Hello everyone!
Radio Joe here,
I have been doing some work in the transmitter room and need to ask whoever may have some knowledge about the following subject.
I have from time to time used ground loop isolators between transmitters and audio sources such as a computer or VCR.
The reason for this is to eliminate hum and buzz which seems to come from nowhere into the audio chain. I am aware of how to eliminate ground loops mainly by making sure everything is plugged into the same outlet/power strip those sorts of things.
I have over the years tried to have all things grounded with grounding straps to a common point and that sort of thing.
The subject at hand is not about eliminating ground loops though, but about the physicist of the ground loop isolator. I have been using ground loop isolators from various venders and brands, most are in the ten dollar and under range, but before you say there is your problem, let me explain that the early Radio Shack “round can type” seem to work the best but why?
Here is the question I am asking for advice on. There seems to be a difference in ground loop isolators when it comes to low audio frequency response pass though. Most of these ground loop isolators claim flat response but from my personal use, I can tell you that is not true. Many have a roll off of bass frequencies, and of course the reason for this I assume is the small inductance of the transformers (1:1) that are used for ground isolation.
The early Radio Shack “round can” type seem to pass low frequencies without any noticeable attenuation. These seem to be physically bigger than most GLI units so this may be the reason. I have never cut apart one to see what size transformers are in that can.
Now here is a question that I myself have answered to myself, but I am not sure if I am correct.
Am I correct in assuming that how efficient these transformers that are used in the ground loop isolators determine how they respond to low frequencies? Or is the frequency response determined by how close the output impedance of the output device is, (computer –VCR) to the input impedance of the transformer in the ground loop device?
In other words, does it make any difference how small the 1:1 transformer both physically and is as far as inductance as long as both output and input impedance are close, and would that guaranteed that low audio frequencies would pass not attenuated if they are a match?
Most line out impedances on consumer audio electronics runs about 10K or so, anyway that’s what I see in specs, so if the input Z of the ground loop isolator is 10K would that mean that there would be a perfect match and no frequency response loss?
I have no clue on how to check the impute Z of something like a ground loop isolator, you can check resistance but that of course is not impedance.
So the question is what factors determine that a ground loop isolator will have flat response? Is it the efficiency meaning larger inductance of the transformers used, or is it more important that the output/input/output Z is a very good match?
I’m wondering if there is a mismatch in Z that may account for loss of signal transfer but would it affect frequency response.
Thank you for giving this some thought!
I have to get back to managing my transmitters now, so many people out there to serve!
Radio Joe
I found this which may be of interest but I personally can't answer what determines the pass through frequency of a ground loop isolator.
https://www.epanorama.net/documents/groundloop/audio_isolator_building.html
But if the radioshack one works good than don't worry about why! Get a few extras and then take apart one to see what's there.
Here's something for you.... https://www.jensen-transformers.com/wp-content/uploads/2014/07/CI-2RR.pdf
Hi Mark, thanks for the response,- the Jensen isolator looks great, but they list it at $200, but you know what, if a person has a real problem with hum and is concerned about frequency response, This one looks like the answer.
I didn’t do a wide search on price yet but im sure it can be had for less than $200
At least someone has come up with a good product to the problem.
Presently I need to run a ground loop isolator between the computer and the audio on my transmitter system, it depends on the computer I use, I ran one computer that didn’t need the ground loop isolator.
For my application I found the RS one works with out low frequency audio loss, therefor I am not too concerned the channels being about phase and all of that if there should be a problem, i haven't noticed any, but it may make a difference when run though a stereo transmitter or a big difference if you’re listening on a good stereo system concentrating on the stereo “image” like we used to do in the “old days’ listen to the equipment not the music!
I’ll look around at pricing, and you also have a good recomendation about cutting a RS isolator apart, problem is the type model that works is like out of the late 80s so these are getting rare, they had several models, the earlier ones are that best.
I just recently bought one off ebay ill have to keep looking I would like to sacrifice one just to see what they have inside the can. Who knows, might be the parts JENSEN uses 🙂
What about looking inside the radioshack one to see what's inside without breaking it?
I personally have found that if I get hum and buzz on the carrier when listening on air with no audio(I am on FM in Canada), there's two reasons. Either the power supply to the transmitter or compressor(all aren't equal) or changing the position of the audio cables and power cords. Just moving the cords/cables around will get it to a spot that eliminates the buzzing/hum or a ferrite on the cables/cords near where it goes into a power jack works too. Larger the better to a point. Fortunately the MS-100 Decade transmitter has the power supply on board and the wallwart is just a 120 to 16 volt transformer and the on board power supply is much better than what's typically in cheap wallwarts.
Have also found the brick style power supplies used for computers and desktop monitors are way better than the other smaller ones. The monitor ones are mostly 12 volts.
Last week HB member Tom Tompkins posted a review about a very inexpensive ($3.95) lSS-02 Audio Ground Loop Isolator' available on eBay, which apparently performs remarkably well. After he received it he ran it through a battery of test utilizing a signal generator and a vacuum tube voltmeter and detailed all results, along with picture of the device unassembled.
"...I'm impressed that the two transformers are offset, as I've seen others where the laminations are almost touching, something I suspect would lead to crosstalk between channels. Anyway, this is a gadget to consider having on hand, because you sure can't beat the price for that kind of performance..."
Damn.. my message got kidnapped by the forum again.. apparently because of the link I inserted - To read the full review go to the hobbybroadcaster user reviews section and select "Shangsheng SS-02 Audio Ground Loop Isolator " Product Evaluation
Last week HB member Tom Tompkins posted a review about a very inexpensive ($3.95) lSS-02 Audio Ground Loop Isolator' available on eBay, which apparently performs remarkably well. After he received it he ran it through a battery of test utilizing a signal generator and a vacuum tube voltmeter and detailed all results, along with picture of the device unassembled.
"...I'm impressed that the two transformers are offset, as I've seen others where the laminations are almost touching, something I suspect would lead to crosstalk between channels. Anyway, this is a gadget to consider having on hand, because you sure can't beat the price for that kind of performance..."
Read full review: https://www.hobbybroadcaster.net/reviews/shangsheng-ground-loop-isolator-user-review.php
@ Rich Powers, I volunteered to be a moderator when admin posted moderators wanted a short time ago and I am not officially moderator yet but have the controls at my end to see how it works. The last post about the link to the HB review of the ground loop isolator got flagged and sent to me for moderation, that's what happened. Don't know why as I can see nothing wrong with a link to some info. so I approved it and the link with the original post is there now.
That one on Ebay for $3.95 that works that good with no frequency response loss... I may get a few of them!
Notice they all come from China and shipped the slowest economy way. One ordered now would take till March to get.