FET847 Microphone Project Circuit By Jonathan Burtner PCB Layout By Poctop

[JMPGuitars]

This seems ingenious.

I'm now awake to the idea that fussing over tubes in a mic circuit is probably more trouble than it's worth considering 1.) the trouble of selecting a good tube, 2.) the added expense of the power supply, and 3.) the fact that most people can't necessarily "hear" any tube benefits since these tube mic stages are designed to be generally linear and low-noise / clean.

My goal is to put the best capsule I can afford into a solid-state mic and call it good for vocal duties. This FET847 seems like an ideal choice for a cardioid-only vocal mic with a quality capsule, and not fretting about the elusive tube mojo.

I'm aware we're not getting the full S/N ratio available by not polarizing the capsule at a full 60v. That has me wondering if anyone's tried jacking 60v in at some point beyond the output transformer. (Probably a stupid thing to ponder.)

Would there be any noticeable difference between this FET 847 and the D-47fET? Or are they essentially the same?

Thanks for any thoughts.

Personally, I don't think tubes are mojo. There's definitely a noticeable difference, but no, not everybody can tell the difference.

This board is different than the FET47. I've built both the FET47, and the EF47, the M49, a couple U87i mics (and some others), and the EF47 is by far my favorite build so far. Though it's odd, from the demos I heard, I initially thought I liked the FET47 version better. My guess is it has to do with the capsules used, or recording conditions, etc... It's hard to compare apples to apples from different recordings. I think transformer/capsule quality is absolutely more important than the presence of a tube.

The FET847 is surprisingly good for what it is. I think it would be even better if I used a nicer capsule, but for me, the point of this project was to keep it budget oriented, while shooting for good results- and it delivered. My next build will probably be a 2nd FET47, but this time I'm curious about trying Danny's M7 capsule.

Thanks,
Josh

 

[kato]

Thanks for your thoughts Josh.
I'm that guy who generally cannot hear the difference in mic shootouts. I notice the changes in the vocalist's performance, and I can hear the difference in different capsules. But same capsule, and same performance, with different electronics, I doubt I'd be able to hear. I do not have the ears of Geoff Emerick.

I guess I'll have to build one of each and find out for myself. Isn't that what we all do eventually anyway?

I've built the IoAudio MK7 with Ben's K7 capsule. Although it sounds great, it occasionally injects a windy noise that I assume is the tube. (It comes and goes with the mic position.) I want to build something with the C12 style capsule for vocals next, just for variation and self-education / comparison.

I just watched this video: The Magic of Tube Microphones! (Exclamation point: his.) And honestly, I think the guy is blowing smoke when he describes the sound of tube microphones as "more 3d." I figure sound waves move through a room in 3d. All audio is 3d. So that seems like a nonsense descriptor.

Let us know how you like Dany's M7. Thanks again, Matthew

 

[JMPGuitars]

Thanks for your thoughts Josh.
I'm that guy who generally cannot hear the difference in mic shootouts. I notice the changes in the vocalist's performance, and I can hear the difference in different capsules. But same capsule, and same performance, with different electronics, I doubt I'd be able to hear. I do not have the ears of Geoff Emerick.

I guess I'll have to build one of each and find out for myself. Isn't that what we all do eventually anyway?

I've built the IoAudio MK7 with Ben's K7 capsule. Although it sounds great, it occasionally injects a windy noise that I assume is the tube. (It comes and goes with the mic position.) I want to build something with the C12 style capsule for vocals next, just for variation and self-education / comparison.

I just watched this video: The Magic of Tube Microphones! (Exclamation point: his.) And honestly, I think the guy is blowing smoke when he describes the sound of tube microphones as "more 3d." I figure sound waves move through a room in 3d. All audio is 3d. So that seems like a nonsense descriptor.

Let us know how you like Dany's M7. Thanks again, Matthew

It's hard to hear the difference, that's true. But when you hear the mic being pushed, or if you hear the warmth in the vocal, that can be a giveaway. I think in general the difference is more noticeable in guitar amps. But some circuits can ruin the dynamics that the tubes bring to the table (both in mics and amps). A lot of it is taste too. I think non-tube mics are more neutral than tube mics, and that can sound sterile...which may be good or bad depending on the application.

To use your own example, and obvious point about the addictive fun of building this stuff, you really need to build two mics yourself with the same mic bodies, transformers, and capsules. One tube version, one FET version. Then record samples with both mics. Then burn them both in for at least 100 hours (500 is better), and record another comparison. It's hard to remove the human inconsistency unless you have a professional singer capable of singing the same lines exactly the same way. After all that, you need to have somebody else play the clips without telling you which is which. GLWT.

I don't recall which circuit the MK7 is. Is that u67 or u47 maybe?

I've built a C12 based on Chunger's PCBs. It came out great. That might have been the first tube mic I built, I can't remember.

Thanks,
Josh

 

[kato]

It's hard to hear the difference, that's true. But when you hear the mic being pushed, or if you hear the warmth in the vocal, that can be a giveaway. I think in general the difference is more noticeable in guitar amps. But some circuits can ruin the dynamics that the tubes bring to the table (both in mics and amps). A lot of it is taste too. I think non-tube mics are more neutral than tube mics, and that can sound sterile...which may be good or bad depending on the application.

The fact that you can hear it, and that other people can hear it, makes it compelling, even if I don't know what I'm missing. Maybe one day, as my ears become better connected to my brain, and my monitoring system improves, I'll hear the difference.

These days (no band) my recording is just a vanity project of my own voice. Since my vocals aren't particularly loud, I'm not sure the tube will ever really get "pushed' too much.

To use your own example, and obvious point about the addictive fun of building this stuff, you really need to build two mics yourself with the same mic bodies, transformers, and capsules. One tube version, one FET version. Then record samples with both mics. Then burn them both in for at least 100 hours (500 is better), and record another comparison. It's hard to remove the human inconsistency unless you have a professional singer capable of singing the same lines exactly the same way. After all that, you need to have somebody else play the clips without telling you which is which. GLWT.

Singing lessons might be a better return on investment in my case.
I'm helping a friend outfit his home recording unit. He has a great quote: "Why do I need a $1000 mic when it's just my $25 ass singing into it."

I don't recall which circuit the MK7 is. Is that u67 or u47 maybe?

The MK7 is an oldie from 2008. Here's the thread if you're interested. Unfortunately, the photos are dead now.
It's roughly U47-ish with an EF86 tube stage and BV8 output transformer. It was IO Audio's project before the MK47 which seems better known these days.

I've built a C12 based on Chunger's PCBs. It came out great. That might have been the first tube mic I built, I can't remember.

I might just do it right and build a full C12 if I can find a reliable, semi-affordable tube for it. It's not that much harder really.

Thanks again. Matthew

 

[JMPGuitars]

I might just do it right and build a full C12 if I can find a reliable, semi-affordable tube for it. It's not that much harder really.

My C12 is using an NOS CV4024 (12AT7) and it sounds great. Inexpensive, and solid tubes.

Thanks,
Josh

 

[rankot]

Anyone tried one of those capsules:
https://www.aliexpress.com/item/4000177581831.htmlhttps://www.aliexpress.com/item/4000165608334.htmlhttps://www.aliexpress.com/item/1005001737656248.html

 

[soliloqueen]

Anyone tried one of those capsules:
https://www.aliexpress.com/item/4000177581831.htmlhttps://www.aliexpress.com/item/4000165608334.htmlhttps://www.aliexpress.com/item/1005001737656248.html

I haven't tried those, but I can confirm that the similar offerings from Getwin on Alibaba are not bad, there's also the TSC-2 from JLI if you're looking for a low-cost capsule for this build

 

[rankot]

That TSC-2 looks fine. Thanks!

 

[Fastunov]

Hi Guys,

I just wanted to share my version of this nice circuit. Have a great weekend

Beautiful pcb, it can be ordered at OSH Park ~

 

[Ricardus]

Beautiful pcb, it can be ordered at OSH Park ~

It can?

 

[Fastunov]

It can?

I wanted to say that I would love to order this version of the board. I like the way the transformer is positioned, very elegant.

 

[Ricardus]

I wanted to say that I would love to order this version of the board. I like the way the transformer is positioned, very elegant.

I like this board too. I didn't search the thread. Is he selling them?

 

[Ricardus]

While I was looking around in the sharing sections of various PCB sites, I did find a transformerless Schoeps board for LDCs that fits in these same enclosues.

 

[Fastunov]

While I was looking around in the sharing sections of various PCB sites, I did find a transformerless Schoeps board for LDCs that fits in these same enclosues.

I do not know if elskardio sells, I wanted to find out from him I answer his post.

And you can link to the payment you found, it's interesting.

 

[JMPGuitars]

Hey Josh,

I am just in the middle of soldering a FET847 in a BM-800 body, also with a 3U GZT-47 transformer. Problem is: I don't quite understand which transformer colors (yellow red orange brown) go on which solder point? Could you help me by any chance? Also, which C2 value did you end up using - 4.7uF (less bass) or 22uF (more bass)? I just put the smaller one in - excited to hear how it sounds...

Thank you so much!!

Joachim

Here's my notes:
GZT-47 Transformer:
Primary:
Red/Brown (934Ω)
Red = in (from C3)
Brown = ground
Secondary:
Yellow/Orange (54Ω)
Yellow = + Out
Orange = - Out

I don't recall what I used for C2.

Thanks,
Josh

 

[jockl]

Thanks so much, Josh!
I pretty much finished the build, except I have to turn the preamp way up, so the output is really noisy. Before I check all the soldering though I'm hoping it's the capsule connection, one of the screws I used is too long, so I'm waiting for the right size screw to arrive to have a proper connection.
Let's hope that's the culprit...

 

[burbela]

The second leg of the R1, R2, C11, C1 you have to solder direct to teflon PIN...from your pic it looks like you solder those to the PCB and then to teflon PIN...that is wrong.

Hello!
Very useful information. Thanks!

If I have 2 sides capsule K12 - it have 4 wires instead 2 and I see in description this PCB have posibility to switch Cardioid - Omni modes.
Where I need to solder another 2 wires from capsule back side?

Thank you again!

 

[Rybow]

Starting on building this circuit today. How many of you didn’t put in the RF filtering? I have the inductors, but don’t have the 330 pf caps. Probably forgot to order them.

 

[Rybow]

I did put the RF in after all. The circuit is perf boarded, FET is biased, but now I’ve encountered another issue.

I used a socket for the FET, but connected the gate pin directly to the stand-off. 1khz tone from Scarlett to get pin, 75pf capacitor across the standoffs. XLR to input 1 gain all the way down. When I apply 48v my noise sits at -80dbfs. After selecting my FET, I trimmed the source and drain leads, and then retested. Noise had increased to about -60dbfs. Thinking I had damaged the fet I put another on in. Noise was back to -80dbfs. Trimmed that one just enough to fit and the noise was about -70dbfs.

It seems that the closer my FET gets to the socket the more noise I get. Should I just pull the socket? Or is there something else in proximity that might be causing an issue.

I tried my best to follow the layout on page 1. I had to change things around due to my circular board and also not paying attention.

 

[burbela]

Hello!
Who can explain me please how to connect Rear side of capsule?
As I can see front side of capsule and back is marked in circuit, but rear side of capsule wire not marked.
And also this jumper for card/omni switch, right?