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Uncle GAS Needs You: Help Design an All Tube Amp!!!

Discussion in 'Amps and Cabs [BG]' started by jokerjkny, Nov 19, 2005.

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  1. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL
    hey all,

    so, on another guitar/amp forum i frequent, Brad Jackson of Jackson Ampworks is planning on building an all tube bass amp. this'll be his first, and isnt too familiar with bassists' likes and dislikes. so, lets help him make this one a doozy!

    he wants to hear what would you guys like to see, hear, and feel from this amp. we know the drill, so let Brad hear you loud and clear!

    so far, he's thinking of:

    - Amp to cop tones of '60s era California, i.e. Beach Boys, Phil Spector, etc.
    - 100 watts (yea, i wanted more, too ;))
    - Maybe 6L6 or 6550 power tubes
    - Line Out as opposed to DI out (i voted for a DI)
    - Cathode Biasing

  2. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL
    btw, here was my laundry list:

    - 100 watts is nothing, especially for gigging. tube wise, 200 watts is minimum, if you can do 400, that's RAWK.

    - also, the EQ section should reflect what a bass player wants. Q's and frequencies that sound great on a guitar dont necessarily sound good on a bass amp. a bassman does sound good w/ bass, but would i use it today? no.

    - a gain knob w/ a master volume knob would be great to get some extra tubey grit to full on overdrive into the mix.

    - DI out is a must, especially for gigging. and a preamp out would be nice to run to another slave power amp in case more cabs are needed.

    - optional (-15) pad is important to have, too, cause most bassist are using onboard preamps, which push out tons of signal.

    - an effects loop is quite handy as well. since, most bassists like myself are incorporating a nice parametric and/or compressor to the mix, having a loop is much needed.

    - comes w/ bias points where i can re-bias the amp myself. i.e. my Demeter VTHF-300M all tube power amp has bias points, which make it really easy to swap out 6550's.

    - 2-3 rack space unit. while i'm kinda figuring you're gonna put this amp into a regular head box, a ready to rack unit is much more conducive for most bassists. modular rack setups are easier to protect in a flight/rack case.

    - and make it as light as possible, pleez. 100 lbs. ampeg's arent fun @ 3am loadout. so far, the lightest i've seen is Roger Sadowsky's SA200 which is only 42 lbs., and the fact that it runs on EL34 could explain the lighter transformers.
  3. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    I agree with jokerjkny for the most part.

    The weight issue doesn't really bother me as long as it stays below 100 lbs. However, the effects loop and pad are a must for me.

    A couple more things I would like to see:
    Foot switchable mute/tuning
    Dedicated tuner out that works in standby mode
    2, 4, and 8 ohm taps

    One other thing that might be nice is if the head was engineered so that it could be in a somwhat tradional head type case but could be removed for rack mounting. 4 spaces or less please. I rack everything so it would be another one of those must haves for me.
  4. Mika

    Mika Guest

    Nov 29, 2002
    I agree with most of the points made by joker and Kelly Lee. However, I'd rather see a taller and more shallow enclosure for the amp (3U or 4U, max 14" depth).

    I'd go with fixed biasing because despite the moniker, fixed biasing is the one you can adjust and cathode bias is the fixed (non-adjustable) way of doing it.

    I'd also like to see something different than the passive Fender tone stack in the EQ section. Maybe a four-band active tube-driven EQ circuit with shelving filters for the lowest and highest band and fully parametric functionality for the intermediate bands?

    2, 4 and 8 ohm taps on the OT would be very nice. Toroidal transformers for the PT and OT à la SA200 might be feasible depending on which price category the amp will be designed for.

    Just a side comment: the fact that the SA200 runs EL34 tubes should not affect the transformer weight because the amp can also run 6550s/KT88s. The power supply and OT must naturally be designed with maximum power consumption and output power in mind.
  5. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL

    no love?
  6. haujobb


    Dec 16, 2004
    I'm going to be quite honest, I don't think this will be all that great unless he A) copies a successful bass amp design or B) spends alot of time with a ew different bass players until they are all pleased.

    Guitarists just don't know what a bassist wants, it's no knock against guitarists, but unless you have done numerous gigs on bass guitar, you just cannot understand what the essentials are.

    Example, 100 watts? switchable down to 50 watts? That thing would be nothing more than a glorified practise amp.
  7. Passinwind

    Passinwind I Know Nothing Supporting Member Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    OK, why not. First off, tell your friend to go to Ampage (www.firebottle.cm) and ping a guy named Ken Gilbert. He's famous for the BAGA, aka Big *.* Guitar Amp. Ken's written up a bunch of stuff about using unusual power tubes and the rest of what goes into makng a megapower audio tube amp for musical instruments. I can't post a direct link (TB rules), but it's easy to find.

    To get me interested, it'll have to have a scary lightweight switching power supply, so it technically won't be all tube. Most bassists live without tube rectifiers though, shouldn't be a deal breaker. It'll likely be very tricky and expensive to implement though.

    Instead of fully parametric EQ, I'd go with switch networks for a few different different frequency centers and Qs. A transformer-coupled EFX loop like the Fender Vibro King uses would also be cool. I'd love to see balanced in and outs in the loop.

    To me, this is a waste of time for anything under 3-400 watts, but I'd shoot for something bigger, just because. I'd probably break it down into two boxes that each weighed 50 pounds or so. I don't want to say a lot more, 'cause I am still contemplating building something like that for sale eventually. Honestly though, I have a lot of other things on my plate that look more worthwhile. But it's fun to speculate on when someone else is doing the work. :cool:
  8. Fretless5verfan


    Jan 17, 2002
    100 Watts is unacceptable pretty much. I'd say at the VERY least 200, preferably 300. And i also think a DI and Pre-out are crucial. If he didn't make these changes i think he'd seriously be short changing himself.
  9. msquared


    Sep 19, 2004
    Kansas City
    You know what I want? A tube amp with the transformer (or whatever the really heavy part is) in a separate package so I don't have to lug a 100lb head around.
  10. Plain Old Me

    Plain Old Me

    Dec 14, 2004
    It seems like this guy makes vintage sounding studio amps, so I don't think high wattage is a major issue. Now, I think this should have 2 channels, one clean and one with a bit of vintage overdrive. It should also be able to take different types of tubes, with at least 4 tube sockets (max 200 watts with 6550s/KT-88s). FX loop would be great. 2, 4, 8 Ohm sockets/switch. Class A, AB biasing switch. Adjustible bias pots. Is there going to be a matching cab? If so, I think it should be a 410 sealed or 115 sealed or both. Thats about all I can come up with... Oh maybe a tube driven para EQ. And it should be a rack mount thing but they should have custom vintage looking racks they can put em in (and look like a vintage head). Must be able to see the tubes all lit up from the front via a grill.
  11. well what is this guy like, does he make feature rich amps, or 'pure' amps that ooze tone? In my opinion it's often a compromise between these, the feature rich amp will sound a bit less good, but that's imo

    anyway, as he's new to bass he should probably opt for the first. He does have to decide what he likes, so get him to listen to a couple of classic tube bass tones, then start comparing what the succesfull tube bass amps have for features, find combinations and comprises, you don't want to make a mistake someone else has made already, but you don't want to make a different looking SVT either.

    I think he should opt for something that will have a good balance between smooth tone and grindy tone, not just the one or the other.
    And a power button on the front
  12. JacksonAmpworks


    Nov 19, 2005
    Keller, TX
    President: Jackson Ampworks

    Hey this is Brad Jackson with Jackson Ampworks.

    That make an excellent question. I'm am certainly about building simple amps that deliver tone above everything else. I'm wanting to build a bass amp tone machine that will deliver some of the warmest, vintage tones along with enough power and flexibility to cover some of the modern tones.

    Right now I'm thinking a quad of KT88's roughly 200W. Baxandall tone stack (hi-fi TREBLE and BASS) with a MID-SHIFT control and either a DEEP or PRESENCE control.

    Definitely I'll have a DI or at least line or mic out. I'm still gathering opinions on the FX loop. I can see that an FX loop would be cool for running compressors or EQ inline with the signal.

    The half power idea is out the window after gathering some feedback from other players.

    Thanks for all of the info guys. Feedback from gigging players is CRITICAL to designing and building an amp that players will dig.

    Thanks again!

    Brad Jackson
    Jackson Ampworks
  13. Fretless5verfan


    Jan 17, 2002
    Why not both deep and presence? Most bass amps tend to have both and they are both pretty useful IMO.
  14. JacksonAmpworks


    Nov 19, 2005
    Keller, TX
    President: Jackson Ampworks
    Not a bad idea really! I think I'll have the real estate for it on this one.
  15. Fretless5verfan


    Jan 17, 2002
    Glad you like the idea :D. The more stuff you change the more i like the way this amp is shaping up! You can put me on the list of future buyers ;)

    oh, and i vote for the FX loop if you can pull it off.
  16. JacksonAmpworks


    Nov 19, 2005
    Keller, TX
    President: Jackson Ampworks
    I may hold you to that! ;)

    Regarding the FX loop, making a simple loop is DEAD easy. Making a tube driven FX loop is a bit more involved. Again this is a decision that will be made after extensive testing of the two to decide which one sounds better.

    Thanks for the support!
  17. Fretless5verfan


    Jan 17, 2002

    With the way you're approaching the project you can definately hold me to that :D (especially since i'm about to get a new higher paying job :hyper: ) Nothing's cooler than seeing people come on here and getting feedback for a new product from the very people who will be using it.

    I never knew there was difference about the loops. I'm a total moron when it comes to the electrical engineering (clearly :p ) but knowing you'll be doing extensive testing beforehand is quite reassuring. I'm sure this badboy is gonna be up there with the heavyweights of tube head-dom. Best of luck bro!
  18. JacksonAmpworks


    Nov 19, 2005
    Keller, TX
    President: Jackson Ampworks
    Thanks so much for the kind words. I take great pride in my products. I have to since I put my name on them.

    Regarding the FX loops, a simple loop that simply breaks the preamp connection to the power amp is easy to make as it is nothing more than two 1/4" jacks with a switch on one of the jacks. When a plug is inserted into the jack, the preamps connection to the power amp is broken and the signal is forced to go into the device that is placed in the loop. Pretty simple really.

    A tube driven FX loop is obviously more complex but still not bad at all. The simple FX loop will likely work great, but it's worth testing the tube driven unit.
  19. jokerjkny


    Jan 19, 2002
    NY / NJ / PHL
    Brad, welcome!!

    so glad you're on here. i know these gents'll hook you up big time, and i'm sure you'll be more than happy to return the favor. :cool: :bassist:
  20. Fretless5verfan


    Jan 17, 2002
    Haha joker, i thought i was the only guy on the east coast still online! :p Time flys sitting in front of the comp practicing and checkin' TB. (you have a PM from me!)

    (This is open to anyone being that i'm sure brad is sick of my posts by now hehe :hyper: )

    What would the theoretical benefits of having a tube FX loop be? Are there any units out there with tube driven FX loops already?

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