Amp tinkerers and people who aren't afraid of 700 volts or so in here....

Moderators: Slowy, Capt. Black

User avatar
BY jvpp
#808204
RectifiedAmps wrote:
jvpp wrote:Noise floor (hum) is there but not too much. I would be interested to hear how the grounding scheme can be improved. Re individual caps, point taken and will modify the BOM.


Ok, here's what I would do:
Jansen-4twelve-R1_GND.png


There should be three earth connections (to the chassis) - the earth wire from the mains lead/IEC socket (for safety), the output transformer secondary and the grounding bus from the rest of the circuit. The OT can be earthed to the chassis at the speaker jack for convenience - shouldn't cause any issues in this design. The mains wire can be connected to chassis near where the cable/IEC socket enters the chassis for convenience (use a separate, dedicated nut/screw and not a transformer bolt or other mounting bolt).

The audio grounding/power supply bus should only be connected to the chassis at one end - the input jack is a good place, provided you're using a metal switchcraft style jack. Or you can just solder/bolt the end of the bus wire to the chassis as close to the input jack as possible. Keep all the same-coloured grounds as close together as possible - don't worry about it too much, but at least try to keep them in the proper order. It probably won't matter as much where you ground the cathode resistor of the power tubes - you could just attach it to the chassis next to the valve sockets if that's easiest. Then the heater/filament centre-tap attaches to the EL84 cathodes (pin 3).

This *should* result in a hum/buzz-free build but other build issues like lead dress and stray inductance from the transformers can always muddy the waters.


Wow, that is a very detailed response. Thanks so much. I'll have a look at a turret board layout for this thing to see if it can incorporate your advice. Personally, I like the old fashioned terminal strips approach, looks much more messy which kinda appeals to me :D
User avatar
BY Anvil Amps Alan
#808253
olegmcnoleg wrote:There's a Jansen Bassman on TM for cheaps, if your appetite is whetted...

https://www.trademe.co.nz/music-instruments/instruments/guitar-bass/guitar-amps/listing-1835966286.htm?rsqid=cc5ca7f34a6b45d1b475254aac8f6e51

That chassis has had none of the components replaced.
Maybe a couple of pots, they still look shiny.
Will need some capacitors to get it sounding good.
User avatar
BY Anvil Amps Alan
#808254
True point to point using tagstrip does not have to be messy.
Mine is not.
https://www.facebook.com/Muddlearth/
User avatar
BY GrantB
#808289
jvpp wrote:
GrantB wrote:Some input kindly provided by John.

Some errors possibly? Requires confirmation from Bruce I suspect.

R17-R18 junction to ground.
R7 6K8
C5 47nF
C5 usually 220pF

Just a note, The mains connection must conform to our Electrical regulations
and will need to be tested and certified before powering up and completion.

Also, John suggested John Veldwijk might be able to assist? https://www.facebook.com/john.veldwijk


Thanks, I will change C5 to 220pF, but it looks like he looked at the original circuit in the OP, not the Rev1 I posted later on.
Testing ? Certifying? Assuming I build this, my test will be power it up, no smoke and there is sound then it is certified :wink:

Interesting that name, Jansen receptionist emailed me his contact details and I thought it was spam or so. Will email him.


Hmm, well, I think testing/tagging an amp so it doesn’t smoke your organs is not a bad idea.
User avatar
BY jeremyb
#808299
GrantB wrote:Hmm, well, I think testing/tagging an amp so it doesn’t smoke your organs is not a bad idea.


Obligatory you can smoke my organ any time post :mental:
User avatar
BY jeremyb
#808301
Wow, that looks incredibly time consuming, bravo!
User avatar
BY GrantB
#808302
jeremyb wrote:
GrantB wrote:Hmm, well, I think testing/tagging an amp so it doesn’t smoke your organs is not a bad idea.


Obligatory you can smoke my organ any time post :mental:

Reaching new levels of uncomfortableness daily!
User avatar
BY jeremyb
#808305
GrantB wrote:
jeremyb wrote:
GrantB wrote:Hmm, well, I think testing/tagging an amp so it doesn’t smoke your organs is not a bad idea.


Obligatory you can smoke my organ any time post :mental:

Reaching new levels of uncomfortableness daily!


Stop being so ruggedly good looking then!
User avatar
BY Anvil Amps Alan
#808400
jeremyb wrote:Wow, that looks incredibly time consuming, bravo!

Thanks.
About 80 hours to scratch build AB763 Deluxe Reverb combo finished in cabinet.
Very low noise and hum.
User avatar
BY jeremyb
#808410
Anvil Amps Alan wrote:
jeremyb wrote:Wow, that looks incredibly time consuming, bravo!

Thanks.
About 80 hours to scratch build AB763 Deluxe Reverb combo finished in cabinet.
Very low noise and hum.


That must kill your hourly rate!!
User avatar
BY jvpp
#808560
Last questions then for the valve amp specialists...

What power transformer that can be bought of the shelf do you recommend?
What should the secondary winding voltage output be? (I don't really want HT+ to go over 300V or so).

I prefer an enclosed unit as per original Jansen RedFern.

There are four 240VAC units listed at Amplified Parts:
https://www.amplifiedparts.com/products ... 240%20Volt

And Digikey is too hard to find one.

Thanks
User avatar
BY jvpp
#808564
Optical wrote:Lots of options, I'd probably go with a Hammond 290XEX which give a bit of sag at max volume and put about ~310V on the plates.
https://nz.mouser.com/ProductDetail/Ham ... dV7Q%3D%3D

Those AP transformers will give you around 450V, good for 6L6, EL34 etc, but too high for EL84s.


Thanks, had a look at that one with respect to how it fits on the chassis. The mounting bolts are almost spot on, but this transformer requires a large cutout in the chassis as it is mounted 'sideways'. Not a problem I suppose but it requires a bit of reorganization underneath.
  • 1
  • 4
  • 5
  • 6
  • 7
  • 8