Mic Pre-amp into Crown XLS1000?

[Matthew_84]

Hi all,

I purchased a VT Bass Deluxe as a pre-amp to go into a Crown XLS 1000, but recently there's been some discussion whether or not the VT Bass Deluxe is capable of performing well as a pre-amp for certain power amps.

I've been doing some reading into how a pre-amp actually works, and by definition (with tonal changes aside) a pre-amp "takes electrical current from (an instrument) and increases its voltage gain to a higher level... A preamp boosts (an instrument's) signal to what is called Line-Level."

I know the VT Bass has a level knob, but I don't know whether that increases the signal's voltage gain, or if it does, will it be enough. I also have a 10-band EQ in the FX loop which can also increase the volume to +12db's, but not being so tech-savy, I don't know if that has an impact on the voltage gain either.

I'm waiting on a cab to be shipped from Europe, but I was hoping to know, when it arrives and I hook everything up, how I can tell whether or not the signal going into the Crown XLS 1000 will be strong enough? Is there a way to measure this voltage gain? I do have the specs for the Crown, so I can figure that out once I know the input's numbers.

Also, if it is not strong enough, would this mic pre-amp, (ART Pro Audio TubeMP - Tube Mic Preamp), be a good piece of equipment to simply bring the voltage gain up to the appropriate level?

I know it's a lengthy question, but I've been spending months doing research on what my rig will be, and when I was certain it was the right move, I dropped like $1,400.00. Then I read how the VT Bass may not work well with many power-amps and I suddenly felt lost.

Any help would be more than appreciated.

Thanks,

Matt

[b15fliptop]

I think the question of whether the VT Bass is suitable as a preamp revolves around the standard stompbox model, not the deluxe. I use the SABDDI Deluxe (which is essentially the same as the VT Bass Deluxe in terms of features) as a preamp with a Stewart World 1.2 power amp, and it works great. You wouldn't get anywhere near the same sound with the Tube MP, either.

[Matthew_84]

Well, I didn't mean I would use it to replace the VT Bass Deluxe, I'd keep the VT Bass, but just use the mic pre after the VT (with the -20db pad on) to bring the level up.

And I was thinking this too (about the Deluxe version), but wasn't certain. I did read in some thread that the Deluxe brings it up to Line Level, unlike the pedal, but in the Deluxe manual, it says that with the XLR pad off the signal is 0db's, and with the 1/4" boost on it's 0db's as well. And that confused me.

[Matthew_84]

But I just found out that the VT Bass Pedal doesn't have the 1/4" Boost, so its output is -10db.

So 0db must be Line-Level. But does that mean that the voltage gain is fine then? It sounds like there's more factors involved, or am I just over-complicating things? ... Which I tend to do....

[Aram]

I'd like to know the answer to this as well. In fact, it would be great if there was a thread or sticky describing how to match gains between separate preamps and power amps. On the power amp side, I think the metric we're looking for is the input sensitivity, so my question would be: "how do we match a preamp's (or DI or pedal)'s output (voltage?) to the input sensitivity of a power amp?"

[rpsands]

Based on my experience with the VT deluxe, I would suggest it's fine as is.

Running a mic preamp to get extra gain would be fine, but it shouldn't be needed. Just turn up the level knob -- it doesn't seem to add nastiness like the gain does.

[b15fliptop]

Originally Posted by Matthew_84

Well, I didn't mean I would use it to replace the VT Bass Deluxe, I'd keep the VT Bass, but just use the mic pre after the VT (with the -20db pad on) to bring the level up.

Ah, gotcha. Sorry I missed that.

I just took a look at the VT Bass Deluxe manual on the Tech21 site, and it says this about the outputs:

BALANCED XLR OUTPUT: Balanced 600-Ohm low Z output. Sends effected or bypassed signal to mixing console/recorder.
XLR Out Pad Switch: -20dB pad to match the output to equipment with different input level requirements. In the line level (up) position, the output is 0dB. In the instrument level (down) position, the output is -20dB.
1/4” OUTPUT: Unbalanced 1KOhm low Z output. Sends effected or bypassed signal to amp rig or power amp.
1/4” Out Boost Switch: +10dB boost to match the output to equipment with different input level requirements. In the instrument level (up) position, the nominal output is -10dB. In the line level (down) position, the output is 0dB.

[Matthew_84]

Originally Posted by rpsands

Based on my experience with the VT deluxe, I would suggest it's fine as is.

Running a mic preamp to get extra gain would be fine, but it shouldn't be needed. Just turn up the level knob -- it doesn't seem to add nastiness like the gain does.

Yeah, that drive knob can be vicious....

I'm thinking it will be fine, especially with the addition of the 10-band EQ, but that VT vs SVT thread just made me think there's much more to it than I thought.

[Matthew_84]

Originally Posted by b15fliptop

Ah, gotcha. Sorry I missed that.

I just took a look at the VT Bass Deluxe manual on the Tech21 site, and it says this about the outputs:

BALANCED XLR OUTPUT: Balanced 600-Ohm low Z output. Sends effected or bypassed signal to mixing console/recorder.
XLR Out Pad Switch: -20dB pad to match the output to equipment with different input level requirements. In the line level (up) position, the output is 0dB. In the instrument level (down) position, the output is -20dB.
1/4” OUTPUT: Unbalanced 1KOhm low Z output. Sends effected or bypassed signal to amp rig or power amp.
1/4” Out Boost Switch: +10dB boost to match the output to equipment with different input level requirements. In the instrument level (up) position, the nominal output is -10dB. In the line level (down) position, the output is 0dB.

Thanks B15. Like, I don't know, it seems to be fine, but some people in another thread kept on about how 0db doesn't mean much because it's not referenced to anything, and it seems like I need to find the voltage gain (or swing) to really know if it's an optimal setup... I just don't know that kind of stuff...

[GrowlerBox]

Originally Posted by Matthew_84

Thanks B15. Like, I don't know, it seems to be fine, but some people in another thread kept on about how 0db doesn't mean much because it's not referenced to anything, and it seems like I need to find the voltage gain (or swing) to really know if it's an optimal setup... I just don't know that kind of stuff...

The lack of a reference voltage is a problem, and does make it difficult to know beforehand if your equipment will gel. However, in this case, it sounds like you already have the gear (or it's on its way), and I think that once you have it all hooked up, your concerns will evaporate. Don't fret over the numbers, wait until you hear it.

[pasta4lnch]

Originally Posted by GrowlerBox

Don't fret over the numbers, wait until you hear it.

wise words indeed!

[xring]

I'm not sure how the voltages work out, but my Presonus Studio Channel pre was not too compatable with my Crown Drivercore 1500. I picked up the Art Studio MP to boost the signal, and it kept me from selling the Presonus. It now provides a strong signal to the Crown, with no (audible) noise added. It works GREAT!
If you boost the Crown to 3 o'clock, and have the gain and volume of the VT at noon or so, and you're not happy with the volume, I'd recommend the above. It's an inexpensive, good fix.

[Matthew_84]

Thanks for the recommendation. The volume is pretty much all that I'm worried about. I'm sure it will sound great without a proper pre-amp in the circuit, but will I get the full volume that my rig is capable of?

I don't really want to go with the Mic Pre-amp route, just because of the extra gear and it messes with my wiring chain a bit, but if I need to I need to. The thing that sucks is that until I get to a gig I won't be able to test it anywhere near full volume to properly find out... I just wish I could get some numbers to know for sure, instead of thinking that everything's fine, when I'm not at my full potential.

And by the way....

Originally Posted by GrowlerBox

Don't fret over the numbers, wait until you hear it.

is sig worthy.

[GrowlerBox]

Originally Posted by Matthew_84

Thanks for the recommendation. The volume is pretty much all that I'm worried about. I'm sure it will sound great without a proper pre-amp in the circuit, but will I get the full volume that my rig is capable of?

I don't really want to go with the Mic Pre-amp route, just because of the extra gear and it messes with my wiring chain a bit, but if I need to I need to. The thing that sucks is that until I get to a gig I won't be able to test it anywhere near full volume to properly find out... I just wish I could get some numbers to know for sure, instead of thinking that everything's fine, when I'm not at my full potential.

And by the way....



is sig worthy.

Pleased you find it reassuring . With respect to your "full potential": you didn't mention which cab it is that you have being sent to you, but it is almost certainly going to top out before your amp does. This is another case of not fretting over numbers -- the cab's thermal rating will be far in excess of what it will actually handle before sounding like your grandfather after a bad omelette.

[xring]

Just my 2 cents but, my pre sounds MUCH better with some a$$ behind it. Even at lower volumes. I honestly don't know why.
It does sound like you don't even know if there's a prob yet. Wait until you have all the gear.

[Matthew_84]

The cab I've ordered is GK 410MBE, 800 watts @ 8 ohms, and the amp gives out 700 watts into an 8 ohm cabinet when it's bridged. And yes, I kind of doubt that I will need the full power of the system, but I'd rather it be there than not.

But like you said Xring, I don't even know if there's a problem yet, so I guess I'll just wait it out and see. If I need to I can buy the mic preamp and return it if I feel like it. I just wasn't sure whether the mic preamp would work with a bass guitar, but I guess it does.

When I get excited about stuff like this, I get very involved and think about everything, usually when I don't really need to.

Thanks everyone for helping me out.

[Bob Lee (QSC)]

Originally Posted by Aram

I'd like to know the answer to this as well. In fact, it would be great if there was a thread or sticky describing how to match gains between separate preamps and power amps. On the power amp side, I think the metric we're looking for is the input sensitivity, so my question would be: "how do we match a preamp's (or DI or pedal)'s output (voltage?) to the input sensitivity of a power amp?"

The pre/ped/DI's maximum output voltage should be equal to or greater than the power amp's "input sensitivity" spec.

If the pre/ped/DI manufacturer only states a "nominal" output voltage, or uses "dB" instead of dBu or dBV, they're assigning you some guesswork. With a nominal output level given, you can at least make a reasonable guess at the maximum by adding about 10 to 15 dB (if the level is expressed in dBu or dBV), or mulitplying by about 3 to 5 if it's stated in volts.

[Matthew_84]

Originally Posted by Aram

I'd like to know the answer to this as well. In fact, it would be great if there was a thread or sticky describing how to match gains between separate preamps and power amps. On the power amp side, I think the metric we're looking for is the input sensitivity, so my question would be: "how do we match a preamp's (or DI or pedal)'s output (voltage?) to the input sensitivity of a power amp?"

I've done some looking around online about this, and there's a 10:1 rule of thumb out there that the power amp's input impedance should be at least ten times higher than the preamp's output impedance to provide a suitable flat frequency response. But a lot of people seem to recommend a 20:1 ratio, even a 30:1.

For example, if this is accurate and a good way to match the two, then my setup matches well, because the input balanced impedance of my power amp is 20,000 Ohms, and the output balanced impedance of the VT Bass Deluxe through the XLR out is 600 Ohms. So my ratio is something like 33:1.

But there is also something about the voltages matching... I'll post what I find.

[Bob Lee (QSC)]

Originally Posted by Matthew_84

I've done some looking around online about this, and there's a 10:1 rule of thumb out there that the power amp's input impedance should be at least ten times higher than the preamp's output impedance to provide a suitable flat frequency response.

It's to have a good voltage transfer, without much loss.

[Aram]

This is great, thanks Bob!