Power Attenuator under $180 for 50watt JCM 800

Discussion in 'The Tone Zone' started by Dwayne Eash, May 10, 2020.

  1. JohnH

    JohnH Well-Known Member

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    Just trying to help figure out if my design will meet your needs. The attenuator works in small switched steps, so I was hoping youd be able to hear what those steps are to see whether they give you fine enough control, I think they do. Sure your amp will sound different, and it will sound like itself. Also, the simplest versions start with a -7 db (ie two steps) setting and go lower from there in 3.5db steps as in the clip. If that is not too much attenuation for the loudest attenuated setting you want, then you can do a simple version (easy to build), and then reduce further from there. Late night on my 50W VM, Im often at -31db.

    Ill shut up now, and I hope you will find the best solution for what you need, within your budget. Happy to help if I can
     
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  2. Dwayne Eash

    Dwayne Eash Active Member

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    Yes, I tend to agree. The Bugera copy of the Jettenator, seems like it has most of what I want in a power attenuator. But it does not seem to be reactive like Weber speaker motor models, and I have long appreciated that bit of inventive engineering.

    So that I could have a simulated reactive effect, cheaply provided without a speaker, is pretty nice, such that a DIY version seems attractive. A straight resistive load, will always sound a little dull or flat, less lively and natural, than a reactive (more realistic and lively) load.

    I have not studied the Bugera clone of Saldono's design much, but I highly suspect it's not reactive, in that it does not include speaker emulation physics.
     
    Last edited: May 15, 2020
  3. Dwayne Eash

    Dwayne Eash Active Member

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    I don't mind if it starts out with minus 15 or 20 bB, so lets simplify even more, LOL. I can see more clearly now, you tend to refer to dB, more than power reduction, when trying to help others attenuate.

    The problem I have is that, I have no meter to reference for dB, just if something sounds louder or quieter to my ears. Although,, I probably could download an app for my cell phone.

    Thanks for clarifying the dB emphasis for your audio comparison, that's more helpful how you described it this time, so I'll give it another listen. But from the first listen, I suspect I'll want a smaller gap between jumps than just 3dB for the finest control step.

    Could I make it more complicated by adding a 2 dB step? And is it worthwhile/possible, to add the footswitch to on / off the 3 dB (or 2 dB) boost?

    I figure your probably a busy man, who isn't, but please don't worry about writing me too much, I welcome your input. This is a very important decision for me, and one I have been wanting to accomplish for the better part of a decade.

    I am hoping you will help me determine the right layout design, according to my wish list, and then see how expensive it is to build. Next up, a re-listen to the volume gap size. How much of a boost, is a typical clean boost? IDK...
     
    Last edited: May 15, 2020
  4. Dwayne Eash

    Dwayne Eash Active Member

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    As to clean boost, I guess it can get a bit complicated. This is from Wompler pedals, on the issue of a clean boost and db's.

    Quote
    "Here is the issue, when I wanted to boost the solos for the dirtiest tones, I need just under 3dB to get to the level. About 5dB for when the TS isn’t on, and upto 10db when it’s clean. And yes, this confused the living daylights out of me!

    Here is what is happening… and how it also ties in with bDub’s video about power/wattage/dB.

    Everything is relative to the EQ of what you are hearing."
    End quote.

    So I guess clean boost can be 10dB, and it can be 2.5dB. Depends on the sonic situation. It makes sense, but I would not have easily guessed, there was such a wide db gap, depending on how clean or dirty the amp is running.
     
  5. Dwayne Eash

    Dwayne Eash Active Member

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    If we could change the resister and associated values,, maybe I would prefer something like the following dB frame of reference, steps of attenuation.

    -2 dB on/off footswitch (fine adjustment for clean boost)
    -4 dB on/off footswitch (med adjustment for clean boost)
    -8 dB on/off footswitch (large adjustment for clean boost)
    -8 dB on/off switch
    -8 dB on/off switch
    -16 dB on/off switch
    -16 dB attenuation always provided, no on off switch
    +
    62 dB's of total attenuation, available in 2 dB incremental steps, and up to 14 dB of foot-switchable clean boost/volume pedal, from a triple footswitch.

    But I don't know what are the limitations of the economical resisters to use and all that. I don't know, maybe your 3 dB as finest control is better. That might look more like the following.

    -3 dB on/off footswitch (fine adjustment for clean boost)
    -6 dB on/off footswitch (std. adjustment for clean boost)
    -9 dB on/off switch
    -9 dB on/off switch
    -18 dB on/off switch
    -18 dB attenuation always provided, no on-off switch
    +
    63 dB's of total attenuation, available in 3 dB incremental steps, and up to 9 dB of foot-switchable clean boost/volume pedal, from a double footswitch.

    I hope this helps. Let me know what you think. This way, I could approach bedroom levels, yet still sound like it's a roaring amp. I mostly just want to shave off the top half of the power, to let the power section finally saturate and get into singing overtones, without so much volume.

    Great stuff AFTER MV 4! LOL! But can only safely do MV 3 at the house. I bet all I need is MV at 4.5, and an attenuator to take the volume back down to MV 3.2, and I'd finally have all the power amp overdrive, and lush singing overtones, I could dream of!!!
     
    Last edited: May 15, 2020
  6. JohnH

    JohnH Well-Known Member

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    Good thinking process but may need to think some more! There s a few issues there:

    That step on your MV from 3 to 4 or 5 I suspect would be less than the 16 or 18 db noted above, so if you want the option of getting to that loud but attenuated volume, id say the base minimum of -7db is a better starting point and switch down to lower volumes from there.

    -63db is a reduction in power of 1/2000000, so probably don't need to go that low.

    All the attenuation levels are different to current designs so the design would be a do-over


    For a foot-switchable system, there are three possible ways, which need to account for dealing with fairly high currents.

    1. Could build it all into the main box, then the whole attenuator with its bulk, has to be on the floor being stomped on, or,

    2. Could have a dc signal and a relay system so that a plugged in floor switch controls relay switching back up at the main box, or,

    3. Build a basic attenuator, to one of the Lite designs, and then once you have that working, make another box to add two more resistive stages, on the floor, with a couple of footswitches. You'd go from amp, to main box at the amp, to floor box, to speaker.

    I recommend option 3. You can order the parts for the main box and build it now. The design is all done and tested. Then when you have got to know it, add the floor box which is an even simpler build, but can have values tuned to give you the variation in boost levels and any finer variation that you want.
     
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  7. Dwayne Eash

    Dwayne Eash Active Member

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    That sounds great. My first idea was to have it all in one box with electronic relays, but after you described option three, that sounds better.

    However, that mean a seriously long length of highly powered speaker cable. So the question naturally surfaces, are long stretches of full powered speaker cables, more prone to noise problems and safety issues, than much shorter runs?

    I would suspect they are.

    So, if a 50' or 60' long speaker cable run, is not recommended over shorter runs, then I would probably opt for option 2, with the attenuator close to the amp, and use some electronic relay switches, controlled by a footswitch.

    Is one method safer than the other? Safety always matters.

    I also wonder about the cost of each approach. I don't know much how to read electronic schematics (that's what I meant instead of IC's, hehe) and have not yet sourced electronic parts like these, so I don't know what to look for yet. So I don't really know where to start.
     
    Last edited: May 15, 2020
  8. Dwayne Eash

    Dwayne Eash Active Member

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    Ok, sounds good. I see we have 3.5, 7 and 14 dB reduction stages. Excellent. Here's my reshuffle.

    3.5 dB foot switchable on-off
    7 dB foot switchable on-off

    3.5 dB switchable on-off
    7 dB switchable on-off
    14 dB switchable on-off

    35 dB total available attenuation. Two lowest attenuation stages on the foot pedal, for three different clean boost volume settings. Plus three set-and-forget, power selections on the base unit, so it's more useful for more different kinds of amps, and different kinds of playing requirements.

    Is that complicating things too much? I prefer this layout, with more convenient selections of dB attenuation possible.

    Is there a reasonable cost effective way, to include a full dummy load with this design? Or is it better to do that separately?
     
    Last edited: May 15, 2020
  9. Dwayne Eash

    Dwayne Eash Active Member

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    “If” it's better to have an even number of attenuation stages, like to create a more proper speaker emulation circuit, then here's me thinking ahead. Plus it's probably more economical, to buy more of the same kind of parts. So then maybe this design is better and possibly more economical.

    foot switchable
    -3.5 dB on-off
    - 7 dB on-off

    set and forget (base switches)
    -3.5 dB on-off
    - 7 dB on-off
    - 7 dB on-off
    - 7 dB on-off

    Only two attenuation stage sizes, 3.5 dB, and 7 dB. That simplifies the parts list, but expands the number of parts to assemble. I don't mind the extra work. I work for myself, free of charge! ;)

    The main thing is, which design arrangement, would be better, a 5 stage, or a 6 stage? I realize another option is available, a four stage. I hope it doesn't only work properly, in four stages at a time. That would s@ck! Or maybe I could double four, for eight total stages.

    So how modular are these things, in terms of number of attenuation stages? If it's feasible, I'd be happy with the 5 volume reduction stages, from the previous post.
     
  10. Dwayne Eash

    Dwayne Eash Active Member

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    I hope you do realize, that 50 watt amps, is not the actual power rating, right? Like mine is more like 60 watts, but I think it peaks at around 150 watts. But don't quote me on that.

    There are two amps, in every guitar amp, a preamp, and a power amp, and they are not always represented in the same proportion, depending on the maker and the design. It depends on the circuit design, and user selection, how much of the preamp is emphasized, and how much of the power amp.

    Some of this might have to do with "peak" and "RMS" figures. That's me pretending like I know a little about electronics.
     
  11. JohnH

    JohnH Well-Known Member

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    All OK, just on the main box, there needs to be in addition, Stage 1 which is the fixed reactive stage at -7db.

    You can add as many stages after that as you wish in any order. It doesn't lose any tone. The numbers and wiring simplicity work best with the simple two-resistor stages if they are in the range 3 5 to 14 each.

    I base the power calcs on numbers using 50W, and then give a factor or x3 on that for speccing parts. So well able to deal with actual output of a 50W amp.

    I think @Gene Ballzz (who was rhe first to build this design) may have built one with several equal stages, but now does the 3.5, 7 and 14 on his builds. It's more compact and saves parts.
     
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  12. Dwayne Eash

    Dwayne Eash Active Member

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    Sounds good! So do you have any ideas for sourcing reasonably priced "two button" foot switching for electronic relays? Or do you think it's safer, and always noiseless, running 50-60' of highly powered speaker cable?

    So far I prefer foot switch operated, electronic on/off relays.

    I can't wait to draw up a diagram, make a parts list, source parts, and find out how much this thing is going to cost to build!

    It's hard to believe all that's needed is one simple "always on" attenuation circuit, to accomplish the speaker physics reaction, to let the amp work, and sound that much better under attenuation. Such an elegant design! Well done!

    If I wasn't doing this DIY reactive load project, I'd be facing buying a Weber MASS 150, for $296, which is twice as much as I wanted to spend.

    Thanks much to you, and Aiken amps for the speaker compensation design, for such a great and effective, DIY amplification attenuation design!!!
     
  13. bad565ss

    bad565ss Well-Known Member

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    I'm curious why you need 50-60ft of speaker cable?
     
  14. Dwayne Eash

    Dwayne Eash Active Member

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    Footswitchable clean boost, pure organic sound provided by the amp, so it's ultra transparent. Lets the attenuator, also provide pure organic clean boost / volume control, at footswitch convenience. Very nice add on, for the attenuator.

    It could save the typical guitarist some money because of possibly loosing a volume pedal, and other than lacking EQ control, stands to out perform (replace!) clean boost pedals (on attenuated amps).

    This 50-60 foot of speaker cable, is a theoretical option, of using a certain kind of a footswitch, that JohnH himself, suggested this option.

    It's like cutting the attenuator in half, you optionally stomp on the half that is near you, some 20-30 feet away from the amp and cab, to where you perform. It's the two cables that connects the two half's of the attenuator, the amp and the speaker cab, with a 20'-30' cable, a cable each way!

    So that's about 50' - 60' of powered speaker cable. I asked about the noise (and safety?) problems, and am waiting on a response, but so far he didn't seem very concerned about it.

    I would not be surprised if this option of splitting up the attenuator, is not the best option, because of the troubles involved in such a long run of speaker cables.

    I guess not many have talked about using foot-switches, to control two of the lowest attenuation stages, so you can turn the attenuator, into providing some excellent organic clean-boost.

    But that is what I am suggesting, an attenuator, that is partly foot-switchable for clean boost, and the rest on the attenuator box, is "set it, and forget it".

    Last but not least. The other way of using foot-switches, the one I suggest is safer and less problematic, is to use electronic relays, that would avoid 50-60 feet of powered speaker cable.
     
    Last edited: May 16, 2020
  15. Dwayne Eash

    Dwayne Eash Active Member

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    Right on, that's sorta what I figured. Because it offers the most options, using the least parts. Elegant, that's how I want mine, but with the addition of two foot switchable clean boosts, a 3.5 footswitch, and a 7 dB footswitch.

    And those combined would offer 10.5 dB of additional attenuation options, for a total of 42 dB total attenuation. But more importantly, it lets the attenuator, also became a foot switchable clean boost, of three different volume levels.

    That's a two'fer, in one awesome design! A great power attenuator, and a clean boost option. Who doesn't want to toss a couple clean boost pedals, if the amp's own power (attenuation) pedals, can do the same job, and probably do it better?

    That might save the typical musician $100 - $300 :bday: in clean boost pedals! Talk about a nice add on bonus. :applause::slash:
     
  16. JohnH

    JohnH Well-Known Member

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    Hi Dwayne
    I think you could go either way with the footswitch system, either a separate resistor box daisy-chained after the main attenuator, or, relay control using a remote footswitch with all the electronics in the main part.

    With the first option, even 60' of cable, using 18ga speaker cable, only adds about an ohm of resistance, about 5% of what the attenuator output is designed for in an 8 ohm system. Not significant and the amp never sees it anyway since its at the speaker end after the main box. interference shouldn't be a problem in an output circuit. The main box is simple, but you need two thickish cables down to the floor and back.

    The relay option, looks like it would be within range of lots of auto-electrical relays for horns etc. A single cable with two or three cores goes down to a simple footswitch, or a double one. I looked at a relay deigned for 12V, but it looked like it would run fine at 9V. Now you have to have:

    all 5 stages in the main box
    a dedicated 9 or 12V dc supply, with socket to plug it in
    extra jack for footswitch
    two relays
    more wiring
    bigger box

    There's no reason why this shouldn't work well, but we haven't tested it and don't currently have a diagram to represent it.

    Note that to build any of this, youll need to get you head around what the schematics show and interpret it into a build sketch of some kind based on the components that you use,
     
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  17. Dwayne Eash

    Dwayne Eash Active Member

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    Attenuator M 4 my version.jpg View attachment 73225
    Awesome! I sorta figured it was time I contributed, and to help better dive into the design better, so I came up with this graphic.

    Based on excellent work! ;) hehe

    I figure this is it, but the last two stages can be foot switched for clean boosts. The 14 and the 7 right next to it, would exchange positions, or the lack of order would drive me crazy. hehe Big to small, and I'm good. ;)

    Let me know what needs changed, cause I just tried to make it look like what I guess it should look like.
     
    Last edited: May 16, 2020
  18. JohnH

    JohnH Well-Known Member

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    OK good, there'll be a few suggestions, later. What amp tap do you plan to use and what Ohms cab or cabs?
    is this to be the relay version?
     
  19. Dwayne Eash

    Dwayne Eash Active Member

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    That's what I was hoping. Thanks. I'm guessing 8 ohm, as I have two 12's in two different cabs. And they are each 16 ohms, so I just plugged them both into the back for 8 ohm tap into the amp, as prescribed on the back of the amp.

    So I guess it would be the amp's 8 ohm tap, to an 8 ohm load from a pair of 16 ohm speakers. Unless you have a better suggestion..

    Yes, I'd like it to be the relay version. Unless it's cost prohibitive.

    I don't play out, but I have heard plenty of horror stories about catching noise in rigs, so I'm a believer in shortest, cleanest signal path, as possible. Just seems safer. We don't want the spinal tap "failure" scenes, hehe, with the local airport or national guard broadcasting over the guitar rig. hehe

    Stranger things happen.
     
  20. Dwayne Eash

    Dwayne Eash Active Member

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    Here's what I think you asked for at one point. Attenuator diiagram.jpg
     

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