Yep. I’ve already put the mod on mine. My MK-012 came from GC about 2 months ago and the ‘leaky’ caps you see in the picture had already been changed to decent electrolytics. I only had to replace these parts: the FET with a 2SK170; the 680Ms with two 1Gs in series (to make a 2G resistor); the 680pF (C1) with a 820pF, NPO cap.Middleman said:
When removing the parts, I have better luck with the braided solder wic instead of a vacuum solder puller. If you use a puller, you run the risk of removing traces. To use the wic, place it over the connection and apply the iron, pressing the wic into the joint. The solder should melt and suck up into the wic. The trick to doing this is that you need to wet the wic or the connection with flux before heating it. If you don't have any flux, the next best thing is to melt a little new solder onto the connection before you remove it. Even though you're adding solder to the connection, you're also adding flux which makes it take to the wic easier. BTW, I’d use a small wattage iron, maybe 20-25 watts.bongolation said:
It isn't actually a 'color', it just has "BL" at the end of the part number to indicate it's "drain" current. BL is 6-12mA. There's also a "GR", 2.5-6.5mA, and a "V",10-20mA. This particular circuit needs the 6-12mA version.bongolation said:
Yes, but they're apparently color-coded: B/BL=blue, G/GR=green and V=violet. Per a post from Scott in a FET discussion on r.a.p.Flatpicker said:
Supposedly, this is the most critical and difficult part of the operation, the defluxing/decontamination and conformal coating of the surfaces which are at least momentarily perfectly clean and bone-dry. Without the coating, almost any contamination or condensation will cause short across the Hi-Z circuit. Almost anything is a short compared to a 1G-3G resistor!Flatpicker said:
I know he says that, but I've bought several and there's no color on them - just a "BL" at the end of the part number.bongolation said:
I'm laughing at the "tech geniuses" part,Rev E said:Any of you tech geniuses interested in modding my Octavas for a modest fee. I am solder-iron-challenged, so reading about this stuff isn't going to do me any good. I'd be willing to buy all the parts and pay a modest fee to anyone interesed in modding mine. If you want, you can send me a PM.
but yeah, I'm interested. Feel free to PM me about it.
I don't know diddly, but I'd think that the only critical part of the circuit, impedance-wise, would be from the capsule to the FET, which is probably a wire, a resistor and the gate leg of the FET and associated circuit board traces, so that's the only part that needs to be defluxed and clean. After that it's a low impedance circuit.bongolation said:Supposedly, this is the most critical and difficult part of the operation, the defluxing/decontamination and conformal coating of the surfaces which are at least momentarily perfectly clean and bone-dry. Without the coating, almost any contamination or condensation will cause short across the Hi-Z circuit. Almost anything is a short compared to a 1G-3G resistor!
Apparently, cleaning the existing flux is no picnic, if it came with grunge from Tula. Scott's told me in the past that this was pretty tedious. All the components must be seriously sanitary. This is the one reason I haven't done any upgrading on my Oktavas.
The coating is helpful in humid environments as far as self noise is concerned. But unless you’re in a damp basement or something it may not be that critical. Here in my room the humidity is 53% and the mic is exhibiting a very low S/N ratio, probably lower than any other mic I have.bongolation said:...Without the coating, almost any contamination or condensation will cause short across the Hi-Z circuit. Almost anything is a short compared to a 1G-3G resistor!
Good point. I have an DVM that measures up to 2G. When I get a minute, I'll open one up and see what it reads. Probably wouldn't hurt to do some cleaning with alcohol afterwards.bongolation said:
Exactly, which is why I'm waiting until winter (~20% humid) to coat mine.
The real hassle is when the flux and/or contamination has been sealed in place from the factory with conformal coating over it, as happens in some of the older Oktavas.
You can do it! Really, it's not brain surgery.Middleman said:
Buy some solder wic, a cheap cleaning brush and take your time. Follow the instructions in the magazine and the ones I wrote above. I guarantee you it'll end up much cleaner then it was to begin with. ).
