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2nd Build-Rob's JTM45 Micro

Discussion in 'Shock Brother's DIY Amps' started by willholt92, Jun 1, 2020.

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  1. Jul 12, 2020 #21
    Tom Kamphuys

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    I just did the headphone check myself, now on the actual aluminum chassis instead of some wooden template.

    IMG_20200712_125120285_HDR.jpg IMG_20200712_125109424_HDR.jpg

    Clearly audible hum. Equal for both orientations.

    IMG_20200712_125217966_HDR.jpg

    Dead quiet.
     
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  2. Jul 12, 2020 #22
    willholt92

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    Wow that's intereting. So spacing the OT off the chassis with a few washers to raise it would be beneficial. I'll bare that in mind.
    Thanks for the tip
     
  3. Jul 12, 2020 #23
    Tom Kamphuys

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    Well... With the aluminum chassis, the height seems not to be important. The slight tilt is.
     
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  4. Jul 12, 2020 #24
    BigDaddy23

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    Bizarre! Did you try rotating it (whilst listening) from position 1 to position 2 in your photos? How you thinking about achieving the 'tilted' position whilst still making sure it is structurally strong and wont stress the chassis? I'd be concerned about damage to the aluminium chassis around the screw hole locations.
     
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  5. Jul 13, 2020 #25
    Tom Kamphuys

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    Listening while rotating around the vertical axis didn't change the hum a lot.

    I'm still not sure where to put the OT. A bit further away also helps. Will also help against the yet unknown choke influence. I'm a bit afraid of coupling of the output current to the circuit inside the chassis.
    It crossed my mind that I could attach the OT to a small plate which was then attached to the chassis with four bolts, but not resting on the chassis, but on nuts. One could then change the tilt by adjusting the nuts. Even after the amp is complete.
    I decided to let it rest for a while, because I feel my overthinking kicking in.
     
  6. Jul 13, 2020 #26
    willholt92

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    To be honest in a "head" IE transformers sitting on top of the chassis I can't see it being an issue the bolts won't really stress the aluminium due to the transformers weight sitting on the aluminium surface.
    If the transformers are hanging from the chassis IE in a combo maybe more so, I'd put a large steel washers under the head of the screw inside the chassis to spread the load.
    2mm aluminium will be pretty strong though as long as you are using decent sized bolts I can't see there being much of an issue.
     
  7. Jul 13, 2020 #27
    Tom Kamphuys

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  8. Jul 13, 2020 #28
    BigDaddy23

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    @willholt92 - of course, it is a head, not a combo. The internal washers are a good idea.

    Play on, gents.
     
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  9. Aug 6, 2020 #29
    willholt92

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    I've been busy with a few other things the past month and not spent much time on the JTM micro.

    So while my Mrs and the little one are away this week I've made a start on the cabinet after work.

    Cut some 12mm (15/32") plywood for the sides and top and bottom.

    I made a finger joint jig using pine 18mm x 32mm glued together and will use a flush cut router bit and the opposite sides to make some finger joints. I saw someone make one of these on Youtube and it is a really neat idea so hopefully I can get some good results with it.

    On the plus side I got the plywood for free as an off cut from work so free cab up to now.

    IMG_1869.JPG

    IMG_1870.JPG IMG_1871.JPG IMG_1872.JPG IMG_1872.JPG IMG_1873.JPG

    Still not got into designing the chassis yet unfortunately but hopefully in the next week or so. Amazing how much time a 10 week old takes up on top of working.
     
  10. Aug 6, 2020 #30
    Paul-T

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    wow, that's impressive (and saves the $80 etc for a template i paid).

    You'll use a template flush router bit ? How do you control the depth? Do post pix when you're doing it!
     
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  11. Aug 7, 2020 #31
    willholt92

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    I know I couldn't bring myself to spend some much on a proper template and I liked the idea of this DIY version.

    Yeah that's the plan I bought a couple flush router bits and I'll just have to try and set the depth of the router, but as the ply is only 12mm it shouldn't be too bad. Hopefully the bits will be long enough, if not I'll probably try and cut the jig down with the band saw worst case scenario.

    I'll take some photos when I do it, I'm going to test it with a few off cuts first
     
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