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Preamp Output?


WCunha

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This my be a dumb question but I was at band practice tonight and we played louder than usual. The thing is I'm using a SVP-Pro pre with a DPC1400X power amp and a 8 ohm Avatar B210 and a 4 ohm Avatar B115(still waiting for my Acme). Anyhow I have the gain set on the preamp to where it clips on only the loudest notes and the gain controls on the power amp all the way up and I have the master volume 3/4 of the way up.

 

To me it seems like it should be louder at that level with 375 watts on one side and another 525 watts on the other side. I can even put the master on the preamp all the way up. I mean it's loud but, I never had the volume on my GK800RB past 1/2 way up.

 

I know there has to be a reason. Is the output from the preamp to low to really drive the power amp?

 

Thanks, Wade

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It certainly sounds like it could be a gain staging issue, however many people are surprised by how little an increase in volume 1,000 watts will give you over, say, 500 watts.

 

For example...

 

I rewired my 4 ohm Eden 210 cab to 16 ohms, so I could use it safely in conjunction with my 8 ohm 4x10 cab. But when I use the 210 alone, it really doesn't seem a whole lot less louder at 16 ohms nominal impedence. The thing is drawing only about 30% as much power off any given amp that may be powering it. And there is a definite drop in volume, but no where near as much as you might expect.

 

Just some food for thought.

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Originally posted by WCunha:

This my be a dumb question but I was at band practice tonight and we played louder than usual. The thing is I'm using a SVP-Pro pre with a DPC1400X power amp and a 8 ohm Avatar B210 and a 4 ohm Avatar B115(still waiting for my Acme). Anyhow I have the gain set on the preamp to where it clips on only the loudest notes and the gain controls on the power amp all the way up and I have the master volume 3/4 of the way up.

 

To me it seems like it should be louder at that level with 375 watts on one side and another 525 watts on the other side. I can even put the master on the preamp all the way up. I mean it's loud but, I never had the volume on my GK800RB past 1/2 way up.

 

I know there has to be a reason. Is the output from the preamp to low to really drive the power amp?

 

Thanks, Wade

WCunha: My general analogy is this: no matter how much water pressure goes to your kitchen faucet, you're only gonna get so much water out of it until you use a bigger faucet. Keep that in mind.

 

Two things are happening here: (1) a log rule that says for every +3dB increase of SPL (sound pressure level) you'll need 10 times the wattage. (2) assuming the SPLs for both speakers are identical (no guarantee here) the 4-ohm speaker will take twice the wattage and sound twice as loud as the 8-ohm speaker.

 

(1) You'll need to discover the SPLs of the speakers you're using (most manufacturers have online specs). Here's an example for a speaker rated at +90dB SPL at 1 watt @ 8 ohms:

 

-at 001 watt, you'll have +90 dB SPL

-at 010 watts, you'll have +93 dB SPL

-at 100 watts, you'll have +96 dB SPL

 

Naturally, if you exceed the maximum power rating you'll chance a blown speaker.

 

SOLUTION: get a bigger faucet... more speakers.

 

(2) and make sure to match cabinet impedances. Once you start playing with over 400 watts, overdriving a 4-ohm cabinet becomes a reality. Save the 4-ohm speaker for club work and get another 8-ohm speaker to match what you have.

:wave:

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If the clipping you are talking about is on the preamp and not the DPC 1400, you should dime the master volume and adjust with the sound levels with the gain knob for loudest setup. Also drop some of the very lowest frequencies and bump the mids to get a significant volume boost.

You can stop now -jeremyc

STOP QUOTING EVERY THING I SAY!!! -Bass_god_offspring

lug, you should add that statement to you signature.-Tenstrum

I'm not sure any argument can top lug's. - Sweet Willie

 

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There really isn't a problem. I was just curious with the difference in volume from going from a total of 400 watts from the GK and going to 900 watts with the DPC1400X. I was surprised I could turn the main volume on the preamp all the way up without blowing out my eardrums. :D
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Fred,

 

You might want to demand your money back on that engineering school diploma ; }

 

3 dB difference indicates a 2x change in power - the diff between say 100 watts and 200 watts. That is a difference that most engineers will agree is perceptible - all other variables equal - but doubling wattage is not considered an especially notable change in volume. The main benefit from a more powerful amp comes in clean headroom (if the specs are honest), improved transients and speaker control, greater reliability, etc.

 

10 dB indicates a 10 x difference in power. If all other variables can be controlled {it's tough to find speakers with the linear repsonse to actually bear this out - they tend to "power compress" and/or blow up ; } 10 dB diff indicates TWICE the volume (or half). So, to get twice as loud, if one had one HUNDRED watts, they would need to replace that with one THOUSAND watts.

 

And for low frequencies, because of loudspeaker inefficiencies and room acoustics and the ears' poor ability to hear low freqs until they get VERY loud (everybody should endeavor to understand the Fletcher Munson curve - it can really aid one in the quest for tone and solving problems) - volume comes very dear.

.
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WCunha,

 

You should be putting out enough unlipped signal from the preamp to drive the DPC-1400X so that it ocassionally lights up the red channel LED(s). If you are using the onboard limiter DDT circuit you can gain about 3dB in volume/power before it begins to limit in an unpleasing fashion.

 

If you can't make more than a typical 1.4 volts with your preamp you will NEVER reach the full power of the amp - let alone get the benefits of this extra 3 dB of clean volume. You either need to get that preamp set right if its specs indicate that it can output that kind of voltage, or find another preamp that can actually make professional-level signals.

.
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Originally posted by :

WCunha,

 

You should be putting out enough unlipped signal from the preamp to drive the DPC-1400X so that it ocassionally lights up the red channel LED(s). If you are using the onboard limiter DDT circuit you can gain about 3dB in volume/power before it begins to limit in an unpleasing fashion.

 

If you can't make more than a typical 1.4 volts with your preamp you will NEVER reach the full power of the amp - let alone get the benefits of this extra 3 dB of clean volume. You either need to get that preamp set right if its specs indicate that it can output that kind of voltage, or find another preamp that can actually make professional-level signals.

I never saw the red lights on the power amp ever come on.

 

I have the pad button depressed (-15db) and the gain knob about 1/4 of the way up so, the clipping indicator light only lights up on the loudest notes.

 

I don't know the specs of the SVP-Pro. It isn't in the manual. I'll have to contact Ampeg for that.

 

Thanks, Wade

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Originally posted by WCunha:

Originally posted by :

I never saw the red lights on the power amp ever come on.

 

I have the pad button depressed (-15db) and the gain knob about 1/4 of the way up so, the clipping indicator light only lights up on the loudest notes.

 

I don't know the specs of the SVP-Pro. It isn't in the manual. I'll have to contact Ampeg for that.

Thanks, Wade

The Ampeg pre should be able to drive the Peavey just fine. Once again try diming the master volume and adjusting the gain for loudness desired and a little cut on the lowest frequencies usually goes a long way.

You can stop now -jeremyc

STOP QUOTING EVERY THING I SAY!!! -Bass_god_offspring

lug, you should add that statement to you signature.-Tenstrum

I'm not sure any argument can top lug's. - Sweet Willie

 

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Originally posted by :

Fred,

 

You might want to demand your money back on that engineering school diploma ; }

You're right, I stand corrected, and I should've waited until I cracked open some books. If I had a degree I would sue to get my money back. But even with my lack of engineering schooling, I think we've presented the same conclusion to WCuhna - get more speakers.

 

For those interested in learning more about decibels and Fletcher-Munson curves, take a trip over to the University of New South Wales:

 

What is a decibel?

FAQs in Music Acoustics

 

But since this is way too technical for me, I'll just go off and buy me one of those new-fangled "online degrees"... with the money-back guarantee, of course.

:D

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Originally posted by WCunha:

I thought I was supposed to set the preamp to clip and then back it off until it only clips on the loudest notes?

 

Wade

are you looking at the clip indicator on the left or right side of the preamp?

You can stop now -jeremyc

STOP QUOTING EVERY THING I SAY!!! -Bass_god_offspring

lug, you should add that statement to you signature.-Tenstrum

I'm not sure any argument can top lug's. - Sweet Willie

 

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Originally posted by WCunha:

Left side red clip light next to the gain knob. Lug are you familar with the SVP-Pro?

 

Thanks, Wade

Kinda, I have the previous model. The clip indicator on the left is the input level clip from your bass into the preamp. The clip level on the right is an indicator that the signal from your bass is too hot for the input stage of the preamp. The Gain and Pad controls are used to control this. The Pad drops the input -15 db and is typically for active basses with hotter inputs. The peak indicator to the right of the EQ sliders is to show clipping at the output side of the preamp. By maxing the Master volume and adjusting the Gain, you can get the max level output from the pre to the power amp. If you are getting clipping on the left side indicator, try using the Pad. This is almost the same as turning down your volume control on your bass.

You can stop now -jeremyc

STOP QUOTING EVERY THING I SAY!!! -Bass_god_offspring

lug, you should add that statement to you signature.-Tenstrum

I'm not sure any argument can top lug's. - Sweet Willie

 

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Fred - you're such a class guy. Thanks for the links, and for stepping back so easily.

 

greenboy - I thought you found a pretty smooth way to tell Fred he was all wet with that analogy.

 

I kill me!

Tom

www.stoneflyrocks.com

Acoustic Color

 

Be practical as well as generous in your ideals. Keep your eyes on the stars and keep your feet on the ground. - Theodore Roosevelt

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Turn that input pad off unless your active electronics are so hot that you drive the amp into clipping with the gain knob at 2.

 

The most important part of gain structure is to have the hottest signal at the front end of your signal chain...otherwise you're amplifying more background noise than signal.

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I'm sure SEARCH would pull up a number of articlettes that I or some other good soul has written on how to set up gain stages (and how EQ affects that).

 

I would also hazard that on the Ampeg site there is probably some manual, if not for the very model, for a SIMILAR model, that would help understand the specifics of where the threshold of the LED indicator are and what it means. I know I have a few Ampeg *.pdf in my extensive collection of manuals, white papers, tech bulletins, etc - they have proven to be well written and easy to understand.

 

EDIT: The ones I've looked at are pretty decent with graphical aids as well.

.
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Originally posted by BenLoy:

Turn that input pad off unless your active electronics are so hot that you drive the amp into clipping with the gain knob at 2.

 

The most important part of gain structure is to have the hottest signal at the front end of your signal chain...otherwise you're amplifying more background noise than signal.

I'm using a single EMG P pickup with 18 volts for headroom.

 

If the pad switch is not depressed it clips at approximatly 2. I'll have to try to experiment with that. But, I did adjust the gain knob so that the peak light flashes occasionally.

 

I'll have to search gain structure in the archives.

 

Wade

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Originally posted by   :

I'm sure SEARCH would pull up a number of articlettes that I or some other good soul has written on how to set up gain stages (and how EQ affects that).

 

I would also hazard that on the Ampeg site there is probably some manual, if not for the very model, for a SIMILAR model, that would help understand the specifics of where the threshold of the LED indicator are and what it means. I know I have a few Ampeg *.pdf in my extensive collection of manuals, white papers, tech bulletins, etc - they have proven to be well written and easy to understand.

 

EDIT: The ones I've looked at are pretty decent with graphical aids as well.

Thanks greenboy.

I'll have to go to the archives. Also, I do have the owners manual for it but, it didn't seem that informative.

 

Wade

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In general let that PREgain trim flash until you can hear the sound quality actually deteriorate ; } Then, back off a hair. You should then either be finding the sweet spot of early gain, or making it apparent to listeners that your tin ear has not yet been transmuted into gold ; }

 

No offenses intended, none whatsover.

.
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Originally posted by   :

In general let that PREgain trim flash until you can hear the sound quality actually deteriorate ; } Then, back off a hair. You should then either be finding the sweet spot of early gain, or making it apparent to listeners that your tin ear has not yet been transmuted into gold ; }

 

No offenses intended, none whatsover.

So, watch it but not to hard and listen for when the tone starts to distort.

 

Which by the way I tried having the preamp gain all the way up and the drive knob all the way up. Didn't really care for the distortion sound that it created. I thin my sansamp TRI-AC does a better job for distortion.

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Originally posted by BenLoy:

Turn that input pad off unless your active electronics are so hot that you drive the amp into clipping with the gain knob at 2.

 

The most important part of gain structure is to have the hottest signal at the front end of your signal chain...otherwise you're amplifying more background noise than signal.

Solid. This is a simple rule that a lot of people overlook.
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You wouldn't believe how many times I've seen a mixing board set like this by "sound engineers:"

 

Input gain (trim): Cranked

 

EQ: Cranked on all frequencies.

 

Fader: -40db

 

Engineer: "You're too loud!!! You have to turn down! Look at where I have to set the fader to keep you from drowning out the band!"

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And vice versa too, of course. There are plenty of people who need to RTM - and even use common sense and the powers of observation and deduction. But many just look for quick fixes and end up building a shole bag of stock tricks that are just sick and wrong.
.
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  • 5 months later...

I'd like to bump this thread and in turn, ask a few Questions about clipping/compressor lights on amps(particularly SVT-3 Pro) during live performance.

 

I'm in a band now that plays a lot of clubs. Last gig we played was at a pretty decent sized venue(holds about 500). Nice stage and sound, too.

I brought my Ampeg SVT-3 Pro, through a 4x10 HLF, and I had my spector euro 4 active P/J bass.

 

I'm also playing with 2 loud guitar players, doing heavy metal.

 

Well, I had the master and tube gain maxed, the gain ( on the left near the inputs) set at around half to 3/4, and the pups on my spector up about half. I also have a vintage Morley power wah w/ boost, I use just a little bit of the boost to give me some more headroom.

 

I noticed at the gig the clip indicator light was constantly flickering. I noticed this in the studio too. My question is, is this the amp's compressor going to work for me or is this something I need to worry about.

 

The tone sounded fine, with maybe just mild distortion at my hardest RH attack, so I'm inclined to think there's no problem. But the last thing I need is a magic smoke show at my next gig. You're experienced input and advice is greatly appreciated.

 

Of course my first thought is, I need a more powerful 2 ohm amp and another speaker cabinet. Hence more headroom. But I'm forced to make do with what I have for now.

 

Thanks!

"The world will still be turning when you've gone." - Black Sabbath

 

Band site: www.finespunmusic.com

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Richard:

 

Which clip indicator was lighting, the preamp or power amp? You NEVER want to clip the output of the power amp...it generally won't hurt the power amp (probably not good for it, though), but it will definitely burn up some speaker coils. :freak: Clipping the preamp input or output generally won't hurt anything, and as long as you like what you're hearing, then do it! Generally, you want to keep the signal as high all the way through the chain as you can so you minimize noise, but not so high that you add unintended distortion.

 

HTH,

Dave

Old bass players never die, they just buy lighter rigs.

- Tom Capasso, 11/9/2006

 

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I can recognize an odd time right away, and if it's a more normal time(3/4, 5/4, 7/4) I'll usually be able to tell you what it is without counting anything...i'll just understand it.....

 

my cousin, who is a great and creative guitar player, recently played me a recording that he did..and within 30 seconds I had figured that it was in 11...so those bizzare times are a little harder for me.

Hiram Bullock thinks I like the band volume too soft (but he plays guitar). Joe Sample thinks I like it way too loud (but he plays piano). -Marcus Miller
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Hey there's one LED by the instrument input jack, it flashes when the signal level into the pre-amp approaches clipping.

It was flickering all during the gig, supposedly this is OK but I just wanna make sure so I'm asking the pro's.

I guess everything is fine. Thanks for gettin back though.

"The world will still be turning when you've gone." - Black Sabbath

 

Band site: www.finespunmusic.com

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Originally posted by musicfiend:

I can recognize an odd time right away, and if it's a more normal time(3/4, 5/4, 7/4) I'll usually be able to tell you what it is without counting anything...i'll just understand it.....

 

my cousin, who is a great and creative guitar player, recently played me a recording that he did..and within 30 seconds I had figured that it was in 11...so those bizzare times are a little harder for me.

MusicFiend...you getting mouse-happy again? :P

Old bass players never die, they just buy lighter rigs.

- Tom Capasso, 11/9/2006

 

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