Ampeg SVT-7 Pro TEST

[tekdiver500ft]

I tested an Ampeg SVT-7 Pro Rev C, and in a thread that was closed down due to unsavory behavior, I posted this reply:

I suspect they didn't drive it hard enough, or there was some other error. When I heard about this over the weekend, I figured this would come up, so I tested a friend's SVT-7 Pro. With 2.8v RMS into an 8ohm dummy load, I calculated (v*v/ohm) (68v*68v/8ohm) 578 watts. Into a 4ohm dummy load, I got (62v*62v/4ohm) 961 watts. While not up to the published numbers, they are close enough for me.

I don't currently own any Ampeg equipment, nor do I work for them.

Passinwind asked me this:

(Originally Posted by Passinwind)

Ruh roh...

If you're proofing ratings for the whole system at a spec'ed THD level, you need to actually test the whole system, no? Can/should we infer that the amp would meet specs with a cleaner preamp driving it? That seems at least plausible. Or put another way: does the amp actually make ~1000 watts at say, 10% THD?

OTOH, your methodology makes me trust your figures a lot more. Not that I didn't necessarily trust them to begin with though -- bench testing powerful amps can be a real can o' worms sometimes.

To which I responded:

Excellent point! I wish I'd thought of that. I generally bypass the preamp to keep the playing field level, and didn't anticipate needing to do differently this time. Sorry about that. I don't know if my friend will let me push his amp that hard, but I'll talk to him, and I'll try to test it this weekend to see if/when I get 1000 watts when running through the front end.

I am posting this in a new thread so that y'all will help me remember to do this.

Please keep it polite, keep the politics out of it, I am not interested in whether Ampeg lied, or made a mistake, or whatever. I am only interested in finding out whether this unit will produce 1 kW when driven through the preamp, and if so, at what THD.

[fenderhutz]

lol

[tekdiver500ft]

Okay, maybe I won't.

[Handyman]

I'm interested, for sure.

What methods are you going to use to for measuring THD and the power dissipation?

[tekdiver500ft]

I'm not sure what you're asking, actually. I use a 2 kW wet dummy load, and a Agilent (Hewlett Packard) 334A.

[will33]

I'm curious as to what you end up with as well, nothing to gain or lose, just curious.

FWIW, the other thread is open, but if people keep pulling stuff trying to shut it down, maybe not for long. It'd be cool if this one could remain a technical discussion.

[tekdiver500ft]

That's the intent, Will.

[arai]

Originally Posted by will33

I'm curious as to what you end up with as well, nothing to gain or lose, just curious.

FWIW, the other thread is open, but if people keep pulling stuff trying to shut it down, maybe not for long. It'd be cool if this one could remain a technical discussion.

I don't know if you or a mod removed your post where you accused me of trying to shut down that thread. I would just like to make it clear that that was not my intention.

[B-string]

So are you are using a caloric watt meter (wet dummy load)?

[JimmyM]

Hey Jon,

Originally Posted by tekdiver500ft

I'm not sure what you're asking, actually. I use a 2 kW wet dummy load, and a Agilent (Hewlett Packard) 334A.

Anyway, don't know if you all saw Jerrold Tiers' lengthy technical post about the SVT 7 Pro in the other thread. If anyone has an axe to grind with LOUD, it's Jerrold, and he pretty much cleared them of any shenanigans with the 7 Pro. Apparently the rev C version now has a limiter that reacts to different voltage conditions and limits the output lower if it thinks it needs to and doesn't if it doesn't. Then he said tekdiver's method was an equally valid if quick-and-dirty way to measure output. This could easily explain why BGM and tekdiver got different results, and all I could think was, "That's a darn good safety feature that sure beats cutting out in the middle of the gig."

So not to get off on a personal tangent, but I will just say that I will always remember those of you who questioned my personal integrity over this matter, you know who you are and I know who you are, and I will ignore your posts forever, and you no longer exist in my world.

[rodl2005]

Count me interested also. 7 pro owner & happy about it.
Good stuff!

[tekdiver500ft]

Very well said, James. I was impressed with the readings I got, & hope to be so again.

[JGR]

Originally Posted by James Judson

So is the SVT7pro 763 watts or 1000 watts? I think the last thread was doing a lot of hair splitting. We need to give up on the idea of one number carved in stone and anything else is some kind of lie.

One big lesson I learned while going to engineering school is "most of the world is not exact". Most components in that amp are probably plus/minus 20%. Add up all the tolerances and you have an amp that does not work. NOT. Sometimes a resistor, any resistor, any value will make the circuit do what its supposed to. Took me a long time to accept this screwy idea from my instructors. Your amp works a 8 ohms or 4 ohms (thats a 50 - 100 % tolerance).

763 watts is one big amp
1000 watts is one slightly bigger amp.
Both amps may test identical under certain conditions.

I don't see any lies or deceptions going on here but I do see how folks without a technical background could come to this conclusion.

Free advice: Use the watts rating on amps to match speakers (keep in mind 50 - 100 % tolerance) and your in the ball park. Use the watts rating for anything else and you might start an argument or cause bad feelings.

Huh? Any power shortfalls are not due to component tolerance. 8 and 4 ohms are not a "tolerance".

[JGR]

Not sure what doing an independant test really proves unless you go back and test a bunch of other amps as well, using the same methodology. If testing the Ampeg in this manner makes it fair better, then likely most of the other amps that were up to snuff to begin with will fair even better yet, so we're just skewing everything towards the optomistic side of things.

The nice thing about BGM is that they are testing everything the same way in a controlled environment, so you get a more apples to apples comparison of how various manufactuer's products stack up, for better or worse. Most of the amps they have tested thus far have all been fairly close to their manufacturer's specs, which leads me to believe that their testing methods are pretty sound. The major outliers to date (if memory serves) are the GBE1200, the TC, and now this Ampeg. There will no doubt be others as more amps are tested, and if we can get a large enough sample size, we are likely to see trends develop with various manufacturs and/or power section topologies. It is what it is.

[JGR]

As a rocket scientist, I can tell you - it's not rocket science. I'm not pointing fingers or making allegations - I think your confusion comes from a lack of understanding, and there is enough misinformation spread on the internet already, so better to know what you are talking about before you start to type.

[sevdog]

Originally Posted by tekdiver500ft

I am posting this in a new thread so that y'all will help me remember to do this.

Please keep it polite, keep the politics out of it, I am not interested in whether Ampeg lied, or made a mistake, or whatever. I am only interested in finding out whether this unit will produce 1 kW when driven through the preamp, and if so, at what THD.

So much for that idea, Tekdiver. Is it me or is Talkbass especially feisty this week?

[will33]

Actually, a speaker can have impedance ranging from 3 to 50 or more at peaks in it's bandwidth. I don't buy the tolerance thing. Part of engineering is to figure out and use those tolerances to insure whatever's supposed to be coming out the back end is actually coming out the back end. Personally, if it came within 3-5%, I wouldn't mention it. Those are more widely accepted tolerances in this type of stuff. That is to say, if it came in at something north of 950 watts, it's a done deal. The power section alone already does, but this isn't a poweramp, it's an integrated "bass head", so I think the more telling results are those derived where you plug your bass in.

[will33]

Originally Posted by JGR

As a rocket scientist, I can tell you - it's not rocket science.

Now this ^^ is sig. worthy material.

[Jheake]

I wouldn't mind seeing a second/third opinion on this subject tekdiver.

I find this whole thing very interesting. Pointless insults aside.

I could see this being very positive, if the watts come out conclusive to BGM's results then I think Ampeg should address the issue somehow. However, if the results are different it could lead to some really interesting technical discussions that I'm sure alot of the folks like myself here have no engineering background in, could indeed learn from.

I say got for it tekdiver.

[will33]

Ya, I learn a lot from these kind of things too, regardless of the results.