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Topic: ProFex 11 PreAmp ByPass |
Gary Steele
From:
Columbus, Ohio, USA
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Posted 3 Jan 2006 11:36 am |
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| A guy in Michigan told me his friend bypassed his ProFex 11 PreAmp so you can run it with another preamp without two preamps clashing. Said he done it in about 20 minutes or less. Can someone let me know how this is done. Thanks!! [This message was edited by Gary Steele on 03 January 2006 at 04:27 PM.] |
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Ken Fox
From:
Nashville GA USA
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Posted 3 Jan 2006 4:54 pm
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I have had a lot of time to study the Profex 2/Bassfex schematic over the past few years. I see no easy way to do this.
The unit is a preamp and puts out up to 1 volt RMS clean. The inputs analog signal is converted to a digital signal for processing and then re-converted to analog by a digital to analog converter. After that it is sent thru several more gain stages and off to the output. Without a major electronic butchering I can't see how he did it!
If I were using it with another preamp I would add the "effects loop" into each preset I was using and then edit the out level to properly drive the outboard unit and the in level to accept a nominal signal from the preamp.
The other route would be to use the Profex 2 in the effects loop of the external processor, a lot easier to do. You would then not need to change every preset on the Profex 2! You would set the output of the unit to drive the input of the Profex 2 and the input to receive the output of the effects unit.
Much more could be said about input and output levels, impedance matching/bridging and the subject of gain overlap and headroom! In other words, an input is looking for a certain level (instument or line level, typically) and outputs can produce either instrument and line level outs or both. Sometimes the use of external "T","H" and impedance matching pads are required to match pieces of equipment properly. Good reading on that subject is the old book "Sound System Engineering" by Don and Carloyn Davis. |
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Jack Stoner
From:
Kansas City, MO
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Posted 4 Jan 2006 3:19 am
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Gary, I have to agree with Ken. These units (and the Transtube Fex and TubeFex) are designed to be both a preamp and an effects unit. The only good way to bypass the units is to have an external switching assembly that completely takes the unit out of the chain. Anything else is as Ken notes is "a butchering job".
If that Revelation preamp has a bypass switch for the effects loop, that would be a good way to bypass anything plugged into the effects loop (My Rocktron pream has that). |
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Gary Steele
From:
Columbus, Ohio, USA
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Posted 4 Jan 2006 2:55 pm
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| Thanks Jack and Ken. Ken i am getting a unit from A guy named Ford and he had you do your handy work on it. We will hope Brad see's this and answers about the by-Pass switch. I like the profex pretty well. People used to tell me i had the best sound using one. BRAD WHERE ARE YOU. I sure hope this will end up working good with the Revelation PreAmp. Thanks Again. Gary |
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John Daugherty
From:
Rolla, Missouri, USA
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Posted 4 Jan 2006 4:19 pm
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Gary, if you want to bypass a preamp, I assume you want to lower the gain of the Profex. You can do that by adjusting the output gain control on the back side of the unit.
My experience with the ProfexII has been a noisy experience. You will have less noise by connecting it into the power amp input on an amp. When you do this, you can't utilize the tone controls on the amp. You will be stuck with programing the desired EQs in the profex.
The profexII does have some good sounds, but in my opinion, is one the more noisy units out there. By comparison,IMHO, the Lexicon effects products are much quieter. It doesn't make me feel good to say this, because I am a loyal fan of Peavey amps and I have a lot of respect for Mike Brown. I guess we all have our own preferences and learn by comparison.
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www.phelpscountychoppers.com/steelguitar
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Ken Fox
From:
Nashville GA USA
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Posted 4 Jan 2006 4:42 pm
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The Brown audio chips really help reduce the white noise from the Profex 2. Good signal to noise )S/N) ratio is a must! In other words set the levels properly. Lowering the output of the Profex greatly increases the preamps noise floor to signal ratio, remember it is a preamp and wants to develop 1 volt RMS signal for maximum S/N ratio! Tis far better to use it in a power amp that is designed for a 1 volt RMS signal for the best S/N ratio.
However for use in an amp, I recommnend using the output into the jack #2 of an amp, thus padding the signal down a bit before it reaches the preamp stages of the guitar amp. Another nice way is to run 2 cables from the left and right Profex outputs to jack 1 and 2 of the same channel on the amp, thus mixing/summing the L and R signals and gaining the -6db pad at the same time!
Any time you preamp a signal and then pad it down and preamp it again, you are adding noise (reducing S/N ratio). Typically an ideal effects device has unity gain (Most do however have a high input impedance and lower output impedance, providing better signal transfer). In other words, no gain at all, just conditioning the signal and delivering a guitar level output. Remember the old tube type Fender Reverb units? They had unity gain, actually a slight loss in signal!
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Mike Brown
From:
Meridian, Mississippi USA
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Posted 5 Jan 2006 6:45 am
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| Ken, that is exactly what I recommend as well. Thanks for the help. |
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