strangeandbouncy

need advice on H-pad optimum impedance with mics . . .
« on: August 23, 2005, 07:52:10 AM »
Hi Guys,

    i am just about to build some in-line -20dB H-attenuators to pad down mic levels for some of my mic-pres, mounted in short XLRm-XLRf cables.  I have all the relevent info to calculate the resistor values, but i am unsure whether to build -20dB H-pads at 200 Ohms or 600 Ohms, or at any other value for that matter, to give optimum performance. Mics in question are Shure SM57/8's,Sennheiser 421's,Yamaha MZ204/5's and Neumann U48's. ie no phantom required. Mic-pres include Helios, BBC/Glen, Audix, and my new home-made API312ish pre's with Neve (Marinaire/Belclere/Willesden) trafo's.

   ANy help/suggestions would be greatly appreciated as ever,


   All the best,

    ANdyP
. . . . RUH ROH . . . . .


NewYorkDave

need advice on H-pad optimum impedance with mics . . .
« Reply #1 on: August 23, 2005, 08:20:58 AM »
Don't use an H-Pad. Use a U-Pad. And H-pad is great for symmetrical impedances; but for a mic attenuator you want to reflect 1.5K-2K to the mic and 150-200 ohms to the preamp.

www.uneeda-audio.com/pads

There's a suitable 20dB switchable pad on the front end of my "One Bottle" preamp:

http://www.groupdiy.com/index.php?topic=6711

strangeandbouncy

need advice on H-pad optimum impedance with mics . . .
« Reply #2 on: August 23, 2005, 08:34:29 AM »
Dear NewYorkDave,

    Thank you so very much for the info and links, v v helpful as always!

    You're a star,

     ANdyP
. . . . RUH ROH . . . . .

chrissugar

need advice on H-pad optimum impedance with mics . . .
« Reply #3 on: August 23, 2005, 12:37:51 PM »
I built myself eight 20dB attenuators into those adaptor tubes with XLR male at one end and female at the other.  U type attenuator with two 680 ohm and one 150 ohm resistors. They work perfect. :grin:

chrissugar
Christian Mike Sugar
        CMS-LAB

alk509

need advice on H-pad optimum impedance with mics . . .
« Reply #4 on: August 23, 2005, 03:32:37 PM »
Quote from: "chrissugar"
U type attenuator with two 680 ohm and one 150 ohm resistors.


That's about 1.5K loading the mic. two 1.1K and a 220 is a little stiffer, and still looks like a low impedance source for the preamp's input.

Then again, chances are it'll make little difference in practice.

Peace,
Al.

Lest laziness get the best of you!

strangeandbouncy

need advice on H-pad optimum impedance with mics . . .
« Reply #5 on: August 24, 2005, 07:39:03 PM »
hi,

   I've just made up 6 XLR-XLR short leads with 1k/220/1k U-pads as suggested by NewYorkDave. Finally, I can patch any mic into any mic-pre, wherre before many were just too hot with gtr/bass cabs, toms, kicks and very hot output from U48's.  :grin: I even tried some phantom powered mics. with Gefell UM70, voltage at mic is reduced from 44v - 38v, and the mic works fine! KM184 has 39v, and now can be used near a drum-kit(Why oh why didn't they include a pad, like the KM84?). U87 appears to have a reasonable voltage, but does not sound right to me(actually they NEVER sound right to me, but heigh-ho . . .). Being able to still use (some) of my phantom-powered mics is a great bonus! :grin:
    just for the hell of it, I padded down the mix output today, feeding it through a variety of pres(Helios, my Neve-trafoed AAPi clones, and Pyes ) enabling a totally new "pallette" of colours . . . I'm in LURV . . . Looking for some extra "pizzazz" in da mix, build yourself some pads, and make use of those pre's that formally sat idle whilst in mix mode! Something for next-to-nothing(actually, 3 resistors and some solder!) Makes me want to build a "proper" passive mixer, rather than the lashed-up one on the patchbay! I think I'll use DOA's as buffer inputs, so I can patch any (Stereo) input in without messing up the balance(as happens at the 'mo).

    God, I love this job! A year ago, I had scant few home-made toys. NOw, I have something new almost every month! They rank amongst my most treasured weapons in the studio, and with the knowledge,help, and confidance found within these hallowed walls, if I can imagine something I think might find useful, it is now probably within my grasp, AND within my pocket! I could never even have concieved my latest project, a dual mono/stereo, fully Class A, discrete SSL type mix compressor, switchable LR/MS . . . whatever next? perhaps a 2 or 3 channel discrete crossover network, dividing the signal, and 2 or 3 of the aforementioned ssl's . . . just think of the possibilities with each band switchable LR/MS! I am still very keen to play with passive crossover networks for this too, though loads of yous tried to discourage me from this(red rag to a bull!). All of this would have been mere pipe-dreams only a year ago . . . .


    THANKS GUYS!


         ANdyP :razz:  :razz:  :razz:
. . . . RUH ROH . . . . .

Svart

need advice on H-pad optimum impedance with mics . . .
« Reply #6 on: December 28, 2005, 11:31:57 AM »
ok for a switchable attenuator for balanced signal, can I use the 220R shunt and just series up the resistors with the contacts?

I still have yet to find a decent model of a switchable attenuator(for MIC inputs), or even info on one!!  I've been looking for forever!!
Welcome to the GroupDIY leper colony! when something falls off, we just replace it with a tube!
occupation: General Electron Mayhem

Alesis X2 information repository:
http://www.theopiumdenproductions.

NewYorkDave

need advice on H-pad optimum impedance with mics . . .
« Reply #7 on: December 28, 2005, 12:41:32 PM »
To maintain the input and output impedances at their design values, the answer is no. You must change the shunt resistor along with the series resistors.

The link I posted earlier gives the equations for a U-Pad.

www.uneeda-audio.com/pads

I'm afraid there are no shortcuts. :wink:

pstamler

need advice on H-pad optimum impedance with mics . . .
« Reply #8 on: December 28, 2005, 03:47:29 PM »
Also: you mentioned padding SM57/58s. You might want to make up some attenuators with 500-600 ohms in and 150 out. The 57/58s sound a helluva lot cleaner operating into lower impedances.

Peace,
Paul

Gus

need advice on H-pad optimum impedance with mics . . .
« Reply #9 on: December 29, 2005, 12:35:47 PM »
WOB   Had a nice switchable att  that was on the web for a short time IIRC.


skipwave

need advice on H-pad optimum impedance with mics . . .
« Reply #10 on: December 29, 2005, 02:11:40 PM »
Link to the WOB attenuator in this thread: http://www.groupdiy.com/index.php?topic=6909
Quote from: PRR
Now, maybe you don't, or shouldn't, grab the ribbon for far-harpsichord, nor the hot condenser for snare-kissing... yet often we do.

skipwave

need advice on H-pad optimum impedance with mics . . .
« Reply #11 on: December 29, 2005, 02:16:15 PM »
Quote from: "pstamler"
Also: you mentioned padding SM57/58s. You might want to make up some attenuators with 500-600 ohms in and 150 out. The 57/58s sound a helluva lot cleaner operating into lower impedances.

Peace,
Paul


That's really interesting, I had noticed an appreciable difference with 57s between my transformer balanced pres and the transformerless IC ones. Now it makes sense. I'm going to have to attempt to make some pads as you suggest.
Quote from: PRR
Now, maybe you don't, or shouldn't, grab the ribbon for far-harpsichord, nor the hot condenser for snare-kissing... yet often we do.

NewYorkDave

need advice on H-pad optimum impedance with mics . . .
« Reply #12 on: December 29, 2005, 02:34:05 PM »
FWIW, S. Dorsey* of Usenet fame maintains that the SM57 works best into a reactive load, not necessarily always low-Z. And many people (myself included) have noticed that the '57 seems to sound nicer with a transformer-coupled input, so he may be on to something. I don't doubt what Paul says, but I'm suggesting that it might go beyond the issue of simply "higher vs. lower" impedance.

You know, I could have sworn that we went into the "'57 Issue" in some detail in another thread, but I honestly cannot remember where.

*(I don't regard Dorsey as a living god, as some seem to do, but most of what he posts seems informed by experience and free of the talking-out-the-ass factor so prevalent on the Internet. :wink:)

skipwave

need advice on H-pad optimum impedance with mics . . .
« Reply #13 on: December 29, 2005, 03:56:41 PM »
Dave, you are right, as usual.

http://www.groupdiy.com/index.php?topic=11843

I completely missed this thread. I'll give it a thorough read-thru now. Sorry for the OT in this thread.
Quote from: PRR
Now, maybe you don't, or shouldn't, grab the ribbon for far-harpsichord, nor the hot condenser for snare-kissing... yet often we do.


 

Related Topics

  Subject / Started by Replies Last post
5 Replies
2173 Views
Last post January 10, 2005, 03:35:05 AM
by zebra50
4 Replies
2305 Views
Last post March 15, 2006, 01:48:17 AM
by hagtech
19 Replies
5573 Views
Last post September 11, 2006, 09:15:13 PM
by bcarso
3 Replies
518 Views
Last post December 09, 2018, 07:06:24 PM
by abbey road d enfer