[Head Injury]

  A question regarding the practical implications of this information:  What portable headphone amps work well with Orthodynamic headphones?  Here, I assume that the question is about which portable headphone amps have high voltage current more than it is about their wattage (as long as they give close to 500 mw per channel)?  
 
I recently got some Mad Dog headphones, and I found it interesting that they are driven better by the internal amp in my iBasso DX90 than by a Bottlehead Crack amp (showing again that OTL is not good for Orthos).  Still, they could use a boost from the DX90, hence the question about a good portable amp for orthos.

If it's about high voltage and current, it's also about high power. Power = Voltage * Current. How much voltage you'll need versus current for the right amount of power depends on the headphone's impedance, since Power also = Voltage^2 / Impedance (so lower impedance means less voltage, and by extension more current). How much power is the right amount of power depends on the headphone's sensitivity, which is usually given as dB/mW.
 
Taking all that into account will determine what kind of portable amp you need. Every headphone will be different. Orthodynamic headphones don't present any new challenges, they just happen to have low sensitivity compared to a lot of dynamic headphones. An amp that works well for dynamic will work well for orthodynamic, if it has the right amount of power, voltage and current.
 
Tyll's measurements of the Mad Dog found here can help you find the impedance and sensitivity. He measures the amount of voltage and power needed to reach 90 dB. You should aim to have enough for 110 dB to be safe. You need to multiply power by 10 for every 10 dB, and voltage by the square root of 10 (or 3.16) for every 10 dB. So you'll need to multiply Tyll's measurements by 100 for power and 10 for voltage, giving you the requirements of 92 mW at 47 ohms, or 2.1 Volts. If the portable amp can manage that, you should be OK.
 
500 mW per channel is overkill for everything but the HE-6.

 

[srkstan]

 
If it's about high voltage and current, it's also about high power. Power = Voltage * Current. How much voltage you'll need versus current for the right amount of power depends on the headphone's impedance, since Power also = Voltage^2 / Impedance (so lower impedance means less voltage, and by extension more current). How much power is the right amount of power depends on the headphone's sensitivity, which is usually given as dB/mW.
 
Taking all that into account will determine what kind of portable amp you need. Every headphone will be different. Orthodynamic headphones don't present any new challenges, they just happen to have low sensitivity compared to a lot of dynamic headphones. An amp that works well for dynamic will work well for orthodynamic, if it has the right amount of power, voltage and current.
 
Tyll's measurements of the Mad Dog found here can help you find the impedance and sensitivity. He measures the amount of voltage and power needed to reach 90 dB. You should aim to have enough for 110 dB to be safe. You need to multiply power by 10 for every 10 dB, and voltage by the square root of 10 (or 3.16) for every 10 dB. So you'll need to multiply Tyll's measurements by 100 for power and 10 for voltage, giving you the requirements of 92 mW at 47 ohms, or 2.1 Volts. If the portable amp can manage that, you should be OK.
 
500 mW per channel is overkill for everything but the HE-6.

Thank you very much for this info - it is extremely helpful.  Two questions - 1) 92 mW into 47 ohms equals how many mWs into 32 ohms (I notice that most portable amps give wattage in terms of a 32 ohm load); 2) In terms of volts, you are referring to the output level, correct?  So, the DX90 specs give output levels of 1.7 Vrms (low gain), 2.0 Vrms (mid gain), and 2.8 Vrms (high gain).  Indeed, on high gain, most recordings are fine - some are a bit lower volume, but the majority sound good, at least if I have my volume maxed out or close to maxed out.  

 

[Head Injury]

 
Thank you very much for this info - it is extremely helpful.  Two questions - 1) 92 mW into 47 ohms equals how many mWs into 32 ohms (I notice that most portable amps give wattage in terms of a 32 ohm load); 2) In terms of volts, you are referring to the output level, correct?  So, the DX90 specs give output levels of 1.7 Vrms (low gain), 2.0 Vrms (mid gain), and 2.8 Vrms (high gain).  Indeed, on high gain, most recordings are fine - some are a bit lower volume, but the majority sound good, at least if I have my volume maxed out or close to maxed out.  

You can use the voltage to figure out how much power into 32 ohms, using the second formula I posted. Power = Voltage^2 / Impedance, so here Power = (2.08^2) / 32 = 135 mW. Since we already know the power needed at 47 ohms you can also just multiply that power by 47 then divide by 32. That'll give you the same thing.
 
It's possible the DX90 can't swing its maximum rated voltage at 47 ohms, the maximum is usually tested into very high impedance loads. Either that, or you like to listen really loud.

 

[srkstan]

Actually, I think my original problem was brain burn-in.  After a day of listening, it now sounds like the dx90 offers plenty of power for the Mad Dogs.  If I have it at high gain, which is 2.8 Vrms, I no longer find myself going to full volume.

 

[ChopperCharles]

I don't know about all of the technological talk in this thread, but I do know that my Koss HV/1's modified with Yamaha YH-3 orthodynamic drivers need a TON of wattage to get to the same SPL as say a bone stock Koss HV/1... or really any other headphone I own. I've got a 65 watt amplifier (Toshiba SC-665) and a 70 watt amplifier (Pioneer SA-720) and I need at least 2/3 volume to get a nice loud listening volume. I have a Panasonic RA-6500 12 wpc receiver that cannot drive these headphones to any usable volume level. Twist the volume dial high enough to get a decent volume, and the amplifier is distorting. Poor little STK-040 power packs just can't provide the needed juice. Needless to say, hooked up to an iPhone the headphones are at a pretty low volume level even with the iPhone maxed out. I can hear it well enough, but it's not loud enough to drown out a work environment, much less a train or bus ride.
 
Charles.

 

[obobskivich]

I don't know about all of the technological talk in this thread, but I do know that my Koss HV/1's modified with Yamaha YH-3 orthodynamic drivers need a TON of wattage to get to the same SPL as say a bone stock Koss HV/1... or really any other headphone I own. I've got a 65 watt amplifier (Toshiba SC-665) and a 70 watt amplifier (Pioneer SA-720) and I need at least 2/3 volume to get a nice loud listening volume. I have a Panasonic RA-6500 12 wpc receiver that cannot drive these headphones to any usable volume level. Twist the volume dial high enough to get a decent volume, and the amplifier is distorting. Poor little STK-040 power packs just can't provide the needed juice. Needless to say, hooked up to an iPhone the headphones are at a pretty low volume level even with the iPhone maxed out. I can hear it well enough, but it's not loud enough to drown out a work environment, much less a train or bus ride.

Charles.

You can't really use "volume level" or the setting of the volume button/dial/knob/slider/whatever as any correlate to actual power output or requirements - things like gain, input sensitivity, output from the source, etc all heavily influence that discussion and make these kinds of comparisons impossible. I'm not at all doubting that you've created a very insensitive headphone that needs a fair bit of power, however.