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Quarantine build 3 of 4: Robinette Blackvibe Micro

Discussion in 'Shock Brother's DIY Amps' started by Drew617, Aug 14, 2020.

  1. Drew617

    Drew617 Tele-Meister

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    Hey all,

    As promised, here's my third build of this quarantine... also ever. This is Rob Robinette's RR763-M Blackvibe Micro built in a Vibro Champ chassis and cabinet, with 1x10" baffle.

    My lead dress sucks this time. In the course of assembly, troubleshooting a stupid wiring mistake, and reassembly, I ended up mounting the board closer to the chassis than it was originally when I soldered everything up. As a result, leads to the tube side of the board are all longer than they need to be. I meant to give more attention to dress, but it's plenty quiet as built and I was impatient. The third output jack will be a line out; I didn't have the right resistors and those will have to wait for my next Mouser order.

    I bought a 10" Weber California for this, hoping it could be an "office Twin." I wasn't and am still not sure that 1W will be enough to make that heavy cone lively. My Cali arrived damaged and I'm waiting on a replacement, so threw the Jupiter in there for now. I'll give the replacement California a shot when it arrives, but wonder if I haven't accidentally stumbled on the perfect speaker for this amp already. The Jupiter sounds fantastic here.

    I knew I'd build this in a VC cab. Between the little OT, the tiny cab, and the 10" speaker I assumed this might sound a little thin and was okay with that. I can't believe how big this amp sounds. Plenty of bass if you want it (I am a clean-ish player and prefer "balanced" but definitely present low end) and the amp is surprisingly loud. BF cleans are gorgeous, just as you'd expect. There is big, big sound here at reasonable SPL. I am really impressed with this design and can't believe amps in this configuration are not more common. I don't know Rob, but: Thanks, Rob!

    Iron is all Hammond: 290AX PT, 125B OT, 194A choke.

    Cheers,
    Drew

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    Last edited: Aug 15, 2020
    Paul-T, BigDaddy23, robrob and 2 others like this.
  2. glenlivet

    glenlivet Tele-Holic

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    Hope it sounds as good as it looks....you nailed it !
    Well done Sir.
     
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  3. Drew617

    Drew617 Tele-Meister

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    Appreciate that, thanks! Perhaps some honeymoon effect happening, but I'm real pleased with the design.
     
  4. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Very nicely done Drew. Most people are shocked by how good a 12AU7 power tube in true push-pull can sound. Can I post your pics on the Blackvibe Micro webpage?
     
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  5. Drew617

    Drew617 Tele-Meister

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    Rob, thanks for saying so. You absolutely may.

    Thanks too for your public service, generosity, whatever you care to say. I'm an engineer (not electrical) by trade but only dug into amp theory and t/s tactics when my $500 Champ needed repair. I can't accept inability to maintain my own stuff. If I have half a clue what I'm doing, your website and writing have a lot to do with it.

    ...for your (literal) service also, from another USAF vet. I just now got around to your "about" page. Too cool.

    Cheers,
    Drew
     
    Last edited: Aug 15, 2020
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  6. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Thanks Drew for the use of your pics and thank you for your service. What would you like me to list as "Photos and build by . . ."
     
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  7. Drew617

    Drew617 Tele-Meister

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    First Last (Sutter) is fine. Looks like others used that convention, and my name's in those photos anyway.
     
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  8. Drew617

    Drew617 Tele-Meister

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    Mostly to satisfy some OCD on my part, here's the amp in it's finally completed form. The big Weber Cali 10" is an entirely different speaker (duh) and to my ears slightly better on average, so it'll stay. It works surprisingly well at < 1W and my fears about it being unlively were unfounded. It does lose some airiness and overtones versus the Jupiter but its low end is much tighter, and its overall tone is thicker and more throaty. Gets a lot closer to my original "office Twin" target.

    I ended up replacing those two Mallory caps on the original build with orange drops. Aside from the Hoffman turret board, this started as a "parts on hand" build. I added caps across the rectifier diodes in an attempt to tame some high frequency noise, but that turned out not to matter. I keep a pair of Line 6 efx modelers in a switchable loop (mostly for their excellent spring reverb and occasional modulation efx that I'll never buy as discrete pedals) that generate some whine only apparent through this amp, I assume frequency response thing. Might be addressable with additional resistors but I'm not sure I really care. I broke my JJ ECC82 on the speaker magnet and replaced it with an ECC82S, to my surprise a noticeable improvement in this application.

    There is a good amount of preamp gain available; The amp starts to break up around 5-6 on the Volume with my G&L CLF-100 single, and a bit lower with my ASATs. Just like I'd expect out of a loud Deluxe Reverb, etc. I didn't hear all of it initially, I think the Jupiter speaker I built with initially smoothed over a lot of midrange texture. That's really fun and useful with the master volume. The master is mostly effective between about 2-4 on the dial but that wasn't unexpected and makes it no less useful.

    Cheers,
    Drew

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  9. Drew617

    Drew617 Tele-Meister

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    OK, no more additions to this Blackvibe, but after saying here that the amp was hum-free as built (it was) I did start to hear some oscillation, no doubt my ugly lead dress. Ended up rebuilding on a new board to clean things up some. The Hoffman turret board I originally bought for this is great quality of course, but just a bit too big in this chassis.

    I settled on a Weber 10A125 in the amp, quite different than what I had in mind originally.

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    Last edited: Sep 27, 2020
  10. robrob

    robrob Poster Extraordinaire Ad Free Member

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    The amp looks fantastic. Can you give us the details on your ECC82S (12AU7) that you liked for the power tube?
     
  11. Drew617

    Drew617 Tele-Meister

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    Thanks, Rob! I've liked the long plate JJ ECC802S. When I first put this together I only had a plain JJ ECC82 on hand plus whatever Shugang tubes I've pulled from amps over the years. This circuit's never sounded anything but great to me, but I hear more low and thicker mid content - and more mids texture - out of the 802S.

    If you're inclined, feel free to replace my original build on your website with this one.

    The first kit I bought, my Weber 6A14, is finally built and ready for testing and burn-in as soon as I can find time. More like Weber cab and chassis as I subbed out nearly all of the other parts save for the PT.

    I will have to give up my workspace to the two older kids over the winter. It's time to buy property but I worry that macro pandemic impact isn't understood yet... but that's a whole other thing. I'm going to sneak in two more builds before then, 2 ea. of your Deluxe Micro which I will try in compact die cast enclosures and with the $25 Weber standalone reverb PT.

    Cheers,
    Drew
     
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