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Thread: Winter Project: Guitar Amplifiers

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    Default Winter Project: Guitar Amplifiers

    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
    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: Winter Project: Guitar Amplifiers

    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.
    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: Winter Project: Guitar Amplifiers

    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.

    Last edited by j44ke; 02-10-2020 at 10:42 PM.
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    Default Re: Winter Project: Guitar Amplifiers

    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.

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    Default Re: Winter Project: Guitar Amplifiers

    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.

    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: Winter Project: Guitar Amplifiers

    Nice! That is some super tidy work there.

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    Default Re: Winter Project: Guitar Amplifiers

    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 70oC. 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.

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    Default Re: Winter Project: Guitar Amplifiers

    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.
    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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    Default Re: Winter Project: Guitar Amplifiers

    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.

    Sean Chaney
    www.vertigocycles.com
    a peek behind the curtain

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