Just a reminder, the hunt is still on for 95-100mm pads with actual 60mm inner holes... Velour or other soft material is preferred inside the hole, to lessen the upper-mids peaking. I have inquired of four sellers in the past week, asking them for actual measurements of their 60mm-advertised...

I think the best way to deal with the the rather harsh peak (it's closer to 4kHz with the damping mods) on these phones is with EQ. The damping mod lessens but doesn't eliminate it.

No longer for sale

Offered here are my AKG K240DF Diffuse Field Studio Monitor Headphones. I am only the 2nd owner of these. They sound great and I know their complete history. I bought them in the late 1990's from a musician buddy who used them in his home recording studio. They sounded great but one earpiece...

Yet another update: Mistakes happen. I recently discovered that I used the wrong calibration file for the network analzyer when making one of the measurements. I redid the measurement. Fortunately, the differences were minor and only two components in the optional passive filter circuit changed...

Another update: A more accurate way to correct for the tonal imbalances of the SRD-7 / SR-X MkIII combo is with digital EQ, such as the excellent (and free) Equalizer APO (https://sourceforge.net/p/equalizerapo/wiki/Documentation/). Configuration and filter files for the EQ have been added to...

Thanks. I've already completed the article, linked to in this thread: Stax SRM-252S Driver Unit Upgrade

Update: Recent communication with someone doing the mods to their SRD-7 made me take a closer look at the situation regarding the parallel LR circuit at the input. I had perhaps not made it clear enough that this input filter is ONLY needed with the SR-X headphones. This was based on using it in...

I didn't concentrate on them, I was looking for big fish, not minnows :) But I think the 50k pot is too high, I'd prefer 10 or 20k. R1 lowers it to 28k, so I left it. Pot + R3/C1 is an input lowpass filter, I live a mile from radio transmitters, so I'd rather have something there than nothing...

OK, that's great, you were definitely heading in the right direction. Your HVPS Z curve is similar to the "Tidy" one except higher due to the 2nd 470Ω still being used. So it will still be very worthwhile to complete the mods. It turns out, the film bypasses do nothing to reduce the switching...

That's clever! Yes, changing the feedback R is the easiest way to get a taste of what's to come. If you have any green LEDs laying around, change D7 and D8 for the extra current until the other parts arrive. Even quicker and easily reversible is to solder a 600KΩ across the existing 300k. The...

Not true. Circuit context does matter. I've tried and tested several of them, and my measurements and listening say that any reasonably-regulated supply is just fine here for the raw -12V. Some of the advantages of using something like a Jung super-regulator (super-low output impedance) are...

1. Sir, you are the one conflating the issues. Your "easier and safer" suggestion only relates to choosing which 12V power supply to use. The circuit mods are a separate matter. The supply you're recommending is good enough and will work fine but it is not any safer and is frankly overkill in...

If someone is not comfortable working with electronic circuits, then it goes without saying that this mod is not for you. Don't undertake this as a "first project". The mods do not compromise the amp's safety or reliability in operation. Do you have something besides scare-mongering to bring to...

It is baseless and irresponsible for you to assume those risks are present for the alternatives I suggested.

Why "easier and safer" ?

Link to the BOM is posted now, just before the parts list..

Am working on it... may be a couple days yet.

I just completed these detailed mods for the SRM-252S amp: Upgrading the Stax SRM-252S Comments/questions welcome.

I just posted a detailed upgrade for the SRM-252S: Upgrading the Stax SRM-252S Comments/questions welcome.

This is not worth starting a new thread for, there aren't many K240DF-related threads, so I'm piggybacking on this one. Back when the K240DF's were designed and made, there was a DIN spec/standard (can't recall the number) that most if not all European headphone makers adhered to. It defined a...

I just completed these detailed mods for the SRD-7 adaptor: Transforming the Stax SRD-7 Comments/questions welcome.

Not sure if this is the right forum/thread to post this, but I just completed these detailed mods for the SRD-7 adaptor: Transforming the Stax SRD-7 Comments/questions welcome.

I received the pads mentioned in the previous post. This is why you ALWAYS should ask the seller to verify any important dimensions. The 95mm pads were listed as having a 58mm inside hole. The pair I got had 40mm. I don't understand how some of these Chinese sellers think they can get away with...

My apology in advance for the photos, the camera badly overexposed them, making the pads look filthy. These were the first pads I bought early last year, long before doing any mods. The seller is no longer around, but the listing, specs, and photos are identical to this one...