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Stand alone vs. built in attentuator question

Discussion in 'Amp Central Station' started by etype, Aug 19, 2020.

  1. etype

    etype Tele-Afflicted

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    The Vox AC15CH has a built in attenuator that will take the 15w down to either 1.5w or 0.15w. Nowhere do I see a warning that you should not set it at either of the lower settings and crank it (same with the Marshall Origin attenuators and with Carr or Tone King and their built-in attenuators).

    However, reading about the Weber MiniMass 50w attenuator (or other brands) online, there are plenty of warnings about not cranking the amp while heavily attenuating the power.

    For example, from the Weber site (unclear if this only applied to high gain amps) regarding the MiniMass50.

    "Do not turn your amp all the way up. Even if you’re just knocking a little off the top with the attenuator, it’s a good idea to keep the amp somewhere in the middle at most. It’s best to find the lowest volume on the amp that is the acceptable tone to you, and then use the attenuator to bring it the rest of the way."

    Is there something Marshall and Vox are doing that Weber and Dr. Z, etc. are not doing in the attenuation? Is the issue simply that cranking the amp puts the same stress on the amp that cranking the amp without the attenuator? Even with the Vox or Marshall, should attenuation be moderately used.

    I have a Carr Skylark, and every once in a while I like to max the volume and attenuate it down to about 1w. It's an expensive amp, I don't want to kill it!
     
  2. scooteraz

    scooteraz Friend of Leo's

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    There are several issues here.

    Any time you crank your amp, attenuator or no, you are stressing it. You are putting full power through, and you have to dissipate the waste heat, which is usually more at full power operation. So there is that.

    You also have the attenuator. Some attenuators may not really be designed to turn 100 watts of output power into heat. Others are. Look at your manual to decide. The built in attenuators should be able to handle full power being attenuated down, if not there should be a manual note about how to limit power into the attenuator.

    I had a Princeton Recording Amp, and the attenuator worked great at full volume attenuated down to bedroom/apartment friendly levels. On that amp, I was let down by Fender’s digital designs, but the actual attenuator was great, and there were no restrictions.

    I currently own a Riveria Rock Crusher, and can attenuate my amps with that and no damage. Amp (and probably attenuator) wear and tear, but no damage.
     
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  3. Cali Dude

    Cali Dude Tele-Holic

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    I have two amps with attenuators built into them. I have never had a problem while running the amp high, and attenuating it a good amount. No damage, nothing. I love attenuators, and find that their sound (which allows one to really get their amp breathing to where it sounds great) is superior to most master volumes, and the buzzy distortion that preamp overdrive is known for.
     
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  4. MervsMods

    MervsMods TDPRI Member

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    How's that Rock Crusher working for you? I've heard it keeps the sound of the amp without losing the high freq. Is this true? I'm looking to get one for my 50W, but just can't believe the hype some ads (and stores) are dishing out..
     
  5. FenderLover

    FenderLover Poster Extraordinaire

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    They have to sell product so you can hardly blame them for lying, but people like to quote the ads. A speaker is a reactive device, so if the attenuator is not reactive, you know it's not the same. But you may still like how it sounds anyway, so there's that.

    The warnings about maximum power fall into common sense to me. If you want to crank a 100W amp into a 100W attenuator, there is zero margin even though one might think it should take it. It might. It might not. If you have a 50W attenuator with a 5W amp, crank that mother up.
     
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  6. etype

    etype Tele-Afflicted

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    Weber's site says if you are going to routinely crank the amp, then you should get an attenuator that can handle 4x the amps power. Their MiniMass50 is said to work with amps "up to 35w". I am wondering if, for example, the Vox AC15CH built-in attenuator can handle 60w.
     
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  7. FenderLover

    FenderLover Poster Extraordinaire

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    I would bet not safely.

    I've used my 50W Weber Mass with 40W and 50W heads, though not fully cranked or for extended periods. The more the margin, the better. Most importantly though, I think starting with the right power in the first place gives the best results. Dialing 50W down to 1W is just not a good idea. If you want 1W, start with 5-10W and take a little off the top.
     
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  8. SamIV

    SamIV Tele-Holic

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    I own a Vox AC4 with the built in attenuator. It has been one of its best features for me for apartment living and while I was in a hotel for a while. But I have to admit, it sounds better while not in use at the same volume. But trying to overdrive it without it at low volumes would not be possible. And I crank it without issues.
     
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  9. VintageSG

    VintageSG Friend of Leo's Ad Free Member

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    The attenuator in the Vox is a bunch of cement resistors. It's about as sophisticated as it sounds.

    http://www.voxshowroom.com/uk/amp/ac15c1_hood.html

    Scroll down to see it in all its glory.

    To call it a reactive attenuator may be stretching the truth on the part of Vox, but they're unlikely to equip it with quick-die componentry so as to avoid warranty claims and bad press.
     
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  10. scooteraz

    scooteraz Friend of Leo's

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    I have the one with the EQ, and it can sound pretty good. It is also pretty doggone expensive. I can’t comment on a any personal experience on any of the lower models. Remember, the speaker is part of the sound, and speaker cone breakup and peaked motor non-linearity is part of your overdrive experience. So does it sound exactly the same, no. But the Rockcrusher does this as well as anything else, and better than most.


    If the attenuator is properly designed to dissipate 100 watts, then there would be no problem hitting it with 100 watts. Any good design rating should have some safety factor built in. Buying a 50 W rated attenuator for a 5 W amp is sort fo like buying 185 mph rated 285 section tires for your Chevy spark. Yes they will do the job (and more), but they are overkill.

    Three issues here.
    1). IIRC, Weber uses a speaker motor in a small box to dissipate the energy of the amp. They then name the device after the supposed peak power capability of speaker motor (in free air) with models like “50W”. They then tell you that model is good up to 35 W because of course the heat cannot be transferred from the motor quickly enough to not damage the windings.
    2) They then say things like “buy an attenuator with 4x the capability of the amp”. If that is the case, would’nt the 50W only be good for a 12.5 W amp?
    3) Manufactures can call their product anything they want (Rivera Rockcrusher, really, what does the crushing of rocks have to do with attenuation of volume in a musical environment?) so Weber is free to call their product a 50 (or even 200 Watt) attenuator, then say “don’t use at over 50%-75% of rating”. What they are really saying is the so called 50W model is really their 35 Watt (electrical load dissipation) attenuator and the 200W model is their 100 Watt attenuator.
    Not knocking their product, just noting that they have some amount of hype and mis-naming of product on their own.
     
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  11. Cpb2020

    Cpb2020 Tele-Meister Silver Supporter

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    I just looked at my Tone King Imperial manual, with built in attenuator, and there is no caution about turning the amp all the way up. That said, we rarely have the volume past 6 of 9.

    With a built-in attenuator, the manufacturer knows the amp output and is designing the attenuator for that given output (e.g., 20w for the TK Imperial). Whereas the manufacturer of an attenuator and a manufacturer of an amp may rate their products differently and, as Scooteraz indicates, they are sometimes hyped. So, if the attenuator is not overhyped, there should be no issue running the amp at max levels.
     
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  12. Wally

    Wally Telefied Ad Free Member

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    that built in attenuator in the Tone King Imperial is not as simple as some attenuators in that it appears to utilize a special design output transformer. Maybe someone could explain?? Ime, the Imperial MKII I had the use of for a couple of months had the best attenuator I have heard.

    http://schems.com/bmampscom/tone_king/20th_Imperial_SC200HB_pg2.pdf


    As for using a 100 watt attenuator on a 100 watt amp with the amp dimed, there is every reason not to do that IF the output of the amp is actually 100 watts RMS. That power rating is made..or should be made...on a clean signal. A dimed 100 watt amp will be making more than 100 watts. The same is true for any other amp of any output power, I would think. Perhaps that is one reason for a manufacturer stating than an attenuator needs to be ‘over-rated’ if one is going to max the output of the amp.
     
    Last edited: Aug 20, 2020
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  13. Cpb2020

    Cpb2020 Tele-Meister Silver Supporter

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    That was one of the reasons went with the TK imperial. Here is from their marketing materials (for their Ironman II stand-alone attenuator) so you’ve got to take it with a grain of salt:


    “Ideally, the load seen by an amplifier should have the appropriate complex impedance curve so that it responds as it does to a real speaker load. A real speaker load varies greatly with frequency. For example, the impedance of a typical "8 ohm" speaker may rise to 60 ohms or more at its resonant frequency (usually around 60-80Hz), and then rise again to many tens of ohms at high frequencies. An amplifier responds a lot differently when driving a complex load like this, compared to a simple resistive load (as is used in most attenuators). Tone King developed the Ironman's reactive load circuit by matching the results of impedance curve measurements, ran on an actual speaker and then tweaked the resulting design through an empirical method in order to create a load circuit that is most effective at preserving the tone and feel of your amplifier.

    The second part of the equation is the circuitry that divides the power from your amplifier between the speaker and the load. In other attenuators, this is often done with a resistor ladder. There are two problems with this approach - first, the resistor ladder itself can become a part of the load, which means that the amplifier sees a simple resistive load. Second, in dividing the power this way, a voltage divider is effectively formed between the dividing network and the speaker. Since the speaker has a complex impedance that varies with frequency, the result is that the frequency response at the speaker is altered, usually dulling the top end and muddying the sound. To address this, the Iron Man II uses 100% transformer coupling via a set of custom audio transformers, so that the connection between the amplifier-to-load and between the amplifier-to-speaker is purely transformer coupled at every step of the attenuation dial. This is an expensive and elaborate design (each step of the dial requires its own tap on one of the custom transformers), but is significantly more effective at preserving the tone and feel of your amplifier than other methods.”
     
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  14. beninma

    beninma Friend of Leo's

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    Some of the built in attenuators are not really attenuators even though they often get called that.

    E.x. the Orange "Headroom/Bedroom" like I have is not an attenuator... it's doing something else around reducing the voltages at the power tubes that reduces the output yet still lets the power tubes go into overdrive.

    Just something to keep in mind.

    I run mine on Bedroom a lot and I asked Orange tech support about strain on the amp... they said theoretically if you had the volume cranked you might be putting some extra strain on the tubes. But if it's not a true attenuator and it's actually reducing the voltage at the power tubes hard to say how that's the case. Maybe it puts more strain on the preamp tubes cause you can turn the preamp up louder without blowing your ears out.

    It really sounds like this kind of design probably puts less stress on everything than a reactive load.
     
    Last edited: Aug 20, 2020
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  15. bigben55

    bigben55 Friend of Leo's

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    I have a Dr Z Z28 with a Z Brake Lite mounted inside its combo cabinet. The amp is an incredibly loud, stout 22 watts. I have cranked the amp and used maximum attenuation multiple times at home, with zero issues.

    That said, I never do this live. Or really, at all anymore. Why? Maxing the attenuation changes your tone. It adds compression and mush, and reduces highs, chime and sparkle. Diming the amp on top of this only exacerbates it. In other words, dimed amp+dimed attenuator=bad tone.

    And THAT said, I find the Brake Lite INDESPENSIBLE, live, with this amp. I love it. It knocks off 2, 5, 8, or 11 dB. 2 & 5 dBs don't alter my tone enough for me to recognize it audibly. I generally use 5 dBs, and find it perfect for most live applications. It gives me the ability to go a notch less or more. 8 dBs starts to alter tone, but not badly. Turn the bass down a notch, treble up a notch, problem solved. If 8 dBs is still too loud, I brought the wrong amp to the gig.
     
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  16. bblumentritt

    bblumentritt Tele-Afflicted

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    etype,

    I would think that the built in power soak resistors in your amp would be enough that the amp can handle.

    You might be able to find a good used Eminence Maverick. Either that or an amp designed for low volume crunch.
     
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  17. Wally

    Wally Telefied Ad Free Member

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    Fwiw, the Tone KingImperial MKII is a great amp, imho. If I were younger, it would be a must have for me.
     
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  18. Cpb2020

    Cpb2020 Tele-Meister Silver Supporter

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    Ha - the primary user of that amp in our household is 12 years old. It is in use as I type this.
     
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  19. FenderLover

    FenderLover Poster Extraordinaire

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    Yes, in a perfect world. You gotta believe Weber puts up a warning for a reason, accepted or not. I don't think it's smart to operate anything at its absolute limit. Absolute gets fuzzy.

    Buying a 50W attenuator allows you to use it for a number of amps with different power, so not really overkill when a cement resistor is just a little bigger.
     
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  20. etype

    etype Tele-Afflicted

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    What I really want is a cranked Vox AC15 tone at reasonable volumes. Perhaps the AC4 is the better choice than either an AC15CH with attenuator or the AC15C with an aftermarket attenuator.
     
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