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Re: Jansen 4/TWELVE SPECIAL
Posted: Wed Nov 14, 2018 5:35 pm
by Jay
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
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 5:31 am
by Anvil Amps Alan
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.
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 5:35 am
by Anvil Amps Alan
True point to point using tagstrip does not have to be messy.
Mine is not.
https://www.facebook.com/Muddlearth/
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 9:54 am
by GrantB
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
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.
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 11:22 am
by jeremyb
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
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 11:25 am
by Jay
Neat as! Deserves to be shown...
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 11:35 am
by jeremyb
Wow, that looks incredibly time consuming, bravo!
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 11:35 am
by GrantB
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
Reaching new levels of uncomfortableness daily!
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 12:13 pm
by jeremyb
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
Reaching new levels of uncomfortableness daily!
Stop being so ruggedly good looking then!
Re: Jansen 4/TWELVE SPECIAL
Posted: Thu Nov 15, 2018 12:28 pm
by Jay
You have seen him on the trampoline then?
Re: Jansen 4/TWELVE SPECIAL
Posted: Fri Nov 16, 2018 1:24 pm
by Anvil Amps Alan
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.
Re: Jansen 4/TWELVE SPECIAL
Posted: Fri Nov 16, 2018 3:40 pm
by jeremyb
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!!
Re: Jansen 4/TWELVE SPECIAL
Posted: Sun Nov 18, 2018 9:53 am
by Jay
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
Re: Jansen 4/TWELVE SPECIAL
Posted: Sun Nov 18, 2018 10:56 am
by Optical
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.
Re: Jansen 4/TWELVE SPECIAL
Posted: Sun Nov 18, 2018 11:38 am
by Jay
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.