is there a reason you chose to sink so much current through the divider? 100k power resistors seem hard to find for me locally, my local shop only does 5w power resistors to 40k
would resistor choice values suitable for half or quarter watt resistors still function properly for this purpose?
im thinking 680k/150k so that way 1/4 watt resistors could be used? or is there stability issues with such high resistance?
would resistor choice values suitable for half or quarter watt resistors still function properly for this purpose?
im thinking 680k/150k so that way 1/4 watt resistors could be used? or is there stability issues with such high resistance?
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yea, 1 watt isnt that much, but i was looking at it from a materials avail point of view. i dont like largely overloading resistor dissipation rating, so 1/4 or 1/2 watt resistors dissipating 1.2 watts isnt any good
i depend on my tubes to suck my power supply dry, and always measure my capacitors before doing anything.
but back to the heater issue, would 680k/150k with a 47uF capacitor across the 150k be acceptable?
i depend on my tubes to suck my power supply dry, and always measure my capacitors before doing anything.
but back to the heater issue, would 680k/150k with a 47uF capacitor across the 150k be acceptable?
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Hi!
Thomas
Bad idea, in case your heater supply fails, they won't draw any currentt
As I wrote above already. Try it.
Thomas
it seems to have helped but not fully eliminated the hum. used meter in current measuring mode for initial hookup, it doesnt seem to draw any current so thats not a issue used a 10 uF capacitor
the filament wires are reading 64v and 76v so the circuit is working properly indeed =)
one step closer to perfection in any case
the filament wires are reading 64v and 76v so the circuit is working properly indeed =)
one step closer to perfection in any case
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Now that filaments are mostly ruled out guess we are back to b+ filtering changes again huh. Ill have to fiddle with that later
you might be onto something Gregg. its in theory safe for the rectifier to go do 47 uF going by psu designer, the rectifier can handle 4 amps single cycle. gets close but not quite but ripple in C1 is way lower.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I think you may have to add another filter section for the 12au7's, either a resistor then cap or choke then cap. You could try choke resistor cap. If you can get enough voltage drop before the 12au7's to get below the ripple level. If all else fails electronic choke or regulator.
Regards
M. Gregg
Regards
M. Gregg
Very efficient, using heater off set voltage divider as B+ bleeder. Great idea!
Regards
M. Gregg
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Note the ripple on C4 on the first graph on the left margin. this setup looks good? it comes at the price of a hell of a lot of inrush. good thing rectifiers come up slowly
An externally hosted image should be here but it was not working when we last tested it.
Rectifier is rated for 5 amps single cycle so its ok i guess
after rebiasing my amp for higher B+ from higher first filter capacitance the hum is even better. cant hear it unless you get within 8 inches of the speaker and sub needs to be turned past 50% to even start to hear it
thank you everyone for helping me get some ideas as to how to fix my amp's hum problem.
i might some time get motivated to install that second inductor but at this moment there is not enough need for me to figure out how to place it, and tear apart my b+ supply
better question is why does C1 ripple matter so much... could the pulses being induced on the transformer be coupling to the chassis? maybe the simulation isnt quite real to life.... stuff to think about.
one question i have is i heard people like to bypass there filters with polypropylene. have you got a chance to play with that yet Gregg?
thank you everyone for helping me get some ideas as to how to fix my amp's hum problem.
i might some time get motivated to install that second inductor but at this moment there is not enough need for me to figure out how to place it, and tear apart my b+ supply
better question is why does C1 ripple matter so much... could the pulses being induced on the transformer be coupling to the chassis? maybe the simulation isnt quite real to life.... stuff to think about.
one question i have is i heard people like to bypass there filters with polypropylene. have you got a chance to play with that yet Gregg?
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Something that does help,
Put an in rush current suppressor in series with the primary of the power Tx. They drop in resistance as they warm up. It wll help protect your supply. You need minimum 40 Ohm start up resistance, some start at 100ohm and work well!
Regards the choke bypassing and resonant choke supply. I have tried a few things, however I have not had much time to play, so it's still on going!
Regards
M. Gregg
Put an in rush current suppressor in series with the primary of the power Tx. They drop in resistance as they warm up. It wll help protect your supply. You need minimum 40 Ohm start up resistance, some start at 100ohm and work well!
Regards the choke bypassing and resonant choke supply. I have tried a few things, however I have not had much time to play, so it's still on going!
Regards
M. Gregg
Resonant choke would require very percise current tuning wouldn't it? Due to cap behavior
Havent tried out poly caps yet I assume?
Reviewing the rest of the thread I kind off like your idea of using shielded wire for audio path. Looking real fast the trick/catch tho its finding 600v+ rated shielded wire at small quantity
I have noticed that,
The sound of a system changes when you put caps across the choke in a supply, However not tried with tube rectifiers. Yes I have used polyester and polypropylene 0.047 and 0.1uF. YMMV.
I just use the caps to "damp" the resonance! Not trying to get a true resonant choke linked to frequency of supply. This is still an interest I am playing with!
Regards screened cables,
I tend to use PTFE silver plated copper and cover with tin foil, wrap a drain wire arround it and connect to Gnd" none insulated to Gnd the foil - cover with heat shrink! Give a gap at least 3-5mm from the end of the cable insulation.
This is only on signal cables to grid. Capacitors act as an open circuit regards hum pick up. If they are by heater supplies then you will get hum!
I also screen these in the same way as the cable "foil & drain wire"! Just wrap with masking tape! you can tell if caps are picking up by holding a meter probe by them and see if the hum increases! These are just a few ideas I use! Obviously all inputs should be screened, you can even make twisted pairs and screen in the same way!
The way to go is work on one channel and if you get improvement do all channels!
Regards
M. Gregg
The sound of a system changes when you put caps across the choke in a supply, However not tried with tube rectifiers. Yes I have used polyester and polypropylene 0.047 and 0.1uF. YMMV.
I just use the caps to "damp" the resonance! Not trying to get a true resonant choke linked to frequency of supply. This is still an interest I am playing with!
Regards screened cables,
I tend to use PTFE silver plated copper and cover with tin foil, wrap a drain wire arround it and connect to Gnd" none insulated to Gnd the foil - cover with heat shrink! Give a gap at least 3-5mm from the end of the cable insulation.
This is only on signal cables to grid. Capacitors act as an open circuit regards hum pick up. If they are by heater supplies then you will get hum!
I also screen these in the same way as the cable "foil & drain wire"! Just wrap with masking tape! you can tell if caps are picking up by holding a meter probe by them and see if the hum increases! These are just a few ideas I use! Obviously all inputs should be screened, you can even make twisted pairs and screen in the same way!
The way to go is work on one channel and if you get improvement do all channels!
Regards
M. Gregg
sounds like you have been doing quite a bit of experimenting with hum.
guess im fortunate that 90% of my hum has been traced to power supplies. with the 47uf electrolytic across my 10uF PIO my hum is basically gone! and a little more B+ for my 807's to boot! i consider the current state of my amp to be near-ideal. needing to have your ear within 8 inches of a speaker driver to hear hum is pretty good in my book.
my guess tho -- i have eliminated all of my power supply ripple related hum, and heater>cathode hum is certainly gone however from experimenting with my amp when i was assembling it, i have noticed that especially as a hanging open circuit, the signal wire leading from my input to the first tube are extremely sensitive to any kind of RF, give me a minute and ill trace my signal path, see what you think are 'problem' spots, i think i understand what your talking about tho. All signal path including inter-stage coupling capacitors? your multimeter probe trick. what are you connecting the other end to?
would be nice to find some shielded ~22AWG wire but your aluminum foil idea sounds great for diy
need to make some high quality shielded cables for my analog input from my sound card too
gosh from straight on my wiring looks like a mess! i however except for ground and b+ paths which i tried to lift slightly from my chassis, i used minimum length wire and mostly crossed every wire perpendicularly, although on the other hand, i have a lot of wiring that had to be done in a small area, not much room for neat and tidy, some high end amp pictures made from back in the day certainly look worse then mine!
have you got your hum levels to the point that you basically cant hear it over background noise yet? my sub channel only hums if i turn the self-powered sub past 50% so its pretty decent already
most interesting thing about the hum out of my speakers, when you get close enough to hear it -- the 'tone' changed. its more like a 'bzzzzzzzzz' not a 'hmmmmmm' now
guess im fortunate that 90% of my hum has been traced to power supplies. with the 47uf electrolytic across my 10uF PIO my hum is basically gone! and a little more B+ for my 807's to boot! i consider the current state of my amp to be near-ideal. needing to have your ear within 8 inches of a speaker driver to hear hum is pretty good in my book.
my guess tho -- i have eliminated all of my power supply ripple related hum, and heater>cathode hum is certainly gone however from experimenting with my amp when i was assembling it, i have noticed that especially as a hanging open circuit, the signal wire leading from my input to the first tube are extremely sensitive to any kind of RF, give me a minute and ill trace my signal path, see what you think are 'problem' spots, i think i understand what your talking about tho. All signal path including inter-stage coupling capacitors? your multimeter probe trick. what are you connecting the other end to?
would be nice to find some shielded ~22AWG wire but your aluminum foil idea sounds great for diy
need to make some high quality shielded cables for my analog input from my sound card too
An externally hosted image should be here but it was not working when we last tested it.
gosh from straight on my wiring looks like a mess! i however except for ground and b+ paths which i tried to lift slightly from my chassis, i used minimum length wire and mostly crossed every wire perpendicularly, although on the other hand, i have a lot of wiring that had to be done in a small area, not much room for neat and tidy, some high end amp pictures made from back in the day certainly look worse then mine!
have you got your hum levels to the point that you basically cant hear it over background noise yet? my sub channel only hums if i turn the self-powered sub past 50% so its pretty decent already
most interesting thing about the hum out of my speakers, when you get close enough to hear it -- the 'tone' changed. its more like a 'bzzzzzzzzz' not a 'hmmmmmm' now
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Quote:
have you got your hum levels to the point that you basically cant hear it over background noise yet?
At night in the quiet I can not tell if its switched off or on. I struggle to hear any hum with my ear touching the speaker cone.
Regards using the multi meter probe just leave it connected to the meter if you put it close to a cap or touch the side if it, if its picking up the hum will get louder. The sound of your hum change is probably pick up from the cables or components.
Regards
M. Gregg
have you got your hum levels to the point that you basically cant hear it over background noise yet?
At night in the quiet I can not tell if its switched off or on. I struggle to hear any hum with my ear touching the speaker cone.
Regards using the multi meter probe just leave it connected to the meter if you put it close to a cap or touch the side if it, if its picking up the hum will get louder. The sound of your hum change is probably pick up from the cables or components.
Regards
M. Gregg
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