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Thread Starter 
We all know how iRiver think about taking off output resistor like this.
 
“Dear All,
 
I think you guys already known about “RWAK100”
Well, here are our mentions for this issue, please refer to it.
 
If you change AK100’s output impedance into 0 ohm (by taking off resistance)
 
PROS :
1. Sound become powerful.
2. enrich sound of high impedance
3. better balance for Armature unit drive earphone.
 
CONS :
1. Each headset has limitation of maximum output. By reducing impedance of AK100, there could be deterioration of headset and it cause short of circuit. In this case, it consume over 2W electric power and make damage of AK100 circuit.
2. When there is Static Electricity, it can easily damage of AK100. In this case, even it plays but there is no sound.
3. VOC and PL regulation issue will be happed by causing hypacusis and deafness.
4. Even it improves the sound power, it reduces smooth and delicate sound detail of AK100.
 
With these reasons, we do not recommend reducing impedance or any modification by users.
To prevent such unauthorized modification by end user, we use special screw driver for AK100. But if they carry out any kind of changes or modification by themselves and it cause any problem or issue, we are not obliged to provide C/S or A/S.”
 
As main AK100 is mostly for people talking about normal AK100 and I don't wanna trainwreck that topic anymore, I'm posting a new thread solely for talking about how we can intepret what iRiver said into something we can use as good information for possibly improving AK100 modification. I'll try to make some technical analysis to findout what iRiver wanted to say in technical terms. As no one should know about product design or schematic diagrams except iRiver and possibly distributor, what I'm going to post below will be just assumptions based on possibility from research and discussion with technicians who work on audio equipments. You can raise your disagreement with your explanations so we all can try to understand more about this mod. Now I'm going to try how they meant to convey in technical terms one by one below.
 
PROS :
1. Sound become powerful.
Technical analysis: Sign of higher output power. It should give you louder and more powerful sound with that.
 
2. enrich sound of high impedance
Technical analysis: Sign of higher gain. Normally we'd have low or medium gain for portable headphones and high gain for high impedance headphones. This should indicate that we have higher gain after modification.
 
3. better balance for Armature unit drive earphone.
Technical analysis: Most armature units have crossover-network and having r series in signal path is one kind of crossover. By-passing this will have fet output directly to crossover-network producing better balance.
 
CONS :
1. Each headset has limitation of maximum output. By reducing impedance of AK100, there could be deterioration of headset and it cause short of circuit. In this case, it consume over 2W electric power and make damage of AK100 circuit.
Technical analysis: Another sign of output power. This could possibly be output power at maximum hardware limit so using without caution can damage connected headphone that couldn't handle output power at that level.
 
2. When there is Static Electricity, it can easily damage of AK100. In this case, even it plays but there is no sound.
Technical analysis: In dry environment, touching equipments with barehand can cause static electricity so many factories with good standards will wear gloves during assembling but we won't do that with our AK100. When there's static electricity, there're mostly drained to either output connection or ground chasis. Normally we have resistor at output so it'll be drained to another but removing resistor will not have this kind of protection.
 
3. VOC and PL regulation issue will be happed by causing hypacusis and deafness.
Technical analysis: Another boring loudness volume warning. The original AK100 may have resistor at 22 instead of possibly lower value due to this reason? Maybe we can reduce resistor value for better optimal level.
 
4. Even it improves the sound power, it reduces smooth and delicate sound detail of AK100.
Technical analysis: Another sign for higher gain. When it goes beyond optimal level, transient dynamics and linearity will slowly be replaced with harmonic distortion. It's possible that AK100 has current gain design to control output gain through limiting current so by-passing it may have this gain set to maximum level.
 
To sum this up, this mod does the following things below
 
1. Increase output power
2. Increase gain
3. By-passed low-pass filter crossover-network circuit.
4. Removed static electricity protection
 
I don't know if there's more but that's what I can summarize from iRiver's explanations. It maybe not entirely correct but I think it should give us some ideas how to improve AK100 modification based on this analysis.