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Crest Prolite 3 and HPF questions

#21
MarkA -

I generally run the EQ pretty flat, graphical EQ unengaged so no boost there. I originally was using the unbalanced previously and it did exhibit the same behavior. I will check the fans.

Aged Horse -
The amp has an ACL limiter, but on this version it can not be turned off.

This cab I'm using at home is an 8 ohm cab. It is shutting down even at very low volume until I run the -20db pad.

Remembering that for the first year I used it I was using a VT-Bass pedal as a preamp makes me wonder if I'm looking at the wrong component of the chain. I had no issues, and thinking back the issues arrived when I started using this preamp.

<edit> I did find this thread here: https://www.talkbass.com/threads/ampeg-svt-ii-non-pro-direct-out-noise.308773/. I thought that was interesting, and may be applicable </edit>

With you folks knowing much more than I, I have 2 questions. Is it possible the preamp output is just too hot and it's causing clipping? Second, I have the knob on the front rotated completely counter clockwise. Manual says to rotate it clockwise as much as possible for maximum headroom. Is this correct? I assume this is akin to amps that have no master and use the gain to determine volume.

Maybe a call to Peavey is in order. If the amp is in fact done for, I'll be pretty disappointed. While I've had this amp for quite a while, it doesn't have much playing time on it.
 
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#22
failuresXbass said:
With you folks knowing much more than I...
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Hey, now, careful who you include in "you folks" -- I'm just a guy who owned a Prolite and googles owner's manuals sometimes. ;)

failuresXbass said:
...I have 2 questions. Is it possible the preamp output is just too hot and it's causing clipping? Second, I have the knob on the front rotated completely counter clockwise. Manual says to rotate it clockwise as much as possible for maximum headroom. Is this correct? I assume this is akin to amps that have no master and use the gain to determine volume.
Click to expand...

You could think of the signal coming from the SVT-IIP as the Gain and the Prolite's attenuator(s) as the Master volume -- if the latter are cranked fully open, then I guess it's more-or-less like a no-master-volume amp, with the overall volume controlled by the Gain control (signal from the SVT-IIP pre, which itself has several gain stages).

Do you really have the attenuator on the front of the poweramp rotated fully counter-clockwise/down/closed? I've practiced at home, at low volume, with high-powered preamp+poweramp rigs (including the 2.0 and a QSC PLX 1804, each channel of which is roughly on-par with the Prolite 3.0's unbridged output) and I do not run the poweramp fully open when I do that (as I might at an outdoor gig), but you've still got to crack them open a little bit to get reasonable gain staging and control over volume. Fully counter-clockwise on your amp looks like -80 dB ("minus 80 decibels" -- 80 dB of signal attenuation vs. fully open -- I'm surprised that it doesn't -- or doesn't appear to -- go fully off ["minus infinity dB"], but I digress).

-80 dB will let some signal through (if you're hearing something, it's letting signal through), but is a huge deficit to overcome and I wouldn't be surprised if you were clipping the front end pretty hard to get audible volume that way. Try cracking it open a few clicks, to -30 dB or -15 dB, and adjusting the SVP's output accordingly for your home practice volume. You can always tweak from there (and crack it open more for actual gigs).

I can't say that there's not something wrong with your amp (Andy -- agedhorse -- would know more about that than I), but I think that'd give you much more reasonable gain-staging. What you're doing now is like trying to walk a hippo through the cat's pet-door. ;)

Good luck!
 
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#24
failuresXbass said:
I'm sorry, I mistyped. I have them rotated fully clockwise, not counter clockwise. Basically running the amp fully open and controlling the volume using the gain on the preamp.
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D'oh... there goes my brilliant theory.

If you've got the Prolite cranked fully open and it's shutting down at bedroom volumes, something, somewhere is wrong. By the time you clip its front end, either of your cabs (810 or SWR 8x8) should be knocking stuff off the walls and making coyotes howl.
 
#26
MarkA said:
D'oh... there goes my brilliant theory.

If you've got the Prolite cranked fully open and it's shutting down at bedroom volumes, something, somewhere is wrong. By the time you clip its front end, either of your cabs (810 or SWR 8x8) should be knocking stuff off the walls and making coyotes howl.
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Thanks Mark,

I'm going to try a different preamp. I don't have another rack mount, but I do have a ampeg pedal preamp. I'll give that a go and see if it exhibits any similar behavior.

Thanks for all the help and advice!

Agedhorse - thank you. Speaker cable is an interesting thought. I have not swapped that. Not saying it's not the amp, but another variable to investigate.
 
#27
Protective shut down has nothing to do with the preamp (unless it's oscillating, which would sound horrendous), it has to do with the OUTPUT of the power amp. There are no protective shutdown mechanisms at the input.
 
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#28
I guess then I wonder why engaging the -20db pad on the preamp output resolves the issue? That is what is leading me down that path. Even when turning it up louder, with the pad engaged, it did not go into protect.

Not an argument, just seeking what I'm missing here and what would cause that behavior.
 
#29
It could be that there was an oscillation in the preamp output stage that changing the gain (or pad) function resolved unintentionally.

Preamp signal output line drivers can be sensitive to capacitive loading unless the circuit is designed to prevent this. I very rarely see this anymore because (successful) designers have learned from previous mistakes. I don't see any issues with the line drivers on the SVT II-pro.

Are you talking about the input stage attenuation, I don't see any output stage level switch. I can't see how the input stage would affect this at all.
 
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#31
DWBass said:
View attachment 5472787
Why are we still running power amps in bridged mode these days? Stereo/Parallel mode is the way to go. That amp has a load of power NOT bridged. You can run both cabs in Stereo/Parallel mode. 3000w (bridged) into your cabs is insane and totally NOT needed! Even in Stereo/Parallel mode you're pushing 900w into a 4ohm cab.
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Because for example Crown XLS 1002 costs 360e (2 years ago 285e) and gives you 1100w at 4 ohms bridged which is pretty good power for modern 810 or 2x 410. The cheapest power I've seen so far and you'll get hpf and light weight (4kg) for free.
 
#33
None of my service documentation shows a -20dB pad switch, just a level pot and a pre-post switch.

I wonder if you have something that was changed or added after the fact?
 

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