Blackvibe in a Princeton-sized chassis: Check my chassis/layout

[aguynamedben]

Hi, I'm new here. This is also my first amp build, so sorry if I'm asking something dumb.

I'm building Rob Robinette's Blackvibe as my first amp. Rob has a DIYLC file and instructs people to use a AB763 Pro chassis because the tube/PT holes are already there. But I live in a tiny apartment in San Francisco, so I'm going for a 1x12" Princeton combo sized Blackvibe.

Here's the layout: https://imgur.com/a/WeQc2tO (I used a Sketch and carefully translated all sizes from inches at a 72 pixels = 1 inch ratio.)
Here's Rob's original layout: https://robrobinette.com/images/Guitar/AB763_Models/RR763_BLACKVIBE/RR763_BLACKVIBE_Layout_small.png

I'm going to order a custom chassis and want to make sure the power transformer cutout is in the right place. I also might have the chassis builder put the tube holes in.

Does the attached layout make sense? The main changes is I've moved the Bias & Balance board off to the left. Will that create noise because there are longer runs between that and the turret board?

Other questions:
* Does the orientation of the PT make sense?
* Should I have the chassis builder put an IEM cutout in the back left? (i.e. near the rectifier)
* Did I screw anything else up? Anything that will create noise?
* What is most likely to make this "Blackvibe in a Princeton-sized chassis" project fail? (aside from it being my first build in general...)
* Do you have a favorite custom chassis shop?

Thanks for any input, I really appreciate it an am excited to become part of this community.

Ben Standefer

[PRR]

Welcome!

> I live in a tiny apartment in San Francisco

Do you play-out? A two-6L6 amp should be ample to break an apartment lease. I've "called the cops" with less; cops from the next town.

Your drawing looks fine but others here have much more experience.

Isn't this the original Mesa Boogie? A high-power amp in a Princeton cab?

[ac427v]

Hey Ben, You will find that you can't install the chassis because the cabinet interferes with the power transformer and first preamp tube. The true footprint of the PT is much bigger than the cutout. The true footprint of the preamp tube and shield is slightly bigger than the chassis hole for the socket. The vertical 3/4 inch braces on the back of the cabinet will block the PT and first preamp tube from sliding in. Yes I know from experience--twice. I'm a forgetful learner.
And I'm sorry to jump on PRR's 6L6 bandwagon. They can be played at low volume but the sweet spot is many decibels louder. My preference is Deluxe Reverb circuit at 400 volts on the plates using a tiny Hammond Princeton Reverb output transformer. It's just about perfect for loud playing in the basement. Your mileage...

[aguynamedben]

Thank y'all for the reply. My coconspirator Derek and I are VERY thankful there is a place like this to ping ideas around. I think we're in the right place when you say "I know from experience, twice, I'm a forgetful learner". :) Part of the fun of this project is NOT doing a kit, so we really have to learn the process vs. just following instructions.

Some more thoughts that might make our goals more clear...

* Sound level: We're very aware that 2x 6L6 amp is completely impractical for an apartment in San Francisco. We also have a 5w 5F1 Tweed Champ and a 15w Matchless Lightning that are already way too loud and have generated noise complaints. We must *always* play with attenuators, even with the 5w Tweed Champ. We use the Fryette Power Station 2 and the Tone King Ironman Mini 2, and play in the sweet spot attenuated to semi-bedroom volume, or go direct with the attenuators as reactive loads into IRs/headphones. The desire for a 2x 6L6 amp is because we want an amp with very high input headroom for pedals. The Tweed Champ and Matchless Lightning are both very nice cranked and then attenuated, but we want to build the opposite, and amp with insane headroom. If we were sensible, we'd probably be playing Roland JC-40s, Peavey Bandits, Quilters, or Strymon Iridiums turned to 1.5, but what's the fun in that!

* The cabinet: We plan getting the amp working, chassis-only, and then we'll order custom cabinets from Mather Amp Cabinet. He does a "tall" Princeton 1x12: https://www.facebook.com/photo?fbid=1125332470823526&set=a.948974455125996 He said it should be fine, but to be sure we can send final measurements for the build and he'll make sure it fits. His work seems very high quality and very reasonably priced. I also like the "tall" idea because in my small apartment I'm fine with using more vertical space, I just don't want to use more floor space. We might even go with a 2x10 tall Princeton cabinet. Having a tall Princeton cabinet may also gain us some bottom end when we can be loud. :) i.e. it's not just a tiny 1x12/1x10 box, but we still save a lot of floor space.

* The chassis: We'll order a custom chassis from someone like Juicy Amps: http://www.juicyamps.com/chassis.html The chassis will be Princeton-sized, but obviously the tube cutouts and PT cutouts will be customized.

So, I guess my main thing to gather from the feedback so far is:

* Make sure the total footprint of the PT doesn't hang OUTSIDE the dimensions of the chassis. Then no matter how tall the Princeton is, the PT wouldn't fit! I'll check that. We ordered the transformers already, they should get here any day, and I'm probably going to order a normal Princeton chassis, just so we can eyeball it and refine the chassis layout before ordering that.

* Make sure we really want to be silly and do a 2x 6L6 amp instead of something like a 2x 6V6 amp. Rob Robinette actually has a design for the Blackvibe but with 6L6s. But we are competitive engineers and I kind of like the ridiculousness of getting a 40w 2x 6L6 into a "tall" Princeton cabinet. We're so accustomed to using attenuators all the time that it actually is kind of liberating us to build a loud-as-hell-amp vs. an appropriately sized amp. ??? :)

Thanks for any feedback. Once we get going I'll make a thread on here to post pictures and track. We have a log going on https://bit.ly/blackvibe if anybody wants to follow along or join!

–Ben and Derek

[PRR]

> 6L6 amp is because we want an amp with very high input headroom for pedals.

The output power stage is like the engine. The input jack is like the controls. So you have a driver with "a loud right foot" and you think you need a 427 engine? I would think you want a long-throw go-pedal and poor leverage to the carb so it doesn't blow itself into the bay

[aguynamedben]

My thought is that I'll rely on the gain staging in pedals for compression (i.e. make the driver have a less-loud foot using pedals). That's kind of the core idea of a super clean pedal platform amp anyway, isn't it? A somewhat neutral sound, headroom for days, and in this case, not even reverb/tremolo because I'll use pedals for those too. That's why I mention the more practical alternative being a JC-40, Peavey Bandit, etc. solid state amps that simply do not break up and aren't designed for break up.

Wouldn't a Deluxe Reverb break up around 4? I'm just going for a 40w amp because in the past I've had a 20w amp, 15w amp, and 5w amp, and I want to go the extreme other direction, extreme clean amps with near infinite headroom, i.e. Hot Rod Deluxe, Twin Reverb. I know that to get the 40w amp to sound "right" i.e. have bottom end, I'll have to use an attenuator, but I have to use an attenuator no matter what, so I'm just kinda going the other way with it.

I'm still learning about this. I appreciate the debate. My current influence is the Matchless Nighthawk, which is 15w but has an EF86 preamp stage. The EF86 preamp amplifies so much into the PI and power section that it breaks up very early, it sounds fantastic, but just want to play with a design that is the opposite... infinite headroom. I'll probably run them wet/dry. I have a lot to learn, but from what I understand of guitar history this is the same thinking that lead players like Jerry Garcia to use clean hi-fi PA systems, country players to play amps like the Dr. Z Stangray, most backlines to have a Hot Rod Deluxe, etc.

I always have to attenuate, no matter what, so why NOT build a louder-than-necessary amp and face the challenge of getting a loud-ass amp into a small cab? All amps for my living setup are way louder than necessary anyways.

[ac427v]

Words alone don't convey the transformer-chassis-cabinet incompatibility. So here is a thousand words  a picture of a proper amp to help communicate. All blackface amps have two cleats 3/4 X 3/4 that run from the floor of the cabinet to the bottom of the chassis. These cleats are needed to hold the screws of the two back panels. Any object like a transformer or tube or power cord that is placed within 3/4 inch of the side of the chassis bottom will hit the cleat and not be able to slide any further into the cabinet. I expect that your cabinet maker did not understand that you planned to place the power transformer and a tube within that 3/4 inch "no man's land" on either side of the chassis bottom. Study the picture until you understand why my Princeton Reverb in a VibroChamp chassis has one cleat that is now an inch short and one preamp tube that cannot be installed until the chassis is in the cabinet.PRR's car analogy works for me. A 427 engine in a commuter car makes sense if you take it to the track on weekends. My Tweed Bassman and Vibrolux Reverb clones haven't been played in a year. They can't get close to the clean sweet spot without being too loud. Playing them with an attenuator would be like driving that 427 with my right foot on the accelerator and my left foot on the brake. But I'm not you. If you get to play this monster in a big room occasionally it makes sense.

[PRR]

> A 427 engine in a commuter car makes sense if....

A friend has a Miata. Original recipe, 115HP. My uncle asked if it was getting boring. He found a 840 HP Hellcat swap. Obviously this builder would not let a couple 3/4" wood strips get in his way. I wonder if there is ANY Mazda left under the skin.

[aguynamedben]

Haha, see now there’s something you don’t see every day!

Thanks for pointing out the 3/4” cleats issue. I see those on the back of my Silverface Champ too. I’ll definitely move the V1 and PT inward in my chassis design as to not have those hit when sliding in the chassis. Having a stock Princeton chassis and the PT in hand soon will hopefully help me figure it out.

Thanks for the fair ribbing. I’ll let you know how it goes. Gather your popcorn to see if I either push through or fall on my face!!! Thanks again. 🙏