Author Topic: Watts and watts (Read 426 times)

dnburgess · « **on:** July 23, 2003, 12:15:00 AM »

I have long been familiar with the practical difference between valve watts and transistor watts. i.e. My hundred watt all valve head sounds louder than my 700 watt transistor power amp.

But today I was told that from a practical perspective there are different kinds of transistor watts. In particular, switching mode power supplies (as used in the modern light weight power amps such as the QSC PLX) were not well suited to bass use because they had trouble supplying currents approaching DC at lower frequencies.

Can any of the more technical club members advise whether there is any inherent limitation in switching mode power supplies that make them less suitable for bass applications than conventional designs with big transformers / capacitors?

David

elzie · « **Reply #1 on:** July 23, 2003, 07:06:04 AM »

Well, as far as bass amps I can't say. However, I have experience with Switched Mode Power Supplies, or SMPS.

The LASERs I repair use them. We run them from 0 to 70 mA and up to 20k volts DC. I very rarely have a problem with them, but they are not exactly the same thing you would find in an amp

So basicly, our application is one that requires the force of the high voltage while using just milli-amps to regulate it's power output. They seem to be suited quite well for this application.

I know it probably doesn't help you much, but maybe it can give you an indication of where these work well....

Paul TGO

stoney · « **Reply #2 on:** July 23, 2003, 12:49:47 PM »

I can't speak technically, however I'm having a LOT of trouble right now with the combination of amps and speakers I'm using. Both amps (I THINK) are the ones to which you refer. I have an iAMP800 and a Stewart World 1.2. I have tried (unsuccessfully) to drive my Acme Low B II (4 ohms) and various combinations of the same Low B II and a Low B1 (8 Ohms) or Two 8 Ohm low B I's. All sounds great for about 10 minutes. the all of a sudden, the sound simply goes away. It comes back eventually once the amp stabelizes. It just seems like there's too much information going in and not enough room for it to come out. Kind of like pushing a basketball through a garden hose. The first time it happened, it happened when I slapped for the first time in the evening. Then it began happening when I'd slide, then on double stopps then on rapid playing. I'm working with Euphonic Audio and Acme at the moment to try and remedy this. Sorry I can't be of much more technical assistance. Perhaps some of the other Stewart owners can chime in as there are a few out there in Alembicland that own them.

stoney

bigredbass · « **Reply #3 on:** July 24, 2003, 10:09:41 PM »

stoney:

While I'm DEFINITELY not an electronic techie, I know players here in town who had similar problems that were traced down to insufficient AC at the wall socket. Evidently these type amps can be very fussy if they are facing low voltage, insufficient amperage, etc. You might want to check the AC where this is happeining. It amazed me how many places would meter out at 80 or 90 volts. At the same time, some of these guys were not aware that the WHOLE BAND can't plug into two wall sockets, run tons of extension cords, cut off their ground lugs, etc.

If this is more than a one-nighter, have someone QUALIFIED check the AC. How many and how big are the breakers the whole band is using? Is the voltage constant, or does it sag when you're all blowing? Are you on the same breaker as the ice machine(my personal favorite!), central air, etc.? Keep your AC line from the wall (NOT a plug strip you're sharing with ANYONE else) as short and as heavy guage as possible. Use a good power conditioner when you can.

In my experience, clubs NEVER plan for proper AC for entertainers. It's just one of those things most people don't consider, unless it's a purpose-built venue.

The fact that two entirely different amplifiers are exhibiting similar behavior would make me check the AC. And PLEASE: IF you AREN'T qualified, find one of the guys' brother-in-laws, dad, uncle, etc. who's an electrician, if this is worth pursuing. It may be less than ideal AC for your amp, but there's still PLENTY left to hurt you!

Best of luck,

J o e y

palembic · « **Reply #4 on:** July 25, 2003, 05:37:38 AM »

I'm not a technical heavy-weight either.
Athough: the guitar player in our ban Drive installed for that reason a -rather expensive- Furman device that stabelizes the power in a ser way. A lot of problems vanished from that moment on!

Paul the bad one

dannobasso · « **Reply #5 on:** July 25, 2003, 08:56:35 AM »

I agree. You must have sufficient power to run your amps. If you try to run them without the proper input, they can pass DC and blow out your speakers. This happened to me last week with a PA. 2 18 EAW subs were killed! Ask where the circuts are and how much amperage each has (if they know). Search around for another plug on a different circut. Run HD extention cords to another outlet and as BRB wrote, take it from the wall. Even catering halls and hotels can have dirty power and less then adequate power .

elzie · « **Reply #6 on:** July 25, 2003, 12:43:16 PM »

One suggestion on the power angle would be to check your documentation to see what the requirements for the amp are. Some amps may accept a voltage variation of up to %15. I think more of a standard would be %10, which, for home use, would be from 108 to 132 volts.

Another good idea that was pointed out was to make your amp on it's own source, as much as you can, then test it again to see if you still have the problems. At the very least, make sure it isn't sharing any circuit with a refrigerator, oven, well pump, ac, etc.......

I would mention again, check your documentation for the amp to make sure you know what it needs. If you aren't sure, post the info here.

Danno, that must've really hurt when those 18's went.

Paul TGO

dnburgess · « **Reply #7 on:** July 28, 2003, 03:53:01 PM »

Returning to the original subject of this thread for a moment...

I have been unhappy with the tone from my QSC PLX. Its fine at home, but falls appart when I crank it in the rehearsal studio.

So I borrowed a PSS Audio Power amp. A traditional dual mono design (i.e. separate transformers and capacitor banks for each channel). Even though its only rated at 250wpc (4ohms) - it sounded a lot better in rehearsal than my PLX 1202 which is rated at 325wpc.

Admittedly, neither is powerful enough to drive my stack to ear shattering volume - but it is an interesting test of the different design approaches.

My hypothesis is that with switch mode type power amps in bass applications, you need a lot more headroom than you would with a traditional design.

I will try to test it out with a much larger PLX.

mattheus · « **Reply #8 on:** July 30, 2003, 03:05:23 AM »

Voltage problems are very common when you have gigs on stages where they are not used to have bands. Some people can't understand that a 'electric' band use a lot of ac/dc....
I would recommend to ALWAYS use a 'clean' circuit!! When you're using a PA system, you should even go further. My band uses 3 'clean' circuits. one for the backline and mixers and two for the PA system amps. Mostly we don't have any problems. Another problem to be very carefull with, are the outdoor gigs. Always make sure that your AC is earthed!!
It's nice being a bassplayer, but you have to know a little tech stuff, be a salesman, know all about taxes, be a good spokesman, always be nice....
What a job.....

Mattheus (tDo)

stoney · « **Reply #9 on:** July 30, 2003, 05:03:23 AM »

Hey David,
Out of curiosity, what kind of speakers are you using and at what ohms are they rated at?

stoney

dnburgess · « **Reply #10 on:** July 30, 2003, 04:04:08 PM »

Stoney - you're asking ME what kind of speakers I'm using. Acme, of course - is there any other?
(A B2 and B4 stacked, both 4 ohms)

As I said, neither of my test amps were big enough for these speakers - so the test was about driving amps beyond their comfort zones. I suspect that a 1000wpc QSC will be fine - and still only weigh 21 lbs - but I will also check out some bigger traditional amps (although the prospect of an additional 20 plus lbs in my rack doesn't thrill me).

There seams to be a lot of noise about the subject of traditional vs switch mode amps. The QSC people tell me that the spectral balance (i.e. tone) of the output doesn't change with load - but my ears tell me otherwise. Other knowledgable people only use big iron in bass applications.

It probably reinforces the dictum that, no matter what design, you can't have too much power.

David

stoney · « **Reply #11 on:** July 31, 2003, 07:31:30 AM »

David,
Yea, I thought you used ACME but I guess I was too darn lazy to research it. Right now the EA iAMP800 is back in New Jersey. Gary is going to try and tweek it for me. I have to contact Andy at ACME but he won't be back until tomorrow. Seems as though I can't get a definite ohm reading from my LowBII?

When I first started this project, all of the higher ups from the various companies from whom I bought equipment all agreed that it should work fine// OY! This is turning into a hardware vs. software war!!!!

dnburgess · « **Reply #12 on:** July 31, 2003, 03:46:34 PM »

Stoney,
When I started out on my tonequest I looked really closely at EA gear. Being so far away, I felt I just couldn't take any risk on reliability. The facilities on the iA800 look great and I watch your progress with baited breath.

David

stoney · « **Reply #13 on:** August 01, 2003, 04:31:01 AM »

Thanks David,
I'm seriously considering buying either a used EA 2x10 or (they have agreed to sell me ) the box for the new iAmp800 combo. I do, however feel the need to preamp the iAMP in order to get the tone I desire. The controls on the iAmp are really filter Q's unlike an EQ section. I either use my GK Micro amp or my Presound Digitube. Both do wonders for the sound. Now if I can just get sound ALL THE TIME, I'll be thrilled.
Stoney