Lightest Poweramp?

[::::BASSIST::::]

QSC PLX1804 11 lbs

Me likey!

 

[::::BASSIST::::]

According to QSC's website the QSC PLX1804 is 13lbs:

PHYSICAL
Dimensions
Height
Width
Depth, Rack mounting surface to rear panel
Overall Depth
3.5" (8.9 cm) 2 rack spaces
19" (48.3 cm)
8.95" (22.7 cm)
11" (27.9 cm)
Weight 13 lbs. (5.9 kg) net

 

[fdeck]

Hmmm... I don't understand the distinction you're making. If it's not a question of having the right output gain to best drive a given input sensitivity (AKA gain matching), but it is a question of increasing the output gain of the preamp (using an external device if necessary) in order to best drive the power amp... You get where I'm lost?

In the last thread where we discussed this, I said some "hot" things to you because I felt you weren't giving forth with a very simple piece of information. I apologise for speaking that way- and I hope you can spell this out in simple terms, if it really is that simple... since a significant number of people seem to not know the answer.

Are you saying the only difference between e.g. an AI or QSC and a CA-9 is how much gain they each have available? So given the same input level, the CA-9 just has the capability to amplify it more?

As I understand it, many listeners will say that one system sounds better than another, merely if one system is louder and all other things are equal. It is a strong enough effect to potentially mask other effects. This could happen if two power amps have different gain but are fed the same input signal amplitude. Since you will adjust the gain of either system in use, to get your desired volume level, the maximum available gain is irrelevant so long as there is enough to get you loud enough.

Therefore, objective audio testing usually starts with adjusting each system so that the two systems so they have the same overall gain. Since different power amps have different amounts of available gain, either one or the other should be adjusted in order to level the playing field, before continuing with testing.

That's what gain matching is. It eliminates the biggest cause of audible differences, so you can begin listening for other differences.

Thus it is quite possible that available gain is the only difference between those amps -- or maybe not -- but gain matching is the first step in finding out.

Let me give an analogy. Suppose you want to test whether Greeks are better fighters than Romans. To this end, the Greeks send 100 men, and the Romans send 1000. You say: No fair, the Romans must send 900 men home before we can continue the test.

That's gain matching.

 

[bongomania]

OK, thanks, I see where the term "gain matching" has a different specific meaning than I had thought.

If the amount of available gain is inherent to the design, i.e. number and type of gain stages, how are those extra Romans sent home? Wouldn't it require physical diversion of the signal from its full path, thus potentially skewing the results, since the audio qualities perceived might be a function of having x number of "not quite sonically transparent" stages of varying types? Feel free to let me know if I'm barking up the wrong tree.

 

[arbitrary]

c'est la vie.

I'm still young, the weight doesn't bother me much. Maybe in 20 or so years.


I suppose I could always default to Jim Berg. told me to, but I should take responsibilty for buying a heavy amp. I'll take that responsibilty tomorrow and sat. night actually.

 

[Passinwind]

c'est la vie.

I'm still young, the weight doesn't bother me much. Maybe in 20 or so years.


I suppose I could always default to Jim Berg. told me to, but I should take responsibilty for buying a heavy amp. I'll take that responsibilty tomorrow and sat. night actually.

Bro,

We should get together and check this all out some more sometime soon. I don't actually need the ABX comparator to do gain matching, but I'd also like to just try various amp/preamp combinations without worrying about the science for a while.

I want to come see you play through that rig soon too.

 

[arbitrary]

I want to come see you play through that rig soon too.

Friday night is in Sandy and Sat. night is in dowtown oregon city. If you're free. The demo packs should be mailed by end of next week, we ran out.

We should get together and check this all out some more sometime soon. I don't actually need the ABX comparator to do gain matching, but I'd also like to just try various amp/preamp combinations without worrying about the science for a while.

As soon as this term is up I should have some more time, 19 credits this terms, work and playing most weekends eats my free time up. Maybe another sunday deal in the beginning of march. I think it would be interesting to try different preamps into different poweramp. Some more ears would be fun for the more subjective side of life, while closing our eyes or something like that (maybe a black sheet).

 

[Passinwind]

Maybe another sunday deal in the beginning of march. I think it would be interesting to try different preamps into different poweramp. Some more ears would be fun for the more subjective side of life, while closing our eyes or something like that (maybe a black sheet).

Hmmm...I've always wanted to be "the man behind the curtain."

 

[8mmOD]

I know of the stewart world 1.2 which is 11LBS, but the overheating/shutdown issue of this amp (seems to be common) makes me want to avoid it.

My Stewie 1.2 overheated on me a few times. HOWEVER... I live in the tropics, I was running it bridge mono, the output of my preamp was relatively low, the amp was all the way up and it was extremely hot in the club on these occasions. I have since tossed a small clip on fan into the rack case and that keeps it cool.

I primarilly use my 1.2 for PA use now and its rare I need to turn it up 3/4 of the way running bridge mono. For $400 used, I am pretty happy, but I wouldn't trust it without the clip on fan.

 

[Bob Lee (QSC)]

"Gain matching" refers to setting two power amps to as exactly the same gain as possible for purposes of sonic comparison. It doesn't refer to setting preamp gain and powrer amp gain to certain point, because there is nothing to match up.

A power amp has gain. A preamp has gain. On most, the gain is adjustable to allow you to dial in the volume you want and compensate for your playing style (some bassists play with a lighter touch and some with a harder one) and how sensitive your instrument is. It usually doesn't matter too much whether you use more or less gain on one or the other, as long has you get the volume and feel that you want. But in general you will improve your signal-to-noise ratio if you use enough preamp gain to get a fairly hot signal (but without clipping the preamp) together with modest gain in the power amp, but enough to get your desired volume at your desired playing style.

Some preamps have pro audio-type output sections capable of full line-level output. For these, you typically won't need to run the power amp at anything close to full gain unless your bass doesn't put out much signal and/or you have an exceptionally light touch when you play.

Some preamps have very weak outputs. These are usually much older designs from when players might typically use the preamp for additional EQ, maybe an FX loop, etc., and then put its output into a head. For these, you'll typically need higher gain settings on the power amp.

Every power amp has a maximum amount of gain. Gain is how much it multiplies the input signal voltage to produce the output signal voltage. Some are designed with more maximum gain than others; that's no big deal, because most uses won't require maximum gain anyway. If an amp was meant to be operated only at maximum gain, the manufacturer would just leave the gain knobs off and save a few bucks on parts cost.



For anyone in the Bay Area who might be interested:

Power Amps—Demystified and Demythified
Audio Engineering Society, San Francisco Section
Tuesday, 20 February 2007 7:30 P.M. (Refreshments at 7)
Cogswell Polytechnical College, Sunnyvale, California
See Invalid Link Removed for details.

I'll be giving a talk on power amp technology to the SF section of the AES on Tuesday, 20 February 2007.

We'll cover what power amps do and how they work, as well as common misconceptions, which specs are useful and which aren't, what to expect from the and what not to, and oddities and pecularities about amplifiers.

The meeting is open to all interested persons. I hope to see you there!

 

[Bob Lee (QSC)]

If the amount of available gain is inherent to the design, i.e. number and type of gain stages, how are those extra Romans sent home?

No, it's not the number and type of gain stages. Power amps typically have these stages:

Input (a buffer, and converts balanced signals to unbalanced), typically gain = 1 ===> Attenuator (gain control), gain = 0–1, depending on setting ===> Output (the power stage, and where all or most of the voltage gain takes place), gain = whatever the designer decides, typically 20–80

The overall gain = Input section gain × Attenuator gain × Output section gain

You "send the extra Romans home" using the gain controls on the front panel.

 

[bongomania]

OK, fair enough, and simple enough, thanks. Just to be clear- is it your assertion that people only think the CA-9 sounds different from lightweight amps because it has more gain? The whole brouhaha is just because it gets louder with the same input?

 

[Bob Lee (QSC)]

OK, fair enough, and simple enough, thanks. Just to be clear- is it your assertion that people only think the CA-9 sounds different from lightweight amps because it has more gain? The whole brouhaha is just because it gets louder with the same input?

Considering that the CA9 has a higher maximum gain than most amps, and in gain-matched ABX tests listeners are apparently not able to tell them apart by sound alone, and that the described differences are consistent with what you'd hear when one amp is turned up louder than the other, it would seem that the gain difference is the deciding influence in the causal listening comparisons, not actual amp performance.

I expect that if the CA9 was set to a lower gain than the lightweight amps, the tables would've been turned.

 

[synaesthesia]

Invalid Link Removed

Have a look at these.

 

[seamonkey]

Invalid Link Removed

Have a look at these.

" Sorry, this store has been closed. "

 

[Kindness]

For my purposes neither amp showed any advantage whatsoever, and I might as well have flipped a coin when trying to differentiate between them.

But as usual, there were many things I would have liked to have done differently.

My test of a QSC PLX3002 and CA9 in a gain matched scenario demonstrated to me that there is nothing to be gained by carrying the extra weight. However, like you, I would have liked to have been more scientific in my tests. Although there were several bassist there, there was no ABX box, we didn't test to the limits of max output, we didn't test specific frequencies, etc. We used recorded material and played through them both and varying (matched) levels. Everyone in the room heard a difference between the two when "matching by ear" at the start of the day. When the test equipment came out and they were truly matched, no one heard a difference. At all.

 

[dood]

I thought I'd throw my baby in the melting pot.

I have one of these

Link Removed

Distributed in the UK by Beyerdynamic among others.

Here'a link to the complete series:-

Link Removed


Have a look at the spec of this sick sick poweramp!

Link Removed

Invalid Link Removed

Thing is, i'm not sure what distro is like on your side of the water, as the amps are built in italy.

news: 25/10/06

ROBBIE WILLIAMS AND POWERSOFT: PRESTIGEOUS MARRIAGE IN OCCASION OF THE PRESENTATION OF THE "CLOSE ENCOUNTERS" WORLD TOUR OF THE INT'L STAR AT RIVER PLATE STADIUM OF BUENOS AIRES -> Details

fair enough.. if its good enough for his house PA.. its fine in my rack he he he he!!!

 

[Passinwind]

My test of a QSC PLX3002 and CA9 in a gain matched scenario <snip>

Thanks very much for the report. Did you find precise gain matching to be a little tricky, as I did? The granularity of the amps' gain pots meant I had to hunt a bit for the "sweet spot". The QSC comparator makes this about as painless as it can get though. It's a really neat piece of gear if you swing toward the Spock side.

 

[Passinwind]

Thing is, i'm not sure what distro is like on your side of the water, as the amps are built in italy.

Powersoft is available here, but it's very expensive as well.

 

[dood]

Powersoft is available here, but it's very expensive as well.

hmmm shame. I had a feeling it might be. I have been very happy with mine.