MP3

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Posted on July 15, 2015 at 21:14:37

rstephen
Audiophile

Posts: 79
Location: Pensacola Beach Florida
Joined: April 11, 2009

I noticed that when I use my MP3 preamp with a single ended amp that it hums
fairly loudly. I used mogami mic cable with xlr and rca ends. What pin configuration should be used to prevent the hum? (No problems with a balanced amp).

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See my response down in this thread nt

Ralph

12:53:20 07/16/15

RE: MP3

Lew

06:36:18 07/16/15

6

RE: MP3

rstephen

08:11:06 07/16/15

5

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See my response down in this thread nt

Ralph

12:53:20 07/16/15

RE: MP3

Lew

06:36:18 07/16/15

6

RE: MP3

rstephen

08:11:06 07/16/15

5

RE: MP3

Lew

11:28:01 07/16/15

4

The 'pin 3' problem- which includes the Cardas adaptor

Ralph

12:52:46 07/16/15

3

RE: The 'pin 3' problem- which includes the Cardas adaptor

Lew

14:25:39 07/16/15

2

Sounds like your adaptors have been modified.

Ralph

08:31:04 07/17/15

RE: Sounds like your adaptors have been modified.

Lew

17:38:36 07/20/15

RE: MP3, posted on July 16, 2015 at 06:36:18
Lew Audiophile Posts: 10911 Location: Bethesda, Maryland Joined: December 11, 2000	Depends on what's going on with your interconnect between the two devices. Are you using an XLR to RCA adapter at the amplifier end of the chain? If not, what? Possibly the ground connection at the input of your amplifier is not connected to system ground, causing the amplifier (not really the MP3) to hum loudly.

RE: MP3, posted on July 16, 2015 at 08:11:06
rstephen Audiophile Posts: 79 Location: Pensacola Beach Florida Joined: April 11, 2009	I want to order another set of mogami cables from Redco: RCA To XLR. I think the pin configuration may need to be changed to solve the problem. Thanks, Stephen

RE: MP3, posted on July 16, 2015 at 11:28:01

Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000

Here is where having an ability to solder would really make life simpler. What you need is (female) XLR pin2 coming from the MP3 to connect to the "hot" center pin of the (male) RCA. Then you need XLR pin1 to connect to audio ground, the outer sleeve on the RCA jack. Pin3 from the XLR can connect to the shield. Anyway, if you explain to Mogami exactly what you are doing, they can get it right. It's XLR to RCA, not vice-versa. Cardas makes a nice XLR to RCA adapter that works well, if you already own a balanced IC.

The 'pin 3' problem- which includes the Cardas adaptor, posted on July 16, 2015 at 12:52:46
Ralph Manufacturer Posts: 4769 Location: Minnesota Joined: April 24, 2002	The problem is that pin 3 of the preamp is floating, as the interconnects don't have a connection between pin 3 and ground (pin 1). The preamp's outputs occur between pin 2 and 3, and so the amplifier is looking at an antenna. The result is hum and buzz. Tie pin 3 to pin 1 and all will be well.

See my response down in this thread nt, posted on July 16, 2015 at 12:53:20
Ralph Manufacturer Posts: 4769 Location: Minnesota Joined: April 24, 2002	-

RE: The 'pin 3' problem- which includes the Cardas adaptor, posted on July 16, 2015 at 14:25:39

Lew
Audiophile

Posts: 10911
Location: Bethesda, Maryland
Joined: December 11, 2000

Funny you should say that. I have a pair of Cardas adapters here, and to satisfy my own curiosity, and to be sure I was not giving bad advice here, I went down and tested the connections with an ohmmeter. Within the adapter, pin2 of the XLR connects to the hot pin of the RCA, as expected. Pin3 connects to the ground collar of the RCA (also as expected), and I measured about a 5 ohm resistance between pin1 and the ground collar. What's up with that? Thanks for chiming in. Hope you had a good vacation.

However, I have never used the Cardas adapter with the MP1, I don't think. I used them with an Aesthetix Janus, which may have a nonpurist balanced output. They work fine with the Janus.

Sounds like your adaptors have been modified., posted on July 17, 2015 at 08:31:04
Ralph Manufacturer Posts: 4769 Location: Minnesota Joined: April 24, 2002	All we have seen so far have had no connection to pin 3. We have modified a few as a result.

RE: Sounds like your adaptors have been modified., posted on July 20, 2015 at 17:38:36
Lew Audiophile Posts: 10911 Location: Bethesda, Maryland Joined: December 11, 2000	I doubt that very much, but it is of no concern to me either way. I don't use them except in an emergency and then only with the Janus.

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MP3

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