2nd Build-Rob's JTM45 Micro

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

Tags:
  1. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    836
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    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.
     
    D'tar, robrob and willholt92 like this.
  2. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    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. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    836
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    Well... With the aluminum chassis, the height seems not to be important. The slight tilt is.
     
    willholt92 and robrob like this.
  4. BigDaddy23

    BigDaddy23 Tele-Holic

    Age:
    47
    Posts:
    675
    Joined:
    Jan 4, 2019
    Location:
    Australia
    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.
     
    willholt92 likes this.
  5. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    836
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    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. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    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. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    836
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
  8. BigDaddy23

    BigDaddy23 Tele-Holic

    Age:
    47
    Posts:
    675
    Joined:
    Jan 4, 2019
    Location:
    Australia
    @willholt92 - of course, it is a head, not a combo. The internal washers are a good idea.

    Play on, gents.
     
    willholt92 likes this.
  9. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    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. Paul-T

    Paul-T Tele-Holic

    Posts:
    635
    Joined:
    Nov 23, 2018
    Location:
    London
    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!
     
    willholt92 likes this.
  11. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    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
     
    Paul-T likes this.
  12. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    Slight update.

    Happy new year all.

    It's been a long time since I've posted any updates on my threads.
    I bought my first house last year and completed at the end of November and have worked on it everyday since doing renovations which has ended up being every single room in the house. We are starting to see the light at the end of the tunnel so I'm hoping I might have a little more time to spend on my guitar and amp projects, even more so when I get my shed/worshop set up.

    Anyway I've been back lurking on Shock Brothers the last week or so and thought I'd give a bit of an update after seeing @D_Hallett 's JTM micro thread.

    I had a change of heart for my speakers and cab, I've always wanted to get an alnico speaker to have in a cab and a mate of mine sent me a facebook listing which I couldn't pass up.

    So I have ended up with these beauties, bought locally only a couple months old for a bargin £150. So the Greenback has gone in favour of these.

    IMG_2877.JPG

    IMG_2878.JPG

    I had a play around with some more cabinet designs to use the 2 x 10" Celestions, including a bluesbreaker style.

    Capture.PNG cabs 4.PNG

    But it was around the same time last year that Marshall launched the Studio Vintage series amps and as soon as I saw the SV212 I knew it had to be a vertical 2x10 in a similar style.

    So I've settled on the below design for the head and cab. I've sourced the cabinet handles and some other parts ready.

    2x12.PNG

    Head Front.PNG


    I've also decided I'm going to have a switch to choose between Valve and Diode rectifier to see how this changes the sound, I think it will be quite nice to have a more JTM 45 option and a more JMP hopefully. Probably won;t make much difference but it's there anyway.

    3 way NFB may also make an apperance on the back panel.

    Head Rear.PNG

    That's all for now, I will get more into the build at some point this year I promise haha
     
    robrob and D_Hallett like this.
  13. D_Hallett

    D_Hallett TDPRI Member

    Age:
    40
    Posts:
    20
    Joined:
    Jan 20, 2021
    Location:
    Alberta, Canada
    The head and cab design look awesome! Can't wait to see more!
     
    willholt92 likes this.
  14. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    Thank you, excited to see yours develop too. Although I feel yours will be done a lot sooner than mine.
    I'll be keeping an eye on it, your last post is something that I've been wondering about myself, so looking forward to any replies.
     
    robrob and D_Hallett like this.
  15. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    Some progress.

    Finally had some time with my engineer to draw up the chassis last week for an hour or so.
    Will be going for 2mm aluminium this time rather than stainless steel, not only is it lighter and I've read that it is beneficial in terms of noise, but it's also a hell of a lot easier to work with.

    1.PNG



    2.PNG

    Back panel with Fuse, IEC socket, Rectifier switch, speaker and headphone outputs. I was thinking about having a impedence selector like a proper Marshall but I don't think you can use the 125B output transfer to give 4, 8 and 16ohm output? Unless someone knows if you can.

    3.PNG

    Still need to work out positions for valve sockets, I am thinking that I will leave the transformer mounting points and wire holes until I have the chassis, I can easily do this with the pillar drill and give me a bit more freedom if things need to move around a little, it's already looking a little tight.

    I've decided I'm going to take the V1A grid stopper resistors off the board and solder them directly to the V1 socket, I've bought some shielded wire to go from the input jacks. I remember reading that Metal film resistors are better for this application is that right?

    I have also been thinking about my 2 inputs and how I can make them a little bit different? I was wondering if I could have different value cathode bypass caps for each one but from my reading that won't work with out a switch.

    Would a different value grid stop resistor have much of an effect? I'm thinking maybe 1 input more suited to single coil and one more for humbuckers?
     
  16. Tom Kamphuys

    Tom Kamphuys Tele-Holic

    Age:
    41
    Posts:
    836
    Joined:
    Sep 18, 2018
    Location:
    The Netherlands
    Metal film resistors have low noise and the input gridstopper is most important as signal levels are still low.

    Grid stoppers form a low pass filter with the Miller capacitance of the tube. Normally input grid stoppers are chosen to have no influence in the audible range.
     
    willholt92 likes this.
  17. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    Ah right okay, that's great thank you very much.
     
  18. willholt92

    willholt92 Tele-Meister

    Age:
    29
    Posts:
    248
    Joined:
    Jun 13, 2019
    Location:
    Sheffield UK
    Small update

    I've been waiting to hear back from multiple laser cutting suppliers to try and get my chassis cut and folded, it seems everyone here in the UK is crazy busy at the moment, I'm hoping to hear back and get the chassis in the next couple weeks all being well.

    In the mean time I finalised my board design, I drew out all the wiring in illustrator to finalise the hole positions for the board.
    I then printed the layout, punched and drilled all the holes in the board and installed the turrets.

    Looking forward to progressing on this amp when I get the chassis.

    chassis and plates.PNG

    Chassis layout and wiring.PNG

    IMG_1105.jpg

    IMG_1141.jpg
     
    robrob and owlexifry like this.
  19. Mad Kiwi

    Mad Kiwi Friend of Leo's

    Posts:
    3,368
    Joined:
    Nov 17, 2009
    Location:
    Land of the Long White Cloud
    Looks awesome!
     
    willholt92 likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.