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Author Topic: Aphex 230 Noisey...  (Read 1694 times)
WB4LCN
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Posts: 134


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« on: August 17, 2012, 06:57:51 PM »

I just bought an Aphex 203 voice channel mic pre-amp/compressor, but when I try to hook it to a mic in through line to mic in adapter, there's a bad hum. It sounds like 2 hums of different frequencies, creating a flange effect. Even with the mic unplugged, I get he same issue.

Any advice?

Thanks much!

dave Smiley
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First, make it work, then make it pretty.
Yaesu Rigs: Kenwood TS-480HX, FT-8900R, FTM-350AR (Bluetooth motorcycle mobile), VX-8DR, SB-102 boat anchor (built one as a kid)

Moderate Spock: "Live for a reasonable amount of time and scrape by."
W9GB
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« Reply #1 on: August 17, 2012, 09:30:03 PM »

Have you ever worked with (installed) professional audio equipment?
I assume you are using BALANCED Audio Inputs (XLR microphone).

RADIO (amateur or commercial broadcast) normally use UNBALANCED Audio Inputs.

Ground Loops are a common issue with many professional/studio/concert sound installs.
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W2RKJ
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Posts: 55




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« Reply #2 on: August 23, 2012, 11:48:13 AM »

I had the same problem with my Aphex Big Bottom. I cured a bunch of issues using the W2IHY iBox. You didn't state what type of output the speaker goes into if anything at all. I had my radio(s) output(s) going to a speaker switch box, doing this caused all sorts of RF issues and when I added the Big Bottom then I had hum. My radio has a floating ground which meant I had to isolate it from everything. The output from your rack equipment is way too hot to go directly in to your radio and has to be reduced or you wont get the ALC down an acceptable level. Here's how I solved my issue at this link. As the previous posted stated you also need to check that the inputs are correct for the application.

Good luck, let us know what you came up with. I fought RF on my Ten Ten Jupiter for 10 years until I read this article and now GONE!

http://www.nu9n.com/tx.html
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KD0REQ
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Posts: 1047




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« Reply #3 on: August 23, 2012, 02:36:40 PM »

(1) use a 1:1 transformer to convert the balanced output into unbalanced line for the ham gear.

(2) measure the V-RMS out of the Aphex and remember that "mike input" is generally 60 dB down.  if you're putting out hot signal, you should build an H -pad between the Aphex and the transformer.

http://www.nu9n.com/tpad-calculator.html

(3) shielding, bonding, etc.  it's not just a good idea, it's the law.

(4) font makes it hard to tell, but am I reading the spec sheet online correctly that this is a line level device with maximum levels in and out +25 dBm?  I thought I remembered Aphex from the 70s as studio processing equipment.  that would drive a class A phone line to a broadcast transmitter directly.  http://www.aphex.com/aphex-products/973/  I read this as a machine meant to go in a NEMO or buss in/out patch, not mike level without amplification.
« Last Edit: August 23, 2012, 02:41:32 PM by KD0REQ » Logged
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