Design Review: Amplifier

Planned design

For this final project, I am planning on designing and constructing a lunchbox tube amplifier. I am planning on using two 12AX7 preamp tubes and a single EL84 power tube in class A operation to put out approximately 6 watts of power. There will be high and low channels that can be used independently or in parallel for more preamp distortion, as well as a Baxandall tone stack and a master volume. Other creature comforts will include an effects loop, switchable impedance, paralleled speaker outputs, and a standard removable power cable.

Proposed block diagram
Proof of concept for an 8″ x 6″ x 2″ chassis

In designing the control scheme, I used an 8″ x 6″ x 2″ chassis size (Hammond 1444-862) for reference, which seemed reasonable enough at the time. However, immediately after constructing the model of the chassis, it became apparent that I would need way more room. More height is necessary as the controls barely fit, and that leaves little room for labels. More surface area will also be necessary as I need more room to fit both of the transformers I’ll need as well as to comfortably fit the PCB. I want to aim for a sort of “open” design on the inside for ease of servicing, so more room is always better.

The rear of the amplifier minus the effects loop, since I ran out of jacks

Other than that, I’m relatively content with the control layout and block diagram, so I just need to get working on the schematic and grab a larger chassis. Out of the available chassis produced by Hammond, 1444-10825 would likely be a much more usable size at 10″ x 8″ x 2.5″.

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8 Comments. Leave new

Hi Gabe,
I really like how practical your project idea is! You seem very passionate about the construction of this amplifier and you seem to have a pretty strong understanding of the electronics involved. I’m super excited to see your final result!

Reply
Alexis Nibbelink
March 15, 2019 1:38 pm

I love this idea. Your presentations was very well thought out. And good job on the prototype. I’m glad you’re getting to build something you’ve been wanting to.

Reply
Andrew Oliver
March 15, 2019 1:38 pm

Hello Gabe, I think its really cool that you are designing your own amplifier. You clearly put a lot of time and effort into this, great job!

Reply
Chris Mcfadden
March 15, 2019 1:38 pm

You prototype is next level cool! I love how the knobs turn. Great that you made it to scale and figured out that your initial chassis design was too small.

Reply
Jordan Nahabetian
March 15, 2019 1:37 pm

It’s obvious that you’ve put a lot of thought and planning into your project. You have great skill and ambition so it might be good to pace yourself and consider the scope of the project as you continue.

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I am very impressed with the sophistication of your project! You put in a substantial amount of work already and it seems like you are ready to build. Your project seems like a handful, but one that you can certainly handle. It is also evident that you have a lot of knowledge in terms of amps, so I am looking forward to a quality product!

Reply
Abdulrahman Alnoaim
March 15, 2019 1:36 pm

Gabe,
Your initial sketches are detailed and well designed. It is really impressive how you sketched every aspect of the project on paper. Great job!

Reply
Tanner Wismer
March 15, 2019 1:36 pm

This is a really interesting and challenging project you have taken on. It looks like you have experience doing something like this before. Your sketches and plan seem really thought out and seems like you know what you are doing. Your prototype is very professional and allows a good visualization of the final product. Good luck on making your amplifier!

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