SEX and grado low impedance phone, newbie question.

[rbruinsma]

This is my first DIY amp project ever, I have ordered a SEX phone amp with the C4S upgrade kit. At the moment I'am using a 20year old SR-30 STAX headphone. I'am looking for a new headphone to buy and tried a Grado GS1000i & RS1i in a music store. I love both headphones but now I'am reading a few posts about low impedance phone in combination with the SEX amp.
I have to less technical knowledge to understand some posts about this subject completely, for example this post: http://www.bottlehead.com/smf/index.php/topic,102.msg403.html#msg403

If I want to buy one of the two grado's, is there anybody who can explain to me in plain English how to modify the SEX to work with the Grado's? Any help on this subject is appreciated!

A little introduction from me:
I'am 35 years old, live in the Netherlands and love music. At the moment I'am listen to CD's on my DENON DCD1290Reference with an Audiolab 8000S amp and my STAX's.

[JC]

Without looking up the Grados, I can at least tell you this much:

The standard SEX amp can be set up to drive loads as low as 4 Ohms.  If built as directed, the headphone jack includes a couple of 120 Ohm resistors in series with the "hot" leads, to meet the IHF standard.  That impedance may be problematic if you use phones of a lower impedance than anticipated by the IHF standard.

In practical terms, this means that you may not wish to wire the phone jack with the 120 Ohm resistors; you may find that a different value is more suitable with your chosen phones, or you may prefer no resistors on the headphone jack at all.  In any case, it is a minor change.

[Doc B.]

Just leave the 120 ohms resistor out and connect the transformer secondary wires directly to the headphone jack instead.

[JC]

Just curious, because I have not taken the time to think this through, but if you didn't want/need the 120 Ohm resistors on the headphone jack, wouldn't that allow the stock headphone jack to be wired to "break" the speaker connections when the headphone plug was inserted?

Again, just curious; sorry if this is not pertinent.

[Paul Joppa]

Just curious, because I have not taken the time to think this through, but if you didn't want/need the 120 Ohm resistors on the headphone jack, wouldn't that allow the stock headphone jack to be wired to "break" the speaker connections when the headphone plug was inserted?

Again, just curious; sorry if this is not pertinent.

Yes, I believe that's correct.

[rbruinsma]

Thanks all for the answers so far, I think I go for the option to leave the 120 Ohm resistors out.

Is there anybody on this forum who has experience with the SEX in combination with a grado GS1000i or RS1i?

[glowboy7]

I have a pair of RS1i's.  They are 32 ohms.  I absolutely love them.  My next purchase is the S.E.X. amp to drive them.