First DIY bass amp plus cabinet with bonus 20th anniversary NGD content

Discussion in 'Shock Brother's DIY Amps' started by Snfoilhat, Jan 27, 2020.

  1. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Hi all.

    After a few years of slowly getting into really playing and enjoying guitar, and slowly learning one end of the soldering iron from the other (ouch), and participating in the extraordinary amp building community here, I'm ready to tackle a nostalgia-driven boondoggle of the first order -- a bass amp. I got hold of a keep-forever bass (Rickenbacker 4001v63) in 2000, and played in a band until heading across the continent to begin grad school. The sale of the bass and a couple inexpensive Ampeg bass amps is what helped pay my relocation expenses. It's through amp building (and picking the cello back up after dropping it too around the time of that big move), that I regained an interest in electric bass. Since I'm still a hack at bass and it and I together will at first be just a glorified signal generator with a low E that can get down to 40 Hz :rolleyes:, I have been resigned to wait until other amp projects were out of the way and I found the right bass. Very inexpensive but won't feel wrong in the hands of a spoiled once-kid who had something too nice way back when.

    Head cab (reclaimed 1/2" plywood and tolex stripped off an old broken solid-state amp):
    IMG_3452.JPG

    IMG_3453.JPG
    Ran out of tolex... :oops:

    Chassis (in progress)
    IMG_3455.JPG

    Rough draft schematic (with a nod to a very well-known 'bass' amp of the past)
    Bass_amp_A_12AB5.png

    NGD
    IMG_3464.JPG

    Thanks!
     
  2. BigDaddy23

    BigDaddy23 Tele-Meister

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    Massively subscribed!

    I am a bass player by design and want to build myself another bass amp so I'll be watching this one very closely. :cool:
     
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  3. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    Snfoilhat, I definitely like your style.:cool: I will watch with interest!

    I built a 5e3 six months ago. I traded it for a 64 blonde showman. That showman through a 2x10 yamaha bass cab is loud and has a very nice tube bass vibe.

    If you have a power transformer with a bias tap, you might want to consider a circuit with a long tail pair phase inverter. It can stay cleaner than the cathodyne PI design of your rough draft.
     
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  4. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Good calls all around and I appreciate it.

    Here are the constraints I'm working within that may help explain the design quirks

    The chassis I'm using is pretty small. Here is how it originally looked freshly pulled from the Zenith powered speaker cab.
    IMG_3340.JPG
    I'm saving that power transformer for another project (it looks perfect for a single-ended EL84 kind of thing), and want to use a much larger PT I've had kicking around for a few years that originally was a 4X 12AB5 power amp in a stereo console.

    So I've got four 9-pin sockets to work with, and I want to use two for the power tubes, which leaves just two more.

    The long tailed pair seemed like a great choice, and fixed bias seems like the right thing, but I am never going to make an SVT out of this, and I don't want to fall into the trap of trying to use tubes to make something that works like a poor copy of a modern, professional, solid-state bass amp. Instead, I'm thinking "What if the guy who designed the Ampeg B12 hadn't been focused on stuff like upright bass and disparaging rock and roll (reputedly)?"

    That's all to say this is about leaning in to the tubiness and all tubes' inefficiencies. I haven't played with a rock drummer on acoustic drums in two or three years, and have no plans to change. I think my ears are still ringing from the last time I spent a couple hours in a little cubical in a warehouse rehearsal space playing at stage/show volume. I don't know how people in active bands do that week in and week out. When I was a kid I knew I couldn't hear what was going on, but I wasn't really preoccupied with musicianship then :eek: and I wasn't singing, and was okay with being deafened by cymbals and guitars or deafened by earplugs. Fun!

    Also, and this is a little hedge that may take a bit of the mystery away, I have used almost this exact preamp in a high voltage all-tube stomp box (like a Matchless Hotbox) a while back, and while the execution of that project was a little lackluster, it sounded cool to me. So if all else fails I can just think of this as a 15 watt sorta JTM45 thing and play guitar through it.

    @Lowerleftcoast I am going to think hard about subbing in the LTP. It'd be a shame to build something that would have a cool overdrive voice but cathodyne problems layer on top a bunch of bad sounding distortion. On the other hand, there are some people on TDPRI (some of whom have chimed in here) who have done some work on the rehabilitation of the cathodyne and have really good sounding amps.

    I'll post more photos of the chassis to give people a better sense of how much space is left to fit capacitors and potentially another 9-pin tube.

    Thanks!
     
  5. Lowerleftcoast

    Lowerleftcoast Tele-Meister

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    I see an octal there. Put another octal in one of the holes. It would leave three 9-pins. You could go the 6v6 route (they take less current than el84s anyhow). It would be easier on the PT and may even sound better with bass.

    Seems like a nice little amp whichever way you go.
     
  6. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Sterling Ray24CA Classic Stingray mini review:

    I like this bass that isn't a Rickenbacker and is MII and not every bit of it was put together really precisely.

    ***

    Amp chassis mini update:

    IMG_3466.JPG
    IMG_3467.JPG
    IMG_3465.JPG

    Next is locating the filter capacitors. The spot in the center that once had the rectifier's octal socket is one of the few good places left that isn't encroached on by that big power transformer. A 40-20-20-20 microfarad multi cap would fit, but without a lot of breathing room. Alternatively I'm thinking about using split ground buss and using a 50-50 there for the power amp, and a 50-50 nearby the input jacks (you can see a pilot hole there already). Crowded either way.
     
    Last edited: Jan 29, 2020
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