Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: worth on August 23, 2010, 11:01:22 am
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Let's say just for the sake of this post , that carbon comp resistors DO sound different than other types. Where in the circuit , ( AB763 ) would you get the benefit of using these ? Pre-amp yes , but what about the input ( 68K- 1M ) , reverb , and the phase inverter ?
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You'll get more qualified people's opinions hopefully but my understanding is that it wouldn't matter much on the inputs as the voltage there is very small.
I would think they would have the most impact between gain stages, like on the plates and grids of the preamp and PI tubes. all the tubes (except rectifier).
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I put them in the signal path where there's big AC wiggle as much as I can after V1. I use 1W carbon films in V1 to cut down on CC noise. I don't hear much if any CC "shhhhhh" when I use the CF's in V1. So, in an AB763 circuit:
Signal path:
1. V1-V2 100K plate loads and the 100K slope resistors in the tone stacks.
2. The two 220K mixer resistors.
3. The 82K and 100K PI plate load resistors.
4. And if you really want to get anal about it, in the reverb circuit, the 470K that's in series with the reverb pot wiper and the 3.3M reverb/dry mixer resistor. I don't do this, btw.
5. There's very little AC wiggle on the 68K input resistors, so I don't mess with them there. Also, some may like using CC's on most/all of the preamp cathodes. Again, there's not much AC wiggle there... So I don't mess with it.
Ooops.. I forgot. Also the 1.5K power tube grid resistors.
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Randall Aiken on resistor types:
http://www.aikenamps.com/ResistorNoise.htm
R.G. Keen on carbon comp mojo:
http://www.geofex.com/Article_Folders/carbon_comp/carboncomp.htm
Some guys insist on using all carbon comps. Some put carbon comps in specific spots (e.g. plate resistors). Some use all metal film for lowest noise, and some use carbon film for lowest cost (I think).
HTH
Chip
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I use all carbon comps so I don't have to use up a bunch of drawers for multiple types of resistors. People with just enough knowledge to be dangerous insist on carbon comps so that's what I use. Anyone that might question it can be told, "but that's how Leo did it." Works every time! I buy 'em in batches of one hundred so they're cheap enough.
Dave
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I use all carbon comps so I don't have to use up a bunch of drawers for multiple types of resistors. People with just enough knowledge to be dangerous insist on carbon comps so that's what I use. Anyone that might question it can be told, "but that's how Leo did it." Works every time! I buy 'em in batches of one hundred so they're cheap enough.
Dave
Now that's an honest explanation!
I built a Super Reverb variation with all metal film resistors. Finally got it dead quiet. Swapped in carbon comps for the plate resistors (except reverb recovery stage) & got slightly audible hiss. Told client results and recommended going back to metal films. His response was "my buddy told me the carbon comps sound better." So they stayed.
Chip
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I use all carbon comps so I don't have to use up a bunch of drawers for multiple types of resistors. People with just enough knowledge to be dangerous insist on carbon comps so that's what I use. Anyone that might question it can be told, "but that's how Leo did it." Works every time! I buy 'em in batches of one hundred so they're cheap enough.
Dave
Bluesbear... I just found a post from you saying that you " hear a difference between cc and cf resistors ", and you were not talking about hiss. You appear to be saying that you PREFER carbon comps. Yet , in this current post , you seem to be saying that you choose your resistors , based on the customers misguided view that there IS a tonal difference ? I have not decided myself about resistor types , but am confused by your inconsistant posts.
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I use all carbon comps so I don't have to use up a bunch of drawers for multiple types of resistors. People with just enough knowledge to be dangerous insist on carbon comps so that's what I use. Anyone that might question it can be told, "but that's how Leo did it." Works every time! I buy 'em in batches of one hundred so they're cheap enough.
Dave
Now that's an honest explanation!
I built a Super Reverb variation with all metal film resistors. Finally got it dead quiet. Swapped in carbon comps for the plate resistors (except reverb recovery stage) & got slightly audible hiss. Told client results and recommended going back to metal films. His response was "my buddy told me the carbon comps sound better." So they stayed.
Chip
Did it sound better with the carbon comps to you, if you ignore the noise? Noise bothers some people more than others. I'd be willing to deal with some noise if the tone was noticeably better.
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Me too
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Did it sound better with the carbon comps to you, if you ignore the noise? Noise bothers some people more than others. I'd be willing to deal with some noise if the tone was noticeably better.
I couldn't hear any difference other than the slight hiss. Otherwise I wouldn't have suggested putting the metal films back in.
People I respect do hear a difference. We'll let FYL chime in on psychoacoustics and double blind tests... :wink:
Another thing to keep in mind is that carbon comps will drift upward in value over time. If I make the effort to figure out that a 220K plate resistor and 2.7K cathode resistor sound "best" (i.e. to my ears) for the first stage, I don't want those values to be significantly different 10 years from now.
Cheers,
Chip
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Interesting that they drift upward in value. I would have thought the opposite. So after a while (years, I assume) they actually provide more resistance?
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I'm not so sure that "time" causes drift. I'd say it's heat over time. No serious player would do a "double blind test".... has nothing to do with that universe you're in. We need fixers , we need players , but they're not quite the same.
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CCs are made from a bunch of carbon particles. Pack the particles loosely and you have a high value resistor. Pack the particles tighter for a lower value resistor. The carbon particles are ever expanding at the same rate as the universe. :grin:
Actually, the carbon particles do loosen up over time. The CCs will increase in value even if they are sitting on the shelf.
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I think this forum needs a " BELIEF " section
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I have a 36x72x18 cabinet that's stocked with 1/8, 1/4, 1/2, 1, and 2 watt CCs. It's been located in an air conditioned building since the early '80s. Many of those CCs have increased in value significantly. Enough so, that I always put an ohm meter on a CC before I put it in my radar system. I may have to check 5 or 6 resistors before finding one that's still within it's 5% tolerance.
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I have a 36x72x18 cabinet that's stocked with 1/8, 1/4, 1/2, 1, and 2 watt CCs. It's been located in an air conditioned building since the early '80s. Many of those CCs have increased in value significantly. Enough so, that I always put an ohm meter on a CC before I put it in my radar system. I may have to check 5 or 6 resistors before finding one that's still within it's 5% tolerance.
Aha! Empirical evidence we can believe in!
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No serious player would do a "double blind test"....
Bah. DBT's are a must when it comes to subjective tests.
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I used carbon comp from Doug because they looked like what was already there, and they're .30 each. I guess my amp has a little hiss when turned all the way up, but how can you hear it over the guitar? :grin:
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bah ?
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Tennessee,
If I said that, it must have been very, very late at night... unless it was METAL film I was talking about. That's not to say I didn't mean metal film but typed carbon film. I get in a hurry and don't always make myself clear. I only say this because I've never used carbon films except when I was out of something and I couldn't wait to order so I had to buy locally. Maybe twice or three times in the last five years.
That being said, I do think metal films are potentially quieter. I've built a lot of noise-free amps with carbon comps, though. Anyway, a little hiss is not an issue unless it's excessive. I've never played in any venue that was quiet enough for it to be heard. As for tone, I've built enough identical amps using the exactly the same components that have all sounded just a little different to believe resistor types make THAT much difference. There are too many factors in play. So, I go back to my original statement. If I build an amp with too much noise, there's a problem that different resistors won't fix. I have to look elsewhere.
BTW, please don't think I took any offense. I'm too old for that crap!
Dave
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I'd suggest NOT using carbon Comps in the power supply. I've seen them bubble up and I actually lit a cigarette off one once (just because I could). I use carbon comps mainly because I can read them easily with my failing eyesight. The vast majority of my flavorite amps used CC's. It's been speculated it wasn't a tone concern back in the day but rather a matter of dollars and cents. There's about a kazillion thangs that have a greater effect on tone beside resistors. Start with the speaker-n-enclosure and work backwards.
Bad amp + good speaker = sounds OK.
Great amp + lousy speaker = sounds crappy.
-Richard
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Bluesbear..... I MEANT to offend you .I thought that you were a closet CC lover.
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bah ?
"Bah! Humbug!"
:wink:
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The CCs will increase in value even if they are sitting on the shelf.
Yeah, and NOS ones (that've been sitting around a really long time) will have increased in value the most (especially when they end up on eBay) :wink:
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The CCs will increase in value even if they are sitting on the shelf.
Yeah, and NOS ones (that've been sitting around a really long time) will have increased in value the most (especially when they end up on eBay) :wink:
This has me re-thinking my plan to buy my caps and resistors at a local surplus/electronics supply store. They have a huge selection of many types and values for cheap and they are not used but I don't know how old they are. Resistors are easy enough to check but I think capacitors need to be checked with voltage applied right? Sorry, I know we're supposed to be talking about resistors here.
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Hoffman has good quality products at resonable prices. Shipping is fast too.
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His prices are good and I was planning on buying some things from him anyway but for the sake of comparison, his 1/2 watt carbon comps are .30 cents each - my surplus place has them for .12 each. I can get them by taking a 15 minute drive. Of course, if they're no good it doesn't matter. I'm just a little upset because I just found out my cost for that kind of stuff will be more than double what I thought it would be, and if I have to order more than once - shipping and waiting.
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Yeah, but you can't get all this info at your supply store, I betcha. :wink:
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Very true.
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I am building a Top Fuel Thunder Tweaks and AA864 Bassman two channel amplifier and have been battling over what resistors to use
I finally decided that even though i think i can hear a little difference between CC and metal films i want a noise free amp
It is a Seymor Duncan Convertible 100 head i have had that i am finally getting around to rebuilding
(http://i356.photobucket.com/albums/oo5/plexijtm45/SDCBAR.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/SDAA8642204.jpg)
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It's worth pointing out that the vast majority of resistor hiss comes from the input grid stopper and the input tube anode resistor. If I were going to use CCs (not that I am likely to), I would be careful not to use them in those two critical positions (and reducing the usual 68k grid stopper to 10k will help too!).
After that, it's generally a free-for-all, since the pot's are probably going to be as noisy as CC resistors anyway.
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I expect that you are more likely to have hiss with higher wattage amps, is that correct? IOW, a smaller 18W like I have may be more forgiving in that regard?
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I expect that you are more likely to have hiss with higher wattage amps, is that correct? IOW, a smaller 18W like I have may be more forgiving in that regard?
A higher gain amp will normally give more audible hiss, but power has very little to do with it.
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It's worth pointing out that the vast majority of resistor hiss comes from the input grid stopper and the input tube anode resistor
Dale CMF55 resistors are perfect for inputs, BCcomponents PR01 / PR02 or similar for plate loads.
After that, it's generally a free-for-all, since the pot's are probably going to be as noisy as CC resistors anyway.
You may use high quality molded carbon (eg. PEC), Cermet (Sfernice) or conductive plastic (Clarostat) pots.
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I have a 36x72x18 cabinet that's stocked with 1/8, 1/4, 1/2, 1, and 2 watt CCs. It's been located in an air conditioned building since the early '80s. Many of those CCs have increased in value significantly. Enough so, that I always put an ohm meter on a CC before I put it in my radar system. I may have to check 5 or 6 resistors before finding one that's still within it's 5% tolerance.
What are you doing with a radar system? Do you got a big dish doing 360's on top of the roof?
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What are you doing with a radar system? Do you got a big dish doing 360's on top of the roof?
We all lose our car keys once in a while, but some people have more elaborate solutions to the problem :smiley:
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What are you doing with a radar system? Do you got a big dish doing 360's on top of the roof?
I work for FAA at a long range radar station. The antenna is much to big to sit on a rooftop. It sits on a huge steel tower inside a 60 foot diameter soccer ball radome.
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What are you doing with a radar system? Do you got a big dish doing 360's on top of the roof?
I work for FAA at a long range radar station. The antenna is much to big to sit on a rooftop. It sits on a huge steel tower inside a 60 foot diameter soccer ball radome.
ahh Well that makes sense. Was wondering how you got that one past the FCC. :huh: