Dummy load box

[rhdwave]

Has anyone here ever created a dummy load box? I want to start using a di box with my tube amp into protools, but with the speaker disconnected so i don't wake my wife, the neighbors, etc...So, it seems a dummy load is needed.  They are expensive, and from what i could gather they're at the core just possibly a few resistors.  Does anyone have any experience or shematics on this topic?
Much thanks!

[ildar]

Just a simple dummy load shouldn't be expensive. AFAIK all you really need for the interior is a resistor of the appropriate ohm rating and wattage rating. It's a good idea to overkill the wattage. If your amp is 50w, go with 100w. Vent your enclosure as the resistor will build up heat.
If you're looking for an attenuator, that's a bit different.

[jonathan perez]

thats it? got a diagram?

[jayp5150]

Not really DIY, but there are some options here:

http://www.partsexpress.com

Just search "dummy load"

Not terribly expensive.  Hope that helps.

[rhdwave]

Thanks! I went to that link and sure enough there are dummy load resistors for sale.  They say non-inductive which i assume is what i want.  They also have heat sink boxes as well.  Now, would this be as simple as say putting the resistor in the box and hooking it up to an input jack? If the box is a heatsink, do i need to somehow attach the resistor to the wall in some fashion? Sorry if these are seemingly simple questions, i just don't want to do this wrong and mess up my amp?

Thanks again for any replies!

[petemoore]

Thanks! I went to that link and sure enough there are dummy load resistors for sale.  They say non-inductive which i assume is what i want.  They also have heat sink boxes as well.  Now, would this be as simple as say putting the resistor in the box and hooking it up to an input jack?
  Other than some possible slight signal loading, hooking up to the input jack will give 0% amp sound, it be, and sound like the source.
  "Dummy Loading" as I understand it involves a fixed resistance attached to the output section of a tube amp, converting output power into heat, as opposed to mechanical energy as the normal thing to hook up to a tube amp output: A speaker or speakers.
  I had one, and at slight reductions, the speaker/output 'tone' was only slightly different, but as I dialed down the volume by dialing up the resistance in the fixed heater circuit, the 'mechanical influence' [speaker loading effect] on the output of the amp became more apparent.
  I get the idea you want the amp tone, but not in terms of air movement via speaker, but at a line level?..if that's the case..you can probably get a line level 'sound', but it will I think involve more than a fixed resistor attached to your amp, and as noted for even dummy loading, which changes the character of the amp sound [if fixed R type], getting a line level that ~sounds like your amp is not easily done with no speaker/mic.
  I'm not exactly clear on what you want 'it to do, or that a big resistor will do 'it.

[rhdwave]

Thanks Pete for the response.
Actually what i meant by input jack was the input jack on the dummy load box not the speaker itself.  Essentially what i want to do is go directly from the speaker out on the amp into a di box that has a speaker simulator and then attach a dummy load to the di box instead of going back into the speaker so that everything is quiet if i don't use headphones.  The other output on the di box will go into my mbox for recording in protools. 
So, i really just wanted to build a dummy load box to keep things quiet in the apartment.  I wasn't really thinking about attenuation, i think some of the di boxes out there actually have that built in.  I know using a resistor is going to create a lot of heat, so my question really is do i attach the resistor somehow to the casing of the box which would act as a heatsink or is there some other way of doing it?
I had the idea of maybe putting a fan in the box hooked up to a battery and venting the box itself to keep good airflow.
And lastly, in terms of the resistor, is it simply a matter of connecting it to the jack on the box directly or should i use a board?

I really appreciate all responses, i'm a little paranoid about frying my amp so i want to do this the right way.

If anyone has any other suggestions on recording direct with an amp without using the speaker i would be open to that as well.

Much thanks to everyone!!!

[bancika]

I made similar thing for my firefly, it has line out with pot, power attenuator and dummy load (and it fits inside very small enclosure).
You can check out here http://storm-software.co.yu/diy/index.php?project=stuff for schematic

[rhdwave]

Thanks! So if i was going to use something like this for a 50w amp, i guess it would be possible to use a large wattage light bulb? This way instead of all the load going to heat, it would be split with lighting the bulb as well.  Is this correct?

[bancika]

well yes, but it's there for other reason: it acts as power attenuator. Read article at www.valvejunior.com about it. I doubth you'll find bulb for 50w amp because it needs to be 12V and 2.5A which is too much. I had hard time finding 2.4W bulb here.
Anyway, you could build just dumy load out of it.

[rhdwave]

Yes, i just read the article.  Now, is the reason you also include an audio isolation transformer and the 10k resistor with 5k pot as a filter in case you want to use the line out into another amp? If i was just going to use the dummy load with say a 100w resistor would i still need this? eg.  amp speaker out-di box-protools/dummy load?

[petemoore]

  I'd say be careful about loading the output of tube amps using resitors only...only because I've read 'be careful'...because the load is different than speakers, which are ... are ... putting a highly variable load on the output section, a fixed resistor is exactly that .. simply resistance, and will tend to 'flatten' the peaks...
  Now I'm rambling, and my vocabulary and wordsmith skills arent' up to par for...faking like I know all about this stuff.
 I do know that if you don't know what you're up to with messing about tube output loading, you should understand that the ability to cause damage exists.
 And .. anytime a fixed load is attached, the response will be different than when a speaker with moving coil is doing the loading. Some of the amp character will be intact, but alot of what makes a tube amp sound like itself is reliant on having a moving coil/cone which has 'variances at frequency' in the way it loads down an amps output.

[rhdwave]

So Pete, is there any way that you know of to mimic the mechanical movement of a speaker rather than just using a fixed resistor?

[bancika]

you can get speaker motor, like weber mass. check out www.tedweber.com

[petemoore]

  Mic inside Islolation Boxxed speaker...
  Bancika's suggestion...goes along with...try reading up on or trying out [cloning?...] commercially available 'get my loaded tube ampspeaker sound into the wire' devices.
 Now I'll go ahead and be mean...short answer 'no'...you will not replicate exactly, all the tones your tube amp is capable of producing, at line level only.
 Workable answer 'possible'...if you work at it you *may find tones very reminiscent of what started the 'line level tone quest'.
 That said, many recorder/players work with small tube amp or isolation boxes, micing the tube amp with multiple amps to try to replicate what an ear hears in a room...none will ever sound like what an ear hears in a room, reasonable facsimile's may be had, maybe even seen as 'improved' playback [with some other studio tricks]...long story short, the quest to insert a tube amps complete characteristical elements into a wire...a really, really long story...lotsa guys like their digital processors for just this application, others use digital, then go to great lengths to mic the tube amps...record/playback/adjust/record/playback/insert comp or eq, reverb or something/record/playback/adjust mic angles, add another mic/record/playback...
 what you're describing as 'my tube amp' isn't what you're hearing, because speakers / air, and other surfaces are playing a role in the tone you are hearing.
 "Electronic Replication' of even the mechanical dynamics of speaker/output section of an amp is a long, involved, 'inexact'...[you might find cool stuff you like to use in your quested efforts, but *'electronics' simply can't sound like the air and room and your amp 'n speakers].
 *Caveat...I've heard digital replications of tube amps as 'digital amp' [like Behringer/Line6]...which IIUC is...a digital processor designed to sound like tube amp, driving a clean-ish [except the speakers maybe] output amp...all the 'tone' is in the processing, the amp mostly adds just clean amplification...and they can do extremely well as 'tube amp' sound, IMO the tone I copped most would call it 'clean guitar tone'...the distortions left thickness to be desired IME...you didn't really describe the character of the sound you're after that the tube amp gets.
  So *maybe trying a digital thing...something to try...as it seems to be the 1rst or 2nd opt' many 'line level players' adopt for recording/headphone use.  *I worked with digital, a little bit, with a little 16bit thingy, kind of impressive for a little box, I found it impossible to dial the 'tone in and digitally-ness out'.
 For me, just getting decent sounds from an amp .. I thought was tough, getting that to line level is 'a whole nuther thing' to be certain..clean, nice isn't as difficult for me as capturing more saturated distorted tones.
 I just use the smallest output wattage I built, 7.5w tube output section into 2x12'' s, still really too loud...
 Since I was so mean, I'll try a 'nice' suggestion, which many have found very useful for recording and bedroom use: teeny little tube amp, working with these...you can replicate a tube amp, loaded and driving a speaker...and get a very nicely 'scaled clone' which will produce much more convincing 'big cranked tube amp tone' than a non cranked tube amp....seems like alot of trouble, but...the smaller wattage is what I'm after when I'm not after volume, getting the tone 'right' [sounding as a loaded tube amp sounds] at lower volumes IMO is much easier to do by just doing it, get 'yer little tube amp on...it'll do nearly 100% of what a big tube amp does at high volume, at low volume.
 I'm absolutely certain there has been and is a market demand for 'tube amp tone' in a wire, many attempts to supply that niche have been made, reading reviews of commercially available units which promise the ability to 'tube amp sound a wire' may be of some good reference if you could filter out 'opinion', like the little bit I gave.
 I tried a buncha ways, some worked pretty good [I did a bunch of work with a Digitech '100'...[I forget the two letters preceding the 100...RP I think], with fair results, but opted back to the mic the cab techniques. Someday I'll get a nice Tube Mic Pre-amp, I've read these help spark up guitar amp recordings.
  Nope...no way I've seen except stuff like Digital, read reviews for more field test feedback info, or LHX Marshall or Fender Amp Sims.
  The speaker, when connected to a tube output, is a very dynamic 'thing' with lots of various events...mimicing this @ line level, exactly like your amp sounds...
  As close as I know to get that would be digital, and if you can find a digital 'line level replication' of an amp you know...that'd be a good barometer for comparing how close you can get to the tone of your amp.
   Nope...no way I've seen except stuff like Digital, read reviews for more field test feedback info, or LHX Marshall or Fender Amp Sims.
  The speaker, when connected to a tube output, is a very dynamic 'thing' with lots of various events...mimicing this @ line level, exactly like your amp sounds...
  As close as I know to get that would be digital, and if you can find a digital 'line level replication' of an amp you know...that'd be a good barometer for comparing how close you can get to the tone of your amp.
  http://www.geofex.com/
  Scroll down to the bottom ... 'tube amp sound in a box' A picture is worth a thousand words.

[rhdwave]

Ok, i see this is quite a bit more complicated than i thought at first.  Thank you everyone for the responses and the time! I'll report back with what i decided to do.  Much thanks!!!

[Seljer]

If you just wanted to use your amp's line out (or fx loop send) for recording without an actual cabinet hooked up to it a simple dummy loud like the high power resistors like mentioned at the start out of the thread would be enough to keep the power amp section happy enough to not burn out your output transformer, no

[petemoore]

a simple dummy loud like the high power resistors like mentioned at the start out of the thread would be enough to keep the power amp section happy enough to not burn out your output transformer, no ?
  Someone knows better than I, but checking out what's commercially available to convert ""tube amp output to line level"" might make you one of those 'someones'...I have heard 'it' can be done [I never tried 'it' in any form other than a MIC]. I would wait until you trust what if any experiment you choose would be safe if done carefully/correctly...
  I had a heater element soaking output from a 100w plexi, and indeed the brick resistors became Very Hot, instant burn hot...and lowered the output level of the amp, and more noticably altering the tone as the ratio between heat output to sound output became greater...[a 6 way switch selected various resistors inserted in the speaker output circuit]...larger resistance ='d more attenuation...the unit was a gift from a soundman, and I did use it, it did enable the 100w to be more usable, but now that I have small tube amps, I prefer opting for not useing heater type attenuators, or any attenuators for that matter.
  From direct experience and from what I've read, scaling your tube amps to be loaded in use is a good option, although you basically have to start from scratch if what you have is a big tube amp.
  There seems to be a recent recurring 'fad' of small tube amp implementation for recording and other small volume usage, it appeared as a bandwagon I wanted to jump on, and I'm glad I did.
  Using a small tube amp allows you to load the darn thing [that's what I bought the wrong too big amps for], reaching a big amps headroom requires 'cumbersome' volume levels. I equate it to driving an F50 on a go-kart track...I figured out these 'scaled' tube amps serve to provide the 'loaded tube amp output section' function...quite well, quite recommendable for low volume/tube amp sound...
  I have  everything I need for Med to High Volume Tube amp 'loaded' tone. The one amp is normally 15w, but I can use one of the two output tubes to have 7.5w of output, then with the other 5e3 of course I can get 30w, so I have 7.5w adjustable up to 15w, then the second 15w amp. 7.5w is larger than I'd want for recording/diddling, 15w is about right for practice..maybe a gig, 30w is pretty dern big through 2 x '2x12'' cabinets with effecient speakers, I also have an instrument mic for PAing the guitar.
  In this way I'm able to achieve loaded tube amp tone at everything exept pretty low volume, I think I'd really like a .5w - 2w amp for that.
 

[d95err]

Randall Aiken has a nice article about reactive dummy loads:

http://www.aikenamps.com/spkrload.html


From what I hear (haven't A/B tested), wire-wound resistors sound best in attenuators and dummy loads. I guess it is *because* they are slightly inductive. Non-inductive dummy loads are probably audiophile stuff...

[vanhansen]

Get the Behringer Ultra-G DI Box.  I use one with my rig.  Speaker out to the box, balanced out to the console, with 4x12 speaker sim on.  Also enable the ground lift when using the speaker out of your amp.  Yes, it will handle it.  My amp doesn't need a load on it this way but I'm going to anyway so I have a monitor near me.  My amp is a Vox AD50VT by the way.  For use with your amp, you will still need the dummy load though. 

I've heard great things about post phase inverter master volumes (PPIMV) on tube amps if you want to get that cranked tone at lower volumes since the PI has a big role in achieving that sound.  Only thing is, MV amps have their MV *before* the PI, not after.