Easy-open back panel on amp head... hinges? Magnets? Clips? etc

TJT1979 · May 2023

I am building the box for my Ampmaker N5X kit which is ready to go.

I was thinking of making the back panel tool-free to open. Any ideas for latches? Hinges? Clips? etc. I don't mind the panel swinging open like a door or coming off completely.

I have some small magnets which would probably work well... not sure if the magnetic field would have any detrimental effect on anything (I doubt it but any advice welcome!!)

Cheers!

thermionic · June 2023

The little Vox amps (DA-5, Mini 3 etc.) have a back panel attached with velcro (for access to the battery compartment). It’s pretty sturdy and solid, although obviously the dimensions are smaller than what you have in mind.

Funkfingers · June 2023

Quick and easy access to potentially lethal voltages? As Sgt. Wilson would say to Capt. Mainwaring, "do you think that's wise, sir?"

DannyP · June 2023

Do you plan to gig it at venues?

I'm not an expert, but if your solution fails the visual inspection part of a PAT test and you use it without the magic sticker, it would probably invalidate the venue's public liability insurance.

elstoof · June 2023

Funkfingers said:

Quick and easy access to potentially lethal voltages? As Sgt. Wilson would say to Capt. Mainwaring, "do you think that's wise, sir?"

Surely they mean a back panel panel for accessing the valves like most amp heads have, rather than internal wiring?

Neilybob · June 2023

I have a Panama 1x12 cab with latches that works well opened or closed and totally tool free. This one is similar.

Panama 1x12 Speaker Cabinet w/ Built-In Attenuator https://reverb.com/item/9944856?utm_source=android-app&utm_medium=android-share&utm_campaign=listing&utm_content=9944856

BillDL · June 2023

The cheapest is probably low profile aeroplane toilet door surface mount sliding catches, but you still have something poking out the back to catch on things and I'm not sure you would want "vacant" or "engaged" showing.

Old style cupboard door "roller catches" might work and would involve minimal work to fit them:

Image: https://tfb-user-images.eu-central-1.linodeobjects.com/fca37f7f7c0d04abde61860a63b5f50c23273ee4753b45a7b9

An alternative and cheap option is your typical guitar case or briefcase type "drawbolt catch" or "toggle catch" that is more flush. You can get toggle catches in all sorts of shapes and sizes, from cheap pressed metal to stronger and more industrial.

[EDIT] I hadn't seen the post by @Neilybob about his cabinet, but it uses toggle catches on the back panels:

Perhaps overkill, but a dished "butterfly catch/latch" as found on flightcases will sit flush because you need to countersink it. I have a 1 x 12 "closed" speaker cabinet that I sometimes like to be half open back. I cut the back panel into two pieces, jointed them with a full-width piano hinge, secured the bottom portion to the cabinet with screws, and fitted a small butterfly latch to each side of the upper fold-down section. It entailed a bit of carving out of the plywood back panel for the main large part of the latch and gluing extra blocks to the sides of the cabinet to screw the smaller part of the latches to, but it's nice and rigid and doesn't vibrate. I think you can also get surface mount butterfly latches, but that would defeat the point of having a butterfly latch as opposed to the cheaper methods above.

I don't think you would be able to rely on weaker magnetic contacts. Much stronger neodynium coin-sized ones would be a lot more secure but they would have to secured very strongly to both sides. As to magnetic field causing issues with the amp, I really don't know about that aspect.

elstoof · June 2023

The tried and tested screw with a finish washer is the best bet imo, you should only need access once in a blue moon anyway

TJT1979 · June 2023

Wow, thanks for so many replies. I'll address a few...

- yes, I am talking about the back panel which gives access to the valves. I'm thinking of tool-free valve changes during a gig (never happened so far!)
- this will be gigged but the PAT regulations are not relevant as I live in Argentina. The amp has been well-built and properly tested so I'm' not worried!
- Those latches seen on the Panama amp would work but they're a bit heavy duty for this use (bulky and heavy)
- Roller latches are a good idea... I reckon they'd rattle but worth further thought.
- Velcro doesn't convince me much as a solution to anything (even my pedalboard is velcro-free)

The magnets I have are neodymium washer-style with a hole in the middle for a screw to pass through. They would be plenty strong enough. My only doubt is the magnetic field mentioned earlier. This whole thing is on top of a speaker with a huge magnet so I would guess there'd be no issue, but the magnets would be near the power transformer on one side, and fairly near the (shielded) V1 preamp valve on the other side.

BillDL · June 2023

Perhaps on the potential issue of magnets near amp components it would be wise to attract the attention of a few other experts in this field that may not have already seen your question eg. @ICBM ; @ecc83 ;; @Modulus_Amps ;;

TJT1979 · June 2023

Thanks @BillDL !

digitalkettle · June 2023

BillDL said:

Perhaps on the potential issue of magnets near amp components it would be wise to attract the attention of a few other experts in this field...

I see what you did there @BillDL ;!

ICBM · June 2023

Magnets will only be an issue if they're *very* close to the valves. After all, most combos have a large speaker magnet very close to them... so far I've only ever come across one issue, which was a Fender '57 Twin (I think - from memory) which caused a problem with some types of preamp valve in a position where the speaker magnet was almost touching the valve. A steel, rather than the usual aluminium, shielding can seemed to solve it.

TJT1979 · June 2023

Thank you @ICBM, that’s really helpful. There would be probably ~10cm between magnets and V1, so it sounds like I should be OK. There’s probably 2cm from magnets to the output transformer, at the other end of the panel.

Modulus_Amps · June 2023

I have used these neo magnets before, they are encapsulated in rubber which stops them corroding and gives a softer close and being Neo they have strong pull strength in a small size.

Type A

https://magnetsales.co.uk/products/office-magnets/

Magnetic strength decrease in distance in a inverse exponential curve, meaning that a small change in distance greatly reduces the pull strength/magnetic field. Just keep them away from valve and transformers and you should be fine.

Fit little ribbons loops to put your fingers through to pull the panel out.

Image: https://magnetsales.co.uk/wp-content/uploads/2016/10/Gripfast-image-e1477650345161.jpg

TJT1979 · June 2023

Thanks @Modulus_Amps ;

One end of the panel would have the magnets ~2cm from the toroidal output transformer. From what you said, this sounds like it may be an issue? If so I'll just go with boring screws.

At the other end, V1 is probably 8-10cm from where the magnets would go.

ICBM · June 2023

TJT1979 said:

One end of the panel would have the magnets ~2cm from the toroidal output transformer. From what you said, this sounds like it may be an issue?

No, it won’t make any difference to the transformer.

TJT1979 · June 2023

Thank you again @ICBM ;

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Easy-open back panel on amp head... hinges? Magnets? Clips? etc

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