My stepmother is hard of hearing. My Dad asked me if there's a portable amplifier I could build that has enough gain for her. We are guessing that it needs 80dB of gain, since -80dB is the threshold of deafness. I've already built one of the O2 amps, and it works great, thank you RS. I don't know how much gain the O2 amp has, or what would need to be changed to give it 80dB. I know, that's a lot of gain! The only other thing it needs is separate Left and Right volume controls, or a balance control, since she is not equally deaf in each ear. My Dad wants Bluetooth interface, but I found a portable device with a 3.5mm stereo plug for that. Can someone help me out?
EDIT: ok, I looked up gain for hearing aids and it's more like 60dB. That's still a lot!
EDIT: ok, I looked up gain for hearing aids and it's more like 60dB. That's still a lot!
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Damping Factor
One area I haven't yet seen in this general discussion about the O2 is that of its damping factor. It doesn't seem to be mentioned in RS's blog, unless I've missed it. I know this can be an important factor in an amplifier's bass response, not so much in terms of frequency response, so much as in 'feel', whereby changing the damping factor can affect the 'punch' of the bass sound. My technical knowledge of this is limited (although I'm looking forward to being educated by those more knowledgable than me!) but I understand that it involves the amplifier reacting to the movement of the transducer by some sort of feedback mechanism, giving a more, or less, tight response to the transducer.
I would be interested what the O2's damping factor is, and how the O2's damping factor using a typical pair of 60ohm phones compared with lower and higher impedence devices.
One area I haven't yet seen in this general discussion about the O2 is that of its damping factor. It doesn't seem to be mentioned in RS's blog, unless I've missed it. I know this can be an important factor in an amplifier's bass response, not so much in terms of frequency response, so much as in 'feel', whereby changing the damping factor can affect the 'punch' of the bass sound. My technical knowledge of this is limited (although I'm looking forward to being educated by those more knowledgable than me!) but I understand that it involves the amplifier reacting to the movement of the transducer by some sort of feedback mechanism, giving a more, or less, tight response to the transducer.
I would be interested what the O2's damping factor is, and how the O2's damping factor using a typical pair of 60ohm phones compared with lower and higher impedence devices.
There's a bit in RS's article at NwAvGuy: Headphone Impedance Explained where he says "most high quality drivers require some sort of damping to control this resonance. If it’s not controlled, it tends to seriously degrade the bass performance of the driver." but I haven't yet found any explanation as to how this is achieved. Also, I was under the impression that damping factor also depended on the headphone impedance as well as the amp's output impedance - I know that the O2 has a low output impedance. I've regularly seen Damping Factor quoted in respect of power amps, but they're driving large 4 - 8 ohm loads at relatively high power, and I wondered how this related to headphones, that have smaller, lighter drivers and, presumably, different resonant frequencies, as well as a much larger range of impedences. Is it simply the case that the damping factor of the O2 will always be very large, regardless of the impedence of headphones used, or are there some combinations that should be avoided? And could some phones sound more 'damped' than others?
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The heatsinks were homemade and designed to extend laterally towards the rear of the enclosure.
Ah yes, Freddysburg. Peaches, kolaches, the Nimitz Museum, its famous "suburb" Luckenbach, Enchanted Rock. Not a bad place to visit at all.
My recollection of NwAvGuy's explanation of damping factor is that the amp output impedance should be 10x less than the load impedance.
Ah yes, Freddysburg. Peaches, kolaches, the Nimitz Museum, its famous "suburb" Luckenbach, Enchanted Rock. Not a bad place to visit at all.
My recollection of NwAvGuy's explanation of damping factor is that the amp output impedance should be 10x less than the load impedance.
Are you talking about using the O2 as a microphone amp, like a pocket-sized hearing aid? There are devices out there that are purpose made for this. If you're looking to do this because you can't afford hearing aids, you might start looking through needymeds.org and see if there's a program you qualify for.
If she wants to use it for music, you would be shooting for an SPL in dB. The SPLs you hit would be determined by the output voltage of your source, the song, the amp's gain setting and the headphones. I couldn't recommend anything specific since I don't know what's safe for the hearing impaired. If I were you, my first stop would be her doctor.
Balance control would necessitate some mods.
@greenalien,
RS talks about imepdances and damping in more than one article. He explains it in the article he wrote for Innerfidelity. It's discussed in his articles on the O2, since the O2's low output impedance (0.5 Ohm) was a design goal. It's also talked about in some of his articles on amplifiers in general.
Ah, I see. I thought a little creativity might be required.
Not a bad place to visit at all. You could do worse, such as where I live (Liberty County). We have blackberries, cattle and... swamps.
RS thinks you're generally set as long as your output impedance is 1/8 the nominal impedance of your 'phones. This is one of the contentious areas. Some folks think it doesn't matter, others feel too much damping is detrimental, while others still believe in much higher values, like 1/20. You know how it is.
On D.F.
Just been reading about impedance etc... This page has a DF calculator at the very bottom, plus one of Benchmark's White Papers [featured on Nwavguy's blog] covers this area also. Plus the subject & it's effects are touched upon in this Stereophile review of the Centrance DACport [The words I have to say... section].
Regards,
Paul
Just been reading about impedance etc... This page has a DF calculator at the very bottom, plus one of Benchmark's White Papers [featured on Nwavguy's blog] covers this area also. Plus the subject & it's effects are touched upon in this Stereophile review of the Centrance DACport [The words I have to say... section].
Regards,
Paul
Also, it's quite interesting to read the Wikipedia entry
Damping factor - Wikipedia, the free encyclopedia
especially the part comparing valve and solid state amps, 'Higher electrical damping of the loudspeaker is not necessarily better. Some loudspeakers sound better with lower electrical damping. A lower damping factor helps to greatly enhance the bass response of the loudspeaker, which is useful if only a single amplifier is used for the entire audio range.'
I wonder how this may apply to headphones, as compared to loudspeakers.
The reason I got onto this subject in the first place was because of Resetter's assertion in his post that a tube amp had more 'punchy' bass that the O2 he's just built, and I've been trying to find out why.
(see post #19 at http://www.diyaudio.com/forums/group-buys/207163-o2-headphone-amp-complete-kits-uk-only-2.html
)
I just want to know how much gain can be obtained from the O2 amp, not advice on hearing aids, thanks. She's already got all the hearing aids and devices from the doctors. This is something different.
O2 gain settings
So what you need is an output of 80dB+ through the headphones. The gain switch on the O2 allows you to tailer the output based upon what headphones your using and the output of your source.
Example; my CD player outputs a 2Vrms signal & I have the O2's gain set to x1 [unity gain], giving 2Vrms output. With my Sennheiser HD650's this will give over 110dB at full volume.
The O2's max output is 7Vrms on mains power, 4.5Vrms on battries. To get your required gain you devide the max output of the O2 by the output from your source. For me that would be 7/2 = 3.5 & 4.5/2 = 2.25. So my gain settings would be 3.5 & 2.25.
Also dependant upon your headphones, the O2's max output might not be usefull and may give you limited use of the volume control's sweep. Knowing the power requirements of your headphones, plus the output of your source will allow you to set the O2's gain to your exact needs.
regards,
Paul
So what you need is an output of 80dB+ through the headphones. The gain switch on the O2 allows you to tailer the output based upon what headphones your using and the output of your source.
Example; my CD player outputs a 2Vrms signal & I have the O2's gain set to x1 [unity gain], giving 2Vrms output. With my Sennheiser HD650's this will give over 110dB at full volume.
The O2's max output is 7Vrms on mains power, 4.5Vrms on battries. To get your required gain you devide the max output of the O2 by the output from your source. For me that would be 7/2 = 3.5 & 4.5/2 = 2.25. So my gain settings would be 3.5 & 2.25.
Also dependant upon your headphones, the O2's max output might not be usefull and may give you limited use of the volume control's sweep. Knowing the power requirements of your headphones, plus the output of your source will allow you to set the O2's gain to your exact needs.
regards,
Paul
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Well, the HD598s have a pretty good impedance spike in the 100Hz area. With a high output impedance, you could get a bump in the FR there. Most people call a 100Hz bump "boomy", but maybe one man's boomy is another man's punchy. Sometimes words like these mean what they mean only to the person who uses them.
Sounds like his hybrid was also rolling off the highs, which some tube amps tend to do. My guess is the O2 flattened out the FR of his headphones.
I know its meant to be transparent, BUT listening to bass sweeps on the O2 or that tube hybrid or a 10 dollar simple thing, it is apparent that there is a lack of volume in the bass over the other amps.
I could run bass test cd`s over the tube and it would sound superb with a lot of "power" now when I play the same tracks on the O2 I find myself upping the volume quite a bit. But it's just as if the O2 does not let the driver make the full excursion as if its limiting the headphone to "move".
I already changed the gain to 1x as the standard setting i could hear distortion on those bass tracks, that tightened everything up a bit.
But it just feels like the other amps had more volume in bass overall, or perhaps the highs where less defined thus making the bass stand out more.
I could run bass test cd`s over the tube and it would sound superb with a lot of "power" now when I play the same tracks on the O2 I find myself upping the volume quite a bit. But it's just as if the O2 does not let the driver make the full excursion as if its limiting the headphone to "move".
I already changed the gain to 1x as the standard setting i could hear distortion on those bass tracks, that tightened everything up a bit.
But it just feels like the other amps had more volume in bass overall, or perhaps the highs where less defined thus making the bass stand out more.
Fair enough. It might be a case of listening habits. My hollow-state amps have a bass characteristic that's different than the solid-state stuff, at least with certain loudspeakers, and I like the sound. I never attempted to identify and measure it; I just took it for what it was. Don't have a tube headphone amp, though.
Some comments: The gain setting itself should not introduce distortion! It may add a slight bit of noise at higher gain settings (my understanding), but certainly not audible distortion (when compared to 1x at the same volume). The only audible distortion from the O2 should be at above clipping levels.
As for the comparision to other amps, it's far more likely that the other amps are emphasizing bass rather than the O2 deemphasizing the bass.The O2 has been measured to be -0.04 dB at 20 Hz and -0.3 dB at 10 Hz--not much of a rolloff. It's also possible that the other amps have higher output impedance and thus have "looser" bass, as you suggest.
Thanks! I appreciate your assistance.
I'm not sure where my Dad wants to go with this. I've found commercial products for the hearing impaired that have 120dB of available gain, for example. So, this may not go anywhere. I have to talk with him about it.
More thoughts...
My pleasure.
The O2 is quite capable of driving the vast majority of headphones to destruction, the upper sound limit being how much your hearing and the headphones can take.
Also, [reading your first post again] It'd be fairly straightforward to implement individual volume controls for each channel. You'd need 2 x single channel potentiometers and a case with enough room for the two controls. Or, if you know exactly the difference in hearing level, you might be able to adjust the O2's gain resistors to reflect the hearing imbalance.
My pleasure.
The O2 is quite capable of driving the vast majority of headphones to destruction, the upper sound limit being how much your hearing and the headphones can take.
Also, [reading your first post again] It'd be fairly straightforward to implement individual volume controls for each channel. You'd need 2 x single channel potentiometers and a case with enough room for the two controls. Or, if you know exactly the difference in hearing level, you might be able to adjust the O2's gain resistors to reflect the hearing imbalance.
The other amps probably have non-negligible output impedance. I concur with the analysis of
When I had a pair here around the time they came out, I found HD598s were quite sensitive to output impedance, as you'd expect from their impedance response. Not sure where the venerable Terratec Aureon Sky/Space ranks (my RMAA results suggest 47 ohms in headphone amp off mode), but for my taste, the lows were a little too much on the boomy side when used on that one already. I ultimately used my Clip+ to evaluate their sound, where the cans sounded about right, still nice and full and by no means lean.
I did notice that they shared a trait with the old HD5x5 series from back in the day, rather present mids tending to "stuff up" things - not a super-analytical 'phone. For classical and jazz I'd still prefer a HD580/600 or the '598's granddad, the HD590.