How does Master Volume work comp'd to Attenuation?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Yossi, Aug 4, 2008.

  1. Yossi

    Yossi Gold Supporting Member

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    I am getting the UA and based on what I learned, it's allowing the power-tubes to get over-driven and then it re-amps or puts a load on the output signal before driving the speakers, resulting in the same amp tone just at a lower volume. It was this understanding that also led me to purchase my first NMV Amp, a Germino Lead 55LV. I'll get that great sound at a safe (both for my ears and my marriage) level.

    My question is: How does a master volume work in comparison? What is the source of the overdrive? I would like to understand the difference.

    It seems that NMV Amps are a Vintage amp feature, whereas Master Volumes are the standard today.

    I understand that the Magus Ultimate Tube Amp is adding Attenuation to their amps and have gotten rid of the Master volume? Do you suppose that that is a trend that may catch on within the industry?
     
  2. Faustine Amps

    Faustine Amps Member

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    The simple answer is that a Master Volume circuit creates "overdrive" by allowing you to drive the preamp tubes into "clipping" before the signal hits the power tubes. All of your overdrive is coming from the preamp circuit and the master volume controls the signal level arriving at the phase inverter or power tubes.

    An Attenuator allows you to create "overdrive" with both the preamp circuit and the power section (the output tubes and output transformer). When you turn a non-master volume amp WAY UP, the output tubes begin to "clip" the signal as well and the output transformer might start to saturate. If the amp uses a tube rectifier, it's voltage may sag a little when it has to supply instantaneous current (such as when you hit a "power chord") and this produces a compressor effect. All of these effects are now under your control and you can go from subtle nuanced clean picking to full-on distorted mayhem by varying your picking attack and your guitar's volume control. The attenuator controls how much of that signal is diverted from the speakers, thus controlling your volume.

    I'm a big fan of the latter approach and that's why I build attenuators into my own amps.

    As for whether that is a "trend" that will catch on in the industry, I doubt it. Jim Kelly used attenuators in his FACS amps 25 years ago, Randall Aiken has been using attenuators in his amps for many years, and I've been using them in Faustine amps for the past few years. I don't know of any others who are currently using them, although I'm sure there must be a few. When you consider how many amp manufacturers there are, I would say it's definitely not a trend! The fact is, designing a good sounding attenuator that doesn't suck the life out of your tone takes alot more engineering effort than putting in a master volume control. A master volume is much cheaper too.

    Okay, it may be time to put on the flameproof suit!;)

    Regards,
    Tim Gregoire
     
  3. Yossi

    Yossi Gold Supporting Member

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    Thank you Tim. I appreciate your answer. Your Amps look very nice too!
     
  4. phsyconoodler

    phsyconoodler Member

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    I have used the type of L-Pad attenuator you use in your amps,and while it does allow power tube saturation,it also increases wear on all parts inside the amp,especially tubes.It's no different than diming your amp all the time except for the obvious volume level.
    For those that prefer the power tube saturated sound,they work well.But some people like an overdriven preamp,so a nice Post Phase inverter master is perfect for their needs.On a tweed amp I would prefer the former,with the PPIMV being a second choice.A good pedal can sound just as nice however,if you get the right one.
    I like old school tones and choose the Electro Harmonix Double Muff.
    I'd rather not pound my output tubes and transformer to oblivion.
     
  5. VikingAmps

    VikingAmps Member

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    Just about any pot on your amp is an attenuator. Most people refer to it happening after the power tubes but putting the attenuation after the phase inverter has pretty much all the benefits of putting it after the power tubes and none of the drawbacks.
     
  6. WesKuhnley

    WesKuhnley Member

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    I prefer either a PPIMV alone, or used in conjunction with some variety of power scaling. Alternative loads on the output of the amp, ie: hot plates, UA, etc, don't sound right to my ear, too much compression and odd-order harmonics added to the signal. Power scaling by itself does some of the same things but when used in conjunction with a MV it works pretty well. Nothing will give you a "cranked stack" sound that won't wake up your wife, but a MV and PS will probably get you pretty close through an inefficient speaker.
     
  7. Faustine Amps

    Faustine Amps Member

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    Well.. you may have used the same L-Pad that I use in my attenuator, but using an L-Pad (which is purely a resistive device) is not the same as using one of my attenuators. The Faustine attenuator circuit is not a simple L-Pad. The volume is controlled by an L-Pad, but the L-Pad is part of a larger reactive circuit that includes resistive, capacititive and inductive elements in a unique configuration that I spent many months developing and tweaking.

    An attenuator does indeed increase wear on tubes and the output transformer, but ALL PARTS inside the amp? That's an exaggeration. And to say it's no different than diming your amp all the time would only be a true statement if the person using the amp had the volumes turned all the way up all the time. That's also an exaggeration. I've never met any guitarist who plays with the volumes all the way up all the time, even with an attenuator. Of course, there are probably exceptions. Nigel Tufnel of Spinal Tap comes to mind. He probably "pounds his output tubes and transformer into oblivion" on a daily basis.;)

    There are certainly many amps that sound great with master volumes and the PPIMV would be my choice as well. No arguments there. But a PPIMV amp does not sound the same as an attenuated amp. They are two different topologies with two different sounds. Same thing with power scaling. Different circuit topology, different sound.

    Let me be clear, I am speaking about the sound created by my own amps and attenuator circuits as compared to PPIMV circuits. Not all attenuators sound the same. I haven't tried all the attenuators on the market and I'm not a spokesman for other attenuator designs.

    OK, flameproof suit back on.

    Regards,
    Tim Gregoire
     
  8. TED STEVENSON

    TED STEVENSON Member

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    I agree, most of my clients who use attenuators only use them to cut back on the volume a little bit and they never dime their amps. These guys are pros and have specific needs on stage. They don't eat through power tubes or other components.
     
  9. scottl

    scottl Supporting Member - Gold

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    I use a Hot Plate with my 100W Bluesmaster circuit amps. Less nfb so they are super loud. I need the -4db click to be able to turn the master up to 11 to 12 oclock. This is the sweet spot since there is a bright cap on it. I prefer this over no bright cap. Two different sounds. So, I guess I am agreeing with Ted Stevenson that a tiny bit of attenuation is all I use. The tone change is minimal at -4 and more than offset by getting volume pot up a bit.

    Plus, -4db really doesn't tax the components.
     
  10. phsyconoodler

    phsyconoodler Member

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    Ah,the perfect world where no one dimes an amp an attenuates it to whisper levels.
    Realistically,an apartment dweller will be better off with power scaling than an attenuator.
    Mr Faustine,I was not trying to say you didn't spend lots of time with adding a high-pass filter system to your attenuator to suit your amps,I was simply stating an opinion.
    We could only hope everyone who buys an amp with an attenuator will be nice and only attenuate it a little bit.
    I like the comment about every knob on the amp being an attenuator,with the best one being the volume control on your guitar.
    I find a PPIMV to be just as useful as any attenuator if you 'only turn it down a little bit'.
    Funny,all the guitarists who dime amps must live in Canada.
     
  11. VikingAmps

    VikingAmps Member

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    Not sure I understand the last sentence. Why would -4db tax the components any more or less than any other setting?
     
  12. Faustine Amps

    Faustine Amps Member

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    Exactly! An attenuator and a master volume are ultimately just volume controls. The original poster, Yossi, asked about the technical differences between "overdrive" that is created with a master volume and "overdrive" that is created with an attenuator. I thought I gave a fairly decent explanation of how the two "overdrive" sounds are created and how they differ. I didn't even go into how "overdrive" is created with a Ultimate Attenuator since that is a whole different animal.

    I think the misunderstanding, and perhaps the negative bias, in regards to attenuators is in the assumption that the amp's electronics are being overtaxed solely for the purpose of creating "overdrive" and that a master volume or distortion pedal is better suited to that task. I wouldn't disagree with that. "Diming" your amp's volume controls and then heavily attenuating the output to create the sonic equivalent of a Big Muff is not good for your amp and it's plain silly. An attenuator shouldn't be used to turn your tube amp into a distortion box.

    So how do you use an attenuator intelligently? I go into a long-winded explanation of this on my web site, but I'll try to be brief. Some tube amps (most, in my opinion) sound good when they are cranked. By "cranked", I don't mean turned all the way up. It's probably somewhere between 30% and 70% of full volume. It's that "sweet spot" where the tubes, the OT, and the speaker are really working together and are the most responsive to your playing. You can cover a huge dynamic range by just varying your picking attack, your pickup selection, and the guitar volume controls. You can easily go from subtle nuanced picking to crunchy power chords or sustained lead guitar lines by working the guitar's controls. That is what I mean by the term "sweet spot". And your amp may also have a master volume control that is set to just the right place to attain that "sweet spot". The trouble is, attaining that sound quite often means your amp is now too loud for the venue that you're playing. Turning down the master volume might very well kill your "mojo" because you have now removed the output circuit from the "sweet spot" equation. That is where the attenuator becomes useful. The attenuator is still going to have some effect on the OT / Speaker interaction, but it's still the only way I'm aware of to maintain that "sweet spot" IF you happen to use your amp like I've described above. How much you can attenuate the speaker volume (and how much the attenuator will affect your tone) is dependent on the attenuator. Some people use attenuators for apartment volume and some don't care for that much attenuation. Personally, if I have to play extremely quiet, I use a much smaller amp (a '72 silverface Bronco). It has been modded with a built-in attenuator (naturally), but I don't need to use extreme attenuation to get very low volume levels.

    Of course, If you find your amplifier's "sweet spot" and are able to control your volume with the preamp circuitry and a master volume control without negatively affecting that sound, then you probably have no use for an attenuator and all my ramblings are irrelevant.

    Psychonoodler: I'm sorry if we got off on the wrong foot. I know you're an amp builder yourself, I've seen your excellent work, and you obviously have no use for attenuators. That's cool and I respect your opinion. Different strokes for different folks.

    I guess I've gone on far too much so I'm stepping out of the fire, removing my flame-proof suit, and taking my amp and attenuator home.

    Regards,
    Tim Gregoire
     
    Last edited: Aug 5, 2008
  13. scottl

    scottl Supporting Member - Gold

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    Because I am using the minimum attenuation available. I am not diming the amp, just using this minimal attenuation to turn the amp up maybe 1 to 2 clock positions. I am not running the output hard at all.

     
  14. TED STEVENSON

    TED STEVENSON Member

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    There's an intelligent way to use attenuators (like the way ScottL uses them) and then there's the balls to wall way. The latter will eat through tubes and cause premature component failure. Scott's way is the way most pros do it.
     
  15. jackaroo

    jackaroo Member

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    I think Tim hit the nail on the head.

    All the parts in the amp can have an impact on the end tone...and to remove the power section from the equation and the tranny too? That's no good. I've owned amps that had very good master circuits...but they get their tone from the pre amp...the power tubes are not really pushed, but when you're talking about a tweed amp or an old Marshall, the OP tubes and tranny are a HUGE part of the tone. The way they distort and react to the signal is the magic part of it.

    Power scaling reduces the voltage to the point of turning your stallion into a gelding at those low volumes too.

    I'd rather have my cake and eat it too. I own some big amps and they sound great through my attenuators- absolutely awesome- no compromise to my ear at all. I cannot even possibly think of not having one of them- simply not an option from so many perspectives- neighbors, clubs, late night recording, wives, babies and my own ears.

    Once again I'd like to stress that certain amps and circuit types play nice with PPIMV and what not, but in my 28 years of playing guitar I've never gotten this tone at this volume any other way-


    To each his own-
     
  16. phsyconoodler

    phsyconoodler Member

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    Hey Tim,
    I did say I prefer the attenuator for Tweed amps by the way.I just lament about guys who crank them to try and turn the sound into a Soldano or Marshall.
    I have built attenuators into speaker cabinets for some guys and they all seem to 'crank' the amp and then complain about it eating power tubes.
    Then there's the guy who bought two new Marshall hand wired amps and cranks them through an attenuator.He blew two OT's and Marshall is getting pissed with him.Buy a freakin' champ for craps sake!
     
  17. Yossi

    Yossi Gold Supporting Member

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    Thank you all for your informative answers. I should have my UA in about a week and I'll have a better idea of how to use it.
    From what I've read, the UA will not cause any more load on the Amp than running the amp at the same level without the UA. The overdrive sound is not caused by the Attenuator, rather by the Power tubes. The Attenuator allows that overdrive, if it exists, to be played at lower volumes. The master volume causes the OD in the preamp stage and if loud enough also in the Power tubes. I'm a long way away from fully understanding everything, but I am one step closer. So thanks again.
     
  18. Yossi

    Yossi Gold Supporting Member

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    Was that the fault of the attenuator or the fact that he had the amp dimed for too long? I am asking because I have an amp on order and a UA and I plan on playing the amp in its sweet spot and dropping the volume to acceptable levels by using the attenuator. I don't want to blow my new amp.:(
     
  19. TED STEVENSON

    TED STEVENSON Member

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    Many players I know of set the amp volume to where they feel the sweet spot is and then use an attenuator to bring it down a little. It has nothing to do with power section clipping, the sweet spot is just a tad too loud for their playing situation. Some also like the sound of a slightly attenuated amp. I have clients who do it this way, play several times a week and change their power tubes once a year.
     
  20. scottl

    scottl Supporting Member - Gold

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    There is wear and then there is blowing stuff like outputs ;)

    Fwiw, in my case, the master volume has a bright cap on it. I use an external loop with specifically chosen cables to and from it. This adds capacitance. The bright cap balances it. The amp sounds best if the master is up to a certain level so the bright cap is not too bright. The attenuator allows me to get there at slightly more reasonable volume. If I remove the bright cap, things do not sound as good. And I am a master tweaker... So, bright cap it is.

     

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