|
|
Post by gouge on Dec 28, 2016 3:32:32 GMT -6
So I need to get a crazy idea out of my head.
I'm looking to make a load box for my sm57. Same thing that has been written about online.
I started thinking what if I use the vp28 in line mode. Would line mode give me 600ohm impedance for the mic.
|
|
|
|
Post by gouge on Dec 28, 2016 3:56:10 GMT -6
Found some spec.
In line mode the impedance is 10k.
|
|
|
|
Post by gouge on Dec 28, 2016 4:16:49 GMT -6
Might have answered my own question. I think the vp28 already has a low input impedance.
Can anyone confirm the impedance is around 760ohms.
|
|
|
|
Post by jeromemason on Dec 28, 2016 18:49:08 GMT -6
|
|
|
|
Post by jsteiger on Dec 29, 2016 9:30:45 GMT -6
Might have answered my own question. I think the vp28 already has a low input impedance. Can anyone confirm the impedance is around 760ohms. The VP25, VP26 and VP28 are all 1k input Z with the mic pad out and 1k5 with the mic pad engaged. The VP28 is 10k when in line mode. The VP312 is the same as above but 1k2 with pad out, when built leaving the 150k load R unpopulated. |
|
|
|
Post by svart on Dec 29, 2016 11:00:23 GMT -6
Use an inline XLR pad rated at 300R or 600R. You'll lose some level, but you'll load the mic down pretty heavily.
|
|
|
|
Post by gouge on Dec 31, 2016 17:46:15 GMT -6
Cheers guys.
|
|
|
|
Post by NoFilterChuck on Jan 1, 2017 0:05:29 GMT -6
what does loading the mic do to the sound?
|
|
|
|
Post by rowmat on Jan 1, 2017 2:33:42 GMT -6
what does loading the mic do to the sound? From my experience with SCA J99's and especially N72's, lowering the input impedance (which loads the mic's output more) tends to attenuate the highs and thicken up the low end. Imagine if the proximity effect, which typically becomes dominate at say 6 to 4 inches with a 1200 ohm input impedance now extended out to 12 inches or more with the input impedance set at 300 ohms. One could argue that this is not ideal for most mics but I have found that lowering the input impedance can really make a weak vocal much more solid, weighty and '1950's'. Impedance switches I fitted to a pair of N72's. (See photo below) Upper switch changes input transformer impedance to either 1200 or 300 ohms. Lower switch adds a 604 ohm load across the output transformer which is already fitted to the preamp but is normally selected by an internal jumper requiring the removal of the preamp from the chassis to change the loading without the external switch.  |
|
|
|
Post by gouge on Jan 1, 2017 4:38:25 GMT -6
what does loading the mic do to the sound? the talk online which has also been confirmed by shure is that the sm57 was designed to see a 600ohm load as that was standard gear 30 or so years ago. because a lot of modern preamps are rated around 1200-1500 ohms it means the sm57 is not being loaded to it's optimum and as such will sound harsher in the upper mids and a little thin in the bass. that is the sm57 sound to me. so using a 600 ohm impedance via a variable impedance preamp or a 1k approx resistor soldered across the xlr pins it is said will reduce the harshness and flatten out the bass. from what I've read the capsule in the sm57 is wanting 10-15 ohms and a 1:4 transformer. there are a bunch of transformers that will suit ami t58 cinemag 1057 lundahl 1636 crimson audio orange crimson audio yellow Hammond 560c however the idea is the loading will make a difference to the stock transformer so i'm starting there. I don't know what the upgrade transformers are designed for loading wise. only way to know is to try a pot and tweak away. |
|
|
|
Post by EmRR on Jan 1, 2017 11:30:10 GMT -6
Again, the talk is wrong, the 57 is just a non-standard design center. 600 input has never been a preamp input impedance standard, all the way back to the mid-1930's. There are, of course, exceptions.
|
|
|
|
Post by gouge on Jan 1, 2017 16:35:16 GMT -6
i thought you might bring some wisdom to the table Doug.
|
|
|
|
Post by EmRR on Jan 1, 2017 17:04:17 GMT -6
The other wierd thing Shure did for years, long since changed, was sell mic pad barrels which were MATCHING 'O' pads that look like 169 ohms to both mic and preamp, rather than bridging 'U' pads.
|
|
|
|
Post by gouge on Jan 1, 2017 17:44:05 GMT -6
am curious about this, do you know what the model number is. it might be interesting to try some.
|
|
|
|
Post by EmRR on Jan 1, 2017 18:07:47 GMT -6
The original A15A.
I actually have a pile of them I 'inherited' from an older engineer, can certainly let some go if anyone wants to try one. Had thought about converting to U pads, but I probably have enough of those built up already.
|
|
|
|
Post by gouge on Jan 1, 2017 18:10:01 GMT -6
i'd be keen to grab 2. see what they sound like with a 57.
|
|
|
|
Post by EmRR on Jan 1, 2017 19:17:35 GMT -6
I dunno if it's worth the shipping for you, Australia right? USPS has made it impossible to send anything out of the US for anything less than a pile of money. Probably cheaper to wire something up in an inline barrel. All you really need for your experiment is a resistor from pin 2 to pin 3.
|
|
|
|
Post by kilroyrock on Jan 1, 2017 21:48:01 GMT -6
I did the inline barrel, 600 ohm resistor as EmRR said. Real easy. Xlr adapter was a solid 2 bucks. |
|
|
|
Post by gouge on Jan 2, 2017 0:10:44 GMT -6
in Australia the neutrik male to female adaptor is between $16-$22 generic version is $6. I've made a few U-pads with the generics costs around $10 each. that said I've got some blanks here and the resistors so gas may have come over me.....  |
|
|
|
Post by rowmat on Jan 2, 2017 0:40:23 GMT -6
in Australia the neutrik male to female adaptor is between $16-$22 generic version is $6. I've made a few U-pads with the generics costs around $10 each. that said I've got some blanks here and the resistors so gas may have come over me..... I developed GAS over the Christmas period but it was due to beer rather than gear!  |
|
|
|
Post by gouge on Jan 2, 2017 1:21:23 GMT -6
there's my issue. I needed more beer...:-)
|
|
|
|
Post by ChaseUTB on Jan 2, 2017 1:39:19 GMT -6
How does impedance relate to pro audio inputs and outputs? And how does this relate to " tone " why does 300 ohm sound different driving a pre tan 1.2k ohm vs 10k ohm?
For example, if I wire my subwoofer in parallel it drops theninpedance by half so the amp can put out more rated power at a lower impedance.. EX.. at 1 ohm 1550 watts at 14.4 V, At 2 ohms 1041 @ 14.4, and 4 ohms 514 wattts at 14.4 V.... any correlation?
So when we say a mic ore has an impedance of 600 ohms and the next input needs to be 10 times the mics output impedance? Is this true? Why 10x? Does voltage affect impedance in pro audio like car audio? Do mics / preamps/ HW/ consoles have impedance swings?
Trying to learn... Thanks
|
|
|
|
Post by EmRR on Jan 11, 2017 10:28:29 GMT -6
These guys. These 3 are spares I can let go, I'll put them in the classifieds.  |
|
