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 Post subject: Re: What's the likelihood of seeing the guitar preamp this y
PostPosted: Tue Jun 23, 2015 8:19 pm 
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Joined: Mon Apr 16, 2012 12:05 pm
Posts: 9
Another question. :mrgreen:

I've been exploring reamping. I use EMG pickups which are supposedly "low impedance." So in my head, I should avoid a reamp box since it converts low impedance to high impedance and would screw up the EMG "sound" or "feel."

If I send a recorded dry track via my interface's line out to the Voodoo Lab guitar preamp, I get the tone I expect, but I also get a noticeable background stuttering noise that sounds like the Predator. (That's on the 1 occasion I managed to set it up right. Normally I just get a loud squeal. :? ) To check, I tried plugging my keyboard into the preamp and got the same Predator drone. Here's a clip (switching from clean to lead channel): http://goo.gl/Oqkrf0

What causes this stuttering sound, as opposed to plugging in a guitar (EMGs or passives)? Am I misinterpreting the whole low/high impedance thing? Should I be using a reamp box with EMGs and the Voodoo Lab guitar pre?


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 Post subject: Re: What's the likelihood of seeing the guitar preamp this y
PostPosted: Wed Jun 24, 2015 9:58 am 
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Joined: Tue May 05, 2009 2:33 pm
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Location: The Lab
This isn't necessarily the differences in the impedance, its the output levels that differ greatly between your sources. The guitar is an Instrument Level and the Babyface and Keyboard are both Line Level. Running a Line Level into any preamp intended for Instrument Level signals will likely be noisy and rather unwieldy.
Line Level will usually be from -10dBu to +4dBu (You have probably seen this as a switch on some audio gear).
Instrument Level isn't really a solid defined level but is is going to be somewhere around -20dBu.

I suspect that the "Predator" growl is just a digital artifact that the gain channels are amplifying since they are rather high gain and you are feeding the preamp a very hot signal.

You may have some luck turning the output level of your interface and keyboard way down before going into the preamp, but it's really just not an intended use of the Guitar Preamp.

Good Luck!


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 Post subject: Re: What's the likelihood of seeing the guitar preamp this y
PostPosted: Sun Jul 12, 2015 7:57 pm 
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Joined: Mon Apr 16, 2012 12:05 pm
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A reamp box did the trick. 8-)

'nother question. What tube config would you recommend to get more crunch or at least more purr out of the clean channel? Even with EMGs and the gain knob dimed, there's barely any breakup. (Right now it's got a pair of Sovtek 12AX7LPS.)


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 Post subject: Re: What's the likelihood of seeing the guitar preamp this y
PostPosted: Wed Jul 15, 2015 10:28 am 
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Location: The Lab
Not too sure what is up with that... not enough breakup is really not something we ever hear about clean channel on the Guitar Preamp. Usually people resort to throwing in a 12AT7, or 12AU7 to clean up the Clean channel to suit their liking.

First, I'd try simply swapping the tubes you have in there around in different positions to see if you just have one flyer tube that isn't working up to snuff. V1 and V4 are both associated with the Clean Channel.

There is certainly variance between different version 12AX7 tubes, but it is still the highest gain tube in the 12A_7 family so I wouldn't really expect any version 12AX7 to not put some hair on the clean channel.

p.s. Here is an interesting listing of basic characteristics of different 12AX7 tubes.
https://www.tubesandmore.com/tech_corne ... made_tubes
For what it is worth, they give your tubes a "gain rating" of 5.7 while the 12AX7WB that the Guitar Preamp was designed around was rated at 8. :|
Not too sure if that is an indication of the issue you are having, but you can certainly try out any tube with a higher rating and see if it makes a difference.


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 Post subject: Re: What's the likelihood of seeing the guitar preamp this y
PostPosted: Mon Oct 19, 2015 12:56 am 
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I tried a Chinese 12AX7 and a 12AX7WC. They made a small difference. With the gain dimed, I can get mild breakup. Is the clean channel supposed to reach "brown sound" crunch?

Also, I just got an Eleven Rack. It has line inputs with a -10dBV/+4dBU switch. What should that switch be set to for the main preamp out? And for the preamp 1/4" record out?


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 Post subject: Re: What's the likelihood of seeing the guitar preamp this y
PostPosted: Tue Oct 20, 2015 12:45 pm 
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Location: The Lab
jscomposer wrote:
I tried a Chinese 12AX7 and a 12AX7WC. They made a small difference. With the gain dimed, I can get mild breakup. Is the clean channel supposed to reach "brown sound" crunch?


The Clean Channel was based on the classic Fender amps, so perhaps you are expecting more gain than is there. For "brown sound" sort of tones I guess I'd probably start off on the Rhythm Channel with its Gain turned down a bit. The Rhythm and Lead channels were the ones that were more "Marshall" based anyway. Your guitar volume would be the key component in going from clean to dirty tones while on the Rhythm Channel.

jscomposer wrote:
Also, I just got an Eleven Rack. It has line inputs with a -10dBV/+4dBU switch. What should that switch be set to for the main preamp out? And for the preamp 1/4" record out?


The Preamp Outputs will certainly be quite hot and may even crush the inputs when set to +4... you'll just have to test that one ;)
The Direct Out is probably going to be happiest on the +4 setting, but you can certainly test with either setting. If you generally keep the Volume knobs set really low then you might be happier with the -10 setting.
In general you can approach this by just listening to the final output. The problems you are listening for are either signs of a hot signal slamming your input and resulting in unwanted clipping or too low of a signal resulting in more background noise preset at the final output. If its clipping, set the switch to the higher setting. If its got a lot of background noise, set the switch to the lower setting. If you are having one of the above problems and the switch is already set accordingly, then you need to adjust the Volume levels and start over ;)

Good Luck!


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