How eliminate this earth loop?

Jon,

liable to getting the hum I want to get rid of! <

Unlikely. If you're on a budget Ebtech makes a line of "hum eliminator" transformers. I wouldn't call these units "audibly transparent," but they're okay for what they cost. There are a few other companies that make similar low-cost devices. If you want better quality and are willing to pay for it, look into Jensen Transformers:

--Ethan

You don't want a core to introduce diferential hum signal, but its unlikely to introduce common mode hum, which is what an isolator is trying to acomplish.

Reversing the plug on the player might work or help.

You could try running a wire from the computer case to the player case.

I just did some bench tests of Radio Shack's "Ground Isolator" 270-054 using test signals that maxed out around 2.5 v RMS. ZSource = 150 ohms, ZLoad =

10K ohms.

The measured performance was truely amazing for a pair of transformers case and cables selling for only $16.65.

All IM, THD, and noise artifacts were at least 80 dB down with most in the -100 dB range or better. Frequency response showed a 2 dB peak at 20 Hz and then 10 dB down at 10 Hz. There was a 3 dB peak at about 51 KHz falling to about 10 dB down around 100 KHz. +0.5 dB at 20 KHz.

No problems with hum pickup were noted.

Amazing since its dual channel.

I never measured the 600 ohm transformer, but some day I will.

greg

Since this part may vary, I should point out that the UUT differed at least cosmetically from the picture at:

The cylindrical case on the sample tested is more truely cylindrical, with sharper corners far less nomeclature. The markings are on a black sticker and lack the pictorals of signal connections and text related to them. A RCA (female) to 3.5 mm TRS adaptor was provided.

The caveat here is the driving requirment. A typical CD player or tape player would have several hundred or more ohms output, and this unit would not work. Just how well would it work??

greg

I don't think that is a given.

Presuming that mutual inductance is high across the audio band, the load on the transformer is equal to the sum of the source and load impedances. IOW in the case of my test, the total load was 10,150 ohms, which is the stronger effect. How that is broken up between the input and output would be the weaker effect.

I did a test where I added an additional 10K in parallel with the output of the transformer. This reduced the bass peak to about 2 dB, and reduced the treble peak to 0.6 dB. Both referenced the midband response which was flat within 0.1 dB from 50 Hz to 10 Khz.

The cassette player has an earth unless it is battery powered. Are you saying it is battery powered, or are you saying it has just a 2-prong plug, not a 3-prong plug. A 2-prong plug has a connection to earth on one of its two wires.

1) If you are running the cassette player from AC, try reversing the AC plug. 2) Try plugging the cassette player into the same power strip the computer is plugged into. 3) Ccan you run the cassette player from batteries? If so, that should eliminate the problem. 4) Have the cassette player actually play the recording (over it's speaker), and plug a microphone into the computer to re-record it. Since it is just telepone conversations, the loss of qualtiy by re-recording is not really a problem. 5) Isolation transformers should work for this problem, but I would try the above first.

Terry

Terry spake thus:

Yikes! No, it should not. That would be a recipe for disaster, man. No,

2-prong devices have a chassis ground that is in no way connected to either of the incoming line leads.

Even with polarized plugs (which can sometimes be inserted backwards), this would be asking for trouble.

--
Pierre, mon ami. Jetez encore un Scientologiste
dans le baquet d'acide.

- from a posting in alt.religion.scientology titled
"France recommends dissolving Scientologists"

Agreed, it's most likely a two prong plug then a step-down transformer isolating it.

Well, maybe we're just used to different language on different sides of the pond. But "earth" does not mean "chasis ground" to me.

My cassette player/recorder (made by Hitachi for the UK market) does not have an earth.

The mains lead to it has only two wires: live and neutral.

On Tue, 25 Apr 2006 12:06:20 GMT, Terry put finger to keyboard and composed:

You may be thinking of the "mains earthed neutral" (MEN) system. In such cases, even when there is no earth pin, the appliance can still be affected by earth loops via capacitive coupling.

See

- Franc Zabkar

--
Please remove one 'i' from my address when replying by email.

Perhaps even more significantly, the lead probably ends in a non-polarised plug. The unit must be fitted with a double-insulated internal power unit. There is no electrical connection from the mains-side of the unit to the low voltage side.

--
Sue

Read above! (as lots haven't)

Are you sure the hum is created when the tape is played to the computer? Have you listened to the tape directly from the player (into stereo, into headphones, etc.)?

That may help. Worth a try, for sure!

Jon

-------- Try a two conductor shielded wire with the shield connected to ground at only one end. This used to work with magnetic phono cartridges connected to a preamp.

--

Don Kelly @shawcross.ca
remove the X to answer
>

I've seen that a couple of times on my system if the input jack is not fully and/or correctly plugged in. What I get is pure 60 Hz hum. I find, when it occurs, that I have moved something and partially unseated one of the jacks. You might want to check to make sure this is not happening and/or your cords/jacks match and aren't giving you a phase to ground connection of some kind.

Re: my post immediately above this -- I guess I should not have used the term "phase to ground" as that sounds like I'm implying 120 VAC across the connection. What I really meant was some kind of current flow from power to ground and/or an inductance that causes/allows the ac sine wave pattern to be present at the audio input.