Another attenuator question - The UA

[alerich]

This is a question about a device known as the Ultimate Attenuator. It's actually not really an attenuator - it's a re-amping device.  In a nutshell it loads the amplifier output with a 30 ohm load, derives a signal from that load and feeds the signal into a small solid state power amp if I understand its operation correctly. A single volume control on the front of the UA controls the volume level of the power amp to the speakers. The manufacturer claims that the device can work safely with any amp at 4, 8 or 16 ohm output. If I understand the mfgr correctly they state that the 30 ohm load is safe(r) because the smaller load on the output makes it work less hard - i.e. less stress on the amp. I have read that the original designer of the UA - who licensed the design to the company who sells them and still builds them to order for his own customers - chose the 30 ohm load because he felt it sounded best but will build to order with a 16 ohm load if ordered that way for customers who are uneasy about the impedance mismatch.

My question is this: My instinct tells me running my amplifier really hard into a 30 ohm load is not a good idea even set at 16 ohms and especially when set at 8 ohms. We are always taught that maximum power transfer occurs when the output and load impedances are matched. My instinct tells me that one of the times when I want all of the power transferred to the load is when I am running the amp balls to the wall. Is it actually safe to run a 50 or 100 watt amplifier hard into a 30 ohm load?

PRR's comments the other day about OT's and matching the impedance of the load to the expected operation range of the output tubes got me wondering about this. Maybe it is safe.

[phsyconoodler]

Here's my take.There is a 10,000 page thread on the gear page about it.

 If you use it to drop your level down when playing live,then it will be just fine.However,if you want it so you can crank your 50 watt Marshall down to whisper quiet levels in your apartment,then you are asking for trouble.
  The loads are prohibitive and some amps can't handle it.The results are blown fuses,shorted tubes and sometimes worse.
Supposedly the UA is a re-amp device and the load is constant and is not an issue.However my experience with two amps is that when you crank the amp and turn down the attenuator volume too low,POP goes the fuse.Both amps were able to be cranked with none of those problems with no UA connected.
  You tell me what made the fuses blow.

[sluckey]

It's probably safe, but if I were going to drive the amp hard I'd be more comfortable with a good impedance match (gotta match power rating too).

This device sounds like a simple speaker line out with adjustable level. And a high power resistor for a speaker load. If so, it would be very easy to build. Cheap too.

[HotBluePlates]

And when you said "re-amp" I thought of something totally different. Namely, a technique to get a more complex guitar sound by taking a recorded track (which already includes the characteristic voice of the amp used for the recording), passing it from the tape to console to the input of a second guitar amp, which is then recorded. A "reamp box" in this sense take a low-impedance recorded guitar signal, drops it down into the 10-100 millivolt range, and feeds it into the regular input of another guitar amp.

Some folks have made recordings with amazing guitar sounds this way (usually with a little tube flavor from each amp).

[jojokeo]

I saw the salesman guy at NAMM and he played a 100w Marshall down to whisper/bedroom levels and sounded pretty good as he didn't lose much if any high end but as for performance on the stage? He couldn't get that loud so it was hard to tell.

You guys are always thinking...that's what I love about this site.

[alerich]

I saw the salesman guy at NAMM and he played a 100w Marshall down to whisper/bedroom levels and sounded pretty good as he didn't lose much if any high end but as for performance on the stage? He couldn't get that loud so it was hard to tell.

That's one thing about the UA. I have not been able to find a spec on the wattage of the internal solid state amp. It would have to be reasonably powerful if you are going to use this thing on stage with a band - especially if it is not miked. The SS power amp is supplying all the sound to the speakers. None of the power to the speakers is actually coming from your regular amp if I am clear on how this thing works. It's roughly the same thing as having an attenuator with a line out to a separate solid state amp. Kinda like what EVH or Tom Scholz did back in the dark ages. I saw a gut shot of an un-badged version that the original designer build and sells but it's very home brew looking and hard to make out what is going on in the circuit.

In all fairness you don't see a wealth of anecdotal reports about amp failures with this thing and most of the folks who use it love it. I would just be uneasy with the matching factor between the amp and UA and was curious about a more technical observation.

Edited to add: Ok, I am a doofus. It's a 100 watt internal amp. Says so right on the web site. Doh!

[phsyconoodler]

Go to the gear page.There are lots of failures reported.I don't trust it as far as I can throw it.

[alerich]

Go to the gear page. There are lots of failures reported. I don't trust it as far as I can throw it.

I'll have to take your word for it. A quick search of TGP reveals that there is no such thing as a quick search of TGP.