Solved my high pitched whistle ;)

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FrankD77

FrankD77

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I've took some time to make sure my set was as silent as possible.

Power supplies are on switches, one group to two power conditioners and it all worked great till i connected my DI signal via a JHS splitter.

As soon as the cable went into the interface there was a very annoying whistle. No Humm no noise just an annoying high pitched very soft whistle.

I've reconnected everything several times and decided to get the palmer line isolator after testing a hd400 (behringer) which did work but destroyed my signal.

It's very affordable and aimed at guitar/bass with a 1:1 transmission. And ... It works like a charm. As soon as I connected the box the whistle was gone.. silence is great ;)

Im not affiliated with palmer but wanted to share my experience seeing it bugged me for months and wish I found this before.

IMG_9156.webp
 
This is a bit concerning, to be fair. The Behringer has a published flat frequency response to 20K - typical of decent audio transformers, which is all that is in the box. If it destroyed the signal, you have something more serious going on. My one got stolen last year, but always did what it was designed to do - isolate A from B, and I never noticed any audio difference. The Palmer device is the same a transformer in a box. Both designs can't really be simpler.

Between the US and the UK we have always had disputes over who makes the best transformers. Sowter in the UK and Jensen in the US, and Europe and Japan also have established transformer manufacturers.

Both products have small differences in transformer design, but the question of course is what is actually causing the oscillation you are hearing. With the splitter, you have multiple devices and it would be interesting to find out which is causing it.

Transformers usually are transparent at audio frequencies, unless they are impedance loaded oddly, or have shorted turns, so the devices connected damp the response? I have one laying around somewhere made by somebody I have never heard of, is going rusty, and still fixes problems without disconnecting the ground - which I hate doing.

What kind of destroying the sound was happening?
 
The hd400 took away a lot of the signal.
Almost like going from humbuckers to single coils.

The palmer keeps it all in tact.
It's in the same spot in my chain.
 
Could very well be.
I know this one works and I have another one coming in from another brand. I'll put that on my console input from the guitar chain.
 
Things like these have been around in telecoms for years Screenshot 2025-06-05 at 19.10.10.webp
The low impedance sources work transparently - but of course feeding a high impedance source into these tends to act as a sort of tuned filter to a degree - wrecking the flat frequency response
 
There's no direct electrical path at all between in and out so any of the usual interference problems can't happen. We used to use things like these (at much more cost of course, before Aliexpress) to do splits for broadcast, or recording. You could build a few into a rack, and use these to provide a 'sniffed' feed to a recorder - even if the circuit had phantom power on it, the transformers didn't pass the DC.
 
I have a few of the HD400s and I've not had problems with them so far. However, I've been using them for synthesizers rather than a recording device where you'd measure the frequency response going in and coming out.
 
Here it was volume. Which destroyed my highs and gain.

I can't find the hd400 anymore but i had it for a while on the DI and it solved the earth loop but i could not get a nice sound out of the plugins when needed.

Maybe it was a defective unit. The palmer does it perfectly luckily
 
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