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Building a Prototyping Homebrew: Pix Posted, QC Wanted.

epluribus

Member
Messages
9,170
Got the nomex ready to go, halon bottle in hand... :)

This used to be a Kalamazoo Model II, and in some distant future will become a hard-wired FrankenZoo. Meantime, to prototype circuits, I started out with alligator clips, graduated to perf board and jumpers, then to perfboard with RF and noise control, and most recently to what you see below.

The point of this build is to make it easy to re-wire tons of different circuits within more or less "Champ" boundaries--single ended, small wattage, either cathode or fixed bias. In addition, the chassis is set up to run any combination of 9-pin and octal tubes throughout, (aka 6SJ7 to 6V6, EF86 to EL84, 12AX7...you get the idea) though obviously not all at once.

But the non-Champ intent is to be able to add cascading gain stages, various types and locations of tone stacks, use several types of rectifiers, add FX like trem and verb, and even remove and replace transformers--all without soldering a thing.

So now that you know the why of the build...I'd love to hear your input. I have several issues with the build thus far, some of which I briefly covered after the pics. But to avoid coloring your thinking or missing ideas that fall outside my box, I'll just let you look and form your own opinions at this point.





The grounding plan was to use a star-ground of sorts, with each bus connecting at the main ground bus and going to the center tap of the PT. The ground busses would include heat, Preamp B+, Power Amp B+, signal, chassis/shield, jacks/pots, and power cord/switch. (Hence the eight-terminal barrier strip.) However, an article at AX84 calls star-grounding into question, so remarks and theory are especially welcome on this point.

Heater lines would run pretty much all on the back of the chassis, with B+ being distributed under the circuit board on the front panel side of the chassis, and the power rail located above the PT on its own board. The two blue sub-chassis are sheet metal, btw.

Courtesy of the various terminal blocks, power can be connected or disconnected for heat, B+, rectifier supply voltage, and plate-to-OT feeds on power tubes. In addition, pre-wired tube sockets can be removed and replaced to accomodate different types of pinouts.

BTW, all of the barrier-strip terminal blocks are velcro'd and can be moved easily, same's true of the perfboards--all on velcro 1/2" standoffs.

The upshot is that not all of the tubes would be active at once, obviously, thinking about the Champ-style PT and all, but A/B'ing configurations would be relatively quick and painless with only the briefest of power-downs.

Anyhoo, this rig actually works, but it's never been put together in one neat hunk like this. That alone should be a major improvement over perf-boarding with the boards jumpered and laying on the workbench. Trouble is, when you pull it all together on one chassis, scads of layout issues arise, not all of which I'm familiar with. So I look forward to suggestions, links, questions, and maybe even a flaming arrow or two.

--Ray

Oh yeah, the rectifier--a Weber substitution box made just for this type of work...and of course the poor little OEM 6X4..
 

TweeDLX

Member
Messages
3,756
Nice job putting all that together Ray! Wish I knew more so I could critique it for you. Have you run into lead dress issues with things strung out like that?

Mike
 
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epluribus

Member
Messages
9,170
Hey Mike.

Yeah, that was a challenge in earlier versions of this rig, back when I had to jumper everything to perfboard sitting on my bench. Layout is something I'm not real familiar with, and it's one issue I hope we touch on here.

I'm still uncomfortable with some of the longer B+ runs, and may just use the board by the front panel for some of the power rail duties--but we'll see how that plays out. I note that many hi-gain rigs cluster the power rail to one side like this, and enclose the whole thing in a shielded doghouse. (I have that enclosure built, btw.)

One thing I can't avoid is soldering grid stoppers directly to socket pins, in that they don't work particularly well if you don't. Figure to solve that by using cermet trimpots instead of fixed resistors, so that shouldn't be a big deal. The rest of the signal path should live rather nicely on the perfboard though.

Fortunately most all of the front-panel circuitry should very closely resemble turret or eyelet board-style layout, and I expect the majority of my noise and signal issues to be no worse than conventional build of that sort.

Hi-gain, however, is another matter entirely. (Hoping to make my Soldano SLO100 front end work a bit better this time around. :)) That's where my ground scheme, additional shielding, and the long heater runs may come into play.

On the heater issue, btw, I'm kinda thinking of placing the entire heater bus in a shielded doghouse as well, and running twisted pairs from there.

Those long curvy PT leads also concern me. As this is a prototype setup, I kind of hate to clip the lines, but I'm concerned that the hi-voltage AC feed to the rectifier and the heater feed is going to be a considerable noise issue.

Incidentally, the earlier versions of this system were hideously noisy, but depsite that worked surprisingly well. Certainly enough to crunch the numbers, measure the actuals, and then prove the circuit in play-testing. I'm hoping that by moving my boards right onto the chassis I can clear up many of those shortcomings.

--Ray

ps...I have two of these Kzoo II's, package deal--the EBay seller had a flood victim in his basement. I made one really pristeen one in all-original trim (except filter caps) out of the two. Cool little amp. Just so our vintage fans don't have heart failure...:)

FrankenChamp Classic



FrankenChamp v1.0, a vastly more controllable circuit. Really sings with a Strat.



FrankenChamp v2.0. This version has been about two or three dozen circuits, including Vox Top Boost, early Marshall, several Fenders, and a variety of others like Supro. It's also been a screamin' 7 Watt metal monster...with the trem 12AX7 hijacked for cascading gain stage duty. Goin' hi-gain here boss...

 

epluribus

Member
Messages
9,170
You are a madman! That's awesome. The only immediate issues I can think of are when you get into higher gain territory... the lack of a metal enclosure (chassis) around the protoboards might allow stray noise to be picked up.

But dude, that's awesome.
Thanks John. I hear ya about the enclosures. I sprayed inside some plastic project boxes with shielding paint, to be grounded on the shield ground bus. Not sure what shielding science has to say about what happens to wiring as it enters and exits a shielded enclosure though...non-conductive goop with shield spray to seal it tight?

Might have to make up some shielded signal wires for coupling-cap-to-grid duty on the perfboard too. I understand, however, that shielded signal lines suffer minor signal loss from capacitance, so more films at eleven on that.
 

VacuumVoodoo

Member
Messages
1,544
I'm speechless...this is a thing of sculptural beauty, I just keep staring at it.
Seriously, I'd put it in a sealed glass box and save it for posterity. It's a piece of "junk electronic art" in the best meaning of the word. Seriously. No sarcasm or irony, overt or between the lines.
 

epluribus

Member
Messages
9,170
I'm speechless...this is a thing of sculptural beauty, I just keep staring at it.
Seriously, I'd put it in a sealed glass box and save it for posterity. It's a piece of "junk electronic art" in the best meaning of the word. Seriously. No sarcasm or irony, overt or between the lines.
Thanks VV, never looked at it that way, I'll have to think about that idea. Intriguing. Junk electronic sculpture... It happens that I'm a huge fan of the art of "junk" insofar as it represents a growth of sorts and illuminates the often rather organic exploration of complex human needs--and the highly un-intuitive way they are often very successful, but successful in complex ways that tantalize our understanding by ignoring our predilections toward "neatness" and "order." Such things are arguably orderly, predictable, and constructive, but defy the anthropomorphisms we like to build around our grasp of science, literacy, art, and taste. The architect Bernard Rudofsky wrote several wonderful books on the subject, incl. Architecture Without Architects.

Frankly, from an amp standpoint, I was blown away that as this rat's nest grew that the thing worked at all. Incredibly noisy, but it functioned just enough to prove or disprove the various ideas behind the circuits, and more than once some of these things actually did cool stuff. The one above oscillated like crazy except at a very narrow band of settings on the volume knobs, and then it sounded eerily like a cranked Mesa-ette.

Unfortunately, the rig no longer exists, exactly...the opening pix in this thread are the same amp.

Anyhoo, now I gotta re-think this idea...electronic sculpture...I like it when my messes turn out to be art... :) I do still have all the original perf boards and jumpers and stuff...hm...

--Ray

BTW, things like this fascinate me too, for the reasons you mention. Funny you saw that but I didn't--or maybe I did but it didn't dawn on me to think about it. As purely visual subjects, I've become intrigued with apparent chaos recently, among other things as expressed in municipal power lines around the world. I find the images evocative for the same reasons you describe above...

Meintz, Germany...



Steel Country, Indiana...



Narita, Japan...



New Delhi...

 

epluribus

Member
Messages
9,170
Bump. Just an update, RE: noise and interference issues. I don't have any good books on this, so I've been googling and searching all sorts of web stuff looking for some definitive theory or even a concensus. I'm arriving at the conclusion that fighting noise, esp in hi-gain circuits, is something of a black art composed of jealously guarded secrets among builders. Y'know you can start a good-sized brawl on amp builder discussion boards just mentioning star-grounding. :rolleyes: More films at eleven...

--Ray
 




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