[Starbound]

Everything is related to basic math here: AKG K240 has a sensitivity of 104 dB SPL/V @ 1 kHz and according to Digizoid we have this:

�

Listening Loudness	Voltage Needed	Current Needed	Power Needed
Safe	85 dB SPL	0.11 Vrms	0.18 mA	0.02 mW
Moderate	100 dB SPL	0.63 Vrms	1.05 mA	0.66 mW
Fairly Loud	110 dB SPL	2 Vrms	3.33 mA	6.67 mW
Very Loud	115 dB SPL	3.55 Vrms	5.92 mA	21 mW
Painful	120 dB SPL	6.31 Vrms	10.52 mA	66.36 mW

Given that O2 has a max. output power of about 7.3 V RMS, I see no problems driving K240.

My DT880 has a lower sensitivity and O2 will not drive them to full power, but I can still get acceptable dB levels to my ears.


Probably folks thinking that a simple resistors added to speakers output will make 600-Ohms headphones sound "better". I would ignore them and use a dedicated headamp with a low output impedance (even if the 1/8-rule will not matter to our 600-Ohms headset, you never know when you'll pair a 16-Ohms headset with that amp).

That Digizoid tool is awesome, thanks. I ran the calculation again at 600 ohms, 92dB/mW (the sensitivity of the vintage K240 Monitor is reported to be between 92 and 95 dB/mW) and the results are still good enough, as I tend to listen to music at a very moderate volume.

I don't plan on getting low impedance headphones and I don't like IEMs, but one of the many things I like about the O2 is its low output impedance.

BTW, doesn't having a source with low output impedance also result in better performance with cans that have very non-linear impedances with respect to frequency?

For whatever reason, I have noticed quite an improvement with my MDR7506 through my O2/ODAC vs through other sources. That could be in part to the ODAC being cleaner, but I think there might be something else going on, maybe the low output impedance in the O2 making the headphone more controlled?

 

[raoultrifan]

BTW, doesn't having a source with low output impedance also result in better performance with cans that have very non-linear impedances with respect to frequency?

I don't see a correlation between source's output impedance and headamp's output impedance. However, a low output impedance is usually providing a cleaner signal and with a lower noise & interference (well, at least theoretically and only if using long interconnects).

 

[Starbound]

I don't see a correlation between source's output impedance and headamp's output impedance. However, a low output impedance is usually providing a cleaner signal and with a lower noise & interference (well, at least theoretically and only if using long interconnects).

I see, thanks. I was under the impression that it was the O2's low output impedance which made it a good match for headphones of very different impedances (and I assume, would also make it a better amp for headphones with very nonlinear impedance vs frequency graphs).

 

[raoultrifan]

By "source" I meant ODAC, not O2. Indeed, O2's low output impedance will make it compatible with most headphones, even with 8-Ohms ones.

 

[Starbound]

Bu "source" I meant ODAC, not O2. Indeed, O2's low output impedance will make it compatible with most headphones, even with 8-Ohms ones.

I see where the misunderstanding was. And just for a final clarification, this is why in theory the O2 would be a more neutral amp with headphones that have impedance/frequency curves which are non linear, is this correct?

 

[raoultrifan]

Usually headphones do not vary much their impedance while playing music, as speakers do, so I don't think neutrality of a headamp is much related to this. Instead, frequency response tested with several impedances across audibile bandwidth will be more helpful here.

More probably, the O2 is neutral because it has a rather low output impedance and is able to drive, with +/- 0.1 dB freq. linearity, all headsets between 16 to 600 Ohms.

 

[Starbound]

Usually headphones do not vary much their impedance while playing music, as speakers do, so I don't think neutrality of a headamp is much related to this. Instead, frequency response tested with several impedances across audibile bandwidth will be more helpful here.

More probably, the O2 is neutral because it has a rather low output impedance and is able to drive, with +/- 0.1 dB freq. linearity, all headsets between 16 to 600 Ohms.

I think I was misunderstanding. Every headphone has a non-linear impedance to frequency curve, but some move than others. My understanding was that because of this, if a headphone has an output impedance that is relatively high, it can cause frequencies where a specific headphone has a peak in the impedance/frequency curve to not be represented correctly. But now that I think about it it I see this doesn't make sense, because in these sense higher impedance actually is not a problem. It's more a matter of the amp being able to produce enough power even at frequencies where there is a peak in the impedance.

So yeah, I get what you are saying there, thanks.

 

[raoultrifan]

On speakers the impedance across audible bandwidth is usually between 3...5 Ohms to 20...25 Ohms, depending on the frequency, so it's varying with at least 500% between min. and max. On headsets the differences are usually below 10% between min. and max., but of course, it depends from one headphone to another.

Not sure this is related to your question, but low impedance headphones might not have the best bass response under some circumstances, especially when the output impedance of the headamp is higher than 1/8 of headphone's impedance.

In case of O2, people and measurements are calling it neutral due to its ability of driving headphones of different impedances with an almost perfect frequency response. Well, electronic engineering advanced a lot in the past years, so most of today headamps are neutral and trying to not alter the input signal at all. So, best bet when buying a headamp is mostly related to THD+N, output noise (in uV RMS), price and warranty (period and who's paying the shipping back and forth).

 

[SuperFlyEDSguy]

I am trying to remove the volume knob so I can put a faceplate on my O2. If anyone could help I would greatly appreciate it because I have no idea. Thanks

I know this is a ridiculously old post, but I actually ran into the very same issue today, literally almost a decade later. I guess that says a lot about the quality of these little amps as they’re still being used in 2022 and even sold band-new. Mine is the Drop variety, BTW. Basically, I wanted to swap the knob out as both of the rubber o-rings have worn-out, cracked, and finally snapped off. This little detail makes it quite a bit more difficult to turn as there is nothing else grippy on such a tiny knob to begin with. I purchased the Black Aluminum Knob by Taiss as sold through JDS Labs for my replacement as it’s (a) far beefier and easier to grasp onto, (b) has no rubber components at all, and (c) actually has a dial marker, something my OEM knob never came with! I am actually curious why Drop’s version of the O2 Amp does not have a dial markers as they make it significantly easier to see exactly where your volume level is currently set at — Hmmm — Anyhow, regarding my upgraded knob, not bad for $5 when considering that I was placing an order with JDS anyways!

So, even after completely unscrewing the Allen screw, it still wouldn’t budge and of course I was using a fair amount of force considering an Alps Pot should be able to take a bit of abuse. I was still not overdoing it as those Alps Pots are not invincible, but won’t break even half as easy as the stuff coming out of China in mass these days. Well, after trying a few ideas something finally hit me — to use a couple of small drops of oil — that’s right, any kind of oil designed for lubricating should work, but I used a couple of drops of Wahl Clipper Blade Oil as that’s what I had handy. The Wahl oil also has a dropper top so you won’t make a mess like you would when spraying a can of WD-40, something I would highly advise against when working near electronic components! A very small and targeted amount of such oil should do the trick, and it did!

Here’s the procedure:

1. Always completely remove the Allen screw from the current knob.
   
   
2. If the knob still cannot be removed from the Pot shaft with a fair amount of force, place 1 to 2 full drops of oil into the screw hole while allowing the oil to penetrate before applying a second drop. You will clearly see the oil level go down, but keep in mind that oil is viscous and may take a couple of minutes to work. Additionally, be careful that no oil works it’s way too far back into the O2 Amp itself.
   
   
3. Periodically wiggle the knob as your applying the oil, e.g. wiggle it a bit after the screw hole fills with the first drop, wait a minute and wiggle it again as the oil level is going down, subsequently wait another minute and wiggle again after the first drop has completely penetrated, you get the idea! You may just get lucky and it will easily wiggle at this point off as it did for me, otherwise repeat the procedure with a second drop. (Note: You could also use the faceplate to help distribute greater pressure a bit more equally in an attempt to remove the knob, but be careful not to apply too much pressure as you could bend the faceplate or worse!)
   
   
4. If after a couple of drops of oil and several attempts at wiggling off the knob don’t prove successful, simply let it sit for a while as the oil will continue to penetrate. You could consider another drop of oil, but prop the O2 Amp in such a way that the oil will not drip back into the device if you do. I really don’t think it should take this much work for anyone, but I am nevertheless listing the steps that I would take. Whatever you do, I would avoid using heat or direct flame to ‘help’ the oil penetrate! Heat may work great to loosen parts in a mechanical setting, but I would absolutely urge you to avoid this method in an electrical setting! (BTW, Yes! Soldering does get extremely hot, but such heat is highly targeted, quick to cool, and the proximal components are built for heat at those specific locations, e.g. the leads.)
   
   
5. Finally, once the old knob is removed, visually inspect the Pot and remove any excess oil from the shaft with isopropyl alcohol wipes. Once the shaft has been thoroughly cleaned of any remaining oil and/or debris, ensure the alcohol has completely dried, and install the replacement knob. Don’t forget to use a new Allen screw when installing the replacement knob.

That’s the procedure, and yes, I didn’t ‘have to’ be so wordy, but I wanted the instructions to be crystal clear. Just to cover my behind, this procedure is to be done at your own risk, and I am not to be held liable for any mistakes, errors, omissions, or the like. Please, only attempt those repairs that you are comfortable with or that you understand may cause additional damage if done incorrectly.

With all that said, it’s time for me to peace out

 

[Starbound]

I know this is a ridiculously old post, but I actually ran into the very same issue today, literally almost a decade later. I guess that says a lot about the quality of these little amps as they’re still being used in 2022 and even sold band-new. Mine is the Drop variety, BTW. Basically, I wanted to swap the knob out as both of the rubber o-rings have worn-out, cracked, and finally snapped off. This little detail makes it quite a bit more difficult to turn as there is nothing else grippy on such a tiny knob to begin with. I purchased the Black Aluminum Knob by Taiss as sold through JDS Labs for my replacement as it’s (a) far beefier and easier to grasp onto, (b) has no rubber components at all, and (c) actually has a dial marker, something my OEM knob never came with! I am actually curious why Drop’s version of the O2 Amp does not have a dial markers as they make it significantly easier to see exactly where your volume level is currently set at — Hmmm — Anyhow, regarding my upgraded knob, not bad for $5 when considering that I was placing an order with JDS anyways!

So, even after completely unscrewing the Allen screw, it still wouldn’t budge and of course I was using a fair amount of force considering an Alps Pot should be able to take a bit of abuse. I was still not overdoing it as those Alps Pots are not invincible, but won’t break even half as easy as the stuff coming out of China in mass these days. Well, after trying a few ideas something finally hit me — to use a couple of small drops of oil — that’s right, any kind of oil designed for lubricating should work, but I used a couple of drops of Wahl Clipper Blade Oil as that’s what I had handy. The Wahl oil also has a dropper top so you won’t make a mess like you would when spraying a can of WD-40, something I would highly advise against when working near electronic components! A very small and targeted amount of such oil should do the trick, and it did!

Here’s the procedure:

1. Always completely remove the Allen screw from the current knob.
   
   
2. If the knob still cannot be removed from the Pot shaft with a fair amount of force, place 1 to 2 full drops of oil into the screw hole while allowing the oil to penetrate before applying a second drop. You will clearly see the oil level go down, but keep in mind that oil is viscous and may take a couple of minutes to work. Additionally, be careful that no oil works it’s way too far back into the O2 Amp itself.
   
   
3. Periodically wiggle the knob as your applying the oil, e.g. wiggle it a bit after the screw hole fills with the first drop, wait a minute and wiggle it again as the oil level is going down, subsequently wait another minute and wiggle again after the first drop has completely penetrated, you get the idea! You may just get lucky and it will easily wiggle at this point off as it did for me, otherwise repeat the procedure with a second drop. (Note: You could also use the faceplate to help distribute greater pressure a bit more equally in an attempt to remove the knob, but be careful not to apply too much pressure as you could bend the faceplate or worse!)
   
   
4. If after a couple of drops of oil and several attempts at wiggling off the knob don’t prove successful, simply let it sit for a while as the oil will continue to penetrate. You could consider another drop of oil, but prop the O2 Amp in such a way that the oil will not drip back into the device if you do. I really don’t think it should take this much work for anyone, but I am nevertheless listing the steps that I would take. Whatever you do, I would avoid using heat or direct flame to ‘help’ the oil penetrate! Heat may work great to loosen parts in a mechanical setting, but I would absolutely urge you to avoid this method in an electrical setting! (BTW, Yes! Soldering does get extremely hot, but such heat is highly targeted, quick to cool, and the proximal components are built for heat at those specific locations, e.g. the leads.)
   
   
5. Finally, once the old knob is removed, visually inspect the Pot and remove any excess oil from the shaft with isopropyl alcohol wipes. Once the shaft has been thoroughly cleaned of any remaining oil and/or debris, ensure the alcohol has completely dried, and install the replacement knob. Don’t forget to use a new Allen screw when installing the replacement knob.

That’s the procedure, and yes, I didn’t ‘have to’ be so wordy, but I wanted the instructions to be crystal clear. Just to cover my behind, this procedure is to be done at your own risk, and I am not to be held liable for any mistakes, errors, omissions, or the like. Please, only attempt those repairs that you are comfortable with or that you understand may cause additional damage if done incorrectly.

With all that said, it’s time for me to peace out

Is there anything WD40 can't do? Last night I wanted to fry some sardines and I had run out of oil. Guess what? WD40 to the rescue.

I used the WD40 to losen the stuck lock of my pantry to get some oil.

Anyway, talking about removing stuff... I was planning on removing the 9V batteries from my JDS Labs O2, and I was wondering if there is something I should be aware of before I open the unit. Are the batteries hooked with a holder, or are they glued? If so, should I get a hair drier to soften the glue, or should I use WD40 again?

 

[HeatFan12]

After 9 years in storage, I brought her out last night. Still going strong and spankin' all the headphones I throw at her with clarity and detail. I still have the different face plates and a volume knob.

Cheers!!!

 

[garlicky]

After 9 years in storage, I brought her out last night. Still going strong and spankin' all the headphones I throw at her with clarity and detail. I still have the different face plates and a volume knob.

Cheers!!!

Where did you get the faceplate and the red knobs from? Also what do you use to clean the amp itself? It looks brand new and shiny in the picture.

 

[schmalgausen]

Where did you get the faceplate and the red knobs from? Also what do you use to clean the amp itself? It looks brand new and shiny in the picture.

Head ‘n’ HiFi was selling them years ago.

 

[garlicky]

Head ‘n’ HiFi was selling them years ago.

OK thanks

 

[HeatFan12]

Where did you get the faceplate and the red knobs from? Also what do you use to clean the amp itself? It looks brand new and shiny in the picture.

I purchased mine from Mayflower Electronics. They had all the various accessories.

Thanks! I clean all my equipment with screen cleaner then store in plastic containers with lids. Keeps them looking new.