Johnny Blue
I made it to 'Member'!
I posted this question on another (headphone-specific) website a couple of days ago and haven't managed to draw any responses. I wonder if folk around here have got any idea about how much DC offset can damage headphones? Here's what I posted previously:
The other day, I was browsing around the Rock Grotto website and came across a section on measuring DC offsets on amps, so, having nothing better to do at the time (!), I dug out my DMM and had fun measuring all my headphone amps. I didn’t bother to open them all up, I just used a 3.5mm jack to 3.5mm jack lead from the headphone socket.
My DIY Banzai (about which the fear of God had been put into me on the RG forum with respect to DC offsets, and pictures of which I've posted here before) measured around -1mV (I’ll not go into left/right channels, and source/no source: all measured differences were minor), which I'd read is nothing to worry about (albeit with fresh batteries).
My Mk.1 Neco portable (from eBay, with the AD 8620 op-amp upgrade) measured around -0.3mV, so again, fine, and my Naim Headline was bang on zero (to be expected!).
A new Guanzo (Chinese, also off eBay) was slightly worse, at about -16mV, but that’s still within the 20mV that the RG web page said was OK.
So far, so good.
I then tried my Electric Avenues PA2V2 (my first portable HPA, bought direct from Gary, but also available on eBay): the 200mV scale on my DMM gave figures that made no sense, I had to switch to the 2000mV (2V!) scale to get a figure: +1215mV! I was shocked (as in surprised, not electrically!). I had been using it with Sennheiser HD565s a few days previously and had not noticed anything untoward, but I’m now terrified of putting any of my headphones anywhere near it.
A couple of days ago, I thought I’d try measuring the PA2V2 with fresh batteries: this brought the offset down to around +650mV, and some alkaline batteries gave similar results. I then realised that gradually the DC offset was dropping regardless of the batteries I was using, so after 30 mins or so the figure was +380mV (still way too high?). I then measured the offset with the amp turned off, and it was around -880mV!
Now, let me be clear here, I have only a vague understanding of the electronics, but can I assume that a third of a Volt going through my headphones is not a good idea?
Can anybody comment on these results, particularly what the PA2V2 amp might have been doing to my headphones?
(I know I can contact the maker/vendor to resolve any problem with the PA2V2, although the P&P to return the amp to Canada probably makes a repair not really worthwhile on an amp that only cost about $50 in the first place.)
The other day, I was browsing around the Rock Grotto website and came across a section on measuring DC offsets on amps, so, having nothing better to do at the time (!), I dug out my DMM and had fun measuring all my headphone amps. I didn’t bother to open them all up, I just used a 3.5mm jack to 3.5mm jack lead from the headphone socket.
My DIY Banzai (about which the fear of God had been put into me on the RG forum with respect to DC offsets, and pictures of which I've posted here before) measured around -1mV (I’ll not go into left/right channels, and source/no source: all measured differences were minor), which I'd read is nothing to worry about (albeit with fresh batteries).
My Mk.1 Neco portable (from eBay, with the AD 8620 op-amp upgrade) measured around -0.3mV, so again, fine, and my Naim Headline was bang on zero (to be expected!).
A new Guanzo (Chinese, also off eBay) was slightly worse, at about -16mV, but that’s still within the 20mV that the RG web page said was OK.
So far, so good.
I then tried my Electric Avenues PA2V2 (my first portable HPA, bought direct from Gary, but also available on eBay): the 200mV scale on my DMM gave figures that made no sense, I had to switch to the 2000mV (2V!) scale to get a figure: +1215mV! I was shocked (as in surprised, not electrically!). I had been using it with Sennheiser HD565s a few days previously and had not noticed anything untoward, but I’m now terrified of putting any of my headphones anywhere near it.
A couple of days ago, I thought I’d try measuring the PA2V2 with fresh batteries: this brought the offset down to around +650mV, and some alkaline batteries gave similar results. I then realised that gradually the DC offset was dropping regardless of the batteries I was using, so after 30 mins or so the figure was +380mV (still way too high?). I then measured the offset with the amp turned off, and it was around -880mV!
Now, let me be clear here, I have only a vague understanding of the electronics, but can I assume that a third of a Volt going through my headphones is not a good idea?
Can anybody comment on these results, particularly what the PA2V2 amp might have been doing to my headphones?
(I know I can contact the maker/vendor to resolve any problem with the PA2V2, although the P&P to return the amp to Canada probably makes a repair not really worthwhile on an amp that only cost about $50 in the first place.)
