Advice Before I Dive In

[mobknarly]

Hi Everyone,

First off, I would just like to thank everyone on this forum, the knowledge spread here is amazing, and learning about cool new projects people are undertaking, is awesome. 

I recently decided that I would love to start building some DIY microphones, and other audio equipment. I think it would be very cool to develop a better understand of the tools I use everyday. Also, looking at something and knowing you built it/modded it to work for you, is a feeling I quite enjoy. (Plus the savings  )

I have little experience with soldering, I understand the process, and have read the spark fun (and a few others) guides on PTH soldering. However after searching (possibly not extensively enough). I haven't found a good way to practice (other than building a few very simple kits). I was wondering if anybody had some suggestions for the best way to practice. I'm thinking about just buying a random board and a bunch of cheap components to practice on. (could still use help figure out exactly what to buy  To sum it up, I would love for you guys to give me some input, any links that helped you in your journey, and any ideas that would help me learn.

I was thinking about starting with the mircophone-parts s12 kit, as it employs a transformer-less design and the whole kit can be had for around $300. I was just wondering if anybody has a reason not to go this route. Aside from that, I'm very interested in the Poctop u87.  However I would like to build that one using premium components, and with a better understanding of the process Especially adjusting the FET. I have tried searching, but cannot find any info, ie. what kind of oscilloscope do i need ect...  Any links to this info would be a huge time saver.

To summarize
- what is good way to learn PTH soldering **cheap** ( I don't need to build something functional, I just wanna practice) 
- is the microphone-parts s12 a good way to start, or should I build something simpler first (ie. another piece of audio gear, this is after my practice phase)
- any links to adjusting the FET on the u87 build, specifically Poctop's PCB design, and what kind of oscilloscope I need, as that would could be a fairly big expense

I tried to search as much as possible, if answers to my questions are readily available just let me know, I would love a link if you feel so inclined.

-Ian

 

[Khron]

1) For soldering practice, if you don't need anything functional, the so-called "strip-board" might provide a cheap enough way Since there's more copper on it than the tiny rings on perf-board, there's less of a risk of exfoliating the copper (too quickly).

2) 300$ for a kit is... anything but affordable, imho For what it's worth, perhaps about a third(!) of my microphone collection comes from mics bought as "faulty" from eBay Most of them i've already modded / upgraded, others are still "in the queue", as it were.  But that would be a reasonable and quite cheap way to get started. If you do find something interesting though, it might be worth searching for photos of the internals - working on SMD circuitry might be a bit too much of a "crash course", i think you'll agree

3) Considering you'd only need it for low-level and low-frequency stuff, instead of a full-blown oscilloscope, a simple little 2-channel USB audio interface should be plenty, i'd say And for the software side of things, there's a nifty little piece of FREE software, called Visual Analyser (www.sillanumsoft.org/download.htm). It's got pretty much everything you need for this application, and then some Signal generator, oscilloscope, FFT etc. Granted, the interface is a bit cluttered / confusing, but once you get the hang of it, it makes sense. The documentation included covers pretty much everything.

That being said though, i kinda remember reading something about adjusting the source resistor until you get to a certain DC voltage on the drain (that is, with no input signal). But i stand to be corrected by more well-documented folks than i

As far as the actual soldering goes, Dave (from EEVblog) did a pretty comprehensive series of tutorials, starting with this:
https://www.youtube.com/watch?v=J5Sb21qbpEQ

I guess you CAN get by with a cheapie (i've used a 30-40$ chinese knockoff of the Hakko 936 station for a couple years) if you really need to, but let me tell you (and i'm sure more experienced people will concur) - there's NO WAY you'll go back to a cheapie after you get your hands on a proper (or at least half-decent) soldering station, with good tips I got myself a 65w Ersa i-Con Nano last year, and i haven't looked back since Yeah, it was a "healthy" 350eu or so, but it works like a dream ;D

 

[Haberdasher]

Hi, I have some prototype pcb's of my own making that had mistakes on them (so they'll never get used for anything).  They aren't mic pcb's, but they're about the same size, and would be ideal for brushing up on your soldering chops.

If you're in the USA I'd be happy to send you a couple to practice on.

 

[mobknarly]

Thanks so much for the replies guys!

Hi Khron,

Thanks for the advice!  I originally found the CAD GXl 2200. This is what lead me to the s12 kit, as I am a little nervous about desoldering components on my first "real" build. I would prefer to start with a kit as opposed to modifying another mic, as I've heard the capsule is 90% of the sound (I could be totally wrong, this info is based on no "real world" research... instead on internet knowledge I've read) (I am also fully welcome to this not being the best option, and if you have time, explaining why, to me, would be amazing!) . I will look on eBay to see if I come across anything that would save me money, however I am worried that I may not have the technical prowess/time it takes to fully rework a mic from the ground up ( correct me if I'm wrong) /*I'm scared of desoldering/*  Thanks for the soldering guide, I will check it out ASAP. Finally, the FET info is invaluable, thanks for the info on that oscilloscope! I will check out the drain voltage thing, but if anybody else has any info/links it would still be greatly appreciated

Hi Haberdasher,

Thanks so much! I pm'ed you

 

[rockinrob86]

The microphone parts stuff is a service - he organizes the parts, makes instructions, etc and this is definitely quality work and they do a great job.

However, if you get more into it, they are quite pricey.  After modding more mics my CAD GXL2200 with the K47 capsule and pushbutton switch kit from them is moving back from "best sounding 1st grab mic" to somewhere in the middle of the pack.

BUT, they do make it easy.

My best value mic (that also sounds great) is a use Badaax T11A that I bought on Ebay for $100, added a NOS 12ay7 I had already, and then upgraded and modified the circuit of with about $15 in parts from mouser.  This mic KILLS.

Poctop on our forum sells a pcb he calls "FET847".  This mic sounds noticeably better than my microphone parts one (I used a MP K47 capsule, and a cinemag transformer),  but it is a much harder project because there are not really any instructions.  It actually isn't that hard to do if you can order the right parts from mouser, order the transformer from cinemag and source a mic body.  I then put it together in an hour or so by reading the schematic, and biased it with my oscilloscope.  I used another CAD GXL2200 , and it has been getting lots of use around here. 

 

[Krumlee]

I think for a relative newcomer to the hobby, you have to factor in the 'risk' involved.
For someone competent in electronics who knows what they're doing and who has all the right diagnostic gear then it's not a problem when your finished project doesn't work. You just follow the schematic and start diagnosing. For someone with less experience you're running the risk of spending good money on a project and ending up with something that doesn't work, or doesn't work as well as you hoped. What then? For most folks on this forum the mic-parts kits appear a bit expensive, but they're very well thought out and the instructions are exemplary. So even a relative newbie has a high chance of getting a working mic with the added satisfaction of building it yourself. And you build your skills and confidence in the process. They're certainly not cheap, but they take away a lot of the risk. I think they're an excellent place to start.

 

[Khron]

Here's another view, though, coming from EEVblog's Dave - he tells "newbies" that he hopes their first projects DON'T work, which will urge the need to troubleshoot And you have to admit, the idea does have SOME merit. Now that i think of it, it points my mind to that old adage, "necessity is the mother of invention"...

So if the M-P kits are well thought out and the instructions exemplary, and you just put the kit together and it all works fine - and what've you really learned? A bit of soldering practice, perhaps, but not much else But that's just MY opinion ;D

On the chapter of gear, between a multimeter and a 2in/2out (usb) sound card and some free & competent software, that's not really a valid excuse any longer. Only more motivation(?) to start racking up experience

 

[mobknarly]

Thanks for all the great advice guys! You make some very good points. I'm just going to focus on learning the basics for now, and reading up as much as I can.  The appeal of the mic-parts kit is that it will give me a good baseline to know that I can at least build a "quality" functioning mic, under the most ideal situation (printed instructions, kit, ect).  However, you guys raise some very good points about learning from troubleshooting your mistakes. I'm just going to learn as much as I can, and see what I feel comfortable with when I'm ready to start my first project. However, honestly, I think I will just get a used a mic and start modding it on my own. The poctop "FET847" sounds very interesting, and I will definitely look into it, thanks for the heads up. I'm really interested in this stuff, and I would like to gain a more complete understanding than a kit would offer. Also, thanks for the link!  Dave's EEVBlog is awesome, those soldering tutorials where top notch, and I'm about to to watch some more of his stuff!

 

[ln76d]

Ian,

if you want to learn something, buy used mxl 990 or 770 and for example chinese  k47 or k67 capsule.
Desolder whole circuit and build it properly using new parts and all the informations about modding schoeps style circuit.
With really good electronic parts it should cost less than 200$. Now you have extra 100$ for oscilloscope.
Buy some old analog oscilloscope with bandwith up to 20MHz. I am using Philips oscilloscope for example.
You can use soundcard as generator,  but used generators aren't expensive
I think it's good option for start.

 

[mobknarly]

In76d,

Thanks for the input. That sounds like a good place to start. Just to make sure, the newer MXL 990 & 770, haven't switched to SMD have they? Also, I have seen some places to source Chinese capsules, but I was wondering if you had a preferred way.  As to the oscilloscope thing, it looks like I might be able to use my soundcard as a oscilloscope/signal generator. (I'm not 100% sure, I have to read a little more) However, thanks for the tip, on what bandwidth I would need to use. I did a quick google search and found some old oscilloscopes for sale, they are so cool!  ;D Thanks again for the ideas!

-Ian

 

[Khron]

You definitely CAN use your soundcard both as a sig-gen and an oscilloscope (up to the limits of the possible sampling rates, of course)

One of Dave's relatively early "tutorials" / "rants" - https://www.youtube.com/watch?v=Xh9FNRpta9s

And i'm afraid the newer MXL 990's at least have indeed switched to SMD's, at least since 2013 - http://audioimprov.com/AudioImprov/Mics/Entries/2013/4/6_MXl_990_Surface_Mount_Version.html

 

[ln76d]

Yes, mxl currently makes smd version, that's why i mentioned to buy used one
You can also look for MXL 440 and MXL 2006. Same circuit.
Another same circuit:
http://recordinghacks.com/microphones/Apex-Electronics/435
At the right you have links to the same microphones from different brand.
Only Nady version have SDC capsule.
Rest of the mikes have pretty good alctron 32mm K67 capsule.
Last week i  did mods (and repair) in two rode NT1a with center terminated capsules.
One had not repairable capsule, so i used exact alctron capsule.
It sounds a lot better than rode capsule!
For start you could buy mike with that capsule and try to make pro microphone from it.
Also check PM

 

[micaddict]

We don't want no surface mount boards. 

If you're looking for older MXL 990s, look for the MCA SP1, too. Those have a less coloring grill (but the same SDC).

 

[ln76d]

As for oscilloscope and generator, personally i prefer real gear than software on pc.
Definately you need fast PC and soundcard with at least 96KHz sample rate for software measurements.
Spending some money on gear is a good motivation to work

For other mod platforms SE electronics X1 and especially X1D are good candidates!
Their k67 is really great capsule and i am curious how titanium version sound.
http://recordinghacks.com/microphones/SE-Electronics/X1D
http://recordinghacks.com/microphones/SE-Electronics/X1
Even if the circuit is THT/SMD, i still think it's good option to try (maybe not for start).
It's cheap as hell and SE quality is much higher than MXL.

 

[mobknarly]

Thanks for the ideas everyone! I have been reading through as much information as I can find on modifying the schoeps circuit. And modifying cheap Chinese mics in general. My plan is to get an GXL 2200 or a APEX 435 as those are the two mics I am fairly certain would be easiest for me to work on. (I am certainly open to any suggestions) Based on my reading I have put together a mods idea list. Any input on this would be incredibly helpful.

Change capsule to Chinese k47

Change C1,C2,C11,C12 to Wima film caps of the same value

Change C3 & C4 from .22uf caps to 1uf Wima Film caps

Change C14 & C15 to 1500pf Wima film cap

Change C13 to 1000pf Wima film cap

Change Electrolytics to Panasonic ones of same value and voltage

Change r3 and r4 to 100k resistor

Change r5 to 3.92k

Replace all resistors with same value except r3,r4,r5 using dale cmf55s metal film resistors

I have put together this information from the various sources I could find. I have the following questions, any information would be incredibly useful.
1. Jim Jacobsen said in another forum that C14 and C15 should be between 470pf - 2200pf & that this slightly effects high freq response. I was wondering if anyone could elaborate. I chose 1500pf because I saw it used in another build and it is middle of the road. 

2. He also said C13 should be between (470pf and 1500pf) but didn't elaborate. I'm not exactly sure what C13 does. I have tried reading about how the schoeps circuit functions, but haven't figured C13 out yet. Any info about how changes in C13 effect the sound of the mic would be appreciated.

3. If you see any errors in my modifications, or would like to suggest an improvement that would be great. 

I am basing this off the following schematic for the MXL 990 which is said to be the same circuit as these mics.

 

[ln76d]

naah...

Tomorrow i will paste better  schematic (in my opinion).
Don't bother with replacing resistors for dales etc.
Save cash for something which is important not fashion from gearslutz
Slightlt difference you could hear with carbon comp or other vintage resistors in place of r3/r4.
Most of original resistors could be in place.
It don't need  to be wima also.
Am using circuit with only three resistors (two for k47capsule)  in audio path + two for RF filtering.
About that earlier
For start you can at least look on original circuit in the attachment.
There are some explenations for circuit measurements, proper voltages etc.

 

[ln76d]

Last tip for goodnight!

If you will have opportunity go for mxl 2006.
Better headbasket for k47 and less work with pcb.
Apex 435 type have sh***y high-pass filter and switch for it inside microphone.

 

[Khron]

Why is that high-pass <censored>?

That's a point i wanted to make - at least in the Apex, there are two more coupling caps in addition to C3 & C4 (~22nF, if memory serves?). When they're on their own, the high-pass is engaged. the switch adds larger caps in parallel with those, to lower the cutoff frequency, ie. the "full-range" setting.

Regarding further tuning, see Zapnspark's circuit mods in the attached pdf (from the Micbuilders Yahoo-group). One important(ish?) point is the elimination of C13 altogether I believe most would agree that the best cap in the signal path, is no cap ;D

 

[Khron]

As a reference, here's the stock schematic, from the same (quite invaluable) source

With this mod, you actually also get to set aside a (rare-ish) 1Gohm resistor for other / later projects That's how i had spares available (for free, basically) for two AKG Perception 200's i revived (one leg of one of the 1G resistors had broken off) ;D

In fact, before starting to "dig" after a K47 capsule, it might be worth messing arround with some corrective EQ inside the mic. It's definitely cheaper than a new capsule, and even if it turns out you don't like it after all, one small cap and a trimmer's not much of an investment anyway, is it?

http://audioimprov.com/AudioImprov/Mics/Entries/2014/2/8_EQ_Pt.3_-_Transformerless_Mics.html

 

[ln76d]

Why is that high-pass <censored>?

That's a point i wanted to make - at least in the Apex, there are two more coupling caps in addition to C3 & C4 (~22nF, if memory serves?). When they're on their own, the high-pass is engaged. the switch adds larger caps in parallel with those, to lower the cutoff frequency, ie. the "full-range" setting.

Why is "censored"?
Beacuase it is stupid idea to put switch inside microphone without normal acces to it
How often you are using hpf in mikes? 
For start i think "simple as f***k" should be the motto.
There is a lot of mikes with hpf so what for in this case?

Regarding further tuning, see Zapnspark's circuit mods in the attached pdf (from the Micbuilders Yahoo-group). One important(ish?) point is the elimination of C13 altogether I believe most would agree that the best cap in the signal path, is no cap ;D

Yeap that's the circuit i want to paste, but with some minor changes.
In my opinion it is the best opttion for schoeps style circuit and LD capsule.
Parts names are diferent on each microphone (apex, mxl etc.)