Something (hopefully) simple first - resistor selection!

[BobRuth]

To set the stage, I will first be doing a new build of an old amp.  So I am not repairing/restoring a vintage piece and there is no reason to to stay "period correct" just because of that.

So, there are carbon comps, carbon films, metal films....  maybe others.   What is a good choice when, again I am not going for vintage, I am going for the tone and hopefully to have the amp last for a long long time.  Which would most of you go with and why?

Thanks!

Bob

[MakerDP]

My choice is metal film. They are tye quietest and more than one builder that i have a lot of respect for say there is absolutely nothing to the hype over resistor "mojo." MF resistors have the least amount of noise.

 

[sluckey]

I switched over to metal film a few years ago. In addition to what MakerDP said, MF values are very close to the stamped value, whereas NOS CCs will usually be higher value. Many of the milspec NOS CCs I have are even out of tolerance already. Also, the MF work better with my style of board layouts. I can easily fit four 1/2W MF leads into the top of one of Doug's turrets. Can only get one of the old 1/2W or 1W CCs to fit. Forget about poking a 2 watter into the top of a turret. Gonna have to wrap that one.

And blue is my favorite color!   

[jjasilli]

Resistor mojo is a real topic.  Whether the mojo itself is real remains open to debate. 


I am not going for vintage, I am going for the tone
This is not a clear statement.  Are you seeking vintage tone, regardless of the physical appearance of the internal components of the amp?  There are reputable amp guru's who believe that carbon comp resistors contribute to vintage tone; others think this is hogwash.  E.g., as a compromise for modern amps Dave Funk suggests using carbon comps in the spots where they were used in vintage amps, and modern resistors elsewhere.  But in a simple amp, like a Champ, there is no elsewhere, except maybe in the power supply.  In a hi-gain amp, modern low noise resistors might be preferable.  But this isn't vintage tone!

the amp last for a long long time.
All resistors last a "long time". 

There is no one-size fits-all answer to your question.

[Jim Coash]

I replaced every resistor in my Princeton Reverb amp project with metal film.  The difference in how quiet it is astounds me.  You could hear the amp idling from several feet away before.  Now you hear nothing even with the volume well advanced and the tone controls in the middle from a few feet.  Pulling the "boost" makes it clearly audible and changes the amp dramatically.  My son and I are both very happy with the results.  I ordered the best gold banded metal film resistors I could find in the same wattage.   Of course, all the caps are new as well.  I am getting a solid 20 watts from a pair of good 6V6 tubes.  My years in the A/V business makes me a clean amp freak.  I like the way it sounds.  Jim

[jjasilli]

Everyone's mileage may vary.  I rebuilt a SF Princeton & a VibroChamp with carbon comps everywhere, except for metal B+ dropping resistors.  Both amps are dead quiet.

[BobRuth]

Thank you all for the responses!

I agree that I was somewhat ambiguous in my application of the "vintage" idea....
When I said that I was not "going for vintage" I meant that I am not having/needing to stick to original component types to maintain "vintage appeal" or "collectibility appeal"

going for  tone.... let's say I am not necessarily trying to achieve a tone that would match a top notch recording of a top notch original piece.  More so, I think that I am just looking for tone that makes my head go "whooo hooo" when I hear it.  Even that is still somewhat ambiguous but this is a learning thing too.   If I build now and it isn't what I want, build another!!!!  The pursuit is the real fun for me.  That said, I have not heard a build that I did not think sounded really good at least the recordings sounded good.

Again, thank you all for taking time to respond!

Bob

[HotBluePlates]

I think you already got your answer, but...

Wirewound are generally the quietest resistor type; I typically use those for power ratings over 1w and for resistances under ~20-50kΩ (because it is exceedingly hard and/or expensive to buy wirewounds in values like 100kΩ which wind up coming in 7w & higher power ratings). I usually use Dale RS wirewounds rather than the cement block type, mostly because they're prettier. 

And yes, metal film for any resistance higher than where sensibly-sized wirewounds are impractical/unavailable.

As others have said, you will be pleasantly surprised how quiet your amp is with these.

[MakerDP]

Yes as HBP says, we definitely should have said wirewound for 1W to 3W and then I'll use cement-block-type for 5W and above.

[drew]

One more thing to think about: if you're geezerly, or just have geezerly eyes, consider using 1 watt or 2 watt resistors where 1/2 watt are specified.  It's easier to see the color bands, and the cost differential for a single amp's worth of them is going to be in the loose change under the car seat realm.

What "old amp" are you thinking of building?

[Jim Coash]

I used to routinely use higher wattage resistors when I had one that matched the resistance I needed but did not have the same wattage.  Several times I heard from reputable people that I was wrong to do that.  They said that larger wattage resistors would likely be "noisier" than the correct wattage, especially in the signal path.  Is there difference of opinion on this?  Jim

[HotBluePlates]

I used to routinely use higher wattage resistors when I had one that matched the resistance I needed but did not have the same wattage.  Several times I heard from reputable people that I was wrong to do that.  They said that larger wattage resistors would likely be "noisier" than the correct wattage, especially in the signal path.

That might be true if you were using carbon composition resistors. Or it might not be true, because the high-watt resistor has a bigger surface area and would have less temperature rise with the same power dissipation; this could reduce thermal noise at the given operating power level.

But there are several mechanisms to create noise in resistors. You should ask the people who told you that what their basis was for saying not to do it.

[Jim Coash]

In two cases a provider of pre-fab kits for amp re-builds told me that bit of wisdom.  When I order parts I can usually get a better price if I buy 5 or 10 of the same value so I got into the habit of buying extras, in common sizes, with 1 or 2 watt ratings and then using them where a 1/2 or 1/4 watt would suffice.  Another habit I was cautioned about was lead length.  My re-builds often have components standing higher off the turret board than the original part.  I assumed that they would run cooler that way.  I also frequently wrap & solder the leads of two or more components that are in parallel around each other into a small "sub-assembly" and then install that.  It reduces the number of times I must heat up and solder the same lug or turret on a board.  My work always looks neat with the values on the parts rotated so that they can be easily read and the tolerance bands running the same way.  I also like to dab a little red Sharpie on the leads of every part I replace for future reference.  I always keep grounds close to where they were originally but sometimes drill a hole for a screw with a flat, lock, nut and a solder lug instead of trying to solder direct to the chassis.  Of course, a convenient transformer or tube socket mounting screw works for me.
Jim

[sluckey]

They said that larger wattage resistors would likely be "noisier" than the correct wattage, especially in the signal path.  Is there difference of opinion on this?

I've heard just the opposite when comparing 1/2W and 1W CCs.

[Fresh_Start]

From Aiken Amps

IIRC there is a theory that carbon comp resistors do have some special behavior (mojo?) in spots where there are large voltage swings. Several years ago, I built a Super Reverb type amp for a friend. Initially it had metal film resistors everywhere except power rail. He played it. Then, at his request, I replaced all of the plate resistors (except the input stage) with carbon comps, along with a couple of resistors in the PI. He liked the amp's tone and feel better, but this was NOT a blind test. I couldn't hear the mojo but I did hear a tiny bit more noise which would have been multiplied if I'd used carbon comps everywhere.

Carbon film are the worst of both worlds - added noise sans potential mojo. 

Cheers,
Chip

[Jim Coash]

I have also encountered numerous scenarios where I "fixed" (or had fixed in my service department) an amplifier only to find that the owner was disappointed in how the repaired unit sounded.  My explanation was that every amp sounds different and there is no way to fix a problem in a piece of equipment without altering the sound.  This was similar to the argument postulated by those who claimed that Bob Carver's Magnetic Field designs didn't sound "good" or "right" compared to others.  Many of those criticisms came from manufacturers and owner's of very expensive "esoteric", "audiophile" amplifiers.  Bob Carver responded to them by duplicating the "transfer function" of any amp chosen by the critics in his own amp by replacing parts until the two amps yielded a "null" when compared out of phase with each other.  This resulted in Carver's TFM line of amps (Transfer Function Modified).  He was even able to produce the results in a special test conducted by a prominent audio magazine in real time at a CES show using a high end tube amp design.  Guitar amps are far less sophisticated (generally) but based on the same fundamentals.   I have used many different amps in the last 50 years.  Some were better than others, some worse.  My perspective has always been based on my devotion to accuracy, purity, low distortion and massive power.  That is not what many players have in mind.  They are appalled to hear me describe what I do to my amps to make them "perfect".  Jim