strat96
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2005/12/15 11:18:26
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This may be a dumb question, but anyways, did anyone get a power cord with their power supply? Mine didn't have one. I was very suprised not to see one, since it is required for the unit. I am thinking about going to GC to complain and have them give me one.
I tried the mic out after finding a spare power cord and there was a faint hum, was suprised because I thought it'd be louder. The mic had a bit of a muffle on the low end but other than that it sounded good.
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ohhey
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2005/12/15 11:51:05
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ORIGINAL: strat96
This may be a dumb question, but anyways, did anyone get a power cord with their power supply? Mine didn't have one. I was very suprised not to see one, since it is required for the unit. I am thinking about going to GC to complain and have them give me one.
I tried the mic out after finding a spare power cord and there was a faint hum, was suprised because I thought it'd be louder. The mic had a bit of a muffle on the low end but other than that it sounded good.
Mine came with the power cord, sounds like yours was a return or demo and it just didn't get put back in the box. It's a normal power cord like a PC uses so it's no big deal, I have a huge pile of those things in a box. I have worked on one of my power supplies till the hum is almost gone but the other one still hums even with the same mic. It's the power supply for sure. On mine I had to switch the US/Euro switch to get hum to go away. This may differ with each one as to what position is correct if the build quality is bad so try it both ways. It can't hurt because if you are on 110 that's lower then 220 so it can only go down not up.
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strat96
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2005/12/16 10:47:54
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I went to GC and they gave me a cord no problem. I didn't think there would be because I used to work there years ago and had to do that a couple of times for displays that were sold. OktavaUSA sells these for $900, but I went to Oktava's site and saw that their price is the equivilent of $600-700 USD. I don't know how much it would cost to ship a mic from Russia to the US, but I wouldn't think it'd be more than $50-60. That's a far cry from $900(especially since dealers get their inventory at 30+% below retail).
I finally was able to see the picture of the Russian PS(prodigey.net or whatever had an error on their board). The transformer looks like a inductor that is in the shape of a circle. I am guessing that the circular design helps cancel out any AC hum, noise, etc. Also some of the polarized capacitors look different between the two boards. The chinese has all electrolytic(except for the two non-polarized ones) and the russian has two that are electrolytic for sure and the others may be of a different type of polarized like tantlum or something else. The russian also has a trim pot inwhich I don't see on the chinese PS. My only point being is that both boards look like they use the same circuit design, except the chinese looks like they used cheaper parts and got rid of some parts that wouldn't be needed for the mic to work(but would be needed in order for the mic to work at pro level). I am only judging based off of the graphics, I haven't opened my PS nor do I have any information on the russian other than the graphic. Between the two the russian looks better built, in my opinion. The transformer is kept at a furthor distance from the other components, it looks as if it is easier to work on if something would go wrong with the PS, and probably some of the parts are a little better.
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ohhey
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2005/12/16 10:58:22
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ORIGINAL: strat96
I went to GC and they gave me a cord no problem. I didn't think there would be because I used to work there years ago and had to do that a couple of times for displays that were sold. OktavaUSA sells these for $900, but I went to Oktava's site and saw that their price is the equivilent of $600-700 USD. I don't know how much it would cost to ship a mic from Russia to the US, but I wouldn't think it'd be more than $50-60. That's a far cry from $900(especially since dealers get their inventory at 30+% below retail).
I finally was able to see the picture of the Russian PS(prodigey.net or whatever had an error on their board). The transformer looks like a inductor that is in the shape of a circle. I am guessing that the circular design helps cancel out any AC hum, noise, etc. Also some of the polarized capacitors look different between the two boards. The chinese has all electrolytic(except for the two non-polarized ones) and the russian has two that are electrolytic for sure and the others may be of a different type of polarized like tantlum or something else. The russian also has a trim pot inwhich I don't see on the chinese PS. My only point being is that both boards look like they use the same circuit design, except the chinese looks like they used cheaper parts and got rid of some parts that wouldn't be needed for the mic to work(but would be needed in order for the mic to work at pro level). I am only judging based off of the graphics, I haven't opened my PS nor do I have any information on the russian other than the graphic. Between the two the russian looks better built, in my opinion. The transformer is kept at a furthor distance from the other components, it looks as if it is easier to work on if something would go wrong with the PS, and probably some of the parts are a little better.
I wish some smart person would determine what all needs to be done to the power supply to fix the noise problem.. I just don't know enough about electronics to get it 100% quiet.
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slowjett
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/22 23:07:06
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Hey guys, i fixed it =] Bad Chassis Ground. I got an Octava MKL-2500 today, and it had this stupid hum. Well most people talked about the cable haveing a bad sheilding connection to the mic. That cuased a BIG hum. I fixed that and the hum went down considerably.  Turns out the big Issue is the power supply. This is a chinese power supply, known to cause a real bugger of a hum. Basically rendering the mic unusable. here is the culprit:  Its much smaller than the good russian power supply. I opened up the chassis, and after prodding around inside the power supply a bit with a jumper wire I discovered the issue. It appeared the the mic cables were not grounded propperly at all. Look at my diagram.  Piont A is the ground from the wall plug. B is the common ground lead connected through the metal plate to point A, and then goes to the circut board. Point C is also a common ground, and it should all be on the same circut. When I touched C to A The hum went down considerably. So I figured I could just solder a wire from A to C.. Point B didnt give as good results as shorting A to B. Then I figured points A and B werent makeing good connection to each other OR the chasis. So I took A and B apart and cleaned up all the contacting surfaces to ensure a good common ground over the whole unit. I used sand paper and cleaned up both sides of the plate around the AC converter where the holes were for the screws. Top and Bottom, down the bare metal. Then I cleaned the power supply chassis (houseing) around the screw holes.. Made sure to get right down to the bare metal there also.  I put the unit back together and to my amazment, no more hum! It was a very simple fix, didnt even have to fire up the soldering Iron. Here are the before and after samples. These samples should not be taken to show the clarity/quality of the mic, since it was in a noisy room and I was about 3 feet from the mic sitting at my desk. Any crackling you hear is me moving around in my chair. Plus I killed it with compression so you can hear it =] Before http://joshnoone.com/temp/mkl2500/mkl2500b4.mp3 And After http://joshnoone.com/temp/mkl2500/mkl2500after.mp3 Small samples of each next to each other... http://joshnoone.com/temp/mkl2500/mkl2500b4after.mp3 Turns a not so usable mic, into a great mic. Hope this helps you! Josh
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ohhey
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/23 01:12:56
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I'm going to work on mine again this weekend and see if I can get them to stop huming.
post edited by ohhey - 2006/03/23 11:23:30
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losguy
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/25 12:59:10
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ORIGINAL: slowjett
Hey guys, i fixed it =] Bad Chassis Ground.
Piont A is the ground from the wall plug. B is the common ground lead connected through the metal plate to point A, and then goes to the circut board. Point C is also a common ground, and it should all be on the same circut. When I touched C to A The hum went down considerably. So I figured I could just solder a wire from A to C.. Point B didnt give as good results as shorting A to B. Then I figured points A and B werent makeing good connection to each other OR the chasis.
So I took A and B apart and cleaned up all the contacting surfaces to ensure a good common ground over the whole unit. I used sand paper and cleaned up both sides of the plate around the AC converter where the holes were for the screws. Top and Bottom, down the bare metal. Then I cleaned the power supply chassis (houseing) around the screw holes.. Made sure to get right down to the bare metal there also.
Great work, Josh. It's always fun to pop open the covers and see what's inside. Looks like an elegant solution. Something else to try: Moving the wire at point B to point A (or vice versa) would provide a more common grounding point, which could improve things further. The wire going to point B looks like it has enough slack to reach point A. So, if both of the lugs fit on the same bolt, it would be easy to try it that way too.
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ohhey
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/25 23:15:14
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Josh.. Woo Hoo ! I got both of mine fixed. I also tried moving both wires to one post as losguy suggested, the wire does reach and it gives me more confidence that they will stay fixed. By the way, on mine the power supply makes some audible (transformer) acoustic hum so when you test you need to have it far away from the mic to get a good test or you will hear the mic picking up that hum at high gain. Otherwise you might think it's still in the siganl. The noise floor on my mics is still not as low as some of my other mics but they are usable now and before they were not. I'm going to try cleaning flux off the bias resistor leads next that can cause noise. I still have my flux remover pen from my last build a mic project and I think it's still good. Thanks to everyone that helped on this project.
post edited by ohhey - 2006/03/25 23:23:54
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losguy
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/25 23:37:10
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I love it when, even in this day and age of disposable high-tech, we can still heat up a soldering iron or twist a nut and get something working for cheap.
O/T, but my latest was modding the sustain pedal on my (now dated) Oberheim Eclipse piano. Mostly a good 88-key controller, but the cord on the triple pedal wasn't done very well. So, I snipped a MIDI cable and rewired it the way I liked it to be, and now it's solid like a tank.
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ohhey
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/26 00:31:06
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ORIGINAL: losguy
I love it when, even in this day and age of disposable high-tech, we can still heat up a soldering iron or twist a nut and get something working for cheap.
O/T, but my latest was modding the sustain pedal on my (now dated) Oberheim Eclipse piano. Mostly a good 88-key controller, but the cord on the triple pedal wasn't done very well. So, I snipped a MIDI cable and rewired it the way I liked it to be, and now it's solid like a tank.
My favorite pedal was from a Liner dictation machine, it's wedge shaped so you don't have to lift your foot so high and it's super quiet, no clicking sound. It also has a huge chunk of pot metal for the base so it's heavy and stays put. All I had to do is cut the plug off and put a 1/4" plug on it. It has an inset smaller pedal also on one side and on my old AKAI AX-80 synth I use that for the "next program" switch.
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losguy
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/26 12:56:13
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That's cool, Frank. I also like my pedals to stay put, feel solid and smooth, and not make noise when you press them. It's silly how such basic things escape most pedal makers.
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oktavuh
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/03/26 16:44:16
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If you're seeking a hum fix PLUS a really great mod for the 2500, I suggest checking out OktavaMod.com. Specifically: http://oktavamod.com/othermods.html Well worth the effort and (modest) expense.
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strat96
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RE: Fake Oktava MKL 2500 from GC hum, fixed !
2006/04/20 20:33:17
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ORIGINAL: slowjett
...
I put the unit back together and to my amazment, no more hum! It was a very simple fix, didnt even have to fire up the soldering Iron.
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ORIGINAL: ohhey
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The noise floor on my mics is still not as low as some of my other mics but they are usable now and before they were not. I'm going to try cleaning flux off the bias resistor leads next that can cause noise. I still have my flux remover pen from my last build a mic project and I think it's still good.
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I soldered point A to point C and the hum went down to around -40 dB(Comparable when light singing/humming registers on the mic at -6dB and you can't notice hum in the signal at that point). When I touch the mic the hum goes up. At this point I may be able to get away with a tight gate on the mic, but I will try to clean up the screws and make sure everything is grounding. Just for reference I read that there is floor noise, what dB level is the floor noise registering at? Thanks, Jason
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