Exec Summary: Can Electret Condenser headphones really lose their charge and degrade in terms of SPL, or is this more likely a XFMR issue?
I'm researching an issue with my old Audio Technica AT-706 headphones. These are electret condenser (no bias supply) that I just pulled out of a box in my basement that they had been in for some 20+ years. I thought I had remembered that one channel was gone and at the time had suspected the transformer unit, and I just managed to buy a new/used one from eBay. Well I plugged them into that new/used transformer unit and they did work but weren't very loud. I then went back to my old xfmr unit and that seemed to work too on both channels (so not sure what had originally been wrong with the unit!). However, the volume is low with both xfmr adapters, so I suspect there is another issue. I am using a Yamaha receiver rated for 50W and have to crank it up to full volume to get a mid-level volume on the headphones. Does this likely mean the headphones have lost part of their permanent charge? I saw some comments on a thread about this happening and then others saying this is not the case. Is there any way to "re-charge" them?!
Thx
I'm researching an issue with my old Audio Technica AT-706 headphones. These are electret condenser (no bias supply) that I just pulled out of a box in my basement that they had been in for some 20+ years. I thought I had remembered that one channel was gone and at the time had suspected the transformer unit, and I just managed to buy a new/used one from eBay. Well I plugged them into that new/used transformer unit and they did work but weren't very loud. I then went back to my old xfmr unit and that seemed to work too on both channels (so not sure what had originally been wrong with the unit!). However, the volume is low with both xfmr adapters, so I suspect there is another issue. I am using a Yamaha receiver rated for 50W and have to crank it up to full volume to get a mid-level volume on the headphones. Does this likely mean the headphones have lost part of their permanent charge? I saw some comments on a thread about this happening and then others saying this is not the case. Is there any way to "re-charge" them?!
Thx
The foil in the headphones loose there 'frozen' charge. This also happens to elektret microphones after so many years the loose the efficiency :-(
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Greetings rekenaar
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Greetings rekenaar
Yes so I've read in just a few places. There's not a lot of info online about it and others say that these things can last over 30 years so I'm just trying to sort out the rumours from the facts. I also saw some technical paper that said that they did not find any evidence of aging and loss of charge. It's also suspicious that both channels seem to be equal in volume. I would not expect the diaphragms to lose charge at exactly the same rate.
The energizer looks like an old Stax unit -two transformers inside .
I still have a pair of Stax Lamba,s with a SB ( self-biased ) box connected to the output of a power amplifier .
I will try to find my original Hi-Fi Choice year book on headphones which I remember includes your headphones --not bad looking phones you have.
Found a website where the poster ( in 2015 ) says he has a 1975 version still going strong.
I still have a pair of Stax Lamba,s with a SB ( self-biased ) box connected to the output of a power amplifier .
I will try to find my original Hi-Fi Choice year book on headphones which I remember includes your headphones --not bad looking phones you have.
Found a website where the poster ( in 2015 ) says he has a 1975 version still going strong.
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yes I have two of the transformer adapters now. They were pretty good sounding headphones but since those days, my wife has now bought me some Sennheiser more modern ones which sound fine to my aging ears. I was going to sell the AT-706 ones as it looks like people consider them to be collector items, but I'm not going to sell something that doesn't work without being candid of any issues. I hate throwing stuff out!
Sure if there is anything further you can find out, that would be great.
Sure if there is anything further you can find out, that would be great.
I've heard "informed" opinions on both sides of whether electrets gradually lose charge over time.
My experience: I have two sets of Fontek electrets which I bought new in the late-80's to early 90's. The set I bought first I definitely overpowered (youthful overexuberance) and they are nearly dead - unusable. The set I bought a couple years later still works fine. The left side is down a couple dB from the right, but make up the gain and the sound is well balanced, and they sound great. That's after 30 years. After modding the xfmrs' terminations, they sound better than my Stax electrostatics. Electrets get a bad rap, IMO. But I'd be careful buying them... there's no way to recharge them.
My experience: I have two sets of Fontek electrets which I bought new in the late-80's to early 90's. The set I bought first I definitely overpowered (youthful overexuberance) and they are nearly dead - unusable. The set I bought a couple years later still works fine. The left side is down a couple dB from the right, but make up the gain and the sound is well balanced, and they sound great. That's after 30 years. After modding the xfmrs' terminations, they sound better than my Stax electrostatics. Electrets get a bad rap, IMO. But I'd be careful buying them... there's no way to recharge them.
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Piezo electrics are used in bone conduction headphones (Audiology depts of hospitals ) /ultrasonic sensors/sonar etc .
The issue here is leakage and the audio signal used to generate an electrical charge .
Believe it or not there are high voltage "boosters " using a battery supply that can --in conjunction with an audio signal that drives a piezo amplifier then the actual device activate it.
So if this is possible then theoretically "electric " headphones could be "brought back to life " .
The issue here is leakage and the audio signal used to generate an electrical charge .
Believe it or not there are high voltage "boosters " using a battery supply that can --in conjunction with an audio signal that drives a piezo amplifier then the actual device activate it.
So if this is possible then theoretically "electric " headphones could be "brought back to life " .
"In theory", perhaps. But I have never seen or heard of it successfully being done to a pair of electret headphones.
Someone at work also told me it might be possible to recharge by heating up the diaphragm coating under an electric field and letting it cool again. All just sounds theoretical to me and without any solid reference or simple DIY instructions, that's not something I'm going to try.
I guess I'm just struggling to figure out if the lack of volume is in fact charge leakage or if something has gone in the transformers. I'll need to take the transformers into work and test them on an LCR meter. There may be some electrolytic capacitors that need changing after all these years but I don't think they would result in a lack of volume but more like perhaps a frequency response change.
jbau what sort of transformer termination changes did you make? Was that to improve frequency response?
I guess I'm just struggling to figure out if the lack of volume is in fact charge leakage or if something has gone in the transformers. I'll need to take the transformers into work and test them on an LCR meter. There may be some electrolytic capacitors that need changing after all these years but I don't think they would result in a lack of volume but more like perhaps a frequency response change.
jbau what sort of transformer termination changes did you make? Was that to improve frequency response?
Yeah, I wouldn't, either, if it generates any heat on the diaphragm...
Transformers tend to be pretty robust; you'd kill the drivers before the xfmrs, IMO.
I'd be surprised if there are any 'lytics in there. Check to see if there is a current-sensitive resistance device at the input. Even Stax used them for input protection. Horrible things. Do you have a schematic of the xfmr coupler?
Basically, yes. All these companies use fairly-wide-tolerance standard resistor values, and the optimum values were a little different. The series resistor at the input of the transformer is the most impactful. Even a couple tenths of an Ohm makes a big difference.
And some of the transformers are not perfectly flat in the passband...
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