Load resistor wattage and DC filaments— is there a right way?

[Steelwitch]

I’m about to start a 15w build. I am trying to snag as many Allen bradley carbon comps as I can, maybe excluding RF filtering (I might even use small inductors for that). Just wondering if 2W carbon comps could be considered for reliable load resistance. Should I consider 5W instead? Output stage is push pull 6V6’s and will probably require 5W for the 300v(ish) load. Is that too low?

Next: I’ve been considering using DC filaments for low noise. The amp is point to point constructed. What are my options for DC filaments in a design like this? I’ve only seen DC used on circuit boards as a $ saver, but objectively DC has to be quieter. Could this be achieved with an additional rectifier from a 6.3vAC supply?

[Enzo]

No DC is POTENTIALLY quieter. DC heaters cures only one kind of hum, and if your unit doesn;t have that issue, you will get no improvement.

I am not sure how you mean DC heaters is a money saver, after all it requires more parts. You mostly see it on circuit boards because most amps are on circuit boards. It matters not how you wire an amp, circuit board, eyelet board, point to point, you can wire the heaters with any method you like.

If you want to wire them DC just as a preventative measure, go ahead, it sure won't hurt anything.

[Chuck H]

You won't find many believers here for CC resistors. In fact I'd recommend NOT using them for plate loads because they can be noisy in these circuits. They also have a tendency to drift with age a lot more than any other type.

1/2W resistors are common throughout most amps with the exception of power supply components. And you can use ohms law in many instances to determine the wattage needs of a given circuit if you have or can approximately guess the voltage drop across a resistance. 5W is plenty for most of the circuit you described, but perhaps not everything. A schematic would help.

[Chuck H]

No DC is POTENTIALLY quieter. DC heaters cures only one kind of hum, and if your unit doesn;t have that issue, you will get no improvement.

I am not sure how you mean DC heaters is a money saver, after all it requires more parts. You mostly see it on circuit boards because most amps are on circuit boards. It matters not how you wire an amp, circuit board, eyelet board, point to point, you can wire the heaters with any method you like.

If you want to wire them DC just as a preventative measure, go ahead, it sure won't hurt anything.

THAT^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

For the circuit you describe I don't think there would be any advantage to DC filaments unless you will be cascading more than three preamp stages. A good grounding scheme is sufficient for hum abatement in any vintage type design. Very complex, uber gain type modern amps with very crowded circuit boards and difficult to manage ground planes can benefit more. Mostly because it's very hard to avoid all hum with the complex boards, the first gain stages are often not fully bypassed so the cathode can impress on the signal and there is just so much amplification that any hum there is amplified many (thousands of) times more than in vintage type designs.

[Steelwitch]

You won't find many believers here for CC resistors. In fact I'd recommend NOT using them for plate loads because they can be noisy in these circuits. They also have a tendency to drift with age a lot more than any other type.

1/2W resistors are common throughout most amps with the exception of power supply components. And you can use ohms law in many instances to determine the wattage needs of a given circuit if you have or can approximately guess the voltage drop across a resistance. 5W is plenty for most of the circuit you described, but perhaps not everything. A schematic would help.

Is the hype about carbon comps being the “best” for audio circuits just hype? A myth? Understandably there are some undesireable compromises for using them: longevity, noise, etc. but is there a clear improvement in tone for a guitar amp? Specifically a low powered one? Not shooting for high bandwidth or fidelity here. Would you suggest metal film as a better alternative? A lot of the resistors I keep stocked already are 1W but I guess the only downside is the marginal extra space they take up.

[nosaj]

Is the hype about carbon comps being the “best” for audio circuits just hype? A myth? Understandably there are some undesireable compromises for using them: longevity, noise, etc. but is there a clear improvement in tone for a guitar amp? Specifically a low powered one? Not shooting for high bandwidth or fidelity here. Would you suggest metal film as a better alternative? A lot of the resistors I keep stocked already are 1W but I guess the only downside is the marginal extra space they take up.

I used carbon film in the champ, and deluxe I built . Both would get downright nasty delta blues sounds. Granted I'm not a player but I loved the sounds that even trying carbon comps in them was not going to happen. Now If I were to ever go that route I would only ever use Allen Bradley and verifying each I I'd use. But I doubt I've ever go that route. It'd be like buying vintage radial tires to put on your show car(why why why?)

nosaj

[Chuck H]

There's actually a couple of reasonable arguments in favor of CC resistors. As it happens, they actually do contribute some distortions of their own in audio circuits! Audible? Maybe not, but real just the same. Here's a geofex article by our own R.G. explaining some of it:

http://www.geofex.com/Article_Folder...carboncomp.htm

So the choice seems valid enough and, being a guy that designs for tone, I'd only argue that the for "me" the drawbacks outweigh the benefits. Note that no reissue Fender amp is using CC resistors (to my knowledge) and they sound just fine and tone guru Ken Fischer of TrainWreck fame didn't use them either in a time when their use was still common.

I will, however, reiterate the drift factor. I think some of the mojo that follows the vintage amps can be attributed to some specimens having significantly different resistances in key places that improved their sound and that could have contributed to the older amps perceived mojo. Not only did these older amps use resistors that were prone to drift (which could be significant) but they also used +/- 20% tolerance parts. A far cry from todays typical 5% tolerances and the use of resistor compositions that don't drift significantly. Unfortunately their haven't been any real blueprinting efforts done on any of these special specimens for the purpose of discovery. And I must admit that if I had an especially great sounding, say, black face Deluxe Reverb, I wouldn't let some amp tech with the best intentions tear it down in the name science for any one else's benefit. Would you? So it could be a matter of value more than component composition. Of course the other side of that coin is that some amps sounded especially crappy. The wide tolerance and drift is just as likely (if not more so) to cause that too. YMMV

So there you go. I don't poo poo anyone for using CC resistors like some here because there is at least some argument in their favor. As noted, there is some argument against too. But then it becomes a valid choice either way.

Just don't ask if there's a tonal benefit to cloth braid lead wire insulation I hope you enjoy the article. I did. In fact it's responsible for me experimenting with CC resistors for a time just to see if "I" was the guy with special ears that could hear the difference. As it happens, I couldn't. So I find it much more satisfying to build (and tweak) with closer tolerance, more longevity stable value resistors for the consistently good results. Rather than any great/lousy roulette.

[Steelwitch]

There's actually a couple of reasonable arguments in favor of CC resistors. As it happens, they actually do contribute some distortions of their own in audio circuits! Audible? Maybe not, but real just the same. Here's a geofex article by our own R.G. explaining some of it:

http://www.geofex.com/Article_Folder...carboncomp.htm

So the choice seems valid enough and, being a guy that designs for tone, I'd only argue that the for "me" the drawbacks outweigh the benefits. Note that no reissue Fender amp is using CC resistors (to my knowledge) and they sound just fine and tone guru Ken Fischer of TrainWreck fame didn't use them either in a time when their use was still common.

I will, however, reiterate the drift factor. I think some of the mojo that follows the vintage amps can be attributed to some specimens having significantly different resistances in key places that improved their sound and that could have contributed to the older amps perceived mojo. Not only did these older amps use resistors that were prone to drift (which could be significant) but they also used +/- 20% tolerance parts. A far cry from todays typical 5% tolerances and the use of resistor compositions that don't drift significantly. Unfortunately their haven't been any real blueprinting efforts done on any of these special specimens for the purpose of discovery. And I must admit that if I had an especially great sounding, say, black face Deluxe Reverb, I wouldn't let some amp tech with the best intentions tear it down in the name science for any one else's benefit. Would you? So it could be a matter of value more than component composition. Of course the other side of that coin is that some amps sounded especially crappy. The wide tolerance and drift is just as likely (if not more so) to cause that too. YMMV

So there you go. I don't poo poo anyone for using CC resistors like some here because there is at least some argument in their favor. As noted, there is some argument against too. But then it becomes a valid choice either way.

Just don't ask if there's a tonal benefit to cloth braid lead wire insulation I hope you enjoy the article. I did. In fact it's responsible for me experimenting with CC resistors for a time just to see if "I" was the guy with special ears that could hear the difference. As it happens, I couldn't. So I find it much more satisfying to build (and tweak) with closer tolerance, more longevity stable value resistors for the consistently good results. Rather than any great/lousy roulette.

Thanks for sharing this Chuck! It answers a lot of questions that I’ve previously had about why / why not. I do mostly have metal film in my stash, and some CC I may try before and maybe in the PI. If the noise floor is too high, I will have to go another route but a huge goal of mine is to capture the vintage amp vibe and to build something that becomes better with age. One of the aspects of this unfortunately is waiting to see what kinds of effects age will have. Maybe positive and maybe negative! I’m only using one stage of amplification before the PI, using a LTP, hoping that I can tweak the PI enough to get most of the saturation from asymmetry.

[nosaj]

Thanks for sharing this Chuck! It answers a lot of questions that I’ve previously had about why / why not. I do mostly have metal film in my stash, and some CC I may try before and maybe in the PI. If the noise floor is too high, I will have to go another route but a huge goal of mine is to capture the vintage amp vibe and to build something that becomes better with age. One of the aspects of this unfortunately is waiting to see what kinds of effects age will have. Maybe positive and maybe negative! I’m only using one stage of amplification before the PI, using a LTP, hoping that I can tweak the PI enough to get most of the saturation from asymmetry.

Mine I built from recycled organs, using new resistors and caps. I think the most important thing when experimenting is to not overthink it and just try it. You can learn a lot more from failures than getting it right the first time(or never getting started.

nosaj

[Chuck H]

I remember reading a quote from an interview with Thomas Edison where he mentioned that it took a thousand attempts to come up with a working light bulb. He was then asked how it felt to fail nine hundred and ninety nine times. He said he did not fail nine hundred and ninety nine times, but rather successfully discovered nine hundred and ninety nine ways that it didn't work.

I have my own ideas about Edison actually. Like many here. But I still like that sentiment. Being told or reading something from a good source is great, but you really need to get your hands dirty too.

[J M Fahey]

a huge goal of mine is to capture the vintage amp vibe

A fine goal.

But then 99% of builders *agonize* over resistor type, capacitor colour, type of wire and 1000 other *microscopic* 0.1dB differences, which often take a team of trained bats to discover, if at all, and forget the SPEAKER where you have 10dB peaks and dips all over the place.
And which significantly DO change with age even within hours.

A few examples.

1) EXACT SAME AMPLIFIER, so same capacitors, resistors, tubes, transformers, a Fender Champion 600, but with 2 different speakers, the icepicky buzzy thin Factory one and a custom built "using the old recipe" warm and smooth Weber Signature.
To boot, delivered already broken-in (meaning Weber drove it HARD for 24/48 hours before delivery)


Speakers are the one sound component where break-in is true.

2) comparing modern versions of the old standard (all Factory fresh of course, sound will change with use)

a) Jensen P10R which is using the old recipe (50´s 60´s) ... with modern materials of course.
Notice the important treble/bite change just with change of *impedance*, everything else being equal:



b) Jensen C10R, in theory exact same components but Ceramic magnet and late 60´s on recipe.



For an even more impressive demonstration of the HUGE importance on speaker selection (and about which 1% of musicians cares about or even notice) here´s a15 speaker shootout.
All with exact same amplifier and player,
Buzzy tone in general, I guess that comes from the amplifier settings, but the point is demonstrating speaker to speaker difference:

now you´ll understand my absolute lack of interest and participation in resistor/capacitor religious wars

[Justin Thomas]

Funny, all my favorites are the "weirdlings" in the bunch. And my most favoritty are the cheapies I mean Emis. Of course, none of my amps do anything like that, so...

I feel like tgat recording wasn't very "LOUD." And, I'd like to see the sensitivities posted on the vid... The TTs are noticeably quieter. As in, won't-piss-off-the-Sound-Guy quieter.
Justin

[Leo_Gnardo]

And, I'd like to see the sensitivities posted on the vid... The TTs are noticeably quieter. As in, won't-piss-off-the-Sound-Guy quieter.

The "San Rafael" Tubbies are something like 93 dB, about 10 dB below most other popular guitar speakers. With their hemp cones, the tone is also mellow. As you might expect? Some of my customers prefer them to tame the sound of otherwise over-bright amps. Works great for electric violin too, takes out the scratchy tone & gets a nice fat sound. Would be nice if they got more popular.

[nosaj]

The "San Rafael" Tubbies are something like 93 dB, about 10 dB below most other popular guitar speakers. With their hemp cones, the tone is also mellow. As you might expect? Some of my customers prefer them to tame the sound of otherwise over-bright amps. Works great for electric violin too, takes out the scratchy tone & gets a nice fat sound. Would be nice if they got more popular.

I've seen some 2x12 cabs where one is a tone tubbie(hempcone) and the other one of the blue Vox speakers.

nosaj

[J M Fahey]

Yes, mixing speakers is almost always a good solution.