Any solutions for hum reduction after removing two layers of inner mesh? I have ground the paint off the headbasket base and strengthened the solder joints, tightened screws and tube base solidly but my mxl definitely now has a hum issue that it doesn't have if I swap to an unmodified basket. Other mods show obvious improvements so I'm very happy overall, but I can hear a quality to the modified basket signal I suspect I'll like if I can just get past the hum...

Thanks

The Dutch site linked to earlier in the thread has a procedure to reduce hum among other things.

Thanks, I'll try the 4.7uf electrolytic bypass. Anyone know a better solution, Jim Williams doesn't seem to be using it on his mod and I know he's a stickler for noise removal...

Great to see this thread thriving! Thanks to all for contributing. I've been out of the loop again for awhile, trying to save more money for gear, so I've missed some interesting movement on this thread since away...

Props to Jim and the gang at Microphone parts for putting together the mod kit; I will definitely be purchasing one in the future! This is how a community of interest can make something move.

I've currently got my SP1 apart again on the bench to run down a bug from the last round of mods; fun fun! If I can't figure it out, I'll post some info and see if the local genii can't shed some light on my fu%k ups.

It's really fun to see everyone participating in the mods process, trying out new parts, even getting into redesigning the circuit. I've learned so much, mostly from the other participants, and owe as much for the help I've received from others as well.

Let's keep this rolling...

@dariuso, have you been testing the mic after fully reassembling it? Mine always hums like the dickens when I have the body apart. Oh wait, I see you're dealing with an MXL, not the SP1. Similar solutions, though; let us know how that bypass works out...

EDIT: Don't see the mod kit link at mic parts.com yet, looking forward to some further info when it comes out, with pricing, etc. I imagine the kit will be worth the searching you have to do to find the 305 and other rather esoteric replacement parts, like the matched transistors. Again, Props to Jim and the microphone-parts.com crew!

Wow. What a great thread. I don't often read every post in a multipage thread, certainly not in one sitting, but I just now finished doing just that. Yesterday I replaced some bad caps in my one of my DAW's lcd monitors that had failed ($2 in caps saved me the $200 cost to buy a new one) and was inspired to dig out the two SP1s that I purchased years ago for $29.00 each and pick up where I left off researching their modification. There's so much more information available now and this thread is a treasure trove. Discovering that I can now replace the capsule in addition to the components is awesome.


I'm also hoping the Microphone-parts.com kit is listed soon. In the meantime I'm wondering about voltage ratings on these caps. I don't see any in the BOM. Also, when choosing to remove a component how do you maintain continuity, a simple wire jumper?

Thanks for the post!
When replacing caps, I usually look to match or exceed the rating of the existing part. You can calculate or look up the values from the ID number on the old cap. Just don't replace with something way lower in value. Also, I think one of the posted schemos shows values for some of the caps.

Yes, you can jumper over a removed component with a bit of wire.

I've not been updating the BOM, as I'm lucky enough to have a great local store that stocks a wide variety of parts (they didn't have the 305fet though, lol). So I haven't really had to order anything online for parts, and since I don't have easy access to a scope I can use to rebias, I've just been tinkering with the simple mods, and replacing suggested components in the circuit. I've yet to replace the fet or transistors, though I'm quite pleased with the results of the mods I've done so far. I'd actually been using the mic more than modding it recently, but I couldn't resist tinkering with it some more, and recently I screwed it up while I was working on it. Now I'm troubleshooting it instead of using it (iiiiiiiiidiot!). Too busy to do much with it at the moment.

When the mod kit is released, I'm sure we'll see some examples of it appear online. I'll certainly buy one if the price looks good. The value in a mod kit comes from the minds of folks like Jim (thanks, Jim!) who create it, then focus, clarify, and implement that design, and in the convenience of getting those exact suggested parts in one swoop from the supplier, which kicks ass. Looking forward to it.

I modified mine but it doesn't sound quite "right" so I'm hoping Jim Williams will chime and tell me what I can add/do to make it as it should. Here's what I did:

Replace the 2SK170 (T3) with Siliconix J305
Replace the 2N5401 output transistors with Hitachi 2SA1084's (T1 & T2)
Replace 1G ohm resistors with Mini Mox metal oxides (R9 and R10)
Replace the 150 k resistors with 100 k Dale CMF55 (R3 & R4)
Replace the 2.2 k resistors with Dale CMF55 (R6 & R7)
Replace the .33uf output caps with 1uF stacked mylar (C3 and C4)
Replace 47uF/50V capacitor with Panasonic FR 100uF/50V (C5)
Replace 220uF/25V capacitor with Panasonic FR 330uF/25V (C6)
Replace high frequency roll-off capacitors with 470pF mono ceramic (C14 and C15)




Should I bypass the electrolytic capacitors? If so, what should I use? Should I replace the ceramic cap feeding the capsule with something else?

Thanks for the help

Did you rebias after replacing the fet?

I would definitely replace that C13 cap going to the fet.

I did not re-bias...any steps on how to do this?

Can you bypass the C13 capacitor completely, or is that only with a capsule swap?

That might be part of it...

Here's what else I've gathered I'm missing:

R5: 3.92K
D3: 9.1V Zener
R1 and R2: 56.2 ohms

Remove R8 and short it out with a wire
Connect wire form the backplate of capsule to that
Remove C13 and connect the capsule diaphragm directly to the FET gate
Reverse the red and white output wires to retain phase

Also Jim, do you have a link to the stacked polyester caps you got from Digikey? The only ones I found are what I installed, which are Panasonics and are much larger than your little blue ones...

And should I change the roll-off caps from cermaics to WIMA FKP's? Will it make an audible difference?

Jim to the rescue!

There's a link on the Dutch mod page that gives a process for rebiasing without a scope, which is the preferred hardware for that.

I've seen a couple of mods where they remove that capsule to fet cap completely, so there's no components in the path between the capsule and gate of the fet. This didn't involve capsule replacement.

Thanks Jim. I think I'll stick with those Panasonic's for now and maybe try the WIMA's when I have some more stuff I need...Mouser isn't the best for small orders!

This is what I used: http://www.digikey.com/product-detai...4675-ND/144391

To save some bucks, would a MKP-2 .01uF be a good bypass capacitors? Maybe if I was upgrading the capsules on these I'd invest in some MIT capacitors...they got a lot of my money recently when I rebuild the crossovers in my JBL 4408A's

Turns out I have a bunch of MKP-2 .01uf/400V so I'm going to try those for now.

I also have some MKP-2 2200pf/400V caps, would it be better to use those instead of the ceramics of the same value for the roll off caps?

Hey all,

Looking for some help on troubleshooting this mod. I replaced the 2sk170 fet with a j305 and replaced the capsule-to-fet cap with a 0.001 uF film cap. when i plugged it back in I get a quick jump in signal then nothing. when i pull the xlr cable out a little bit (while still being plugged in) the signal will jump very quick on my meter then go back down to nothing. I'm positive I put the j305 in the correct orientation.

any help would be greatly appreciated. I did this mod to two of these and am having the exact same problem.

thank you

How about a group buy of a different sort. Something along the lines of a reverse Kickstarter for microphone modding?

The SP-1 seems a simple enough design with a small enough parts inventory that someone with the in-depth knowledge could put together an instructional kit. Something small and concise with a specialized textbook, using a print-on-demand service if necessary, with not only instructions about doing the mod but, more importantly, a detailed analysis of what each component does within the context of mic design in general and the SP1 modification in particular. Think of it as a lesson in microphone circuit design using the stock SP1 and it's subsequent modification as the instructional platform.

A compete "instructional curriculum kit" could be put together and offered for sale: the blister packed mic, modification parts, and a textbook (okay, a pdf document that can be printed would be all that's really needed, I guess).

I know it wouldn't be cheap but if it's well put together and presented properly I don't think most people would have a problem paying the same as they might pay for some online college semester credit hours.

I'm just sayin'.

Is there an HF peak in the 3/4" capsule? I revisited an old Michael Joly thread where he stated this and I'm thinking it's an error.

Different microphone, but I understand the reason for changing the capsule is to get rid of the bump as shown on the chart at microphone parts. RK-47 Microphone Capsule | K47 | Microphone Parts

Starting to wonder when we'll see that upgrade kit? I thought it was coming out in Mid-August.

Yea, still waiting on the upgrade kit.

I think it will go a long way toward the instructional kit optophonik mentions, though the idea of a teaching kit is brilliant! I hope that's the way they go with it. I had a vague idea this thread could serve a similar purpose, but it's more of an intro and touchstone for the interested. It's too diffuse to be a linear instruction.
Not that I discourage continued posting here for the fanatical, or just vaguely curious...

Changing the capsule in my mic definitely smoothed the high end. It removed a funny buzzing timbre I didn't notice till I compared it to my KEL hm7u. There are clips earlier in the thread if you want to hear a sample...

But then you'd be switching to a different diaphragm diameter. You'd get a U67-ish reponce instead of KM84-ish.

https://www.gearslutz.com/board/213602-post40.html

My impression from earlier in this thread and other threads here is that the stock capsule is not too shabby, especially if you upgrade the other components-especially that one in the middle of the two circuit boards Boschen pointed out very early in this thread.

I feel like a kid waiting for Christmas to get here.

My thoughts, exactly. Considering how many people have expressed an interest over the years, going back to Scott Dorsey's newsgroup posts about the Oktava mics, there appears to be a market ready and waiting for just such a package. I think a more linear approach akin to an actual college course, way more in depth than the EQ or TapeOp articles, would be well worth the money for anyone who is looking for that kind of serious academic technical instruction.

Again, I wouldn't expect it to be cheap but I would hope it could be done for a reasonable cost considering the amount of interest. Although I don't know much about it, Kickstarter seems like it could be a good way to create an equitable plan for someone wanting to put the package together and those wanting to purchase it while minimizing financial risk on both sides.

My thoughts, exactly. Considering how many people have expressed an interest over the years, going back to Scott Dorsey's newsgroup posts about the Oktava mics, there appears to be a market ready and waiting for just such a package. I think a more linear approach akin to an actual college course, way more in depth than the Recording Magazine or TapeOp articles, would be well worth the money for anyone who is looking for that kind of serious academic technical instruction.

Again, I wouldn't expect it to be cheap but I would hope it could be done for a reasonable cost considering the amount of interest.

Greetings. I understand I waited too late for J. Williams or M. Joly to mod this mic and make it even quieter. .... Question: Is there any other person or place to spend a hundred or two to lower the noise floor quieter on this already surprisingly quiet mic?

I would love to send it off. I have health problems else I would pull out the soldier gun. Thanks for any replies.

HVAC pump noise beneath me is in the walls, radiated in the air, and is in my brain - but this cheap MCA mic helped my recordings even more than buying the $350 or so CAD Equitek E100S, which is said to be the quietest self-noise mic. No kidding. The cheap MCA SP-1 had a little bit of self-noise, but it made recorded parts sound quiet, I'm not sure why.

On the other hand the super quiet (self noise) CAD E100S mic's sensitivity to HVAC vibration noise in my imperfect room was too much to to track with. I'm not sure why but the MCA surprisingly cut the ambient HVAC crazy room noise-humming in the drywall down better. Something to do with high-end rolloff in the MCA ?, I have no idea if this mic has lower specs that way though.

Results anyway: The cheap MCA SP-1 was quieter on tape, no doubt. In my singular case. I want to stack tracks of it. I hope someone knows of a reclusive genius who mods them.

All Jim Williams posts gone.

This is a sad day for Gearslutz.




Henk

I wholeheartedly agree.

You never know what you've got until it's gone. What an exceptional man.