HiFi Haven Group Project - Building The "World's Best Tube Phono Preamp"

Discussion in 'Tube Gear' started by Prime Minister, Mar 28, 2018.

  1. I was curious if that tape amp used a transconductance amp or whether the reference was to servo-based DC coupling.

    I originally rejected the idea but a servo can do a lot to simplify the audio path, at the expense of DC control complexity.

    I got that current source circuit from Camille before Valve existed. I loved that guy. He really schooled me on grounding and noise, even beefed up a Tek 7000 scope so I could get rid of gremlins in some radio gear I was working on. That's how I learned that almost all 417A preamps, a popular design of the 90s, are likely putting out a signal on ~150mHz! I had to go to extraordinary lengths to get mine stable. He was a great teacher.

    That experience and education is why I worry about D3as going wild. Not all builders have the test gear to know for sure.

    I used the Bottlehead C4S a number of times but I was too "vintage crazed" back in the day, wouldn't use anything thought up after 1948. Now I am a lot more open-minded and even have a bag of Ixys current sources on my desk right now! Alas, I am too lazy to crank out builds and compare stuff like I used to.

    Putting a new spin on well-worn circuits as Shindo does, and Kondo did in the M7, using tubes in odd operating conditions, is a Japanese artform that appeals to my vintage side. I suppose it can sound good too.

    The linked article talks about the Shindo circuit sounding almost too nice. Erring in that direction might not be such a bad thing.
    Last edited: Apr 2, 2018
  2. paulbottlehead

    paulbottlehead Active Member

    Camille was a very valuable resource, I came along after his death, but PJ and Doc B have been meticulous about keeping his notes around. You are certainly right to worry about what a D3A can do without some efforts applied to tame potential oscillations. We end up using a lot of MLCCs, shielding, and stoppers to keep things happy.

    The Tape Preamp has constant current sources between B+ and plate but plate loading resistors from plate to ground (I believe Bench was doing this back in the 90's). There is a servo that permits the direct coupling of the two stages.

    How have you found the IXYS parts? My last experience with them left me thinking that you'd want to have a bag of them around to periodically replace them.
  3. I have used the IXYS parts a few times myself but jc and Dr. Bae use them by the boatload. They are illegal to sell in/to Korea for some (contractual?) reason, but I smuggled in a couple hundred 10M45s There have not been any failures in the field as far as I know, but I'll ask if I remember to do so.

    Back in the old days we used 2 port "preset" Motorola CCS the size of 1N4004s. Those things were expensive, limited in available values, and died like crazy. Discrete jobs like the Camille C4S are definitely a step up from those firecrackers.

    I was talking to somebody at ETF who reported big sonic shifts between the different models of INYX CCS. There might be more to it than is obvious from the spec sheet.
    Salectric likes this.
  4. mhardy6647

    mhardy6647 Señor Member

    umm... :p
  5. Prime Minister

    Prime Minister Site Owner Staff Member

    Just to make sure this doesn't go off the rails, it's time for everyone to get back to work. :)

    So, from my understanding, we have two chassis. We are using D3A tubes. Now, what else do we need?
  6. paulbottlehead

    paulbottlehead Active Member

    The D3A is a good choice for the first stage, but the tougher choices come with the second (and potentially third) stages.
  7. mhardy6647

    mhardy6647 Señor Member

    speaking of vacuum tube phono preamps and our friends JE and JROB and Sound Practices...
    see this one posted at the Tribute to Sound Practices "group" at Flikr.

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