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

Moderators: Slowy, Capt. Black

User avatar
BY GrantB
#808024
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
User avatar
BY Optical
#808033
jvpp wrote:
Yes, but Amplified Parts don't stock it.... Will call Brian tomorrow and hopefully GrantB can get some more info from his guy re transformers as well.

More importantly, is the pricing acceptable or does it look expensive? I found AP very reasonable for previous purchases...


Prices look within ballpark.
FYI you get free shipping from Digikey and Mouser if you spend over ~NZ$65 and the 1760E for example is about $70. I cant imagine AP being cheaper than the wholesalers but I havent cross referenced... But I would recommend just ordering from wherever has the ideal parts rather than making a compromise like limiting your output impedance options.
User avatar
BY jvpp
#808064
RectifiedAmps wrote:How's the noise level on the original amp? There's certainly room for improvement in the grounding scheme, but it's not a complex circuit so it might not be worth it unless it has a noticeable hum. Assuming you have a centre-tap on the heaters/filaments in the DIY build, you could elevate it onto the EL84 cathodes to cut down some noise, but again- might not be necessary. Personally, I try to avoid multi-cap cans whenever possible and use separate capacitors instead - you can physically locate and ground them closer to the nodes they're feeding, which makes things tidier and usually quieter, too. Individual caps are also cheaper and easier to source, too.


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.
User avatar
BY jvpp
#808068
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.
User avatar
BY jvpp
#808071
calling card wrote:Have you a photo of the faceplate?


Will post frontal shot

Spoke to Brian the winder but he needs more info on trannies. He was going to talk to Clarry so I said I will visit Clarry as I he lives 10 minutes away from me.

Requesting permission from Slowy to take amp to Clarry (if he asks) so he can cast his magic eye on it.
User avatar
BY jvpp
#808072
Optical wrote:
jvpp wrote:
Yes, but Amplified Parts don't stock it.... Will call Brian tomorrow and hopefully GrantB can get some more info from his guy re transformers as well.

More importantly, is the pricing acceptable or does it look expensive? I found AP very reasonable for previous purchases...


Prices look within ballpark.
FYI you get free shipping from Digikey and Mouser if you spend over ~NZ$65 and the 1760E for example is about $70. I cant imagine AP being cheaper than the wholesalers but I havent cross referenced... But I would recommend just ordering from wherever has the ideal parts rather than making a compromise like limiting your output impedance options.


I started off with doing the BOM with Digikey but struggled finding the parts. Will try again and search for 1760, etc

The only one Digikey has in stock now is this one (125E) which I think will work:
https://www.hammfg.com/electronics/tran ... /125a-125e
User avatar
BY Optical
#808099
Really? Mouser and Digi each show 13 in stock for me...
https://nz.mouser.com/ProductDetail/Ham ... VEHA%3D%3D
https://www.digikey.co.nz/product-detai ... ND/2358167

Those AP silver mica and coupling caps look very cheap actually. Just be aware they will likely be china components. This may or may not be a bad thing, but compared to name brand caps they are a fraction of the price. I doubt the Jansen parts are of any particular quality either though so *shrug*
User avatar
BY Optical
#808105
JHorner wrote:Ignorant question:

More easy or more difficult to mod another Jansen to the 4/12 spec?

https://www.trademe.co.nz/music-instrum ... 966286.htm


More difficult from a sense that the circuit is PCB built. Gain stages are not hard to reconfigure but the phase inverter would be tough to rewire neatly and we suspect the PI is a not negligible part of the tone of the 4/12. You'd be better off gutting and building a point to point amp inside that chassis, but you'd destroy a perfectly good amp in the process
User avatar
BY Slowy
#808123
calling card wrote:Have you a photo of the faceplate?

IMGP0006.JPG
User avatar
BY Slowy
#808124
jvpp wrote:
RectifiedAmps wrote:How's the noise level on the original amp? There's certainly room for improvement in the grounding scheme, but it's not a complex circuit so it might not be worth it unless it has a noticeable hum. Assuming you have a centre-tap on the heaters/filaments in the DIY build, you could elevate it onto the EL84 cathodes to cut down some noise, but again- might not be necessary. Personally, I try to avoid multi-cap cans whenever possible and use separate capacitors instead - you can physically locate and ground them closer to the nodes they're feeding, which makes things tidier and usually quieter, too. Individual caps are also cheaper and easier to source, too.


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.

With the volume off, there is a noticeable low frequency hum. Turn the volume up to 4 or 5 and it goes away.
User avatar
BY RectifiedAmps
#808151
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.
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