Heil PR-40 Hum Problem Mod

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Newbie

hum

Post by Newbie » Mon Apr 25, 2005 4:25 pm

Ran into a hum problem, for some reason when I use a TRS going to the input of my MIC2200 for my microphone everything sounds well. When I switch to a XLR cable to the input and press the mic switch, I get a hum?

The hum is really more evident when running the DEQ2496. All I have is a line out of the final mixer going to a speaker set up for now to hear myself.

Any ideas?

Newbie

Hum

Post by Newbie » Mon Apr 25, 2005 7:54 pm

Well the hum is definitely coming from the MIC2200!

I disconnected everything one by one and narrowed it down to the pre-amp.

When I use the XLR cable to the input is when I get hum. If I use the TRS input for my mic and not the XLR I don’t get the hum, but then I don’t get the same power out with the pre amp for some reason?

Crazy!

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XLR

Post by Voodoo Guru » Mon Apr 25, 2005 9:06 pm

Well,
The way the MIC2200 has the Input connectors wired is like so:
MICROPHONE INPUT - Only the XLR can be used for this.
LINE INPUT - Both the XLR or the TRS can be used for Line Level.

So you will want to use the XLR input to use this unit as a Mic Pre.

Now the Hum...
We would look at the wiring of the Audio Cable first. Sounds like it is miswired. Be sure that is good.

What kind of Microphone are you using?

Also, How are you connecting the AC Power to the units?
Are you using some sort of Power Strip?
The Hum could be a result of a vicious "Ground Loop".
Last edited by Voodoo Guru on Sat Mar 24, 2007 8:02 am, edited 1 time in total.
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Newbie

Post by Newbie » Mon Apr 25, 2005 10:39 pm

Im using XLR input to use this unit as a Mic Pre.

I am using a power strip with multiple toggle switches to turn on 120 AC to each rack piece. I isolated the MIC2200 and connected it strait to the wall outlet and the hum is still present. I also put .01 across the neg. pos. to shied, helped a little.

I am using the PR-40 with a microphone cable going into the XLR input on the MIC2200. I am using headphones connected to the output to listen. I have the preamp parameters set up per your previous post.

Maybe some hum I hear is normal?

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PR-40 Hum

Post by Voodoo Guru » Mon Apr 25, 2005 10:58 pm

Ahhhhhh,
That must be one of the first PR-40's.
Bob had about the first 50 of these microphones went out wired unbalanced inside the microphone. The Pins #1 and #3 where shorted together at the Mic XLR Connector. This will cause a hum.
He said If we ran across any of these to tell the owners to send them back to him and he would fix them.
My Padnah Joe, N3JI got ahold of one of these Mics....bad hum.
We told him to check the resistance between Pins #1 and #3 of the Mic, sure enough it was 0 ohms, which is unbalanced.
He took it apart VERY carefully (it aighnt easy the leads are real short) and cut the jumper between the Pin #1 and Pin #3.
Presto...no more hum.

Image

Check the resistance....see what ya get.

.....and Hum is not normal. :)

Oh, and .01uf is only for the AC Power Chords.
Use .001uf for the Audio Cables, .01uf is too much capacitance.
Last edited by Voodoo Guru on Sat Mar 24, 2007 8:04 am, edited 2 times in total.
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Newbie

Post by Newbie » Mon Apr 25, 2005 11:29 pm

Well I think yur all over it like fly on rice Dr. VooDoo Audio! You graduated from Mr. to Dr. in my book. Did a ohm check between pins #1-3, your right dead short. Started to dissemble and yur right again, wire leads are short. The column of the mic is threaded into the base of the mic with lock tight. I dont want to mess with that. The wires are so short I cant pull the pins out of the base all the way. There is a "peek-a-boo" machined notched out area where I see one black wire with a smaller red wire together.

Well if I cant get to it I will have to send it back to Heil. This is a brans new mic straite from the factory in China (just kidding :lol:).
I guess my Voodoo progress has come to a halt for now.

Thanks again Voodoo Guru, I will report back my conclusive findings when done.

Chris

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Peek a Boo

Post by Voodoo Guru » Mon Apr 25, 2005 11:48 pm

Yea, thats what Joe had said. He went thru the "Peek-a-Boo" window (thats funny!!) and seperated the connection.
He said it was not easy.
Good Luck!!
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Newbie

Hummer

Post by Newbie » Tue Apr 26, 2005 12:00 am

Yippy Yiyoooooooooooooo! That was it sherlock!

I went into the XYL stash of microscopic finger nail clippers and cut that jumper, then it was on like donkey kong!

Reassembled and pluged in, wallah presto shazam! It works! Haha!

I am one happy camper cause now I can sleep tonight.

Thanks a again Doc!

Chris

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Post by dg7lan » Tue Apr 26, 2005 8:08 am

he´s the man

he already fixed my agc problem.. should invite him for a beer!
...if in doubt, increase bandwidth

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Da Man!

Post by Guest » Tue Apr 26, 2005 2:08 pm

Sho yur right Andy! I would invite over for a sud or 2, but he is a loong way from Cali.

I do have to say I was a little dissapointed to reveal the guts of the PR 40, nothing inside but a lil element. With the weight of the mic I was sure that there would be some elaborate circuitry inside, NAAY!

As long as it works good thats all I care.

Chris

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Post by dg7lan » Tue Apr 26, 2005 11:22 pm

right chris, those mics seem almost empty, but who cares. you get the desired sound out and thats the point.

see what you have in these elktret condenser mics sometimes.. nothing... think of the mics used in talkshows these days.. how small is the element? but how good does it sound? amazing stuff..

need to get one, maybe a headset, cause i want to use the radio from my garden, using the laptop and wlan. but it hast to sound well of cause :)
...if in doubt, increase bandwidth

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Post by !KANT » Sun May 01, 2005 12:40 am

dg7lan wrote:he´s the man.... should invite him for a beer!

Again with the beer.....let's just have a BONG night!!! :twisted:

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Post by dg7lan » Sun May 01, 2005 1:42 am

ha thats gonna be funny :)
...if in doubt, increase bandwidth

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PR-40 Mod Update

Post by Voodoo Guru » Fri May 11, 2007 8:32 am

PR-40 MOD UPDATE

This is an update for the mod to the PR-40 Microphone for the Hum Problem.
This is due to the internal Pins #1 and #3 being shorted together from the Factory.
The disassembly is easier then previously reported.
This is how to gain access to the Wires on the XLR connector.
Reference the Picture for help.

Image

Just unscrew the 3ea screws on the circumference of the main body and carefully remove the windscreen.
Then remove the one screw down on the neck of the mic holding the internal XLR plug.
take something plastic and lightly 'push' the connector up into the microphone.
Then slightly 'rock' the rubber piece the mic element is attached to out of the mic body.
Don't pull on the Mic Element!!
Grab the rubber part and work it out of the mic neck.
then push the connector a little further into the mic, and work the rubber out some more until the whole assemble comes out of the top of the mic body.
Now you can work on the XLR plug.
Cut the jumper wire that is between pins #1 and #3.
Be sure to remove any wire pig tails that may short to the mic body.
Assembly is the reverse of disassembly.

Image
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