1. Register NOW and become part of this fantastic knowledge base forum! This message will go away once you have registered.

Post-preamp, pre-converter ATTENUATOR

Discussion in 'Preamps / Channel Strips' started by patrick_like_static, Jun 10, 2008.

  1. I'm running my GT The Brick preamp into my interface. I tend to crank the gain for mic'ing guitar amps, but this is causing clipping at the digital stage as it hits the converters. My chain:

    The Brick ---> XLR-to-TRS balanced out ---> [attenuator] ---> interface line-ins

    I want something cheap and transparent to maintain the sound, just attenuated to a manageable level. The A Designs ATTY is out of my price range, but something comparable would be perfect.
     
  2. I guess I overlooked the clipped-on-the-cable-style attenuators. Include these in your recommendations as well.
     
  3. RemyRAD

    RemyRAD Well-Known Member

    Patrick, if you need a pad a simple resistive balanced "H" pad, with resistors available from Radio Shaft, is all that's necessary. But on the brick, you want to overload input, not output.

    Conversely, you may want to just try a stereo ganged volume control from Radio Shaft between the Brick & your analog-to-digital converter. This ain't brain surgery you know. But this sounds to me like you are attacking this whole thing the wrong way? Not many devices can tolerate an input of over +24 DB and if you're doing that, it's probably the output of the Brick that you are distorting in a most unflattering way? After all, your Brick is said to indicate that of the vintage Neve. That sound comes from overloading input sections not output sections.

    Plus, you may actually need to terminate the output of the Brick with something like a 600 ohm resistor for proper operation. Otherwise the residence of the transformer can't be realized if it's not properly loaded. This will cause frequency response problems & distortion issues.

    Down the tubes
    Ms. Remy Ann David
     
  4. Kev

    Kev Well-Known Member

    yep Remy is right
    and it " ain't brain surgery "
    but so many get it wrong

    so simple and so valuable

    it's a cool idea to have many interfacing boxes that can apply terminatiion and provide a PAD
    add an earth lift
    add a polarity flip

    stuff like this is so simple and easy to make

    I have a couple that can terminate with 300, 600 and 1.2K

    you have to listen
    sometimes you have to do a fequency sweep to see the differences

    Joe at JLM Audio has some graphs on his site that show the correct termination of the Neve Pre-amps
    ... and the incorrect


    The Brick can probably overdrive your interface line-ins without itself clipping ... 6db perhaps 10
    check the specs for
    maximum output
    and compare to
    max input for the interface
     
  5. Thanks for the replies. Remy:

    The Brick behaves ("distorts") differently at different settings, and unfortunately, the unit's one dial controls both input and output gain. So getting the desired sound risks making the signal really hot. Any clipping occurring at this stage sounds euphonic to my ears and is something I'd like to preserve going into my interface.

    I'm just looking for a flavorless, no-frills attenuator (10dB or so) to put at the preamp's output stage.


    Kev:

    You and I probably have different ideas of "so simple and easy to make." I'd much prefer buying something I have confidence in to risking the likely outcome I'd screw something up.
     
  6. Boswell

    Boswell Moderator Distinguished Member

    This is what you need for a 9.5dB in-line attenuator:

    Take three equal 1% resistors (1 KOhm will do) and an XLR cable plug and cable socket. Wire the three resistors in series and take the outer ends to pins 2 and 3 of the XLR socket. Take the ends of the middle resistor to pins 2 and 3 of the plug (not crossing over the 2s and 3s). Wire pin 1 of the plug to pin 1 of the socket.
     
  7. RemyRAD

    RemyRAD Well-Known Member

    In-line balanced, XLR resistive pads are available from Shure. I have a couple and one is actually switchable. Some are line level to microphone level or, -50 DB. Whereas the other one is switchable for -5, -15 & -20 DB. Just what you need. It Shure beats having to build one.

    All sorts of in-line thingies in my bag of tricks.
    Ms. Remy Ann David
     
  8. Kev

    Kev Well-Known Member

    so important are those simple little thingies in the bag of tricks
    including a 57 or two
     
  9. Thanks, Remy. I wasn't sure if I was making it clear that I wanted to buy---rather than build--something.

    It was a toss-up between the Shure A15AS you mentioned and Audio-Technica's AT8202, but I ultimately wound up going with the AT.
     
  10. Kev

    Kev Well-Known Member

    yes I know you want to buy

    but there are times when there is no commercial product available
    or
    the commercial product is not quite right
    or
    it is just silly expensive for the job at hand

    these simple resistive devices are too simple to make

    ALSO
    the listed attenuations are only correct for the specified source and load impedance values

    things are not always so standardised ...(ized)

    but sure
    go ahead and buy the Shure

    or
    the AT

    it's all good
     
  11. orbit

    orbit Guest

    okay so is that Shure A15AS something i can put between my preamp out and the input to my delta 1010? and that would allow me to drive my preamps harder without clipping my delta? because in another thread i posted someone suggested getting or making some attenuators because i generally drive my drum oh's and they clip in cubase but i cant HEAR the clipping, so i guess im losing headroom at this point...

    i have the presonus adl 600 2 ch tube preamp and it has 2 knobs, gain and trim of course...gain knob will be at like 35 and the trim knob at 1/4 (halfway between 0 and unity i suspect) and the oh's will be clipping my delta at that point...so im hardly able to drive my preamp at all (its a +4 output and i made sure the delta is toggled to +4 on those 2 channels)...

    correct me if im wrong but driving preamp more = generally good (to a point) since they are tube and you want to drive enough to find a "sweet spot"?
     
  12. Kev

    Kev Well-Known Member

    yes you are losing headroom ... somewhere ...

    mmmm
    yeah .... but naah
    ...
    just too generalised

    from the presonus adl 600 spec page
    http://www.presonus.com/products/Detail.aspx?ProductId=10

    maximum output +23dbu
    output impedance 600 ohm

    I think the output impedance is rated for 600 ohms rather than actually being 600 ohms

    terminating the output of the presonus with a 600 ohm load ... or near to ... could be interesting and make a difference

    The maximum input level to the Delta is NOT specified at the web site
    http://www.m-audio.com
    but
    say it were +18dbu

    then in theory you could introduce a 6db pad and be set such that the input to the Delta would not clip before the Presonus.
    in fact
    you may never see a red light in Cubase because the output through the attenuator may never get there

    the resposibility would now be on you to hear clipping in the presonus and turn it down

    it would help to proove where the clipping is occuring
    it is a good experiment and will help you to learn the sound of the presonus ... especially if you want to try ... driving the presonus


    gain structure
    it's all about gain structure
     
  13. orbit

    orbit Guest

    hmm...so i have always been under the impression that clipping is quite audible...would you mind hearing some test mixes and giving me some opinions?

    i know that my presonus is usually looking like its hitting +6 to +12 at times but its hard to tell precisely because the VU meter just goes "WHACK" and comes back to the left and "WHACK"...but im not even having my preamps up much and the mics are having alot of output...

    also this preamp has switchable mic impedance...i just leave it on 1500 (other options are 900 300 150) since it seems to sound a little more detailed, but overall its hard to tell that much of a difference <shrug> any tips on that? i just got some rode nt5s that im using it to power.
     
  14. RemyRAD

    RemyRAD Well-Known Member

    I'm talking about some very light, inconsequential upper peaks from drum transients getting clipped. Not other instruments which will all sound bad. So if you're clipping electric guitars? Kind of bad. Clipping vocals? Real bad. Keyboards? Don't go there.

    Clipping audio is like getting ripped off. Nobody likes to get ripped off except stupid rich people who don't realize they're getting ripped off because they feel better about paying more for something. A sucker born every minute.

    So rule of thumb is unless your preamp makes a certain kind of desirable sound just before it begins to clip, avoid clipping at all costs.

    Remember, if you're utilizing analog " steam gauge" mechanical metering, and it's of a "VU" (ANSI Volume Units) variety, the peaks are not indicated. The peaks are in fact 15 DB or more above what you are visually seeing. So when you see proper levels, you have already overloaded the crap out of the front end of your preamp. Nowhere to go from there. So when recording drums, your mechanical VU meter should be indicating around -10 to -6. Any higher and you've clipped. That's why so many folks love peak reading meters be they mechanical, LED, plasma, fluorescent or a combination thereof. You have a better idea of what you are recording when it comes to bedroom. That's what separates the men from the toys and us real women.

    Man-made woman
    Ms. Remy Ann David
     
  15. orbit

    orbit Guest

    so then....are you suggesting that i run my drum OHs at basically nothing? the first knob i have, it clicks in increments of 5db and i can go to the first increment (35) and then put the other knob, trim, at about 1/4 (9 o clock) and im pretty sure this is WITH the -20 pad on, and thats when im beginning to clip probably via the preamp itself, and it definitely shows on the delta drawn waveforms.

    Remy as much as I love your answers, i still dont feel like the point of this thread, at least as far as since i have joined it :) has been addressed...the title of the thread perfectly sums up what it SEEMS like i could use...a post preamp (adl 600) , pre converter (delta 1010) attenuator. it just doesnt seem right that i cant even turn my preamp up just a LITTLE or face the consequences of clipping noobery!
     
  16. RemyRAD

    RemyRAD Well-Known Member

    If it takes the lowest gain setting & turning on the pad to prevent front-end clipping, THAT'S WHAT YOU DO. YOU DON'T HAVE TO WORRY ABOUT UNDERRECORDING IN DIGITAL MULTI-TRACK RECORDING. Especially if you record at 24-bit as opposed to 16 bit (I generally record at 16-bit because I know how to). No reason to pump up those levels that high. That's the beauty of digital recording! My last console had inputs very similar to what you indicate. I had my choice of +15, +20, +35 gain settings, which were additive so you can have up to 70 DB of gain & -20 & -30DB pads, along with a slight inconsequential trim of 2, 5 or 10 DB settings. I never had any overloads only wonderful sounds coming from the old Sphere Eclipse C, tracking into the analog Ampex MM 1200-24 or the tascam da-88's. So banging meters was just something we did to analog machines on drum tracks and/or guitars on occasion since they were so bandwidth limited to begin with.

    As to your summation that you believe you need another post preamp?? That's idiotic. You may think you need something like that but you certainly don't. You just need to understand your equipment better and how to use it properly. Which you are obviously not doing.

    Getting an additional preamp will only make matters worse. Much worse. You have no understanding of proper gain staging. That's your only problem. A huge problem since many people have trouble understanding the concept of the boost & losses from one circuit to the next. So believe it or not, generally the rule of thumb for setting level for microphone preamps is: if you're using a standardized console, you would push your fader up to its "nominal" gain position or 0. You would then dial in some gain on the trim. If the levels are too hot? Engage the pad. Leave your output control at its nominal gain position as indicated by the 0, which is two thirds of the way up. That fader should not be any lower. It's a juggle between gain and pad, without raising or lowering your output levels from zero nominal level position.

    You don't have to believe me, I've only been doing this for over 37 years and have built more than 7 control rooms, for NBC-TV & radio, Hallmark Films & Recordings, Golnick International Advertising & Marketing & others. Not to mention 3 separate installs and reconfiguration's of my studios which have included large-format Auditronic's 501's, Sphere Eclipse C & custom 36 input NBC Neve. So think what you want. Not sure why you're asking questions since you seem to already know what's wrong? You don't.

    Delivering quality audio for over 37 years
    Ms. Remy Ann David

    Does that answer your questions?
    Ms. Remy Ann David
     
  17. orbit

    orbit Guest

    i think there is a massive disconnect in the language being used...i didnt mean to infer in any way using ANOTHER preamp. if that is what i said, then obviously my lack of knowledge on the vernacular of the audio world is sorely understudied. im not trying to invoke your wrath :)

    so my drummer is starting to do his thing as i type this, and im now recording him with my gain knob all the way down, the trim at 0. i also pulled my bass drum mic way way lower also.

    it looks like nothing is ever hitting more than about -8, that being the biggest transient thus far in about 5 minutes of his spastic hard drumming.
     
  18. orbit

    orbit Guest

    http://i27.photobucket.com/albums/c173/jprumers/untitled.jpg

    this is what just happened....i am assuming those really fast spike lines are the transients or whatever? so in that fact, i was always clipping out the transients...?
     
  19. Greener

    Greener Guest

    What is that spike? Kick, snare, hat, screams?
     
  20. RemyRAD

    RemyRAD Well-Known Member

    There is nothing in your screen capture that would indicate you've clipped anything. It looks like a normal waveform of percussion instruments. What makes you think your clipped? What seems to be the problem? You want to post an example of what this sounds like? If it's clipped, it's clipped in your microphone preamp and not going into your computer. This has to do with proper interfacing & gain staging. Now if you zoom into those spikes down to the sample and observe flattopped waveforms that are not 100% excursion, you are overloading your preamp.

    If on the other hand the spikes appear to go more than full-scale in the display and you find those are flattopped, you are overloading your analog to digital converter.

    If you just think those spikes are clips, you don't know what you're looking at. You're looking at waveforms and waveforms look like that depending on what instruments you are recording.

    Time to pick up a book
    Ms. Remy Ann David
     

Share This Page