Hello, I recently acquired a DAC/Headphone amp combo with Line level out (Schitt Fulla E) to use with my PC monitors and headphones. The headphone input is supposed to mute the line level output when headphones are connected, and it does, but when I do so, the speakers play a very loud high frequency buzzing sound (I can identify the frequency but its definitely not 50/60 hz and shouldn't have anything to do with mains noise). No such buzzing occurs when the headphones are not connected (except from the much quieter, different in tone, hum noise every amp has ) The DAC is powered with usb directly Form he computer, in-between them i have a isolation transformer(groundloop isolator) since I had problems with ground loop noise because the pc and speaker amp share a common ground. Any Idea on how i should approach this? The buzz is very loud and I keep having to turn on and off my amp.
Could you post a pencil sketch of the setup -- both the signal paths and the power paths?
When I hear 'isolation transformer', it's usually to separate the incoming AC-Neutral from DUT / test equipment Ground. What you described sounds like it might be a full-audio-range signal transformer.
Any chance the Schitt Fulla E was 'modded' by a well-meaning amateur.
Next most likely thing might be . . That the mute circuit shorts the Line Output and the (usually very) inexpensive speaker amp hates that. (Oscillation would not be unusual, and might be described as a 'squalling' sound.)
Cheers
When I hear 'isolation transformer', it's usually to separate the incoming AC-Neutral from DUT / test equipment Ground. What you described sounds like it might be a full-audio-range signal transformer.
Any chance the Schitt Fulla E was 'modded' by a well-meaning amateur.
Next most likely thing might be . . That the mute circuit shorts the Line Output and the (usually very) inexpensive speaker amp hates that. (Oscillation would not be unusual, and might be described as a 'squalling' sound.)
Cheers
Here's the diagram
The isolator is a Dynavox (here's a link from there website, and you are right it's probably a "full audio range signal transformer")
The fulla wasn't modded, I got it directly from Schiit . The amp is indeed a cheap tpa3116 Chinese design from aiyima, so maybe it's the shorted output? Any chance the amp hates it that much that it damage it's self? The computer and the fulla have both toslink ports, i dont have a cable to try but would using that for data make any difference?
Is there any chance the Aiyima switches itself to BlueTooth when it detects No Input on the MP3? Seems unlikely that it would damage itself; unlike many inexpensive Class-D amps there looks to be plenty of input processing. That eliminates one possibility -- that the Class-D section is interacting with the isolation transformer because it needs a lower driving impedance.
Using the TosLink would be fun, probably not too expensive, and could remedy several problems -- but not this one.
The Dynavox link didn't say anything about impedance. Once upon a time that wouldn't have been a big deal: All gear was valve . . or later, all gear was solid state. But today we need to know. Since the Aiyima has a full-function preamp / crossover, it likely has a somewhat higher input impedance than typical Class-D boards. The Dynavox probably needs a proper load resistance. See if you can determine what impedance it expects -- most signal transformers need either a controlled impedance source, and / or a definite load impedance. If the Dynavox hasn't already provided that internally, you will need to.
Sorry it took me a while to get this posted -- I'm always shocked when Chrome hasn't totally hosed me . .
Cheers
Using the TosLink would be fun, probably not too expensive, and could remedy several problems -- but not this one.
The Dynavox link didn't say anything about impedance. Once upon a time that wouldn't have been a big deal: All gear was valve . . or later, all gear was solid state. But today we need to know. Since the Aiyima has a full-function preamp / crossover, it likely has a somewhat higher input impedance than typical Class-D boards. The Dynavox probably needs a proper load resistance. See if you can determine what impedance it expects -- most signal transformers need either a controlled impedance source, and / or a definite load impedance. If the Dynavox hasn't already provided that internally, you will need to.
Sorry it took me a while to get this posted -- I'm always shocked when Chrome hasn't totally hosed me . .
Cheers
The input source changes only using a button so its line in only. The amp indeed has a lot of processing, but keep in mind that it uses two tpa3116 chips maybe that lowers the input impedance since one signal need to drive two amps? Unfortunately I have no idea how to measure impedance and as you can imagine neither dynavox nor aiyima supply these information. I do have some new information thought. When I remove the isolator, the ground loop buzz obviously comes again, but this time if I connect the headphones into the DAC the amp goes near silent, no ground loop noise nor that weird noise i was refereeing to at my previous messages. So I suspect you are right, the isolator is probably responsible. Maybe a toslink connection could solve the ground loop issue and I don't have t o use the isolator in the first place?