solderdude
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Post by solderdude on Dec 5, 2013 9:10:15 GMT
 Measurements of the stock K551 below. Basically almost an K550 but with a mic and remote added in the cord, slightly different colour scheme and shorter cable (intended for portable usage)  Quite good isolation. It runs down VERY deep even down to 5Hz (did not measure lower). The highs are a bit 'off'. the upper mids/lower treble is lacking a bit resulting in a bit 'incomplete' sound when compared to headphones that do not have these issues. The dip around 5kHz is actually a resonance. Have been playing with it for a while and now have it measuring this way:  The mods are: Lacing the inside with white felt (did not change anything at all FR nor CSD wise) Used the HD681-EVO felt discs in front of the driver (perfect !) Made a small filter that 'flattens' the lower mids/lows. I have to say I like this headphone a LOT now and seeing it is very close to the filtered T50RP and it doesn't need an amp to be driven well it is a great sounding headphone now. I figure the K550 can possibly benefit from the same mods. |
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Dave
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Post by Dave on Dec 5, 2013 14:03:42 GMT
Hi Frans,
The second set of measurements show great improvement and I am greatly encouraged by your favourable comparison with the filtered T50RP which I know enjoy a great reputation with both you and Ian.
Regarding your mods: -
"Lacing the inside with white felt (did not change anything at all FR nor CSD wise)
Used the HD681-EVO felt discs in front of the driver (perfect !)
Made a small filter that 'flattens' the lower mids/lows."
can you provide me with a bit more information that will enable me to identify the two items of felt please and perhaps a schematic of the small 'flattening' filter that I can ask Sean to quote for?
TIA,
Dave.
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Rabbit
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Post by Rabbit on Dec 5, 2013 14:53:03 GMT
Frans, I use the mk2 HD681 filter to 'calm' the top. It might not be flat but I much prefer it to the K550 as it is.
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solderdude
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Post by solderdude on Dec 5, 2013 14:53:25 GMT
When I have finished modding and finalised it I will publish everything in a pdf.
I use the felt disc from the HD681-EVO to tame the top... a perfect match.
Because the dip around 5kHz is also a resonance the dampening action of the felt cures that too (ringing is shorter).
An electronic filter just lowers the dip and doesn't work as well as it does for the HD681.
The bass flattening filter consists of 1 capacitor and 1 resistor.
Final values will be known when I have listened to it and measured it intensively.
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Rabbit
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Post by Rabbit on Dec 8, 2013 11:48:02 GMT
Actually, the Mk2 filter is good with it. I've been using it now since I got the Mk 3 to lower the bass on the HD681. The Mk 3 is too much for the K550 tbh, but the Mk 2 tames the treble while still leaving the extension. It makes into a much nicer headphone and yet the changes aren't massive; just enough to take that top sting down so that the K550 is my favourite closed headphone as long as I have that filter on!!
I forgot to mention it to you Dave since I know that you're not keen on the K550. With the filter, it's a gorgeous headphone. I'm sure once Frans has 'flattened' it, it'll be even better.
It's the best closed headphone I have for home use. I prefer it to the HD250 II as well.
Having the top slightly tamer means that it focuses at a louder volume better and so the bass is warmed up quite a lot too as a result. It just blooms a bit more, which I really like.
It would be interesting to see what that filter is doing to it Frans. It's a very pleasant sound.
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solderdude
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Post by solderdude on Dec 8, 2013 21:01:50 GMT
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Rabbit
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Post by Rabbit on Dec 10, 2013 16:53:34 GMT
Here's another funny 'mix and match' - the Mk3 filter with the Sony V6 works quite nicely. It takes the top edge and possibly shaves a little bass hump away at the same time!!
Those filters are really useful Frans. They have a calming effect on many headphones in the treble!!
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solderdude
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Post by solderdude on Jan 8, 2014 14:09:59 GMT
Because not everyone is willing to buy and sacrifice a set HD681-EVO to salvage the felt discs, I have been looking for some alternatives. I found 2 mm thick acrylic felt and 3 mm thick wool-felt which both perform very similar (measurement- and sound-wise) to the EVO felt.  blue = EVO felt orange = 3mm thick wool-felt (not acrylic) The FR above is of a modified K551 so NOT just the felt discs but also internal damping and electronic filter components. I suspect this to work equally well for the K550 which is the same headphone but with a longer cord and no remote/mic. For our forum members I am offering a set of 2 handmade (so not nicely round !) felt discs for this mod. price (included shipping) will be a whopping € 2.- when paid with IBAN/BIC and when paid with PayPal € 2.40. Will be shipping to all countries. Alas the biggest portion of this price are the shipping costs and PayPal fees  € 1.- = around GBP 0.85 € 1.- = around $ 1.35  I will only have a limited amount of discs in stock and when out of stock might take a few days to buy felt in 'desired' colours. At this moment I have some black felt. PM me if interested and to see if I have any in stock. Another option is to look for 3mm thick wool-felt in craft shops. The material itself usually isn't very expensive. |
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Rabbit
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Post by Rabbit on Jan 8, 2014 17:10:42 GMT
The ability to measure headphone response is such a bonus, Frans. That way, you know that it's closer to what you aim at rather than a guess job. I must admit that I'm less and less keen on modding without really knowing what it does since some of the mods that you see change one aspect but introduce another. (ie ringing) If you can't measure and therefore see what is going on, it's just an 'alternative' sound rather than 'better' imo.
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Post by snowtiger on Mar 16, 2018 11:00:16 GMT
Hello solderdude,
I followed your instruction to modify my K551, because the provided cable broke, so I had to do a cable mod anyway. So I combined your filter mod and a detachable cable mod. Now I have two questions:
- Is it still possible to order the felt discs?
- I must have done something wrong when soldering, because I can hear the left chanel on my right ear. Right chanel is only on the right ear. Do you have any hint for me?
regards, snowtiger
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solderdude
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Post by solderdude on Mar 16, 2018 11:06:34 GMT
I still have felt left.
You can contact me via PM.
Just click on 'solderdude' above my avatar.
Swap the L and R incoming wires, or when the plug can be opened just swap the ring and tip wires.
Ring = Right channel
Tip = Left channel
Sleeve = common = ground
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Post by snowtiger on Mar 16, 2018 12:13:58 GMT
OMG, thanks for your super fast answer. I checked the cables on the 3.5 jack port and changed ring with sleeve and now it works like a charm.
I will contact you via PM for the felt.
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dahbs
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Post by dahbs on Sept 15, 2019 22:24:18 GMT
Hi, i'm a new member. I build and repair pc for fun (for family and friends) and this is the first time I try to fix audio stuff. Few days ago I received a pair of AKG K551. If i connect them to my AVR I can hear something, but it's a strange sound (no voice, music seems very far, like is coming from another room and the wall filters it). I opened the left pad and I did this image to compare the wires I found in a pic from the web versus the current wires (current wires go to a female jack...someone probably tried to replace the original male cable with a female cable?)  Maybe I just need to solder a new (male) cable...but first I need to know which is the function of the original white wire. Thanks |
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solderdude
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Post by solderdude on Sept 16, 2019 19:19:35 GMT
That would explain the weird sound.
It seems like the common wire is missing/broken.
The upper picture shows how it should be wired.
The headphone cable must have 3 wires.
Tip (Left channel) must be connected to L+
Ring (right channel) must be connected to R+
Sleeve is common for both channels and is missing here. It should be connected to LR-
Then there is the thin cable from the right cup.
These should be connected as shown in the upper picture and seem to be correctly mounted in the bottom picture.
Once the 'sleeve' is connected again it'll work as it should.
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dahbs
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Post by dahbs on Sept 29, 2019 13:18:42 GMT
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