Attenuators for Twin Reverb

Take a look at this:
https://www.amazon.com/Behringer-DI...nuator&qid=1533452062&sr=8-16&ref=mp_s_a_1_16

 

The Aracom PRX150 will do what you want...but it ain't cheap. If you configure the Aracom properly, you can run without speakers, or you can configure the box to run with speakers at various levels of attenuation. I own the DAG version. In my opinion, these sort of devices sound/feel best at relatively low levels of attenuation, but you can lock down a 100W amp as much as you want.

The Aracom has a line out, so you might be able to forego using a DI. FYI, my brother loves the sound of a Countryman Type 85 on the output of his vintage Twins, but he runs with the speakers connected instead of using a loadbox.

Aracom Amplifiers Crank it up! Power Rox PRX150-DAG Power Attenuator

Also kinda cool, you can use the Aracom as an impedance matcher. For example if you want to run a 16 ohm Marshall 4x12, simply configure the input of the Aracom to the Twins 4 ohm output transformer, and then configure the output of the Aracom to match the 16 ohm speaker load. I have done this with my Dual Showman Reverb and a Marshall 1960AX and it worked really well. The DAG version works with 2,4,8,16 ohms on input or output and will handle 150 watts.

The Pro version is a bit less expensive, so it has a few less features. See attached manual.

 

Rivera mini rockrec, two notes captor, mesa cab clone, and radial headload all do at least 100 watts at 4 ohms and have DI outputs. Or go with a countryman/JDI and a dummy load.

 

These are amazing and gives you a digital interface to your computer. It comes with speaker emulators for both guitar and bass cabinets.


Two notes Audio Engineering - Torpedo Live - Digital Loadbox

 

If I understand your need, you want to be able to crank up the amp, but have the speakers be relatively quiet?
You want that cranked amp overdrive sound without filling the room with high levels of sound? FWIW, this is why they make pedals. That being said.
The following are based on the above understanding. Some of what I will offer will be quite out there, so for what it’s worth advance at your own risk.

If you attenuate between the instrument and tha amp input, it just seems that you will have more noise to deal with.
And that won’t really cut the speaker level very much.

To be able to crank the amp but not the speakers, you may have to attenuate between the amp output and the speakers. This is a Twin Reverb right? A combo amp right? If not you have easy access to the cable between the amp and speakers, otherwise a combo requires getting inside to open up the speaker leads.

A Twin Reverb? It has two speakers? It has an open back cab?
If you were to reverse the leads on one speaker so they were opposite polarity and out of phase with each other, you might achieve some level of speaker cancellation. If this works well for you, install a switch that lets you select in-phase, out of phase.

Disclamer: These ideas are not for tech noobs or those who otherwise have no idea what they are doing in making these changes. Any experiment in this area should start out at very low levels and gradually increase while listening for problems.

 

Isn't the main tone issue with a resistive dummy load is that it does not replicate the non-linear speaker load?

 

It also won’t replicate the tone of a speaker cone moving in a box.

It kind of depends on what the OP is really trying to accomplish.
Does he want the amp to provide all of the tone, sans speakers?
Or is he counting on pushing air to be a part of the equation?

I guess it helps to know if he want’s to use an output from the effects loop, or mic the cab?

 

OX | Amp Top Box | Universal Audio

 

That’s a pretty cool box.
Even right down to the upside-down labels on the back so you can read them while leaning over the top.

 

Some units do have a reactive load that emulates a non-linear speaker. The Two Notes Torpedo Live unit that I referenced above does.

 

And within reactive loads, the reactance may be different than that of the speaker.
This partly due to the reactance of a speaker that changes with and is affected by movement of the voice coil.
In other words, a speaker may exhibit dynamic reactance where a fixed reactance will be just that, fixed.
How much of a difference does all of this make when considering the affects of reactance on tone?
Hard to say without seeing some hard numbers.

But yes, I would think a reactive load that can somewhat simulate a speaker at at least one point in the reactance curve would be better than a purely resistive load.

 

Is this non-linear load related to the output power and frequecny based on X brand speaker?

 

There are more sophisticated circuits than these, but you will get a dynamic response with an L-R-C network. Some load boxes have a speaker motor as part of the circuit. I have a unit that has this. BTW, Weber sells speaker motors for those that want to build load boxes.

Of course, there is the option of emulating a speaker digitally. They can really refine the response that way.

 

Not sure about specific speakers. In the documentation they list a number of different cabinets, so indirectly they do. Two Notes has a very good reputation for their cabinet emulations.

These are the bass cabinets that they have built in, there are also guitar cabs:

• 2Notes CSB : Two notes Custom 1×15”
• Alu XL : Hartke® XL 4×10”
• AZ Ben : SWR® Big Ben 1×18”
• AZ Work : SWR® WorkingMan 4×10”
• Calif Low : Mesa/Boogie® 2×10”
• Fridge : Ampeg® 8×10”
• Heaven Bot : David Eden® 1×15”
• Heaven Top : David Eden® 4×10”
• Marco : Markbass® 2×10”
• Voice V125 : Vox® V125 2×12”

They also emulate power amps and mic type and placement. Of course, you can dial in your own. There is a more expensive studio version that offers more functionality.

 

This

 

Speakers can be simulated
MOrcad speaker/crossover simulation page

There's more to cabinets and rooms simulation, but it can easily and effectively done with software.
IK Multimedia | Fender Collection for AmpliTube
And other SW, but this one has been certified by Fender.

And it saves the amp

 

THD Hot Plate. The best imo.

 

The Aracom is one of the best attenuators you can buy. Their marketing materials mention patent pending tech used to emulate speaker reactance. Despite their proprietary technology, as attenuation in increased, the sound becomes less resonant, dull, and lifeless. However from comparative reviews I have read, the degradation with the Aracom is less severe than with many similar devices.

IMHO, the sound is still very usable, I just find the unattenuated sound superior in all areas except volume. I keep the Aracom around because I have some vintage non-master 100 watters with the bright caps intact. The Aracom allows me to play these amps at a reasonable volume level. It's also useful if I want to crank any of my 100 watters into output distortion.

I believe what you have written captures part of the puzzle...I think there's a bit more, but I am not an engineer so consider this uniformed speculation. I agree there is a bit of an organic interplay between the speaker and the amps output transformer, and this interaction is unique for each amp speaker combination due to the variable reactance of the speaker.

To go one step further, the speaker is driven, but also drives the output transformer. Consider the speaker's mechanical compliance and the voltage that is generated when the cone is moving. The speaker is both a motor and a generator.

The more attenuation that is used, the more the interaction between the amp and speaker is suppressed, partly because the output transformer is isolated from the speakers variable reactance, partly because the signals coming back from the speaker are attenuated to the point of insignificance, and partly because the speaker cone is moving less so the signals are smaller to begin with.

 

My God, I'm such a dinosaur.

I've used a Tom Sholz Power Soak for close to 30 years now.

I have one for my Twin and another on my Bandmaster Reverb.

I was told that it would kill my output transformer.

Both amps retubed about every 5-7 years.

I did finally lose the transformer on the Bandmaster, but it is the original one from 1971, so I'm guessing it wasn't the Power Soak.

Power Soak is just a bank of resistors that are progressively switched in by a knob.