Regulated DC is too cheap today to ignore it's advantages, even when they are not so audible.
But regulated DC contains several 'newbie traps':
1. the transformer needs more VA than AC heaters (maybe at least 2x)
2. the (voltage) regulator needs to cope with cold heaters without doing a current/temperature foldback and shutting down
3. current regulation avoids '2' but can mean slower warm up
1. the transformer needs more VA than AC heaters (maybe at least 2x)
2. the (voltage) regulator needs to cope with cold heaters without doing a current/temperature foldback and shutting down
3. current regulation avoids '2' but can mean slower warm up
Thinking over a reply I realize it could sound judgemental or contentious , which I don't feel so please take this as a friendly reply.
You've been around for a while , know a lot, so it's hard for me not to wonder why you're actually asking the question. You've made it clear by your comment that you ascribe a positive sonic difference to AC heating, so why the doubt in this case?
I don't really disagree with the answers above but the engineer's fast cut to the finish to me carries the danger of shorting out exploration. I'll thump my personal bible and put in that everything makes a difference and you just have to decide what you care about. I can't imagine not breadboarding the circuit and trying different stuff.
You've indicated that you have heard a difference between AC and DC so it might not be unreasonable to think you could also hear a difference between different types of DC circuit - unregulated, voltage regulated, current regulated, etc. There are posts by some who have switched from one dc supply to another and commented on what they heard. These days, notably Rod Coleman's regulators get high billing.
Which one do you like the sound of , or is the difference so small that it's not worth the financial cost, space allocation, or level of complexity, etc. . . . .
To me , it's not a question you can really answer without trying different things, and by then you know the answer without having to ask.
Anyway, just some thoughts.
The capacitor most likely is not required as well. (You can't reaonably make it large enough for it to have a meaningful effect) This is my least favorite form of battery bias right after sticking a battery in the cathode circuit. I've tried a number of variations, the batteries are not perfect either and some of them markedly color the sound (sometimes to a measurable extent at least in so far as distortion is concerned).
I use battery bias a lot in phono stages as the two or three people who read my threads will have noticed.
I use battery bias a lot in phono stages as the two or three people who read my threads will have noticed.
There is a lot of rhetoric on the subject. Like most subjects simple questions like this often get simple answers sometimes based on supposition. AC filament supplies are very simple and don't vary much. DC filaments are another story, so hard to make generalizations about them. AC may be fine for the last stage in a power amp, especially if paired with relatively inefficient speakers, however if you are using them with highly efficient speakers, or in earlier stages in a an amplifier chain, maybe not so much.
I had a single ended 300B amp driving 96dB speakers, the amp had simple DC filaments on the 300Bs The DC filament supply I was using on the amp at first was a just a simple CRC supply using cheap electrolytics and a good power resistor. In an attempt to improve the sonics of the amp, I then built a second DC supply. The second supply had high quality electrolytics and used a CLC topology employing a large high quality vintage Chicago potted filament choke. That 2nd DC supply was a BIG improvement.
I decided to A/B the new DC supply with an AC supply. I made a second AC supply, I could balance the hum with a balance pot to get the hum to acceptable levels, and could switch the two supplies back and forth on the fly with a DPDT switch. Myself and others thought the DC supply sounded livelier than the AC supply. The Rod Coleman filament supplies I expect would sound even better than my CLC supply, but I've never tried one. I always wanted to, but never seemed to get the time and money together to give them a shot, but others rave about them.
I'm one of the few who has bothered to build a better than average DC supply, and actually A/Bd it instantly with an AC filament supply in the same amp/system. This really allowed me to explore the generalizations on the subject. My conclusions are that a typical cheap CRC DC supply will not sound as good as AC, however a more sophisticated DC supply may beat AC.
twystd
I had a single ended 300B amp driving 96dB speakers, the amp had simple DC filaments on the 300Bs The DC filament supply I was using on the amp at first was a just a simple CRC supply using cheap electrolytics and a good power resistor. In an attempt to improve the sonics of the amp, I then built a second DC supply. The second supply had high quality electrolytics and used a CLC topology employing a large high quality vintage Chicago potted filament choke. That 2nd DC supply was a BIG improvement.
I decided to A/B the new DC supply with an AC supply. I made a second AC supply, I could balance the hum with a balance pot to get the hum to acceptable levels, and could switch the two supplies back and forth on the fly with a DPDT switch. Myself and others thought the DC supply sounded livelier than the AC supply. The Rod Coleman filament supplies I expect would sound even better than my CLC supply, but I've never tried one. I always wanted to, but never seemed to get the time and money together to give them a shot, but others rave about them.
I'm one of the few who has bothered to build a better than average DC supply, and actually A/Bd it instantly with an AC filament supply in the same amp/system. This really allowed me to explore the generalizations on the subject. My conclusions are that a typical cheap CRC DC supply will not sound as good as AC, however a more sophisticated DC supply may beat AC.
twystd
Build one channel with the DC polarity in one direction the other channel wired opposite, swap tubes from left to right occasionally. The only time I use DC filaments is with DHTs and phono stages
twystd
I too use AC for heaters in everything except vacuum tube phono stages. Like others I twist the heater wires with my cordless drill and a vice. I usually use a center tapped filament winding and elevate the CT with about 35 to 40vdc via a resistor divider off the B+. If I have a transformer that has no center tap, I will connect a 100 to 220 ohm resistor to each side of the filaments and elevate the common connection of both resistors to elevated B+ as mention earlier. I have made many amplifiers in this manner and I am unable to hear any hum what so ever in the speakers, even with my ear up very close. Thus, I believe simple is more reliable and ditched the DC heaters in all application except those that absolutely demand it. Happy hobbing to all!
Regard, Mickeystan
Regard, Mickeystan
I once built a phono preamplifier with AC heater supply. I used an EF86 as first valve (because of its exceptionally low heater-to-control-grid capacitance, among other things), AC grounded its cathode with a big capacitor (220 uF, prevents hum due to heater-to-cathode capacitance) and DC coupled the control grid to the cartridge (keeps the impedance driving the grid as low as possible, minimizing the effect of hum current injected into the grid). The DC level at the heaters was raised, although I didn't notice any difference (this is supposed to prevent hum due to heater emission).
I have a very slight hum in one of the two channels of the amplifier, but that's completely due to the field of the supply transformer. I did experiments with the transformer placed at about a metre distance and then the noise floor just sounded like noise, with no hum at all.
I have a very slight hum in one of the two channels of the amplifier, but that's completely due to the field of the supply transformer. I did experiments with the transformer placed at about a metre distance and then the noise floor just sounded like noise, with no hum at all.
gabdx, I have never experienced this.
Perhaps it happens if you just use simple capacitive filtering? I either use proper filament chokes, or design my own regulated supply.
Its not soooo hard to design a regulated supply btw. Just look for a nice regulator and read the datasheets. If you want to get fancy, you can combine a voltage regulator with a current regulator.
I am sure that Rod Coleman's regulators are the stuff to get if you don't want to do it all on your own though. Its nice that he offers his extensive experience in this way.
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I think we could do with some definitions here:
1. Indirectly heated tubes with heaters
2. Directly heated tubes with filaments
3. Directly heated tubes used in filament bias
Whereas in the case of 1 and 2 you could argue each way, filament bias demands extremely clean DC which is why Rod Coleman's DC filament supplies became so useful to DIY builders. Add some chokes to taste, chokes being the choice of constructors like Thomas Mayer, the guy the popularised filament bias in the first place. Since filament bias demanded the best possible DC supplies, this then had a useful knock-on effect of raising the quality of supplies for 2. Rod would argue that his supplies are superior to AC in sound quality. They certainly ensure low noise and hum where this is critical.
1. Indirectly heated tubes with heaters
2. Directly heated tubes with filaments
3. Directly heated tubes used in filament bias
Whereas in the case of 1 and 2 you could argue each way, filament bias demands extremely clean DC which is why Rod Coleman's DC filament supplies became so useful to DIY builders. Add some chokes to taste, chokes being the choice of constructors like Thomas Mayer, the guy the popularised filament bias in the first place. Since filament bias demanded the best possible DC supplies, this then had a useful knock-on effect of raising the quality of supplies for 2. Rod would argue that his supplies are superior to AC in sound quality. They certainly ensure low noise and hum where this is critical.
That must be a northern hemisphere phenomenon due to the earth's magnetic field, because we only get sub-harmonics down-under. And a good way to tell the positive end is the heater glows more at that end when power is applied.
There may be a tiny element of truth in this. However, most unlikely to be of any practical significance.gabdx said:
Given the relatively slow thermal mass of the cathode structure it is astonishingly unlikely that the cathode surface can tell the difference between DC heating and heating at 100/120Hz (from 50/60Hz AC). Maybe someone told you a story and you believed them?
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