NMV Marshall amp volume control options?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jackaroo, Jan 16, 2008.

  1. jackaroo

    jackaroo Member

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    I'm looking at vintage Marshalls, and I'm a little overwhelmed by how much volume they have. It's just incredible. So Fing loud. They sound great, but it's kind of impractical and in this day and age.

    So volume control is obviously an issue- something that's paramount on small stages and in my home studio. Here are options that I know of for taming the beast along with their respective cons. I'm not sold on anything, because frankly I need to do more homework. What am I missing, what tricks are there that I should know about? BTW if my assumptions/factoids are wrong regarding the cons listed below- please set the record straight!

    PPI Master- good if not on a vintage amp, also the power section isn't working as hard as it should so tone and feel are different/suffer.

    Variac- expensive, heavy, only effective to 85v after that tube damage- squishy response (I like that BTW). Not that much attenuation. Damage amp's tranny and tubes is possible?

    Power scaling- expensive, and not an option on vintage gear. Questionable efficacy depending on tech who installs it.

    Inefficient speakers 96dB vs 100 dB. Not too much attenuation- but at least it's natural.

    Number of speakers 2 vs 4. Less air, less oomph.

    Attenuators. I'm told sacrifice tone/feel and can be dangerous to trannies

    Reamp. Ultimate attenuator- all this money to then go SS? Big $$$ still has risk to tranny.

    Load boxes to poweramp. Another thing to haul around and maintain!


    I'm already looking at smaller amps, like the JTM 45 which is closer to 30-35 watts- not 45 or 50 like the 1987 series. And I plan on using just 2 Heritage GB speakers @ 96 dB (G12m) rather than the 30 H mags which are 100dB I believe. I'd use a variac if it was safe, but how much does that really lower volume?

    I wont be running the amp full out, more with a touch of breakup, and plan on using boosters and fuzzes to get the gain cookin'. But still, is there a way to get the volume down say to 10-15 watts without any risk to the amp or irreversible mods.? Say... someway of fooling the amp into thinking it's feeding more speakers? By sending a portion of the signal out to a dummy load that just goes nowhere while a portion of the signal goes to the cab unaltered?

    Please let me know what you know works but wont kill my old amp, cost a fortune, add too much gear to my insanely cluttered world, or make my nice amp sound like poop.

    Thanks,

    Jack
     
  2. Swarty

    Swarty Member

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    Get a 20, plenty of volume and plenty of Marshall honk.
     
  3. jackaroo

    jackaroo Member

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    Those 84s sound way to bright and not smooth enough to my ear. Though it is the right size and volume...Cute little buggers too.
     
  4. doctord02

    doctord02 Member

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    Drop a pair of good 6V6GT tubes in your 50 watter and rebias it... Wont sound exactly the same, but should still sound muy bueno.
     
  5. jackaroo

    jackaroo Member

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    Is that safe? Mmm I wonder what ramifications there will be tonally?
     
  6. John Phillips

    John Phillips Member

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    Yes, 6V6s are an option in many (but not all, some have higher voltages) 50W Marshalls. You will get about 20W... still pretty loud. These should be a drop in and bias mod - and set the impedance selector to half that of the speakers for the best match. The tone will change surprisingly little - it's not going to suddenly make your Marshall into a Fender Deluxe ;).

    THD Yellowjackets (EL84 converters) will work too, and will give both slightly less power (probably 15-18W depending on the exact plate voltage) and also a more compressed feel - less apparent volume - because they run cathode-biased. You also want to halve the impedance selector setting ideally. These also won't turn the amp into a 20W Marshall, you'll keep most of the big-transformer and full tone-stack tone of the 50.

    An attenuator set to -4dB (the difference between 50W and 20W) won't affect the tone or feel much either. You can also use one as a parallel dummy load - which is effectively like having a silent speaker cab plugged into the amp as well - but you're limited to a fairly small volume reduction (3dB normally, unless you deliberately mismatch the loads), although this is probably the most natural-sounding way of using an attenuator.

    You can probably rule out a Variac - you'll only get about 1dB reduction before you're into the region of tube damage (although nothing bad should actually happen to the amp).

    Less efficient speakers will help, but only if your original baseline was more efficient ones :). At least if you bring down the power of the amp you can use fewer (and possibly smaller, 10"s are less efficient than 12"s usually and some sound very nice) of them.

    The best option is probably a combination of two or more of these methods, you could really achieve quite a big reduction while still actually using the fully cranked distortion tone that you bought the amp for in the first place... but there's not much way around carrying at least a couple of extra bits of kit.
     
  7. doctord02

    doctord02 Member

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    Do you know what your plate voltage is on the Marshall? If it's under 450V you should be OK. If in doubt, buy a set of JJ 6V6's - you just about cant kill them...

    edit-

    what John said...
     
  8. trisonic

    trisonic Member

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    Jack,
    Take a look at the JTM45. It's about 33 watts - put it thru a pair of Greenbacks. Not too loud. Personally I prefer its tone to the later more powerful models, more Beano enhanced!

    Best, Pete.
     
  9. jackaroo

    jackaroo Member

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    Pete-

    That's the amp I'm looking at getting, but it's still pretty full volume compared to my Deluxe reverb- even that can get a little nutty at times.

    John- Thanks for the advice-

    "You can also use one as a parallel dummy load - which is effectively like having a silent speaker cab plugged into the amp as well - but you're limited to a fairly small volume reduction (3dB normally, unless you deliberately mismatch the loads), although this is probably the most natural-sounding way of using an attenuator."

    How do I do this "parallel dummy load" ? That sounds like the ticket right there, how do I safely "mismatch the loads"... I want to avoid damage to ears, domestic bliss and the amp itself- not to mention preserving the tone of those KT 66 tubes.
     
  10. hamfist

    hamfist Member

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    Don't rule out power-scaling as too expensive. Certainly, in the UK, it costs the same to get it properly installed as you would pay for a Hotplate.
    Tube life is increased considerably. My power-scaled Jtm45 worked really, really well at lower volume.
    You do need to find someone who is experienced at installing it though, which could possibly be a problem I suppose.
    JP's advice is, of course, also all good. As my mum says - "There is more than one way to skin a rabbit " !!
     
  11. John Phillips

    John Phillips Member

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    To run an attenuator as a parallel load, simply connect it to the second speaker output and set it to 'load' if it has such a setting or the quietest volume it has if not.

    Normally, you'll be using an attenuator of the same impedance as the cab, so you set the impedance of the amp to half that of either (8 with two 16-ohm loads or 4 with two 8-ohm), half the power goes to the dummy load, and you get a 3dB volume reduction.

    But you can deliberately use a load different from the cab, if you have the right cab and amp settings.

    If you use a 16-ohm cab and an 8-ohm dummy load, or an 8-ohm cab and a 4-ohm load, 2/3 of the power goes to the load, which is a 5dB reduction. You should set the amp to 4 ohms in either case.

    Finally, if you have a 16-ohm cab only, you can run a 4-ohm dummy load as well, which sends 4/5 of the power to the load and is a 7dB reduction. The amp must also be set to 4 ohms.

    All these are in the safe mismatch range for the amp at 4 ohms - the lowest is 2.66 ohms (8 and 4 ohm loads) and the highest is 5.33 ohms (16 and 8-ohm loads).

    Don't be afraid of using different impedances if you know how to work out the combined load and know what's safe.
     
  12. jackaroo

    jackaroo Member

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    John Thanks for hipping me to this approach-

    I'm not quite sure what all of it means, but just knowing I can get things down in terms of level naturally and safely is a real plus.

    I guess I need to look at what types of attenuators can do this type of work well.

    Cheers,

    JD

    BTW I just PM'd you a link to some pics if you're interested-
     
  13. jackaroo

    jackaroo Member

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  14. Bussman

    Bussman Member

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    You can buy a few speaker motors from Weber (about $30 each I think) and hook them up to soak power. many configuration can be devised to maintain proper impedance. Similar approach to John's but possibly more reduction choices and cheaper than a ready built attenuator. Incorporate it in your cab and you don't have to carry more gear (could be switchable also).
     
  15. jackaroo

    jackaroo Member

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    huh?

    I guess I should talk to Weber?
     
  16. Bussman

    Bussman Member

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    The motors are what they use to make the MASS attenuators (scroll down the page and you'll see them).

    Let's take my 2 x 12 for example: the cab is rated @ 8ohms. if I hook up an 8 ohm motor in series with the cab and a 16 ohm motor in parallel with the cab/8ohm motor you'll get -6db of attenuation @ 8 ohms (sort of like dividing the power among four cabs, three of which are silent).

    If you make a second load with an 8 ohm motor and hook it up in parallel with the whole shabang you'll end up with -9db of attenuation @ 4 ohms (like dividing the power among eight cabs, seven of which are silent.

    The formula for figuring out attenuation level: 10 log (Watt @ Speaker / Watt from amp ). It's not precise but gives you a rough idea.

    John Phillips mentioned in other posts that speaker in series or parrallel have different sounds so it might have quite an effect on sound. The motors are not speakers so I'm sure it'll have a strong effect also. John also seem to favour purely resistive loads so you could always try a purely resistive L-pad along the lines of my first example (resistors are even cheaper than speaker motors so it's an easy thing to check with minimal investment). John, care to chime in with your thoughts on this?
     
  17. Lonely Raven

    Lonely Raven Member

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    I have a Trainwreck styled amp, non-MV. Loud as hell, so I'm having similar issues you are.

    To add to what JP said, and getting back to speakers.

    Keep in mind, that 3db is a noticeable amount.

    For each speaker you *add*, you add 3db. The same works in reverse.

    So if you are using a 4X12, cut it down to a 2X12 of the same speakers and you just dropped -6db. Go down to a 1X12 and you are down -9db.

    If you are starting out with 100db @1m guitar speakers (WGS speakers come to mind), sticking with inefficient speakers can bring you a few more db drop. So going from 100db WGS to ~96db Greenbacks easy -4db.

    Also, the recommendations I've received from other Trainwreck owners (both real and clones/styled) is that stacking attenuators set at -4 to -8 does less damage to tone then 1 attenuator set at -16.

    So, if you could go to inefficient speakers, cut down to 1 or 2 speakers, and stack a Hot Plate with an Airbrake, you could get yourself down to some reasonable volumes....and also double the cost of your setup. LOL

    Sorry, I'm rambling a bit. As I said, I'm in the same boat as you are, and I'm in an apartment, so I've been doing a lot of research. I figured I'd just share with you what I've learned. So far I've changed speakers and gone down to a 2X12. Major drop in volume, but still loud. I'm shopping for a Hot Plate and looking to build myself an Airbrake. I really want to dial in the Trainwreck clone without going deaf or getting thrown out of my apartment building. :)
     
  18. John Phillips

    John Phillips Member

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    For attenuators, I think the reason resistive ones sound better may be because the errors caused by the part in series with the speaker load cancels out those caused by the part in parallel (as all conventional attenuators must be basically arranged), possibly more 'by accident than design'.

    But with a purely parallel load (no series component), you probably want to get it as close to the same impedance curve as a real speaker as you can, otherwise the power distribution will be different at different frequencies.

    No, it's not as simple as that. If you halve the number of speakers, each individual speaker is then getting double the power, and so will be louder.

    In theory - if speakers were perfectly linear in response and cabinets didn't have interactions and cancellations between the speakers - the final volume would be independent of the number of speakers. In practice, it doesn't quite work like that because things aren't so perfect, and you do get a difference - but more like 1-2dB with each halving or doubling, and it begins to run out beyond a certain point - you can't just go on increasing the volume forever by adding more speakers.
     
  19. Lonely Raven

    Lonely Raven Member

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    Thanks for clearing that up John. This is the kind of stuff that't been drummed into me for about 20 years now.

    I have a clear drop in volume with my 2X12 setup with less efficent speakers. I probably should have measured before and after to quantify it better. But it is there...I just didn't realize it would be so little.
     

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