Pre-Amp Plate Load Resistors

[defaced]

cmf70s are even better.

I'd hate to have to build everything with .6watt resistors.

tiny little things. leave those to robots.

Even better? Quantify "better". BTW, this isn't a pissing contest.

[jrfrond]

To quote Elton John: "All the science, I don't understand. It's just my job five days a week".

Screw the numbers, theory and noise figures. Vintage Fender amps have survived for decades with 1/2W CARBON-COMP plate resistors. Sure, they can become noisy over time. However, carbon comps have a sonic/feel vibe, and stand up to transient damage much better than film resistors, two VERY good reasons to stick with them.

There's no way that anything like that comes through my shop and doesn't get new carbon comps installed. I even use them for new builds.

In amps with multiple gain stages and cumulative noise, you sometimes MUST use metal films, but for low-medium gain vintage stuff, it's carbon comp all the way. For me at least.

[Chuck H]

I've used CC's at customer request. But since my builds are usually leaning toward high gain (not high gain preamp, but high overall gain when cranked up) hiss is a constant battle. I try to minimize it wherever I can. Some hiss at bedroom volume is OK for wanking around. But crank up a hissy fifty watter and it sounds like your playing in the shower. Not having been familiar with all the aspects of thermal noise I've just used 1/2 watt MF's for plate loads. I'll be trying 1 watters next time.

[R.G.]

Quoting Albert Einstein, everything should be as simple as possible - but no simpler.

CCs have one real advantage in tube amps - they give a soft asymmetrical distortion in certain specific places where the DC and signal sizes are appropriate to this. That accounts for the sonic feel/vibe. In locations where the voltage-coefficient-distortion doesn't happen, there's no tone/sound advantage. Pulse/overload characteristics are good for CCs. However, there isn't any pulse/overload to speak of to be handled inside the audio path between input and power stage. In the power supply, CCs offer pulse advantages on tube failures, but wirewound would be even better. And CCs have worse drift and excess noise.

Using low noise resistors with the right power sizing makes sense wherever noise can be an issue and where your customers can handle rational explanation, not simply insisting "but carbon comp is better; I read it on the internet" much like Nigel Tufnel insisted "but these go to 11". Actually, there are probably customers who *like* the hiss letting them know it's really, really going to be loud.

If you want sturdy, instead of metal film, go wirewound. They're tough, and have no excess noise, like metal film. I can hear dozens of readers thinking "butbutbut they're inductive!" Yes, they are, to some extent. How much? For that, you'd have to read a data sheet. In almost all instances, the inductance is way outside the audio band. And there are noninductively wound wirewounds.

In the end, you have to do what your customers will pay for. But it's far better to know the details than to actively not know.

[tedmich]

surely tantalum resistors are the best, at $5 each

Shinkoh TAF Tantalum Resistors, 1 watt

seriously though anyone see downside of MetalOx in audio circuits?

[Steve Conner]

According to Doug Self, thick film resistors (I think metal oxide qualify as such) are slightly noisier than the ordinary metal film kind, and also slightly non-linear. The non-linearity is much better than carbon comps, though, it is at levels that take an Audio Precision test set to detect.

[drewl]

Heck with it,
I have a ton of 100K metal oxides I use for replacements which lowers the noise and gets rid of the typical "popping" in old Fenders.

Wonder why Marshalls aren't as prone to this behavior, or at least alot less than Fenders.
Whatever they used in the Sound City amps for all those 1M resistors in the active preamp models seem to be the worst for noise.

[diagrammatiks]

Even better? Quantify "better". BTW, this isn't a pissing contest.

they are the higher wattage and higher voltage rated version of the same resistor.

[defaced]

they are the higher wattage and higher voltage rated version of the same resistor.

They look like 500v, 0.75/1w parts to me. At ambient temp, they have the same ratings at the CMF/CCF60 parts. So according to the data sheet, the only thing they are is larger, and according to Mouser more expensive. Sounds even more better to me

[diagrammatiks]

They look like 500v, 0.75/1w parts to me. At ambient temp, they have the same ratings at the CMF/CCF60 parts. So according to the data sheet, the only thing they are is larger, and according to Mouser more expensive. Sounds even more better to me

how do you figure?

http://www.datasheetcatalog.org/data...2/127800_1.pdf

a cmf60 is a half watt 300vdc rated part at the same standards where a cmf70 is a 1 watt 500vdc.

[defaced]

Use current info: http://www.vishay.com/docs/31018/cmfind.pdf

[diagrammatiks]

right except the new data sheet has 5 pages of qualifications.

specifically


(1)
Continuous working voltage shall be or maximum working voltage, whichever is less

and the chart at the end explaining the differences in load life versus wattage rating.

It's not that big of a distinction but I'm happier putting 65s and 70s in the anode circuit then 60s.

oh wait...you're also looking at the commercial ratings while I'm looking at the mil ratings.

http://www.vishay.com/docs/31027/cmfmil.pdf

stupid standards differences.

This is like that bucket of screws I need metric nuts for.

edit: they are even better in space. the end.

[defaced]

stupid standards differences.

Yep. Every detail counts.

[diagrammatiks]

Yep. Every detail counts.

in space