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Problem with new Ampeg rig

M

mgray87

Sep 5, 2006
20
0
The Other Mike
www.lessthanunder.com
#1
OK I read the FAQs and searched and didn't see anything along these lines, so here you go:
Bought Ampeg SVT3-Pro and 410 HE cab (8 ohms) new in June. I added a 2x15 cabinet, also 8 ohms, and usually only play one at a time. I have never pushed this setup since it has plenty of power even at half volume. Tone settings are pretty unremarkable. However, now I am getting distortion with the lower notes (I play a 5 string) and at mid to higher volume. This occurs with both cabinets either separately or in combo, and there is no visible damage to the speakers. Have checked cords and they are of good quality, tight and undamaged.
Does this sound like an amp problem or like I've blown both cabinets? And if so, any ideas why?
Rig is still under warranty and I'm taking it down to authorized service center tomorrow, but they have been less than enthusiastic about any advice.
I sure appreciate any help and/or ideas.
 
#4
In addition to all those good questions, I would ask if you have the "texture" button pressed. I belive the SVT-3 has one. That will give you a little crunch when you're really driving the signal. I don't know if this is a pleasant "overdriven' distortion, or an unpleasant one (though your starting a thread implies an unpleasant one). I would also try listening directly through the line-out, to isolate whether it is or isn't the preamp.
 
#9
Awesome response! First of all:Thanks.
Answers to good questions:
I'm playing Schecter 5 string basses (Stiletto Elite and a C5), both with the active EQ, and I did change the batteries during my troubleshooting attempts (obviously to no avail).
I *am* using a good heavy cabinet cable and the connections are guten tight. My instrument cables are Monster cables and are in good repair...I think...gonna test another ...
Settings on the bass are both volume pots on "11", high end pot at midway and the low end pot on about "9".
The amp settings are something like this:
The tube gain is cranked. The master is cranked (both as per suggestion in manual and preference). I have been using the -15 db switch since I have the active pickups. The gain starts to distort at around 11 oclock and of course, only gets worse.
I have been bypassing the EQ. The bass knob is at about 1 oclock, midrange about 9, treble is about 10 and the "frequency" knob has been used in all 5 positions all without effect on the offending problem.
Gearhead17 correctly stated there is no texture button.
I would describe the "bad Distortion" sound as a blown speaker variety...
The distortion occurs both with and without the low button pushed. I have not been using the push buttons (high, low, brt) since the problem surfaced.
There doesn't seem to be a problem at lower volumes.
Hope I didn't miss anybody.
And again: thanks for your help and suggestions.
 
#10
Well there is no texture button. .There is however an Ultra Lo, Ultra Hi, Mute and Eq button as well as a -15 pad.. If your red LED is not lighting and you are playing at a low volume check your Tube Gain knob...

If you are taking it for Warantee work tell them to check the Mosfet BIAS adjustment.

If you still get a gritty type of distortion at lower volumes and very low volumes I think it may be your Mosfet BIAS... there are a few threads about that exact problem.. they may be under SVT-III Bias..
I fixed mine with an internal tweak, but if you dont know what you are doing you will get a molten pile of mosfets or a cold under powered distored amp.
Jerold Tiers works for ampeg and has answered a few threads about that problem.
 
#11
So far you've eliminated:

bass batteries
cables
settings on amp pre and power section and any tone shaping
speaker cabinets (probably)

I also have an SVT-3 with active bass p'ups and I can push it very hard before it distorts and the clip light has to be on pretty solid before that happens. I would try substituting another bass (perhaps a passive bass) if available to test if there may be a problem with the active electronics. I find it hard to believe that you blew both cabinets at the same time since you'd have to abuse them really nasty to do it, and would certainly KNOW what caused it.

If you rule out the bass active electronics as the culprit, I'd bring in the amp to the store you bought it from and try playing with their basses, cables and speaker cabinets and if it still does it then it MUST be the amp internals and they're on the hook to fix it.
 
#12
I had one also, & if U are only getting this prob at higher vol.
U might've tried already this, but U say U have the tube gain cranked---this will give a bit of distortion at higher gain, but I wouldn't have thought at 11 oclock on the gain- but If U haven't tried already- try with the "tube Gain/Voltage" pot turned totally the other way- all the way to the left(counter clockwise) is on full BTW:hmm:
Rod.
 
#13
mgray87 said:
The tube gain is cranked. The master is cranked (both as per suggestion in manual and preference).
Click to expand...

This seems contrary to what I've read and my experience Both with this amp and many many others. I'd guess the suggested settings graphics have the master at 10 only as a matter of having it set somewhere...

-Set the gain so that the red LED flashes just a little when you strike your hardest note (slap on the low string).
-Set the tube gain knob to your preference (1 being softest sound with gentle OD if the gain is high/10 being harshest with distortion if the gain is high)
-Use the master to adjust overall volume.

Also set the onboard bass pre to flat.
 
#14
If you have another amp from which you can use the pre- and poweramp section, you can split them up, so you can find out if the problem is in your pre or poweramp. But it was ok and now suddenly without any changes it distorts? The problem with the biassing of the mosfets occurs also at low volume, but that doesn't sound like a blown speaker, more like a subtle background fuzz.
Overdriving the tubes in the preamp is something that happens in the pre-amp and will also be noticable at low volumes of the poweramp. When you set the tube-gain knob to 0, there will also be some distortion because of the compression.
My guess is a faulty tube. If they are good tubes they can live almost forever, but if there is a bad tube it will probably die in the first 24 work-hours.
Since you have warranty, just bring it in and let them fix it for free.
 
#18
mgray87 said:
The local Ampeg service center guy tells me there *is* no BIAS adjustment on the SVT3-Pro...but I think I've read enough from forum members about it to question the Ampeg dude...
Click to expand...
Tell your local service - Yeah there is a BIAS adjustment on the SVT3 Pro. It is the small blue Bournes pot on the left side of the PC board if you are looking at the amp with the cover off from front to back.
It is very touchy and he needs to get the spec on the mv at the bias point across the resistors.
That is if it actually is the Bias adjustment. It may not be.. But that distortion you described seems to be a thing that crops up with the 3 pro often.

I hope you find what it is and get it going.
Mosfets can and do get BIASed.
 

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