[Pharmaboy]

*** New York Pharmaderby ...

(image of lame, riderless horse at keyboard)

 

[lauthoerer]

Agree, the Icon Audio HP8 is a fantastic transformer coupled amp. It runs both dynamics and planar HP's very well for me and the adjustable impedance works with all my ZMF's. It gets just a little warm on the casing and only the tubes are hot. I found mine used and it had an annoying hum as well. Recently I sent it to a certified Icon Audio distributer in Canada and they were able to replace a part that significantly improved the hum issue.

(Bringing this over from the Violectric thread)

The weird/annoying thing with the hum is that it’s practically all but gone with the E3 (27Ω), not that big an issue with the HD820 (300Ω), noticeable with the Bokeh (80Ω) and totally annoying with VC (300Ω), which makes no sense in my view. But the impedance setting basically governs the amount of hum, which probably does make sense. What’s worse is that the positive effect of the tubes and the overall enjoyment the HP8 brings to the music is equal (in reverse) to this rundown. E3 sounds pretty much the same on the US5. But when the band is playing in full, overpowering the hum, the VC sounds just amazing, probably even better than on my US5. However, on the US5, the background couldn’t be any darker and they also already sound great.

I got a power conditioner in for testing the other week (Lab12 gordian) and the first thing I tried was to tackle the hum. Connecting the HP8 first, then the DAC, I was able to localize the source of the hum in the connection to the DAC, being able to "play" sounds by tapping the RCA jack to the output of the DAC. So immediate result was: no change to the power supply I used before (only talking about the hum issue here). What did reap immediate results was using a Puritan Classic+ Cable for my DAC (instead of the Audioplan PowerCord S I was using). This reduced the hum, but sadly didn't get rid of it completely.

Next steps will be trying more/other power cables for the HP8 as well as for the rest of my chain. And maybe trying some grounding options, but would think the HP8 itself isn’t actually the issue, but the connection to the rest of the electronics…

 

[G8torbyte]

@lauthoerer When I was troubleshooting the hum issue on my own I ruled out no ground loop, isolated the HP8 so there were no other running electronics nearby (it is sensitive to wireless and EMF) and tried an ifi GND Defender but there was no difference. The hum in mine was not impacted by volume control and only went up with the impedance switch going from low to high. It was a low frequency hum that was tolerable in open backs but likewise with the ZMF VC it was significantly annoying. I sent it to an authorized Icon Audio distributor that I mentioned and they ran tests and replaced a failing part. I'm thinking it was an internal component associated with the power supply that was causing the issue. The tune up was well worth it for me because they got rid of the noise and I love this amp.
It works so well with dynamics and planars. Jamming on it as I type this with the Caldera Open

 

[lauthoerer]

Thanks for the insight, @G8torbyte ! The hum does increase with turning up the volume, but, indeed, when it’s negligible (E3, HD820), that’s only when turned up to a measure way too loud to listen to anyway. I guess I’ll write to icon Audio and see if there’s a shop in Germany they can recommend.