Options for input wiring, shielded cable, grid stopper location?

Discussion in 'Shock Brother's DIY Amps' started by King Fan, Sep 25, 2021.

  1. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Cool. I've never built a 5F10 or 5F11 or studied their input scheme. My powers of circuit analysis are not up to figuring out the input resistance and the various values of grid stop / attenuation, but this thread on The Amp Garage at least *sounds* convincing.

    upload_2021-9-28_16-21-54.png upload_2021-9-28_16-22-48.png
     
  2. NSB_Chris

    NSB_Chris Tele-Holic

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    Those are actually 1W metal film resistors that I purchased from Mouser. Since in some places I want higher wattage, I just ordered all the regular sizes in 1W metal film so that I don't have to think about it. It is such a PITA to order resistors from Mouser, that when I do, I order a bunch of each type I need.
     
  3. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Aha, I hear ya. They look tiny, but scale is funny in amp photos; maybe they really are. I got some modern 1/2W resistors from Mouser once that were the size of, um, Mouser droppings.

    An important input thing we haven't talked about (that all the experts mention) is metal film being preferred for these locations as having the lowest hiss -- waaaay lower than CC, and significantly lower than CF -- which is extra nice in a spot that gets amplified most. As for your 1W, I know you ordered them for simplicity, but all the experts point out that even with MF, 1W has much less hiss than 1/2W.
     
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  4. NSB_Chris

    NSB_Chris Tele-Holic

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    That was my thinking exactly. I wanted the metal film for key signal path and some locations were said to be better with higher wattage. It may have be Aiken that said they put 1W everywhere.

    When I got the first shipment from Mouser (Vishay, I think) I thought they were all the wrong wattage because they were so small.
     
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  5. owlexifry

    owlexifry TDPRI Member

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    this prompts a quandary i have:
    at my local electronics store, I have x2 choices:

    1W carbon film
    1/2W metal film

    which would have less noise?
    ie. which has a greater bearing on hiss - the wattage or the type?
    i've always defaulted to metal film for obvious reasons. but this 1W vs 1/2W concept is quite new to me. didn't realize it was that significant.
     
  6. NSB_Chris

    NSB_Chris Tele-Holic

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    My read of Aiken's advice would lead me to believe that metal film is the better of those two choices: https://www.aikenamps.com/index.php/resistor-types-does-it-matter

    Honestly, I would order typical values from Mouser metal film 1W so that you have input stage, plates etc. covered and then back fill with 1/2W metal film when needed. Just my opinion. Other more experienced people may think otherwise.
     
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  7. Hyakuya

    Hyakuya Tele-Meister

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    I used this method for my Bassman Micro. Shielded cable, shield grounded at the input, with the grid stopper directly attached to the tube base via a tag strip.
    The green resistors are carbon film Kiwame. Said to have a lower noise floor than metal film and a 0.5% tolerance. I can attest to the tolerance after measuring every one I've used in 3 different amps.

    upload_2021-9-29_14-4-36.png
     
  8. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Did I say I love a resistor discussion? In my innocent youth, I started a joke-y MF v. CF discussion, which eventually ran to 5 pages. I recall our master researcher and archivist @Bendyha came up with a detailed research paper. If I’m right, this link offers you a download button.

    https://www.icloud.com/iclouddrive/0qXO5bKm6Rah5wW9TKc84FIEA#Resistor_noise

    By all means read, don’t take my word for it, but it seems to support the experts (I thought Merlin, Aiken, *and* Keen?) who say MF is even quieter than CF (and the paper found, more invariant under voltage). Seems like the multiple was very large, whereas I *think* the difference by wattage is much smaller. So for purely hiss reduction in the input chain, I go 1/2W MF over 1W CF.

    But but but but: In our ordinary (not super-gain) amps I’m pretty sure the MF:CF and ½ v. 1W differences aren’t very important for hiss, even in the input chain. Aiken also has a deep discussion of the 1M v. 68K hiss factor. Smart folks who build a lot like CF because they're cheaper. Other places in the amp, wattage matters. Merlin's discussion of hiss reduction with a small grid stop+cap, cited above, is always available. So I leave MF v. CF as academic for most ordinary amps.

    The only comparison I can provide is CC:MF in the input chain. My first boutique-ish 5E3 had all CC across the preamp, and replacing 'em with 1/2W MF *in the input chain* wayyy cut the hiss. And, FWIW Mr. Keen shows how CC mojo can’t possibly occur there.
     
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  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    OK, I hear you KF. To keep this scientific, I just have to question the observation. Were these CC resistors in good shape? I have heard plenty of amplifiers with CC throughout that have no discernible hiss. Would replacing them with new or even different 1/2W CC wayyy cut the hiss?

    Quoting from Mr. Keen, "The manufacturers also document that CC's have excess noise and bad drift with temperature and aging."

    Ok, so the manufacturers say they may hiss with aging.

    Most of the CC datasheets say they have a shelf life of 6 months. There are NOS Allen Bradley Resistors available that were manufactured in the twentieth century. Many on TDPRI and elsewhere buy these even though they are past their shelf life. How many of them meet the manufactures specs after all these years? How many hiss?

    My point is... for a *guitar* amp, ime, there is very little audible difference between properly functioning resistors. Sure as Mr. Keen wrote, "we should be prepared to replace CC's every few years" but that is a discussion of life expectancy not sound quality.

    I fully agree resistors can be rated for quietness by type/construction on a scale. They can be rated for quietness by wattage capability on a scale. I would like to see a double blind test on a *guitar* amp where one could determine the type/wattage of resistors. Can one really hear a difference?

    Carvin uses 1/4W resistors on several of their amps. (Even for plate resistors.) Where do we see all of the conversation about changing these resistors to 1W or 2W to reduce noise? Where is the conversation saying Carvin amps are noisier than the next brand?
     
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  10. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    The CCs in my pro-built 5E3 were brand new modern-make from a busy builder, and I replaced them in the early going. There’s also always a subjective piece in this, but the difference was obvious. I think Keen is saying to use CC *very* sparingly, and *also* replace the few you use as they age, cuz they get even noisier (and drift in value). All my reading seems to suggest replacing CC in the input chain even if they aren’t aged — I can’t recall reading a source that doesn’t suggest this as an early or first step — *if noise is a problem.*

    We see lots of pro builds and good kits that supply CC there. If you don’t have hiss, or it isn’t a problem in your use, of course I wouldn’t replace.

    Opinions differ, and it wouldn’t be a forum if they didn’t, but for science? I'll go with Aiken on resistor types:

    “Wirewound resistors are the quietest, having only thermal noise, followed by metal film, metal oxide, carbon film, and lastly, carbon composition.” And…

    “The most significant contributor to noise in guitar amplifiers is the use of low-wattage carbon composition resistors.”

    Re wattage and the proportional difference: “Since the noise is proportional to resistor size, the use of 2W carbon comp resistors will improve the performance over that of 1/2W resistors. Studies have shown a factor of 3 difference between a 1/2W and a 2W carbon comp resistor operating at the same conditions.”

    But if you like Keen on CC mojo (and I do) in the few places where it does happen, recall he notes the soft distortion we want is suppressed by increasing resistor wattage. Hey, Carvin may be onto that… :)
     
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  11. NSB_Chris

    NSB_Chris Tele-Holic

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    In the end we are all resistor cork sniffers! :lol:
    If you drink enough wine, the vintage does not matter and you cannot tell the difference.
    If you play loud for long enough, it does not matter if you have CC or metal film and you cannot tell the difference... so build what you want and play loud!!!!

    Well ... as I am building amps targeting moderate dB levels ... drive the amp hard and play at reasonable levels and you probably still cannot tell the difference ... or is that more related to how much I drink when I play at reasonable dB levels so that I cannot tell the difference ...
     
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  12. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Heh, well said. For resistors, I think science and evidence at least *exist,* even if we can't always sniff 'em out. Caps? Now that's some good pixie dust. Sure I have preferences and opinions, but I recognize they're just opinions. Still, hey, they're more fun and less harm than most opinions in this world...
     
  13. NSB_Chris

    NSB_Chris Tele-Holic

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    No truer word were ever spoken!

    Honestly, I would love to have the ear to be able to voice amplifiers to tone like a fine Swiss watch like others, but I don't. I like trying to understand how things work and I like implementing "good" practices as defended by people with more skill and experience than me, even if I will not be able to tell the difference. It is just part of the process and what makes it enjoyable.

    Edit: One other aspect that is probable most influential is that so much effort and commitment goes into a build that I don't want to get bitten by something that was easily accommodated by a small change. Leave nothing to chance. However, every build I discover or get advice that alerts me to things that I probably should have done differently on previous builds ... even if they sound good to me.
     
    Last edited: Sep 29, 2021
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  14. chas.wahl

    chas.wahl Tele-Meister

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    Hey, I have a resistor question, as long as things are trending in that direction:

    I wasn't aware until recently that non-inductive wirewound resistors exist. Is there any reason to prefer that type (using bifilar or Ayrton-Perry winding pattern) for dropping resistors or cathode resistors? There's a little FAQ at Digi-Key:
    https://forum.digikey.com/t/inductive-vs-non-inductive-resistors/62
    that suggests that film resistors may also be inductive, like wirewound resistors with "common" winding.
     
  15. NSB_Chris

    NSB_Chris Tele-Holic

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