I'm really new at using mic preamps and stuff, and I guess a few things are not clear to me. Hope someone can help.

I have a Groove Tubes Brick and Studio Projects VTB-1 preamps. I run my mics, be it dynamic or condensor into the XLR input on the preamp, then from the XLR output on the preamp to the XLR input on my Tascam FW1804 firewire computer interface (I use Sonar 5). I have the phantom power off on the interface.

My problem is that if I don't have the condensor mics REALLY far from the amp, everything overloads. I have my Vox Valvetronics set to one watt and was still overloading the input using an MXL V69ME. The next day using an SM57 in the proper place, and an AKG C1000S small condensor pencil mic, the inputs were a lot better, but still hot.

On another forum last night someone told me that when using a preamp, you don't go into the XLR input on the interface. However, looking at my stuff, the Brick's output says balanced and the input on the Tascam also says balance. I just thought it was normal to use everything XLR. Can anyone straighten me out on this, and if I do have to use a 1/4" jack from the pre to the board, do I use a guitar cord, speaker cord, TRS? I'm really a newbie, thanks everyone!

I am not framilar with your recording device, but have some general comments. Once you come out of your preamp, you must go into a line level input on your recorder. Usually that is 1/4 TRS if ballanced, or 1/4 TS if unballanced. When you use a preamp, it takes the mics -40 to -60 db level, and boosts it up to somewhere around -10 to 0 db. You need to connect that hot of a signal to the device that excepts that hot of a signal. That would be considered a line input.

So just to recap, if you plug into a mic input, the device is going to amplify the signal (increase the signal level) by 30-60db. If you have already boosted the signal once, you do not want to plug that into another device that also boosts the signal.

Therefore, on your recording device there should be a line level input, and a mic level. If you use an external preamp (brick) you need to enter the FW 1804 at line level. Most of the time that is 1/4 TRS on a Neutrik connector. Otherwise there will be a PAD or software way to determine if the input on the TASCAM is set for Mic or Line.

Hope this helps.

JD

See if this helps too:

JD--my battle cry for many years,lol.

This was exactly what I was looking for. It just seemed to me that when connecting, you would use like for like. I wonder why preamps even have XLR outputs? So on the Brick, it does not have a 1/4" out so to speak but it does have an "instrament thru" which I guess is the output to the Tascam.

EDIT: I just looked in Musician's Friend for a TRS cable and they have XLR to 1/4" cables. Is that the way to go? XLR out from mic pre to 1/4" input on interface? Thanks again.

Again, thanks JD. I'm going to contact Groove Tubes just to be sure. Again, much appreciated.

FWIW, connector type has no effect on signal level. You can run mic signals through 1/4" and line level signals through XLR. You need to check what the input/output is rated for. There are preamps that have XLR outs, and there are interfaces that have XLR ins rated for line level. The instrument through is NOT the output of the pre. If you were using the Brick to DI a bass, and wanted to send the uneffected signal to an amp, for example, you would use the instrument through.

Contrast is correct. The type of connector does not dictate the signal level. Most pro audio uses XLR for ballanced signals. But more and more we see TRS too.

No need checking with Groove tubes. The XLR out is what you want. What you need to check with is Tascam. You need to understand where to plug "line" level inputs into that device. It may or may not be TRS. But rest assured it will one of two ways. 1) It uses the same XLR jack that you use when plugging a mic directly into the Tascam. Then you must switch the input of the tascam to line. Or 2) it uses a seperate 1/4 trs jack, that is dedicated to line inputs. My guess is that the TRS on the Tascam is at line level.

One other thing. The brick and other preamps are capable of large amounts of gain. You do have to watch your output levels. Also, If you close mic a marshall amp, you may need to "PAD" the input to the mic pre, or reduce the gain control of the preamp as to not overdrive the preamp. Loud sources can overdrive the mic. This means, choosing the right mic for the right source. It also means that you have to watch your entire signal chain to make sure you are not adding to much gain (amplification) to the signal. If you do, it will distort your Tascam, just like when you hooked it up wrong.

Okay, of course thinking that all inputs are the same and one just has better sound quality than the other (that's how the difference between XLR & 1/4" was explained to me many years ago) I never thought about db levels.

I looked at my manual and on my Tascam the XLR/1/4" combo inputs are +11 dbu balanced TRS inputs--these are the ones I've been using. The other four 1/4" only inputs are +4 dbu balanced TRS inputs. I now assume those are the inputs I should have been using all along coming from the balanced XLR out of the pre. Not being too familiar with the difference between decibal levels, I assume that the 7db difference is more than enough to overload the input.

Since I only have XLR cables, I'm going to get four XLR to 1/4" TRS adapters. If I'm wrong, please let me know, but from the info everybody's given me, I think that's the problem.

+4 is what you want for line level. Yes the adapters are fine to use.

I am not sure exactly what Tascam is rating by the numbers you gave. But it does seem that the Line TRS inputs have been padded down. That is what you need.

By the way there is not any difference to speak of using XLR vs TRS. I personally use XLR only on the mic side of the box. Everything after that in my studio is TRS. It makes it easy to connect any box with any other box. My patchbays are also TRS. I only have to stock two types of cables. Mic XLR-XLR and "interconnect" TRS to TRS.

Just remember that your preamps can amplify your signal by as much as 80db. So depending on what your source originates at, you adjust the input/output accordingly. You want the output to be around +4 db.

EX: If my mic is rated at -40 db, I need to add 44 db of gain to reach +4. If I am using an old ribbon mic rated at -65 db, I have to add almost 70 db of gain to get it to reach +4 db. BUT:::::::::: If I gave the mic more than 70db, I will have a final output of more that +4. That will distort the front end of the interface device. So it is much more a practice of "Make Up Gain". You want the preamp to make up the difference of gain between your mic, and the input of the Tascam.

Good luck!

Jacl, that is the best explaination that anyone has given to me about my lack of knowledge. I can't begin to thank you enough. I am a perfect example of what I call a "guitarist"--someone who plugs in and plays like a chick gasses up and drives and knows nothing about the machinery itself or what makes it run, LOL

Boy is my wife mad at me now.