Where to use metal films?

[leadfootdriver]

Is there an audible noise difference between using metal films on plate resistors compared to carbon films?

What about the grid leak resistors?

What about the 1 Megs in a phase splitter?

[jmaf]

I believe the most critical resistor noise-wise is the plate resistor. Of course anything facing the grids may be a source of noise, but you'd have to have a really bad grid leak resistor to fail under such low voltage and basically pico-current. You can detect grid leak resistor failure without applying high voltage, which isn't always possible with plate resistors. Some test good on the multimeter, then once you turn on the standby switch they go noisy.

About carbon x metal: when I clean carbon comps and get them humid for some reason, the amplifier sounds like an AM radio. That doesn't happen with metal films I've tested, so that's my 2 cents about that.

[Steve Conner]

Metal films everywhere!

Check the voltage rating for the parts you're buying. Often the little 0.25 watt size will have a low voltage rating, so won't be suitable as plate resistors, you'll have to use the larger ones, which are metal oxide as far as I know.

*puts on asbestos hat and dives for cover*

[leadfootdriver]

I read an interview where Ken Fischer said that (paraphrase) metal films had excellent specs, but sounded harsh in guitar amps.

Assuming that's the deal, maybe you could use them in spots where the signal doesn't pass.

'Just thinking out loud...

[jmaf]

I read an interview where Ken Fischer said that (paraphrase) metal films had excellent specs, but sounded harsh in guitar amps.

Funny. From the tons of gut photos I've seen of Trainwreck amps, I thought those blue ones looked like 2 Watt metal films.

[hasserl]

Metal films everywhere!

^^^This!

[deci belle]

I've been using the metal film resistors on the preamp plates. The color codes are different looking. I did notice a harshness to the amp when placing them on the PI plates, so I put 1w carbon films there. Yes, the 1M metals work good on the phase splitter, too. About the only place I have 1/2w carbon comps is on the pwr tube sockets' 1k5 gridstoppers.

[Gtr_tech]

I'll use metal film/oxide for all plate loads and pwr supply droppers. Carbon films elsewhere.

[defaced]

Yep, metal film everywhere I can. The Vishay CCF60 and CMF60 series (there are others, but I have or seen these used) are metal film and suitable for plate resistors. For B+ dropping resistors, Vishay CPF 3w (also metal film) are good (if even a bit overkill), though I've used CCF60s here before.

[tedmich]

tantalum!
Angela Instruments Online Catalog - Resistors - Tantalum Film Resistors


kidding! MF everywhere cept MetalOx above 3w

[jmaf]

tantalum!
Angela Instruments Online Catalog - Resistors - Tantalum Film Resistors

kidding! MF everywhere cept MetalOx above 3w

well today I learned there are tantalum resistors

[diagrammatiks]

looking at ken's designs I'm not suprised that he thought a metal film would sound harsh.

I'd say that observation was true for him but not to take it as true for every circuit.

[jrfrond]

In amps that use C-F or M-F, I'll use those as replacement. But when building new amps or "vintaging" reissues, I'll go for new-issue carbon-comps? Why? Because they sounds and feel good. A tiny bit more noise, but a whole lot more feel and better tone. Amps with all M-F do sound harsh to my ears, and after much experimentation and replacement, I know that it's not my imagination.

[Gregg]

Metal films everywhere!

+1. I always use 2 Watt for plate. It just looks right.

[Steve Conner]

Well, we know there is a scientific basis to the carbon comp resistor mojo thing: they generate sweet-sounding 2nd harmonic distortion when hit with high AC voltages.
http://www.geofex.com/article_folder...carboncomp.htm

If you want some of that sweetening, you can sprinkle some carbon comps in places where they'll see lots of AC signal voltage. RG recommends the plate resistor of the last stage before the PI.

Metal films don't distort, so I suppose they might well sound bland in comparison, or the lack of sweetness could seem harsh. But they are quiet and stable.