5E3 1/4 power switch?

Discussion in 'Shock Brother's DIY Amps' started by Uncle Daddy, Jun 13, 2018.

  1. Uncle Daddy

    Uncle Daddy Tele-Holic

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    So I got around to wiring it up today. It seems to work best at higher volumes. It feels like about a 40% drop in volume, which guess is to do with the way power and volume interact. 75% less power doesn't equate to 75% less volume. For some reason, this build breaks up late, and at the moment I'm running a 12AY7 in V1 and a 5751 in V2, so cutting the power still doesn't get into bedroom filth. I'll report back with a tube swap later.

    It it worth it? Maybe. Time will tell.
     
  2. timewaster1700

    timewaster1700 Tele-Meister

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    Thanks for reporting back. I’m curious to here what the tube swap will do. Maybe a couple 12AX7’s will get it where it needs to be. What are your Power transformer voltages? Maybe lowering those would help too
     
  3. Outlaws

    Outlaws Tele-Meister

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    I run my THD hot plate at the -12dB setting with my 5e3 build and it’s perfect level for living rooms with a 93/94dB Custom 20oz ceramic speaker, or with a Weber 12A125A Alnico.
    It’s not apartment quiet, but nothing is shaking and the amp doesn’t feel like it’s suffocating.
    Any quieter and I’d just get a modeler so I don’t waste my vintage tubes life. I find the sound is destroyed beyond -12dB on it. Same with a JTM45 and Boogie Mark V.
    I tried opening the Hotplate up to measure what gets to their “-12” but I cannot open it. Something will break if I follow the internet instructions.
     
    Last edited: Aug 19, 2018
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  4. Uncle Daddy

    Uncle Daddy Tele-Holic

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    I'm going to build this in a pedal box. Should prove interesting.
     
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  5. timewaster1700

    timewaster1700 Tele-Meister

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    Oh good idea. Please report back when you finish it. Only concern I could see is it having enough heat dissipation.
     
  6. Uncle Daddy

    Uncle Daddy Tele-Holic

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    I've noticed that the positioning of the resistors between the board and the transformer seems to add a bit of background hum, probably coming from unshielded wiring running up to what was the standby switch. The good news is the 1/4 power position filters out most of it, making the amp quiet again. I recon it might be better as an external unit.
     
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  7. Uncle Daddy

    Uncle Daddy Tele-Holic

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    Turns out the extra hum was partially caused by a rough V1 load resistor. I swapped them both for a 1w metal film and much of the hum is gone. There's still a bit, probably from the extra wring in the noisy end of the amp, but the 1/4 power switch totally kills it now. Putting the resistors and wire in the bottom of the chassis may well be a better alternative, that or shielded wire to the switch. It's nothing like a Deluxe Reverb on tickover though!
     
  8. Musekatcher

    Musekatcher Tele-Afflicted

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    Absolutely. Trying to tame a 5e3 right now, that's giving my Twin a run for the money. I like the idea of a 1/4 power switch. Or maybe a less efficient speaker.
     
  9. Ricky D.

    Ricky D. Poster Extraordinaire

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    I once had a stereo rig at home that had a power meter on the amp. I was amazed at how loud it was even at 1/2 watt, much to loud for "bedroom volume". Loud enough to interfere with normal activities in the rest of the house.
     
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  10. jhundt

    jhundt Doctor of Teleocity

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    a friend of mine bought a massively inefficient 6" car stereo speaker which he uses when he's testing amps in his home workshop. It's small and easy to move around. He can put it in a cardboard box for less volume, or throw a pillow over it for even quieter sounds.
     
  11. Uncle Daddy

    Uncle Daddy Tele-Holic

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    Ah, the old pillow over the amp trick. I'd be starting to sound like Wes.
     
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  12. dannieh42

    dannieh42 TDPRI Member

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    I tried the 1/4 power mid and did not like it because of the loss of some of the treble. So, I installed a pre-PI master volume. It was an easy mod and gets you to bedroom levels of you want. My circuit is a little different because my my 5E3 has the Tweedle-Dee mod, but here is a link to when I was doing it.
    https://ampgarage.com/forum/viewtopic.php?t=31140
     
  13. Uncle Daddy

    Uncle Daddy Tele-Holic

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    It's been a while, but I eventually built this configuration into the amp, using 25w resistors with the 12 and 16ohm values. I used the standby switch hole, and mounted the resistors to the back wall of the chassis. It works really really well. For indoor use it really tames the 5e3. 1 or 2 watts is still loud in a small room, but I can take it up to the edge of breakup and still keep the neighbours mostly happy. At the moment I'm using a 12ay7 in V1, but I plan to experiment with an ax7 to see if it give up the juice even earlier.

    All in all, a happy bunny for the price of two resistors and a switch.
     
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  14. Wally

    Wally Telefied Ad Free Member

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    It takes a reduction in power by a factor of 10 to cut the volume by 50% through the same speaker/s.
    A reduction of 25% in power output is maybe perceptible but not anything close to significant.
     
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  15. Uncle Daddy

    Uncle Daddy Tele-Holic

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    I gather that the 2 resistors do just that, dropping around 90% of the current to the speaker. At a guess, I'd say the effect on the volume is about 50%.
     
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  16. jtcnj

    jtcnj Tele-Holic

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    just ordered the 8Ω and 16Ω 25w pair.
    will probably build as a hardwired cable (no switch) in a pedal box with a length of speaker cable and plug in and out and use on my 5e3 and 18w TMB builds.
    Can always drill ventilation as needed.
     
    Last edited: Nov 29, 2018
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  17. mcentee2

    mcentee2 Tele-Meister

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    Hi, did you get around to building this? How did it go?

    This sounds great flexible way of doing it!!


    Does anyone know the maths for this so I can work out all the possible combinations downwards in power?

    I get the calculation for total ohms kept at 8r, but I can't see the method to get the resulting power left ?
     
    Last edited: Feb 9, 2019
  18. jtcnj

    jtcnj Tele-Holic

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    I did; in hindsight I would have preferred to use jacks, not use the plywood and caulk to mount the components, and used the values for 10%.
    the cable is a little short
    It gets warm but not hot
    It cuts some volume but not enough.
     
  19. mcentee2

    mcentee2 Tele-Meister

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    Does anyone know where the 8 series/ 16 parallel, and 16 series /12 parallel come from?

    Just used the Weber lpad design tool and it shows:

    6dB loss ( 1/4 power)
    4 ohm series
    8 ohm parallel

    10dB loss (1/10 power)
    5.47 ohm series
    3.7 ohm parallel


    Why should I choose these instead of the ones in this thread?


    Thanks
     
  20. harleytech

    harleytech TDPRI Member

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    I put Rob's pre-PI master volume in... I love it.. works great !
    I can dial in what I need or go full volume.. Used the Ground/standby hole
    1M audio pot,a couple of wires and no big resistors...
     
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