1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Proper lead dress - "as short as possible" vs "tidy" vs wire separation

Discussion in 'Shock Brother's DIY Amps' started by itsGiusto, Sep 11, 2020.

Tags:
  1. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    604
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    There's something that's been bothering me for a while. Many people and amp-kit companies advocate for proper lead dress meaning that you should make your wires both "as short as possible" and "tidy". And it seems that most of these kit companies, in their published pictures, have their wires almost always running along the chassis, and often bending at right angles.

    I never really understood this, because it seems like a contradiction to me. If you truly wanted your leads to be as short as possible, the you'd have to give up the right angles, as well as the wires running along the chassis, and instead connect them in a straight line in the 3rd dimension from one component to another. In addition, the advice for neatness also can go against the general advice to keep the wires separate from each other, when wires are bundled together and run along the chassis edge.

    Take a look at the Ceriatone image here, for example:
    https://www.flickr.com/photos/[email protected]/26343801374/in/album-72157665828886623/
    For the twisted white wires running to the indicator light, it's definitely not as short as possible. They have it bending around the indicator, climbing up the wall of the chassis, and connecting to the indicator's terminals from behind. Same thing goes for the twisted purple wires running from the PT to the diodes. You could easily cut out half the length of that wire if you had it run directly, instead of bending around, hugging the chassis wall, before coming out at a right angle from the chassis wall and coming up to the diodes on the board. Same thing goes as well for the brown wires running from the PT to the heater of V5. And at the input jacks, the green wires running from the jacks to the board don't go directly there, they first run down to the chassis floor, then run along the floor, and then come up to the board.

    And we can see more on page 31 of the Metroamp instructions here:
    http://valvestorm.com/sites/default/files/50_WATT_KIT_INSTRUCTIONS.pdf
    The green heater wires going to V5 make this huge arc, coming at the tube pins perpendicularly. And the yellow wires coming from the 2nd can-cap make this right angle near the PT, instead of running directly toward the board. And if you take a look at the right edge, you can see that tons of wires are bundled together and run along the chassis wall.

    So I'm kinda wondering, what the guidance really is. Is it "keep your wires as short as possible, but this is not as important as having them neat and running at right angles to each other"? Or does it vary for different types of wires?
     
    Last edited: Sep 11, 2020
    Sidney Vicious likes this.
  2. D'tar

    D'tar Friend of Leo's

    Posts:
    3,159
    Joined:
    Jan 11, 2013
    Location:
    WNY
    Just do what Lupe did. Take a proven layout as such...


    [​IMG]

    and turn it into this...

    upload_2020-9-11_11-14-56.png

    Use the chassis to your advantage. I will go "around" if it stays quiet and adds to aesthetics. If it's not quiet then try something else.
     
    David Barnett likes this.
  3. Digital Larry

    Digital Larry Friend of Leo's

    Posts:
    2,616
    Joined:
    May 30, 2017
    Location:
    Silicon Valley, CA
    It depends on the signals.

    Wires running in parallel will be prone to picking up signals from each other. This could result in oscillation due to unintended feedback, or hum for example if you run your input leads right next to the heater power supply wires.

    Big loops will pick up magnetic fields (like from your power transformer) much better than twisted pairs.

    Coupling is more of a concern where signal levels are low and there's a lot of amplification afterwards. So running the heater supply next to your speaker output is less of a concern than running it next to the amp's input.

    That's about my level of understanding.
     
    LongbeardAmps and itsGiusto like this.
  4. telemnemonics

    telemnemonics Telefied Ad Free Member

    Age:
    61
    Posts:
    24,325
    Joined:
    Mar 2, 2010
    Location:
    Maine
    I'd say it varies with the function of the wires in question.

    Work on some old classic amps, moving wires to the preamp tubes around with the amp running so you hear what happens when you move the wires.
    There are styles or approaches to wiring and a neat look alone is not the most quiet, but a quiet lead dress doesn't have to look bad.

    As short as possible might mean as short as possible without adverse effect.
    Move those wires around while listening and you'll hear the adverse effect.
     
    LongbeardAmps likes this.
  5. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    604
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    That might be what's meant... but that isn't really helpful in trying to communicate what should be done. I'm trying to learn this as a (somewhat) newcomer to amp building, and I'm trying to learn the rules. I'm trying to learn when there are adverse effects and how to minimize them, I can't just magically know. Moving wires around might sometimes indicate, but there's no way to actually shorten the wire while the amp is still on to listen to that. It seems like somewhat circular logic, if the "keep the wires short" advice is meant as the means of minimizing adverse effects.

    And I think I've learned as well that sometimes noise and adverse effects can creep into the signal little by little. It's not always completely straightforward to pinpoint noise and bad sounds, it's not like I'm always able to say "ah, because this wire was 2 inches too long, that's why this sounds bad". Sometimes it's the full system, a confluence of factors that contributes to the bad sound. In those cases, it seems very very difficult to know why there are adverse effects, and it's helpful to work from preexitsting guidelines
     
    Last edited: Sep 11, 2020
  6. Dan_Pomykalski

    Dan_Pomykalski Tele-Meister

    Age:
    30
    Posts:
    300
    Joined:
    May 16, 2019
    Location:
    Madison, WI
    I kind of thought the guideline was “keep the wires as short as possible (while running them along the chassis/and avoiding noise/oscillation).”

    But I honestly have no idea what I’m doing like some people do. I usually take the “good enough” approach...
     
  7. telemnemonics

    telemnemonics Telefied Ad Free Member

    Age:
    61
    Posts:
    24,325
    Joined:
    Mar 2, 2010
    Location:
    Maine
    Well I doubt there's ever a wire that you can make 2" longer and gain anything, basically longer wires never make the amp better, except in cases like heater wires that need to be kept away from signal carrying wires, and signal carrying wires need to be just long enough to be kept away from heater wires or power supply components.

    So a good starting point might be to keep all wire runs as short as possible except for the wires you need to separate from other wires.
    And like the input signal wire from the input jack to the first preamp tube might need to be kept away from all other wires plus maybe even get a shield.

    Notice that BF Fender runs heater wires up in the air while vintage hand wired era Marshalls run heaters against the corner of the chassis. Then you start to see some sense in the way wires are run, at least that there is a master plan and it's not random.

    Same with signal carrying wires on the preamp tubes, some builders run them up in the air while others lay them on the chassis.
    If you get an old amp and move those wires around listening to the sound, you can get a sense of which wires are a routing concern.
    Every amp preamp tube socket wire has the same basic functions dictated by the pins on a 12ax7.
    In general, if the heaters are up in the air, the signal wiring goes down by the chassis, while if the heaters are down by the chassis, the signal wires run up in the air. Not all the preamp wires other than heaters carry signal, but in general terms those are not friends so stay apart.

    Those wire functions become a language you will understand after some practice.

    As far as the value of neat lead dress, poke around in some SF Fender amps and see what sloppy lead dress looks like.
    Maybe you like the look of Hiwatt ultra tidy lead dress with all the RA bends?
    Not the best for quiet performance!
    That obsession with appearance adds noise, but there more due to ground wiring schemes IIRC adding multiple final ground points.

    Really, study vintage amp lead dress, and think in terms of preamp tube pins on the sockets each having a standard function common to every amp. Preamp tube wiring is where the most noise vs quiet comes from, though grounding dress is also a factor but not as subtle dress related, and PS filtering is also a noise and hum factor that is not related to lead dress unless you design from scratch.
     
    bftfender likes this.
  8. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,620
    Joined:
    Dec 30, 2019
    Location:
    california
    Don't wire it like this:
    Inked85439CF6-4B87-40BD-95A6-D744E8076FAF crop_LI.jpg
    ------------------------------------------------------------
    Wire it like this:
    5E3V1V2.JPG
    The kit companies seldom show proper wiring IMO. As you have noticed there are many discrepancies.
    As you suspect, it does vary for different wires in the amp.
    Unshielded signal wires benefit from laying on the chassis to help shield them from picking up RF or other noise, so they are longer than a straight line shortest approach.
    Parasitic capacitive coupling is an issue which can lead to noise or oscillation so, some wires should not run parallel or be twisted with other wires.
    As you have noted, a lot of the right angles you see are more for looks than proper wiring. (Wires should cross at right angles to avoid capacitive coupling.)
    The heater wires are often longer than a straight line shortest approach. This is to keep them away from other wires. Some wiring schemes seem to go overboard, such as the lamp wire that you noted running the long way around the chassis. IMO that one should have taken a shortcut.

    Anyway, I think you are getting it. With a little thought, most wiring can be improved.

    I think I should mention the Ceriatone white wire that wrapped around the pilot light. I wire some parts of the amp like that. Marshall style lamps have high voltage AC to them. Heat shrink can easily cover the terminals when it is wired like that which protects some of us from accidental contact when we have our paws in there. I heat shrink the back of the fuse and the power switch as well.
    Since the Ceriatone amp did not appear complete, let's hope a little heat shrink was intended to be used.
     
    telemnemonics and LongbeardAmps like this.
  9. FenderLover

    FenderLover Poster Extraordinaire

    Posts:
    5,790
    Joined:
    Jun 11, 2009
    Location:
    Minnesota
    If you strive for tidiness and separation of signal wires from AC wires, you will likely be as short as practical and have good performance. I read dress of ground wires being important above, not really. You still want to be neat, but some use 'split ground' wiring that intentionally takes the longest path possible through the chassis (adding an intentional ground loop) while others can't copy it fast enough.
     
  10. printer2

    printer2 Poster Extraordinaire

    Posts:
    6,971
    Joined:
    May 24, 2010
    Location:
    Canada
    All of the above?


    Anyway, with high impedance circuit, high gain circuits or high frequencies beyond what we deal with layout patters. Each wire is a transmitter and receiving antenna. If the current is low then the transmission is low. If the wires are close to each other the interference increases with the square law. An efficient antenna is relatively long, also the greater the loop size of the antenna the more signal it will catch. (a triode circuit has the input loop from the grid to the cathode resistor, through the ground to the input jack (ignoring the guitar) back to the grid. The output loop is from the plate through the plate resistor to the next stage grid, though the tube, the biasing, back to the cathode and to the plate. Another loop is the power supply but generally the capacitor acts as a short and loads down the interference that can be picked up. Which brings up impedance, a low impedance run is more immune to interferance as it loads down the source interference to low levels. Knowing the difference between how a wire picks up magnetic verses electric fields can be important at times.

    That is a quickie explanation.
     
    Last edited: Sep 11, 2020
    Digital Larry likes this.
  11. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    One thing to add - I think 2020 state of the art inside guitar amps is more thoroughly thought out in terms of layout for grounding and low noise than the state 50 years ago. We're really doing a good job of optimizing these issues now, and we're down to very small problems and very small differences between methods in general.
     
    telemnemonics, bftfender and Nickfl like this.
  12. Nickfl

    Nickfl Friend of Leo's

    Posts:
    2,383
    Joined:
    May 24, 2016
    Location:
    Florida
    This. Lots of ways to get the job and neatness for neatness sake is not of great practical importance, though it can be satisfying.

    Sometimes inexperienced builders confuse OCD neatness with proper lead dress. Having all the wires running at right angles like a city street grid isn't a sign of thoughtful lead dress. Critical wires should cross at right angles when they have to cross each other, sensitive signal wires should be short, DC current loops should be kept as physically small as possible. Pure "neatness" is secondary to addressing things like this. This is why a true point to point "rats nest" can be quieter than a beautiful turret board build that compromises best practices for looks.

    The best builders can do both, but it takes a lot of skill and gives the rest of us something to work towards.

    This too. Perspective is important, in most amps the difference between perfect lead dress and beginner lead dress is marginal. Again, perfection is worth striving for, but its not going to make a noticeable difference unless its so bad it is causing noise or instability.
     
    Last edited: Sep 11, 2020
  13. dan40

    dan40 Friend of Leo's

    Posts:
    2,026
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    In the rebuild of your Plexi circuit, I would follow the wiring shown in the Metroamp instructions but also take a look at pics of vintage Marshall amps. The wiring layout they used has been tested with 1000's of amps over the years and if you stay true to all of their little details, your rebuild should turn out good also. The preamp wires need to be short... but... not so short that you can't run them with a bit of separation from each other. The main thing is to avoid long and loopy wire leads that can act as an antennae. Keep the plate leads flat against the chassis and crossing the filament wires at a 90 degree angle. The grid and cathode wires should gently arc around the socket with a bit of space between them. These two wires can lay flat on the chassis though I like to elevate them in sort of a "flying arc" on there way to the socket pins.
     
    itsGiusto likes this.
  14. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,142
    Joined:
    Dec 29, 2012
    Location:
    United States
    "As short as possible" is just plain bad advice. If you actually did that you'd most likely have interaction between plate and grid wires. There's plenty examples of good lead dress out there.
     
  15. itsGiusto

    itsGiusto Tele-Holic

    Posts:
    604
    Joined:
    Dec 31, 2017
    Location:
    Massachusetts
    I wish I could follow the Metroamp instructions exactly, but unfortunately, the fact that I started with the Ceriatone build forces my hand a little bit. Like for example, the metroamp's lamp is fed with a different voltage value, and thus a different power source, than the Ceriatone (120v vs 6v). And the Ceriatone build uses diodes instead of a bridge rectifier, so I'll need to run wiring to the board. But I will try to follow it where possible, and where I can't, I'll follow the Ceriatone layout.
     
    Last edited: Sep 12, 2020
  16. dan40

    dan40 Friend of Leo's

    Posts:
    2,026
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    Just try to keep the preamp sockets and tonestack wiring as close to the layout as possible and you should be good.
     
  17. DavidP

    DavidP Friend of Leo's

    Posts:
    2,971
    Joined:
    Mar 16, 2003
    Location:
    Vancouver BC, Canada
    I follow the 'short as possible' philosophy but with a little allowance if I need to tweak the location afterwards or cut/resolder for whatever. I'm not talking about doubling the lead length, just an additional 1/4 - 1/2".
     
  18. Norris Vulcan

    Norris Vulcan Tele-Afflicted

    Posts:
    1,185
    Joined:
    Aug 7, 2015
    Location:
    Somerset, UK
    I always thought the old Hiwatt was the gold standard in lead dress :

    [​IMG]
     
    David Barnett, dan40 and tubegeek like this.
  19. elpico

    elpico Tele-Afflicted

    Posts:
    1,173
    Joined:
    Sep 14, 2011
    Location:
    Vancouver BC
    That Hiwatt looks the way it does because of another factor to consider, serviceability.

    The building style Harry Joyce used came from military gear. When you're in a place far from help a guy with little training may need to fix a piece of gear. It's a benefit then if it's very straightforward to look at and replace parts in. Imagine trying to talk a guy through a point to point rats nest over a radio... On this amp you just say "the third doo-hickey from the left"

    They're very quiet amps as well, but that's not the reason for their layout.
     
  20. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,882
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    I thought it was done that way in case a starving musician had to eat off of it one day.
     
    D'tar likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.