Post-preamp, pre-converter ATTENUATOR

Posted: Tue Jun 10, 2008 8:06 pm

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.

Posted: Tue Jun 10, 2008 8:17 pm

I guess I overlooked the clipped-on-the-cable-style attenuators. Include these in your recommendations as well.

Posted: Tue Jun 10, 2008 11:16 pm

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

Posted: Wed Jun 11, 2008 1:54 am

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

Posted: Wed Jun 11, 2008 2:52 am

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.

Posted: Wed Jun 11, 2008 6:19 am

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.

Posted: Fri Jun 13, 2008 2:06 am

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

Posted: Fri Jun 13, 2008 4:47 pm

RemyRAD wrote:

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

so important are those simple little thingies in the bag of tricks
including a 57 or two

Posted: Fri Jun 13, 2008 5:20 pm

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.

Posted: Fri Jun 13, 2008 5:43 pm

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

Posted: Sat Jun 14, 2008 1:25 pm

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"?

Posted: Sat Jun 14, 2008 4:32 pm

orbit wrote:

but i cant HEAR the clipping, so i guess im losing headroom at this point...

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"?

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/products/en_us/Delta1010-main.html
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

Posted: Sat Jun 14, 2008 7:11 pm

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.

Posted: Sun Jun 15, 2008 12:17 pm

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

Posted: Sun Jun 15, 2008 12:25 pm

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 Smile

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!

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