[pkjames]

Dear DIY fellows:

Okay, new project for me, I somehow found my missing IPOD 4G recently, and since I own a 5G already I decided to IMOD the 4G.

Now, the sole idea of the IMOD is to bypass the stock coupling capacitor at output stage and feed it with some damn nice caps such as the black gate or Nichicon muse.

As I will have to order some black gates from the US (damn, can't find any black gates or similar stuff from syd, if you happen to know where I can find them in AU, please do let me know), I will have to know exactly what capacitence I need to buy.

According the RWAudio, they uses the "Non-Polarized NX-Hi-Q coupling capacitors", so here is the question: do you know what specifice value of the black gate do they use? If I use higher values, does that mean I will get stronger bass but slower response? I may just get a couple of those and try to IMOD the IPOD myself!

Thanks in advance,

Sincerely,
James

 

[NelsonVandal]

I don't know about iPod, but I got some 47 uF 6.3 V for my iRiver IHP120. The default in iRiver is 46 uF and they look like tantalums (in series with a 46k resistor). Also, I couln't fit any larger Hi-Q's than 47 uF.

Here's another HeadFier who used the same value:
http://www.head-fi.org/forums/showpo...7&postcount=15

If I understand it right you should have a very low cut off frequency using this.

http://en.wikipedia.org/wiki/High-pass_filter

f=1/2piRC
R should be input impedance of the amp 10 kOhm or something like that.
f=1/2xpix10000x0.000047=3Hz

Even when I plug in my 300 Ohm Senn's to line out, the bass sounds fine.
f=1/2xpix300x0.000047=11Hz
No wonder there's a lack of bass when plugging in 32 Ohm phones (there's also distortion due to the lack of current)
f=1/2xpix300x0.000047=106Hz

Have I got this right? I'm definately no electronic wiz, and there's a high risk I got it wrong.

 

[pkjames]

Did a bit of research, here is waht I came up with:

The calculation is correct, but the chocie of cap value should not based on headphone impedance.

Reason is: coupling capactiors really depend on the appliaction.

For Line out, the typical R selection is 47K, so
f3db = 33.9Hz (0.1u) or 7Hz (0.47u) or 0.07Hz (47u)
Or if Rout = 10K, then
f3db = 159Hz (0.1u) or 33.8Hz (0.47u) or 0.3386Hz (47u)

For HP out, the typical input impedance is say, 32ohm
f3db = 23Hz (22ouF)

Conclusion:
Quote:

Even when I plug in my 300 Ohm Senn's to line out, the bass sounds fine. f=1/2xpix300x0.000047=11Hz No wonder there's a lack of bass when plugging in 32 Ohm phones (there's also distortion due to the lack of current) f=1/2xpix300.0.000047=106Hz

So, your calculation is correct in sense that you are directly using the DAP to drive the headphone, that is the reason that you can hear sound from LINE OUT (which not suppose to) but since we will use amp for sure, the idea is, depending on the output resistor value, choose either 0.1u or 0.47u.

Also, normally the input impedance of an amp is around 100k to 500k, therefore we can almost certainly get a damn good -3db cut off.
15Hz for 0.1u @ 100K.

Hope I got it right

 

[NelsonVandal]

Many portable amps seem to have 5 - 10 k input impedance, that's why I used it in my example.

I know the line-out isn't meant for headphones. It was just an example. But... the line-out from iRiver drives my Sennheiser HD650 well, very well. Any amp will have a hard time to compete to this. I know this is an extreme impedance mismatch, but I like the sound of "no-amp" - I don't like coloration. E.g. a CMOY or a PINT does nothing but degrade the sound. It has to be something better than that. Most of the time I use an open loop buffer.

iPod owners, have you ever tried your 300 Ohm headphones from line-out?

 

[pkjames]

so, you really driving the senn without amp?
then 47u seems a very good choice

I think 100u BG Ns could also be considered in such app.

 

[Logistics]

Quote:

Originally Posted by NelsonVandal /img/forum/go_quote.gif Many portable amps seem to have 5 - 10 k input impedance, that's why I used it in my example. I know the line-out isn't meant for headphones. It was just an example. But... the line-out from iRiver drives my Sennheiser HD650 well, very well. Any amp will have a hard time to compete to this. I know this is an extreme impedance mismatch, but I like the sound of "no-amp" - I don't like coloration. E.g. a CMOY or a PINT does nothing but degrade the sound. It has to be something better than that. Most of the time I use an open loop buffer. iPod owners, have you ever tried your 300 Ohm headphones from line-out?

Wow, you've tried a cMoy as well as a Pint in front of your iRiver and it did not sound good to you?