan and has found local talent to do the REAL DEAL of the cabinetry involved with his preamp. He is selling all units that he has parts for, even tho obtaining the quality parts he needs - like switches - has gotten to be almost impossible.
He does use some kind of cable compensation on the front end to eliminate or reduce the cable capacitance. Apparently derived from the approach Ampex used on their pro decks. Something about the head cable having TWO concentric shields.
As has been mentioned, Input loading is important. I ended up using 47K in parallel with around 100pf on all my pre's; which after experimentation with Jonathan's Flux Loop turned out to be pretty close. As the K/C can also work with phono cartridges, the compromise works for that also (at least for MM cartridges). For tape, the loop indicated that; depending on the head inductance and what impedance the preamp front end "looks like", there can be quite a HF bump around 25Khz. which can be minimized by tuning the input R. As I remember, something like 60K was optimal for an 810 with an FM PB head - enough acronyms.
JohnP mentioned an pre overload problem he experienced. I caused that. He bought a Technics 1500 I made up that had a Nortronics head and a one-off tape pre I designed and mounted in a little box on the back of the deck. Power was from the 1500 supply with added post regulation. Problem I created was having a fixed gain of 50dB or so, the level I normally keep my K/C at, BUT it only ran off of +/- 12VDC versus the +/- 25VDC on the K/C so I lost a few dB of headroom which showed up on some of the new, really hot tapes available.
As an aside, should mention that most of the tapes I have or listened to are master/dubs (of some kind) and a lot of them have input levels all over the place, in addition to various Dolby/DBX/AME curves, so after putting them thru the various decoders, levels can easily get shifted again. Fortunately my K/C has 3 (selectable) gain levels, 40-50-60dB, so overload was never a problem. And FWIW, At one time Jonathan had hundreds of dubs.
First off - have known Jonathan for many years. Worked with him on a few projects. He LOVES to experiment and brings novel approaches to all his endeavors. Lives in Japan and has found local talent to do the REAL DEAL of the cabinetry involved with his preamp. He is selling all units that he has parts for, even tho obtaining the quality parts he needs - like switches - has gotten to be almost impossible.
He does use some kind of cable compensation on the front end to eliminate or reduce the cable capacitance. Apparently derived from the approach Ampex used on their pro decks. Something about the head cable having TWO concentric shields.
As has been mentioned, Input loading is important. I ended up using 47K in parallel with around 100pf on all my pre's; which after experimentation with Jonathan's Flux Loop turned out to be pretty close. As the K/C can also work with phono cartridges, the compromise works for that also (at least for MM cartridges). For tape, the loop indicated that; depending on the head inductance and what impedance the preamp front end "looks like", there can be quite a HF bump around 25Khz. which can be minimized by tuning the input R. As I remember, something like 60K was optimal for an 810 with an FM PB head - enough acronyms.
JohnP mentioned an pre overload problem he experienced. I caused that. He bought a Technics 1500 I made up that had a Nortronics head and a one-off tape pre I designed and mounted in a little box on the back of the deck. Power was from the 1500 supply with added post regulation. Problem I created was having a fixed gain of 50dB or so, the level I normally keep my K/C at, BUT it only ran off of +/- 12VDC versus the +/- 25VDC on the K/C so I lost a few dB of headroom which showed up on some of the new, really hot tapes available.
As an aside, should mention that most of the tapes I have or listened to are master/dubs (of some kind) and a lot of them have input levels all over the place, in addition to various Dolby/DBX/AME curves, so after putting them thru the various decoders, levels can easily get shifted again. Fortunately my K/C has 3 (selectable) gain levels, 40-50-60dB, so overload was never a problem. And FWIW, At one time Jonathan had hundreds of dubs.
It is called driven shield and it has been used in electronic instrumentation for very long time.
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