D.C. filaments
- Thread starter noth
- Start date
Re: D.C. filaments
Probably.
DC filtered heater supplies may make sense for the first couple of preamp stages. Then it becomes a cost vs benefit situation.
Applying a positive voltage to an AC supply will reduce the noise over strict DC operation. Tightly twisting the AC heater leads will further help reduce noise.
But the bottom line - an AC heater supply adds very little noise. Carbon composition resistors add much more hiss than AC heaters add hum.
Probably.
DC filtered heater supplies may make sense for the first couple of preamp stages. Then it becomes a cost vs benefit situation.
Applying a positive voltage to an AC supply will reduce the noise over strict DC operation. Tightly twisting the AC heater leads will further help reduce noise.
But the bottom line - an AC heater supply adds very little noise. Carbon composition resistors add much more hiss than AC heaters add hum.
Vasshu the humanoid typhoon
Unseen
Re: D.C. filaments
DC poweramps....not for any hack to build!!
That takes skill!!
Plus they are very uncoloured soundwise.
DC poweramps....not for any hack to build!!
That takes skill!!
Plus they are very uncoloured soundwise.
noth
New member
Re: D.C. filaments
Uh-huh...interesting.
Speaking of carbon comp. resistors, do they make the amp hiss that bad? And can you describe what they do for the tone?
Thx,
Noth
Uh-huh...interesting.
Speaking of carbon comp. resistors, do they make the amp hiss that bad? And can you describe what they do for the tone?
Thx,
Noth
Rich_S
HomeGrownToneBrewologist
Re: D.C. filaments
Filament hum is a non-problem that's mostly solved long before you get to the expense of a highly-filtered, regulated, high-current DC heater supply. Simply twisting the heaters supply wires helps a lot. Also, most preamp tubes (12A?7) have their heaters set up so they are humbucking. Similarly, provided you wire the heaters in the proper phase, the hum in one push-pull output will cancel the hum in the other.
About the worst case is a one-tube single-ended output stage, but by making sure the preamp stages are clean, there isn't all that much gain applied to the final stage's hum. Also, elevating the heaters can kill most of it.
Using the hum to cancel itself is a far less expensive means to quiet an amp than eliminating the hum completely from the filament supply.
Filament hum is a non-problem that's mostly solved long before you get to the expense of a highly-filtered, regulated, high-current DC heater supply. Simply twisting the heaters supply wires helps a lot. Also, most preamp tubes (12A?7) have their heaters set up so they are humbucking. Similarly, provided you wire the heaters in the proper phase, the hum in one push-pull output will cancel the hum in the other.
About the worst case is a one-tube single-ended output stage, but by making sure the preamp stages are clean, there isn't all that much gain applied to the final stage's hum. Also, elevating the heaters can kill most of it.
Using the hum to cancel itself is a far less expensive means to quiet an amp than eliminating the hum completely from the filament supply.
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Re: D.C. filaments
Yes they do make the amp hiss like crazy. No they do nothing for "tone" unless you like a hissy amp.
They are by far the cheapest resistors ever made. That's why they were used in vintage amps - for their cheapness, not their tone. Remember, vintage amp makers didn't make their amps the way they did because they knew they would wind up to be vintage amps.
Oh yes, boutique amp makers use them also - due to the hype they have generated about them. Only now they can charge you more for putting them into amps than they ever could in the past.
Yes they do make the amp hiss like crazy. No they do nothing for "tone" unless you like a hissy amp.
They are by far the cheapest resistors ever made. That's why they were used in vintage amps - for their cheapness, not their tone. Remember, vintage amp makers didn't make their amps the way they did because they knew they would wind up to be vintage amps.
Oh yes, boutique amp makers use them also - due to the hype they have generated about them. Only now they can charge you more for putting them into amps than they ever could in the past.
noth
New member
Re: D.C. filaments
This is fascinating, LJ! I agree completely, but coming from hi-fi, I didn't know if carbon comp had some magical sonic signature to them. So would you go so far as to say high quality metal film resistors would sound better, and of course be much quieter?
Noth
P.S. I'm the guy who put the West Labs conductive plastic pots into my guitar - what an improvement (though I know many here are skeptical).
This is fascinating, LJ! I agree completely, but coming from hi-fi, I didn't know if carbon comp had some magical sonic signature to them. So would you go so far as to say high quality metal film resistors would sound better, and of course be much quieter?
Noth
P.S. I'm the guy who put the West Labs conductive plastic pots into my guitar - what an improvement (though I know many here are skeptical).
noth
New member
Re: D.C. filaments
Yes, I've certainly learned here that hi-fi type amp qualities are NOT what guitar amps are about. That said, if LJ is correct (that carbon comp resistors add noise and nothing else), a vintage amp could be improved upon with careful use of today's technology (I know I'll be beheaded for saying that).:scared:
I'd love to see others weigh in on this issue.
Noth
haha - you can't build a full tube amp and ruin it's status by
adding a ss-rectifier for dc filaments
additionally most musicians prefer musical amps, not hifi-like amps
Yes, I've certainly learned here that hi-fi type amp qualities are NOT what guitar amps are about. That said, if LJ is correct (that carbon comp resistors add noise and nothing else), a vintage amp could be improved upon with careful use of today's technology (I know I'll be beheaded for saying that).:scared:
I'd love to see others weigh in on this issue.
Noth
Fresh_Start
New member
Re: D.C. filaments
I have not tried to A/B an amp with carbon composition vs. metal film resistors, but have read a lot about component selection. This article from GeoFX seems to hit the bottom line, and is consistent with a recent thread on component selection over on the Hoffman Amp board (lots of true professionals there).
Short version: carbon comp = hiss and value drift. Might be mojo in spots with large voltage swings like plate resistors. Probably a fire hazard for power tube screen resistors though...
Here's the thread about resistor selection: http://hoffmanamps.com/Forum/yabb2/nph-YaBB.pl?num=1174876636/15#15 Seems like there was a very similar one on 18Watt.com recently too, with the basic conclusion that modern electrolytic caps are probably "better" than bigger, older varieties.
Now all you have to decide is what kind of coupling cap to use... NO consensus there
Chip
P.S. Tying the virtual ground (or center tap) of your heater circuit to an elevated DC voltage does eliminate a lot of hummmmm. That I do have direct experience with. Why bother with a DC filament supply if proper lead dress and a couple of resistors plus 1 cap get you what you need?
Somewhere I got the idea that there are some PCB amps that use DC filament supplies because the heater supplies are on the board with everything else. Must be cost effective in some situations to facilitate board-mounted tube sockets. Saw some photos of the inside of a Champion 600 with a twisted pair of green wires in the air apparently running from the power tube to the preamp tube... heaters maybe?
I have not tried to A/B an amp with carbon composition vs. metal film resistors, but have read a lot about component selection. This article from GeoFX seems to hit the bottom line, and is consistent with a recent thread on component selection over on the Hoffman Amp board (lots of true professionals there).
Short version: carbon comp = hiss and value drift. Might be mojo in spots with large voltage swings like plate resistors. Probably a fire hazard for power tube screen resistors though...
Here's the thread about resistor selection: http://hoffmanamps.com/Forum/yabb2/nph-YaBB.pl?num=1174876636/15#15 Seems like there was a very similar one on 18Watt.com recently too, with the basic conclusion that modern electrolytic caps are probably "better" than bigger, older varieties.
Now all you have to decide is what kind of coupling cap to use... NO consensus there
Chip
P.S. Tying the virtual ground (or center tap) of your heater circuit to an elevated DC voltage does eliminate a lot of hummmmm. That I do have direct experience with. Why bother with a DC filament supply if proper lead dress and a couple of resistors plus 1 cap get you what you need?
Somewhere I got the idea that there are some PCB amps that use DC filament supplies because the heater supplies are on the board with everything else. Must be cost effective in some situations to facilitate board-mounted tube sockets. Saw some photos of the inside of a Champion 600 with a twisted pair of green wires in the air apparently running from the power tube to the preamp tube... heaters maybe?
Re: D.C. filaments
Correct, those are for the heaters.
That's my amp also lol, here's the picture again:
Correct, those are for the heaters.
That's my amp also lol, here's the picture again:
Fresh_Start
New member
Re: D.C. filaments
Not the photos I saw, but thanks for confirming my suspicion. Someone on 18Watt.com took detailed gut-shots.
Off topic: I'm still puzzling over the electrolytic cap in the near, left corner of the board. Could it be a distributed power supply? (only explanation I can come up with short of seeing a layout)
Chip
Not the photos I saw, but thanks for confirming my suspicion. Someone on 18Watt.com took detailed gut-shots.
Off topic: I'm still puzzling over the electrolytic cap in the near, left corner of the board. Could it be a distributed power supply? (only explanation I can come up with short of seeing a layout)
Chip
Re: D.C. filaments
I think my regular camera got stolen so I had to use my cellphone.
Do you have the detailed gut shots? If so link em here.
I think my regular camera got stolen so I had to use my cellphone.
Do you have the detailed gut shots? If so link em here.
Re: D.C. filaments
Not sure if I'm misunderstanding you but the preamp tube sits under that electrolytic.
Not sure if I'm misunderstanding you but the preamp tube sits under that electrolytic.
Rich_S
HomeGrownToneBrewologist
Re: D.C. filaments
Doesn't matter - there are two tube sockets, and they each have one of those electrolytics in their vicinity. Gotta be cathode bias caps.
Take a look at the Soldano SLO gut shot in the link in this thread from earlier today. See all those nice straight, parallel wires connecting all the preamp tubes? See any twisted pairs in there? Care to guess what kind of filament supply Soldano used?
Of course, the added expense of a several-amp, super-clean DC supply for heaters compared to the overall price of an SLO is not a big deal. Same for many PC-board-based 100-watt high-gain monsters. But a DC filament supply would be a major cost contributor in a Champion 600. Not including traces for the heaters, and simply adding the two twisted jumpers is a simple, elegant, inexpensive solution. Notice the jumpers are on the component side of the board, so they can be wave-soldered with everything else. They probably have to be inserted by hand, but do not add any expensive hand soldering to the process. Leo would approve.
Doesn't matter - there are two tube sockets, and they each have one of those electrolytics in their vicinity. Gotta be cathode bias caps.
Take a look at the Soldano SLO gut shot in the link in this thread from earlier today. See all those nice straight, parallel wires connecting all the preamp tubes? See any twisted pairs in there? Care to guess what kind of filament supply Soldano used?
Of course, the added expense of a several-amp, super-clean DC supply for heaters compared to the overall price of an SLO is not a big deal. Same for many PC-board-based 100-watt high-gain monsters. But a DC filament supply would be a major cost contributor in a Champion 600. Not including traces for the heaters, and simply adding the two twisted jumpers is a simple, elegant, inexpensive solution. Notice the jumpers are on the component side of the board, so they can be wave-soldered with everything else. They probably have to be inserted by hand, but do not add any expensive hand soldering to the process. Leo would approve.
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Fresh_Start
New member
Re: D.C. filaments
Power supply filter caps - it's the only place you typically see electrolytics, and both tubes need B+, preferably filtered
The cathode bypass caps for the preamp tube probably are the smaller black caps (C3 or C10?).
Chip
Power supply filter caps - it's the only place you typically see electrolytics, and both tubes need B+, preferably filtered
The cathode bypass caps for the preamp tube probably are the smaller black caps (C3 or C10?).
Chip
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