Hi all,

Noob here getting ready to start my first amplifier project.  In researching some other potential projects, I stumbled upon several discussions about the different types of resistors, and more specifically, how noisy and unstable the carbon comp resistors are.  Has anyone here replaced the carbon comp with metal film for that reason?  Better yet, has anyone done a comparison?  I’m wondering if there is some desirable sonic character to the cc resistor and that’s why it’s specified?  I’d rather not worry about the resistor changing over time, but also don’t want to change the character of a well regarded amp, if that’s a concern.  Thanks….still learning the basics so I appreciate any constructive input.

Thanks John, I appreciate the comments.  I’m definitely not trying to second guess Steve’s choices for sound quality…I’m not qualified to do that.  Knowing that choices generally  involve compromises, I guess I was wondering if anyone chose to go for the stability/reliability of metal film, even if it changed the sonic character a bit.  If you listen to some folks talk about CC resistors, they’d have you believe the amp will sound like crap within a few months if you use them (water, degradation, whatever).  Being new to all this….I can’t tell hyperbole from sound advice.  All that said, I’ve got the CC resistors so I’ll use them.  Once I get comfortable with my listening and soldering skills, maybe I’ll do some experimentation.

I built a prototype, "test platform" of the circuit using "leftover" parts (I have a basement full). I used metal film resistors across the board, and some signal caps I salvaged somewhere, just cheap poly... and those cheapo 5K amazon transformers. Plays through 88db B&W VM1s plenty loud. The weakest part of this amp is the output transformers.

It makes music. In fact I now listen to it as I build other stuff. Hard to comment as to critical listening, and my future builds use carbon comp in the power supply to the plates.

I think of this amp as simple rustic Italian cooking, fewer, high quality ingredients. With fewer ingredients, each one affects the whole. The chef's recipe says carbon.

Some say carbon comp are noisy, some say they age poorly, some say metal film is more stable, glass anyone? Resistor basically functions the same regardless of core technology. Point is, they will work, the input tube gets its voltage. I wouldn't sweat the reliability concerns with cc resistors.

Resistors are also cheap relative to other components.

CC resistors give a very natural musical feeling to the music.  Metal films are more detailed and clear sounding.  Wirewounds should be used in high power and high heat settings.  CC are excellent for lower power settings in the power supply filter.  For a zen amp I'd try to find some good quality 2 watt metal films and use them throughout.  Use a good quality wirewound for the main step down resistor 10 watt rating. Welwyn W20 series are very good at Mouser.  You could also try to find some nice carbon film resistors(different from CCs) for the input tube cathode resistors.