Read Custom Bass Purity preamp- the inside scoop

Discussion in 'Amps and Cabs [BG]' started by Jack Read, Nov 14, 2003.

  1. Hi All!

    I was told that there was some talk about the Bass Purity preamp so I
    thought I'd pop my head in and give you all some details. I'll try to reply
    to responses, but I don't get to visit TalkBass all that often (much to my
    dismay). I try to keep myself shackled to my workbench whenever possible.

    Here's a little history of the Bass Purity for those who really have too
    much time on their hands. :) The rest of you can skip right over this... The
    development of the Bass Purity has taken place over the last year or so
    (with many years of electronic design and amp work behind it). The very
    first prototype is still in existence, although rather mauled by
    modification on top of modification. It was pretty cool, though. It was as
    close to a straight-wire preamp as I could get. The bass signal went through
    two stages of tube gain and then out to the power amp. Nothing too exciting
    there, but for kicks I had two sets of tubes: one 12AX7 and one 6SL7, with a
    toggle switch to select one, the other, or cascade both for an interesting
    effect. Lots of folks tried it out and really liked the sound, but said "Where's the eq?", so
    I added an Alembic/Kern/Fender tweed style eq section. I was not happy with
    that at all. I changed it to more of an audio style eq, but wasn't happy
    with that either. I eventually developed my own eq design, which is a 4 band
    eq (bass, low mid, high mid, treble) along with a unique mid emphasis
    control. There are also deep and bright switches which do a very good job of
    helping to shape the overall tone without ever mucking it up. My primary
    design goal was to keep the bass signal Pure, yet offer tonal flexibility.
    The eq system took a long time to develop and is certainly the most complex
    part of the design. Speaking of complexity, I spent far more time
    eliminating components from the signal path than I did designing them in. The first "real" unit was a 2 space box finished in Shoreline Gold with
    white chicken head knobs. Why? Partly because I had the paint and the knobs laying
    here. Don't ask me for pictures of that one! After that was built I had some
    custom toroidal power transformers made so I could get this all down to one
    rack space. I also incorporated an effects loop, a DI level control,
    transformer coupling for the output signals, and an EQ Bypass switch. The
    latter was something I had in mind from the very beginning and is an
    indispensable feature. I strived to make the preamp as open and natural
    sounding as possible; capture some of that tube magic (warmth, depth, and a
    certain three dimensional quality that I have never found in solid state
    designs); and maintain quick response and clarity without any harshness. I
    think I can probably walk a tight rope now, though I've never tried. :) I
    use very high grade components in every part of the signal path wherever it
    makes a difference. I build high end tube audio gear now and then and much of the Bass Purity design was influenced by that. I don't
    use any printed circuit boards (not that there's anything wrong with them if
    they are designed properly). Components are mounted on a 1/8"
    epoxy/fiberglass board and are soldered to turrets (not eyelets). Everything
    is point-to-point wired. Tubes are 12AX7 and 12AU7.

    The final result will show here if I can figure out how to post a picture.
    Hey, I'm a TalkBass newbie, what can I say!

    Some of the features of the final design I've already mentioned. I've
    included an impedance selector switch for the input. I find that most basses
    sound great using the high impedance setting (equivalent to the "passive"
    input on some amps), although there is a slight difference in tone with some
    active basses if you use the low impedance (aka "active input"). The setting
    to use is the one that sounds best, really.

    I'm also offering a version of the Bass Purity with a 6SL7 preamp tube as a
    custom order. It's pretty cool- a slightly softer, more rounded sound. If
    someone wants a full blown custom preamp I can build a 2 rack space unit
    that has *both* sets of preamp tubes and can be switched back and forth
    between the two, along with lots of other neat tricks. I'm afraid it would
    not be cheap, though. I was interested to read that the Alessandro preamp
    uses 6SL7s. I've seen that he's fond of them for his guitar amps. I tried 6SL7s,
    6SN7s, and a host of others, but I liked the 6SL7 the best of all the
    non-12AX7 variants that I tested.

    The Bass Purity will be up on the Read Custom website as soon as I can get
    around to it. Full production starts in a couple of months, and right now
    I'm building each one by hand.

    Now, to clear up any possible misconceptions:

    -I did not reverse engineer from alien space craft, and I am not related to
    Corso. As far as you know.
    -I didn't invent the EQ bypass, by any means! Lots of amps have it, and many
    high end audio preamps have it.
    -Plugging a bass directly into a power amp with no preamp works, but
    generally not all that well. The voltage swing at the output of your bass is
    not enough to drive the power amp to its full potential, and the low input
    impedance of your power amp will probably suck some of the high end out of
    your bass (especially if it's a passive bass). You might get away with it using an active bass depending upon the impedance match/mismatch.
    -A few folks tried out some of the later prototypes; the real thing is a big
    step up.

    I hope this didn't bore anyone to tears, and I hope this isn't the longest
    post to ever appear in this forum! Sorry for yammering on like this.


    Jack Read- Read Custom Instruments, Inc.
    Custom Guitars & Basses
    Custom Tube Amps & Tube Preamps
    Pay us a virtual visit:
    (978) 779-0075
    Also offering Stewart Audio power amps and more.

    Read Custom is featured in the new book, American Basses, by Jim Roberts
    (Backbeat Books,
  2. vanselus


    Sep 20, 2000
    Boulder, CO
    Jack - that pre sounds like it sounds absolutely great! Can't wait to try it...

    thanks for the post
  3. Fran Diaz

    Fran Diaz

    Mar 28, 2002
    Santander, Spain

    A few questions:
    how much is it going to cost?
    does it use a wall wart? if not, will it be available in the 230V/50Hz we use on this side of the pond?

    thanks and congrats.
    keep groooovin'
  4. Hi,

    No wall warts!

    A 230V/50Hz version is imminent. The toroidal transformers are on order and are due within weeks- there are a couple of folks in Europe eagerly awaiting them.


  5. Fran Diaz

    Fran Diaz

    Mar 28, 2002
    Santander, Spain
    Thanks for the quick answer Jack.

    Is there a price for the 230/50 units?

    keep groooovin'
  6. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    what are the eq frequencies for the various boosts?

    Also, is it +/- 6b6,12db etc.

    I called and left a message with you. Very interested in trying one out.
  7. jokerjkny


    Jan 19, 2002
    NY / NJ / PA
    awww yea... :cool:

    thx for the non-hyped, straight dope info on your preamps, jack!

    the thought process that got you to your design and specs alone are enough to make me GAS. :p
  8. emjazz

    emjazz Supporting Member

    Feb 23, 2003
    Boston, MA
    The preamp is as good, if not better, than any of the hype I've created before. I just took home #000001 and it exceeded my expectations. This pre is the end all to be all for me. I'm sure that it will be just the same for many more. I've been hoping for this preamp for about ten years now (that is to say that nothing out there has made me this fullfilled about my tone in the past). For those who take the leap of faith, enjoy!:bassist:

  9. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas

    What variety/manufacturer of 12AX7's are you using?

  10. Anything you like, really. "Standard" is JJ/Tesla. I have found them to offer consistent quality and excellent tone. I have NOS tubes as well (5751, RCA black plates, Telefunkens... the usual suspects). Some of the NOS tubes are horrendously expensive (like the Telefunkens). I test each set of tubes befor the preamp leaves here and make sure they are low noise and no microphonics.

    Some of the best current production preamp tubes include JJ/Tesla, Ei, and "winged C" (former Svetlana factory... *not* the tubes currently being sold under the Svetlana name).


  11. Brad Johnson

    Brad Johnson Commercial User

    Mar 8, 2000
    Gaithersburg, Md
    Boom Bass Cabinets, DR strings
  12. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    Cool. That's the kind of strategic flexibility that we bassists really like to hear from manufacturers.

    Sounds like a preamp I'd like to hear.

    Thanks Jack.
  13. Sorry for talking over the PA system, but here goes:

    Fran, I got your email about the 230V/50Hz preamp but I can't answer it- my replies get bounced. Do you have another email account, or can you turn off whatever filter is causing the bounced messages?


  14. Fran Diaz

    Fran Diaz

    Mar 28, 2002
    Santander, Spain
    I'm sorry for that problem. Send it to my work address: fdiaz(at)enyca(dot)es.
    It's the first time that I have problems with the other account. I'll check what's wrong and thanks again.

    keep groooovin'
  15. emjazz

    emjazz Supporting Member

    Feb 23, 2003
    Boston, MA
    Fran PM'd me about my thoughts on the Read Pre now that I've had it through a gig. Just to let you know, my rig is a Crest ST2000 poweramp and two Bergantino 112 cabs. I've already said how much I love this pre and after a bit of time with it I only continue to see it's beauty. What I like about it so much is that the only color that you're getting is the warmth of the tubes, that's it.

    This is also the quickest responding tube preamp that there is. The transient response is almost like a solid state amp. Until now the quickest pre available was the Demeter. Many have said, and I agree, that it sounds too hi fi; too clean.

    Other popular pre's are the Kern and the Alembic. I believe that these preamps are too limited. I've never liked the idea of using the old Fender curcuit as the basis for a bass eq. It just doesn't work in my opinion. These preamps are also too dark sounding and much too slow responding for my taste.

    Every pre that I've played in the past has had some sort of noise, either out loud or through the DI out. There is absolutely no noise from the Read Pre. Actually, an oscilator picks up noise that you can't even hear and Jack plans on getting rid of that as well.

    Some preamps have perametric or semi-perametric eq's. I've always really like this option. Well, now I believe this to be unnecessary. If you're bass sounds great to begin with than the Read pre is just going to enhance that. All of the eq points are extremely intelligently chosen. I believe that the single
    enhance knob takes the place of any added eqing that you'd ever need.

    What does the Read pre not do? I've already alluded that it doesn't fix a bad sounding instrument. It's always going to give you what you put into it. It doesn't have an extreme eq capability. I find this to be exactly what I want. I've needed something that enhances the instrument and the cabinets that I already have. It will quickly adjust your sound to each individual space that you play in, whether you are indoors or out.

    I believe that this preamp is for those who already like the way that their bass and cabinets sound. If you do than I can guarentee that this preamp will excite you like you've never experienced in a bass pre before.

    One more thing. I got to play two of my favorite instruments through this preamp; a Tyler five string and an F bass BN5. The Read pre was going through my Crest ST2000 poweramp and into a Berg HT322 cabinet. I wish that you all could have been there. Those instruments have never sounded so good!:cool:
  16. Fran Diaz

    Fran Diaz

    Mar 28, 2002
    Santander, Spain
    Hey! Thanks a lot for the quick reply.

    A couple of questions:
    1 - How does the emphasis knob works? how does it change the sound? Does it have a flat position and/or is it bypassed by the eq bypass switch?

    2 - can you (or maybe Jack) post a picture of the back of the preamp?

    3 - I don't know if this has been thought about, but would it be possible to add a footswitch for the eq bypass? This would come handy in a live setting.

    keep groooovin'
  17. A: The emphasis knob works by boosting a broad range of middle frequneces along a unique response curve. This is an excellent tool for cutting through a mix, or for making tweaks to your eq without losing "your sound". As you turn the emphasis knob clockwise you can hear your bass cut through more. Flat is full counterclockwise. It can still be used when the eq is bypassed.

    A: Incomiiiiinnnngggg!

    A: Absolutely. I'd be happy to offer it as an option. I could even employ a two-button footswtich so you could control the mute as well.


  18. I hope a picture of the back of the preamp appears here... If it doesn't, can someone tell me how to do it?


  19. vanselus


    Sep 20, 2000
    Boulder, CO
    Wow, how'd you get the "Pillar of Alembic"?