Winter Project: Guitar Amplifiers

[VertigoCycles]

I built a guitar last winter to keep myself busy while some injuries kept me from building bikes. It turned out to be a pretty great way to engage my brain during the months that the trails are either too wet or too snowy to ride.

The whole project went so well that I've decided to try to make it an annual thing. So this year I've started building a couple of guitar amplifiers. I'm generally terrible with electronics and approach it with extreme caution but there's a great web forum called ampgarage that is a helpful resource when trying to sort through all the little things that aren't exactly obvious.

I actually bought a chassis last March, but it arrived about the same time I could work and ride again and it's taken a back seat for nine months. By the time I got around to starting it back up, I decided to go in a slightly different direction with a different, more complicated amplifier that wouldn't fit into the chassis I purchased. I studied the schematic every night for several weeks and started making a bill of materials. While waiting for parts to arrive, I cut, drilled and installed eyelets in the various circuit boards.

873CC6A9-602F-4AF7-9962-12559A2A18D3.jpg . 25EB49C4-860C-4DC1-B4BD-65E9D90F2875.jpg

The blue circles were supposed to remind me to layout and drill tube access holes before I started soldering in the components

[VertigoCycles]

Well...I can't embed anything from Instagram anymore, and my image uploads keep failing so...

needless to say, I forgot to drill the holes, made what seemed like several hundred soldered joints and then went back to cut the holes. Not ideal, but it worked.

It was at this point that I began to struggle to decide whether or not to build this chassis myself, or design it in Solidworks to have someone waterjet (or laser) cut and bend up for me. I ultimately resolved to do it on my own and the project hit the brakes when my buddy (who owns the Diacro brake) started full-on building out a flat tracker for The One Moto Show coming up this weekend. If he finishes the bike by then, it'll be a miracle, but there was no way I was going to interrupt his work flow to bend up an amplifier chassis.

So...

I changed direction again and decided to move forward on the amp for which I already had a chassis. More studying of schematics, more excel spreadsheets making a bill of materials and more scoping out a layout that would work with the circuit boards I already have.

To rewind things a little, it should be said that I'm trying to build a reasonable facsimile of Dumble amplifiers. If you're a guitar nerd, you likely already know about them and that most people aren't able to afford them. Stevie Ray Vaughn, Eric Johnson, Robben Ford, Joe Bonamassa, and Ben Harper are a few of the people who have used them. The Steel String Singer is the one I'm trying to build from scratch and the OverDrive Special is the more common one that I'm trying to build with a chassis and boards that I purchased. If you're familiar with the SRV album, "The Sky is Crying" he supposedly used a 150 watt Steel String Singer for that.

more later as I sort out my photo problems.

[j44ke]

On this forum, I think you have to select "Go Advanced" to get to the advanced editing page for a post and the Instagram icon will be in the tool bar above the text posting window. Then go to the Instagram post you want embed here, copy the letter/number code for the post, then click the Instagram icon here and paste that letter/number code between the code bookends. Should work.

So for example, this is the URL in the browser when viewing the specific post:

https://www. instagram. com/p/B8UBiCoJIcG/

The red letters/numbers are the code for the post. Click on the Instagram icon to get the code bookends to appear.

[72gmc]

Great project! I've had a lot of homework this week and James May's reassembly of an electric guitar was part of my accompaniment. instruments and sound equipment are fascinating.

[VertigoCycles]

After being drawn away from this for a while, I've been able to spend some time on this over the past few weeks.





And a little sorting out of the neck finish I want to have on a strat style guitar that I'll finish up one day.

[Diablo de Acero]

Nice! That is some super tidy work there.

[Mark Kelly]

If I may offer a minor critique, on the circuit board in the middle pic you have polystyrene capacitors tied cheek by jowl with carbon resistors.

The achilles heel of PS caps is very poor temperature tolerance: they start to degrade about 70^oC. Overheated PS caps do not return to their previous values so the circuit will exhibit drift.

Resistors are designed to throw off heat, so putting them right next to PS caps is not good practice IMO.

Also assuming the middle noval socket is a 12A_7 and the resistors on pins 2 and 7 are grid stoppers, I would have them closer to the pins. The one on pin 2 is OK but IMO the long lead on pin 7 is asking for oscillation problems.

Nice work by the way, especially if this is your first effort. My first efforts looked like a pig's breakfast.

[VertigoCycles]

Thanks Jay and Mark.

Mark, I appreciate your input but I'm sure you know that the layout sometimes has to compromise the ideal for the practical. I didn't create this layout, it's pretty faithful to how Dumble originally made it and the end result is in how it sounds. My guess is the compromise to save space is to keep the point to point connections under the boards as short as is practical to reduce the possibility of them picking up noise that will get amplified through the gain stages. If the values drift significantly over time, these amps still generally sound fantastic so it would seem to me that heating up the PS caps on this circuit is a non-problem. Just for fun, I'll hit them with my thermometer as I'm dialing in the voltages after my power tranny arrives next week. If I have any oscillation problems, I'll keep an eye on those grid stoppers too. Thanks for pointing that out.

[VertigoCycles]

Swinging back around to finish this up. The wiring has been "complete" for a while now and I built the head cab for it a week or two ago. About ten years ago now, I bought some blue alcantara fabric to re-cover the seat on my motorbike but lucked out when James Renazco offered to make me a custom saddle. He makes the hell out of a saddle, so there was no way I was going to turn down an offer like that and I was left with a yard of a hideous blue fabric that might never get used. Rather than use a tolex that everyone has seen a thousand times, it seemed like a good opportunity to use this stuff up, even if it's obnoxious.

This ended up being one of those situations where it looks good from a few feet away, but don't spend too much time scrutinizing the corners. This stuff has a stiff fabric backing and didn't lend itself well to wanting to wrap the corners. I was trying to avoid using bumpers, but they very well may end up being installed to hide my work. Not great, but not terrible either.

[VertigoCycles]

I machined a mold to make leather corners for the blue amp

IMG_1142 by Sean Chaney, on Flickr

and then made a punch and positioner to punch holes in them

EC150E2E-9606-49F2-9D74-258C1E4F4BF6 by Sean Chaney, on Flickr

03536831-5A5F-4CD0-B324-4343FB764CAC_1_105_c by Sean Chaney, on Flickr

9A7A31C7-1510-47F5-8985-25B90AD87405_1_105_c by Sean Chaney, on Flickr

and then made another amplifier. this one only does clean, but it does it REALLY loud. It's perfect for making you feel bad about how sloppy your playing is.

5C026FAF-38DA-4529-AED9-2BA7927C50E3_1_105_c by Sean Chaney, on Flickr

[Bob Ross]

I'm trying to build a reasonable facsimile of Dumble amplifiers.

Whoa... as if I wasn't already totally sucked into reading this thread! Mad props to you my friend, can't wait to read how it worked out.

(Can't believe I haven't seen this 'til now.)

[VertigoCycles]

Whoa... as if I wasn't already totally sucked into reading this thread! Mad props to you my friend, can't wait to read how it worked out.

(Can't believe I haven't seen this 'til now.)

I'll have to post a thorough update soon the. The ODS copy is pretty much "done" as you can see above. It does have a grille now with some black Vox style grille cloth. The SSS circuit is "done" and I had finished the cabinet for it, didn't like how big it was, experimented with the location of the reverb pan and decided to cut about 60mm out of the sides. I've got some british racing green tolex cut out but it's been tool chilly here lately to apply it in the shop and I don't want to stink up my house with neoprene glue to do it where it's warm. It happens that I picked up a pair of Mesa cabinets today with some EVM12L's for a steal, and they're black so I might do black tolex, brown Vox cloth and then redo the grille's on the Mesa cabs to match.

"done" meaning that I'll probably be tweaking the circuits to experiment with them as my learning continues. The SSS amp is distorting more than I'd like and I've tweaked the negative feedback circuit on the first tube a little bit to inject a bit more NFB into it. It didn't fully clean it up, but the harmonics are less harsh then they were. I'll try putting some grid stoppers on V2 soon to see what happens with that.

I've got a tele, a strat, a jazz bass and two LP copies in the beginning stages at the moment but didn't think folks here were into it, so didn't want to clog up the board. I'll do some updates if it turns out that people are interested.

[VertigoCycles]

for you, Bob.

Here's the ODS with the Tele that I built a couple of years ago.

DD14A347-AC6E-45EF-9830-9E0DFC6F1048_1_105_c by Sean Chaney, on Flickr

The effects loop on the ODS leaves a lot to be desired and folks generally feel that a buffered loop, like the Dumbleator, really help keep the amp sounding good with anything in the loop...so I built one. It turns out that it's pretty useful as an attenuator as the "recover output" knob essentially becomes the master volume. Without any effects at all in the loop, the -lator adds a harmonic richness to the overdrive channel that didn't exist before and there's still great note separation. The great thing is that you can set the master on the amp pretty high (I set mine around 7 on the dial to push the power tubes just a little) and keep the volume level reasonable with the -lator.

I found a schematic and made a layout for it with a program called DIYLC

Image 9-7-20 at 3.07 PM by Sean Chaney, on Flickr

If you take the time with your traces, you can turn off some layers on the layout and create a mask to etch your own PCBs

Screen Shot 2020-09-07 at 3.07.55 PM by Sean Chaney, on Flickr

IMG_0742 by Sean Chaney, on Flickr

IMG_0794 by Sean Chaney, on Flickr

I may have recruited a little help

IMG_0753 by Sean Chaney, on Flickr

The populated boards

IMG_0801 by Sean Chaney, on Flickr

Then I drew up some graphics in Illustrator to cut vinyl masks for the control lettering, followed by some careful weeding.

IMG_1248 by Sean Chaney, on Flickr

did a little paint filling by adding just a touch of aged nitro lacquer to some white lacquer

IMG_1255 by Sean Chaney, on Flickr

It turned out OK

IMG_1258 by Sean Chaney, on Flickr

I figured it was slightly risky to machine post-paint, but it was easier to align the mill to the print than the other way round

IMG_1260 by Sean Chaney, on Flickr

IMG_1261 by Sean Chaney, on Flickr

I wanted the IEC mount to sit flush

IMG_1262 by Sean Chaney, on Flickr

This is what happens when you have a metric radius on the IEC and only have imperial sized endmills. It's OK, it's on the back and no one will ever see it.

IMG_1263 by Sean Chaney, on Flickr

After drilling all the mounting holes in the chassis (and maybe one or two extra ventilation holes) it was wired up

IMG_1267 by Sean Chaney, on Flickr

With the power of hindsight, I wish I had just built the loop into the amp like this. I didn't know enough to get it done at the time so I guess I'll just have to build another one one day but with a different circuit that's a bit more oriented to single coil pickups. First I need to finish the work on our house so we can move in the spring. If I add another amp, I'll surely be in hot water with my wife.

[Diablo de Acero]

Beautiful work! Sean

[VertigoCycles]

Thank you Jay!

[defspace]

I've got a tele, a strat, a jazz bass and two LP copies in the beginning stages at the moment but didn't think folks here were into it, so didn't want to clog up the board. I'll do some updates if it turns out that people are interested.

Are you kidding, man?! Heck yeah we want to see 'em!

I've done a bit of hobby loothin', so this is right up my alley. I've thought about ordering an amp kit from Mojotone or somewhere... but then I see you do this. Phew!

[VertigoCycles]

Are you kidding, man?! Heck yeah we want to see 'em!

I've done a bit of hobby loothin', so this is right up my alley. I've thought about ordering an amp kit from Mojotone or somewhere... but then I see you do this. Phew!

Last time I looked on the AmpGarage.com forum, Taylor from Amplified Nation was selling some ODS chassis. There are several well documented Dumble style builds on that forum and it's a good group of folks who are willing to share their knowledge. If it's something you want to do, give it a shot. Between Mouser, Tube Depot and Amplified Parts you should be able to get 99% of the parts you need. I definitely will be building more, but will wait until I have time to design the chassis myself so I can get exactly what I want

[VertigoCycles]

I have too many projects going at the moment so they're all slow going.

Finally put some tolex on the SSS cabinet. I regretted the green immediately and am thinking about pulling it in favor of black. It'll be fine for a while though.

2E10F8F1-8690-44B0-AE0C-CCD43B7A22DA_1_105_c by Sean Chaney, on Flickr

With so many instruments on deck, I needed a router table. The top of my MFT was pulled off and I cut some 3/4" MDF to fit. But before I could even start, I had to make a pattern follower for a big surfacing router bit. I bought an inexpensive Jessem blank insert so I could drill holes and mount my Festool router underneath and the insert has .75" radius corners. Making the big surfacing bit into a pattern bit allowed me to easily get the correct radius since the OD is 1.5"

7A1F5FDD-7B8F-4126-9BE8-E025D4151DB5_1_105_c by Sean Chaney, on Flickr

My 8y/o daughter helped me layout for the router plate and attach some BB off cuts as a template with double stick tape.

B1E489FE-BEBD-4235-82A5-8994695E1502_1_105_c by Sean Chaney, on Flickr

A few trips around the perimeter with the pattern bit and then we cut out the center with a jigsaw.

D48C13AE-8AB1-4793-A9D5-9B65828AC6D9_1_105_c by Sean Chaney, on Flickr

I soaked the newly exposed flats and corners with thin CA glue and the router plate is a perfect fit

7ACAD003-B033-40D6-836C-65C4ED9647D4_1_105_c by Sean Chaney, on Flickr

I was a little shy with my buddies bandsaw...

E8582613-F6CE-44D0-8120-62CE106F910E_1_105_c by Sean Chaney, on Flickr

...so I robo sanded the body down to the template so the router wouldn't have to work as hard

C0FA3527-6976-4E09-926A-B9CBD5E9B840_1_105_c by Sean Chaney, on Flickr

then cleaned up with the router and a pattern bit

D3A57F91-1180-45A5-808D-71294821E606_1_105_c by Sean Chaney, on Flickr

These Radian bits have been pretty good to me up until now. It didn't handle the endgrain very well this time despite only cutting about 10 thou. I'll hone it before doing the next few bodies. But it's obvious which one of these is destined for opaque lacquer.

7AF12570-7652-4D2C-B28E-C9B55E16DD05_1_105_c by Sean Chaney, on Flickr

[j44ke]

This is kind of mind boggling. And visual. Too bad it gets put in a box.

[ColonelJLloyd]

Wow. Great thread.