Attenuator Questions

[Milnoque]

What, if anything, is the downside to oversizing an attenuator?

The amp I want to attenuate is a Gibson GA20 RVT (12 watts). I'm looking at a Weber Micro-Mass rated for 15 watts. I am not likely to dime the amp. I want the sound I get well shy of that at lower volume. I'm convinced that the Weber unit can handle my application. The standard advice is to buy a larger attenuator than your amp rating. This caused me to wonder if there was a price to be paid for using a 100 or 150 watt unit on a 12 watt amp.
Just Curious.

Many of the attenuators I have seen claim that they can serve as DI boxes. Has anyone ever had a positive experience doing this? I was thinking of feeding the PA, not recording.

I spent some time with the search but didn't come up with what I was looking for on the above questions.

In the meantime, If you want to tell me what you're using and how you like it I would like to hear from you. I have no experience with these.

 

[DrewPeterson7]

What is the maximum power the 15-watt attenuator can take? Like, is it rated for a tube amp rated at 15 watts, or for handling 15 watts peak power?

I'm not really up on the physics here, but the gist is when a tube amp is rated, it's rated at a certain % Total Harmonic Distortion (THD). So, it'll put out X number of watts when it's distorying Y%. The problem with tube amps, though, is that while this is the accepted rating system for audio amplifiers, 99% of amplifiers on the market (car stereos, home stereos, etc) are designed NOT to distort, while guitar amps are. So, at a given %THD, which due to ratings conventions is really a pretty clean signal, you're not even close to diming the output; depending on how the circuit is designed, you might not even have it up halfway. The total peak wattage in full distortion could be way higher.

This is why a Marshall head may be rated at 100 watts, but its corresponding cab will be rated upwards of 400.

So, if anything, I'd be worried that an attenuator rated for 15 watts may be too low. And, to the best of my knowledge, there's no harm in running an attenuator rated for way higher than you need - I play a 50-watt Mesa Rectoverb, and use a THD Hot Plate which the manual claims is safe up to amps rated at 150 watts, but not above. I've had no issues.

EDIT - oh, your other questions. Um, the DI... I haven't really experimented with it, but for feeding a live PA it's probably a bad idea, unless the DI out is speaker emulated. If not, well, you could run it through a Palmer or something first, but even then I'd just mic up. And I love my Hot Plate. It's not totally transparent (the bright and deep switches go a long way though - with them on even -16db is pretty good), but the difference between a Rectifier (even a 50 watt one) at a sane bedroom volume unattenuated and one at a sane volume with an attenuator in line kicking the signal down -16db is pretty stark. It basically lets you have sort of a "poweramp gain" control for your amp; I tend to cut rhythms with less attenuation and a clean poweramp, and then get the poweramp to start compressing a bit by upping the attenuation and turning up the master. It's pretty damned cool for a home recording nut.

 

[Zaphod B]

The attenuator should be rated at 50% higher than the nominal rating of your amp.

That way you can dime the amp if you want, and not damage the attenuator.

 

[Milnoque]

Thanks Drew,

I've been playing with a cellist and an acoustic guitarist. We've been adding some electric guitar for some of our songs. The amp sounds sweet at low volume but not as low as it needs to be for this application. I'm not after crunch, just a little tube compression.

You're probably right, I ought to get an attenuator that can handle my biggest amp (18w Ampeg M-15) dimed. You never know when you'll get a wild hair. When I want crunch I usually want to damage my ears at the same time though.

I'll look at the 50W units. It would be the smart thing to do (first time for everything).

Another question.

When an attenuator craps out does it tend to fail maintaining the load or connecting fully to the speaker? In other words, could you all of a sudden be runnung your amp full out without a load on it? These old Gibsons have a funny transformer that, I understand, can be hard to find.

 

[kojdogg]

The attenuator should be rated at 50% higher than the nominal rating of your amp.

That way you can dime the amp if you want, and not damage the attenuator.

+1
This is what Weber recommends stating that if you don't it can have a detrimental effect on the output transformer of the amp

 

[kojdogg]

What, if anything, is the downside to oversizing an attenuator?

....
This caused me to wonder if there was a price to be paid for using a 100 or 150 watt unit on a 12 watt amp.
Just Curious.

I have owned and use the Micro Mass, a 50 watt Mass Lite and currently have a full Mass 100. I find that the Mass 100 reacts similarly to my 15 watters (Vox AC15 HH and a Tiny Terror) and my 50 watter (Sovtek Mig 50) though the uneffected tones are obviously different. It seems like the output level is similar for the Sovtek and the 15 watters when the attenuator is engaged-- the resulting volume is more dependent, for the most part, on where the attenuation dial is set-- especially with a lot of attenuation, than the starting wattage of the amp.

YMMV

 

[stevieb]

What, if anything, is the downside to oversizing an attenuator?

The amp I want to attenuate is a Gibson GA20 RVT (12 watts). I'm looking at a Weber Micro-Mass rated for 15 watts. I am not likely to dime the amp. I want the sound I get well shy of that at lower volume. I'm convinced that the Weber unit can handle my application. The standard advice is to buy a larger attenuator than your amp rating. This caused me to wonder if there was a price to be paid for using a 100 or 150 watt unit on a 12 watt amp.
Just Curious.

Many of the attenuators I have seen claim that they can serve as DI boxes. Has anyone ever had a positive experience doing this? I was thinking of feeding the PA, not recording.

I spent some time with the search but didn't come up with what I was looking for on the above questions.

In the meantime, If you want to tell me what you're using and how you like it I would like to hear from you. I have no experience with these.

To answer your question directly...

AS IT RELATES TO TONE: there is a downside to "oversizing" an attenuator- as you attenuate the output signal ("speaker out") of an amp, high frequecies get more and more lost, and the resulting sound gets overly compressed- it really takes on a "squeezed" quality that is not very pleasing.

To elaborate, if you use a high-watt rated attenuator with a low-power amp, the poor sound quality comes on at low attenuator settings- possibly so low, you can not get a good sound out of the rig. I have an Altair PW-5 50-watt attenuator. (see my "Road Test" thread) and using it with my Ampeg VT-40 and Deluxe Reverb returns wonderful results. A Vibro Champ- not so good- in fact, the VC/PW-5 combo was really a near-pointless excersize in taking the thing to an extreme, but it illustrates the point- you gotta be VERY conservative when attempting to attenuate low-power amps.

AS IT RELATES TO AMP LIFE: Probably a downside here, too- Attenuators cause you to be able, nay, need to, drive your tubes hard. Thus, power tubes will wear out sooner. In my road test, I compared the tone a amp gives you when pushing an attenuator, to the tone a performance car gives you when pulling a trailer- you are making them both work, and the resulting tone, either speaker out or engine, is much more pleasing. But if you pulled TOO big a trailer, your car would not last long. I imagine the same thing would happen with an amplifier- really, in either the mechanical or electronic realm, physics are physics- overwork something, and it breaks.

The PW-5 can serve as a DI, and it seems to work well for that purpose, but I believe it is pre-attenuation- so there is little or no benefit to using it if you are wanting that hard-driven tone to go to the PA. Mic your amp.

I know of no attenuators for 15-watt amps. There may be some, but IMHO, there is no real market for them- no way to make any money making them. You will probably have to build your own.

 

[ggunn]

To answer your question directly...

AS IT RELATES TO TONE: there is a downside to "oversizing" an attenuator- as you attenuate the output signal ("speaker out") of an amp, high frequecies get more and more lost, and the resulting sound gets overly compressed- it really takes on a "squeezed" quality that is not very pleasing.

To elaborate, if you use a high-watt rated attenuator with a low-power amp, the poor sound quality comes on at low attenuator settings- possibly so low, you can not get a good sound out of the rig. I have an Altair PW-5 50-watt attenuator. (see my "Road Test" thread) and using it with my Ampeg VT-40 and Deluxe Reverb returns wonderful results. A Vibro Champ- not so good- in fact, the VC/PW-5 combo was really a near-pointless excersize in taking the thing to an extreme, but it illustrates the point- you gotta be VERY conservative when attempting to attenuate low-power amps.

AS IT RELATES TO AMP LIFE: Probably a downside here, too- Attenuators cause you to be able, nay, need to, drive your tubes hard. Thus, power tubes will wear out sooner. In my road test, I compared the tone a amp gives you when pushing an attenuator, to the tone a performance car gives you when pulling a trailer- you are making them both work, and the resulting tone, either speaker out or engine, is much more pleasing. But if you pulled TOO big a trailer, your car would not last long. I imagine the same thing would happen with an amplifier- really, in either the mechanical or electronic realm, physics are physics- overwork something, and it breaks.

The PW-5 can serve as a DI, and it seems to work well for that purpose, but I believe it is pre-attenuation- so there is little or no benefit to using it if you are wanting that hard-driven tone to go to the PA. Mic your amp.

I know of no attenuators for 15-watt amps. There may be some, but IMHO, there is no real market for them- no way to make any money making them. You will probably have to build your own.

FWIW, results may vary with the newer designs (I've had my PW-5 for 30 years) which present a reactive load to the amp rather than the purely resistive load that the amp sees with the PW-5. Also, the line output of the PW-5 is not pre-attenuation; it's a line level signal, so it's even more attenuated than is the speaker output. BTW, it cannot serve as a DI because it's unbalanced.

 

[Milnoque]

Thanks Guys. This has been very helpful.

 

[stevieb]

So, Ggunn, is that the reason some folks believe the PW-5 can damage an amp? Frankly, I think it's a myth, but I could be wrong.

 

[ggunn]

So, Ggunn, is that the reason some folks believe the PW-5 can damage an amp? Frankly, I think it's a myth, but I could be wrong.

I don't think it hurts the amp, but the load that the amp sees from a speaker is a reactive load, which means its impedance is constantly changing as it cycles through the output waveform. What it sees when you have a PW-5 in the circuit is a static resistance in parallel/series with a reactive load, and the more attenuation you use, the more static the load. It affects the instantaneous current through the output transformer and changes the shape of the waveform, which is probably what you were referring to when you said that the sound was "squashed" when you use a lot of attenuation.

Newer attenuators use some sort of "motor" in the circuit which more closely approximates the reactive impedance load of a speaker to the amplifier.

 

[WhiteStrat]

I know of no attenuators for 15-watt amps. There may be some, but IMHO, there is no real market for them- no way to make any money making them. You will probably have to build your own.

What about the THD Hot Plate? They work with most anything.

I've got a couple Webers--the 100/150 watt & the 50 watt--I think the 50 watter is called the Mini Mass. In any case, it works great on my 15 watt amps. I've got a Blues Jr, and a Valve Jr. Don't like the breakup on the Blues Jr. anyway, so I leave the Weber on the Valve Jr. Let's me get the full tube breakup and talk on the phone at the same time!

 

[WhiteStrat]

I feel special. It finally happened to me. My response to Outlaws (even quoting him) showed up before his post! I loves me a good time warp...

 

[Outlaws]

I know of no attenuators for 15-watt amps. There may be some, but IMHO, there is no real market for them- no way to make any money making them. You will probably have to build your own.

?

What about the THD Hot Plate? They work with most anything.

 

[stevieb]

Yeah, that time-warp thing is wierd...

My PW-5 worked on everything down to, and including, a vintage Vibro champ- but did not sound particularly good on little amps.

 

[Milnoque]

Do these ever fail open so that you're diming your amp without a load?

 

[stevieb]

Do these ever fail open so that you're diming your amp without a load?

That would suck...

 

[Outlaws]

My PW-5 worked on everything down to, and including, a vintage Vibro champ- but did not sound particularly good on little amps.

The THD is not as simple as a PW-5.

 

[soundchaser59]

I dont know how they really work, but all the explanations above make a lot of sense. I had a couple of Weber's mass type units. They use a speaker motor, like a speaker without a cone so it reacts the same but makes no sound. Its best use is as an impedance matcher, me thinks.

I felt like the mass was like smoking pot.......you wont realize what it's doing to your tone until you quit using it. Especially with a lower watt amp, you will be much happier building some kind of miniature mic booth and putting an extension speaker in there with a mic, and then listening to it thru a monitor.

Sorry if that's not an option. But you will be surprised some day when you return from a jam, you have your amp dimed and you forget to connect the attenuator......the tone you were missing will be quite a pleasant slap in the face.

 

[Milnoque]

I'm trying to use an electric guitar in a setting with two acoustic instruments. I'm not interested in diming the amp. I just want to get it up enough for the amp to sing a little. I don't have much tone with the amp on "1". It's better if I run it up to "5" or "7" and use the guitar's controls to limit the volume. If I wank it back as much as I have to the ton is less than stellar. I was hoping an attenuator would help. I've hated all the pedals I've tried.