MK47 PCB tube mic kit - build thread

[david-p]

Hey guys, I am working on building the power supply and I am having trouble locating some of the parts on mousers site. Can someone please tell me what fuse type and value would be most appropriate. A mouser part number would really help me out . This is for a US model.  Also, what lamp have people used and liked so far? I have noticed a lot of Fender amp style lamps being used, which I think looks really cool.
Thanks

I find it easier to get simple things like these at Radio Shack.

David

[grantlack]

david- what's yours fused at?  the inrush current blows a .125A fast-acting every time here, and i haven't been able to find slo-blo's even close at a brick and mortar store.  the mouser price for a typical glass fuse is a bit high.

[david-p]

If you are using a toroidal transformer, which I am not, you need a slow blow fuse.  I dont usually bother with fuses that small.  0.5 Amp is the smallest I use, even 1 Amp, on the basis that if something is going to go wrong it will blow a fuse that size easily!

David

[electrisizer]

Hello again
Ive still no glue for my problems with that built.

Lot of windy noise very low output...
When the capsule is unsoldered the mik is quiet. All voltages are good.

Could a faulty capsule cause such strange mik behavior?
I would be glad to get some help

[kante1603]

Hello again
Ive still no glue for my problems with that built.

Lot of windy noise very low output...
When the capsule is unsoldered the mik is quiet. All voltages are good.

Could a faulty capsule cause such strange mik behavior?
I would be glad to get some help

Hi,

you wrote about using the t-bone housing in your previous post.
If you´re unsure about your capsule simply put in the original one and see what happens (check in cardioid mode-as far as I remember it is a single sided capsule).
Always assembling the complete housing for testing is a must-otherwise you´ll pick up tons of noise (or do max´s trick putting it in metall coin box ("Münztresor"/"Geldkassette")).
This piece must have a well done shielding,so exept for the housing the wiring between psu and mic must be done pretty well too.
Please don´t use the cable that was delivered with the microphone:I opened mine and noticed super-bad solder joints and unisolated part carrying the B+ nearly touching the xlr housing-HORROR!
Use a good cable and follow the instructions in this thread as there is a lot of information about this issue.
BTW:Have you burnt in the tubes for 48-72 hours?-Could solve some problems concerning noise...
About lowish level on output:Don´t know what you mean or what gain you must have to get a good signal.On the other hand it is well known that the level falls back about some dB when the mic is in omni mode-exactly like it was in the original u47.You can find infos on that on the Neumann homepage looking for "Historische Mikrofone".

Hope to have helped and good luck,

Udo.

Edit:Forgot to mention that you should check the mic housing for good continuity too.When assembled measure the resistance from headbasket to the housings bottom;from there to the psu ground.Shoud end up very close to 0 ohms.

[electrisizer]

thanks kante!!!

today ive tried the original t.bone capsule - no change.

ive ordered an high end micro cable right now... i measured a 0.2 ohm resistance between capsule housing and mic bottom and 19 ohm!!! to the PSU ground. i think thats the faulty dog 

the low output means that my G9 preamp is cranked up nearly all the way to get an useable level. other miks need (maximal) a 45 o clock setting. but perhaps a new cable does the job...

[kante1603]

thanks kante!!!

today ive tried the original t.bone capsule - no change.

ive ordered an high end micro cable right now... i measured a 0.2 ohm resistance between capsule housing and mic bottom and 19 ohm!!! to the PSU ground. i think thats the faulty dog 

the low output means that my G9 preamp is cranked up nearly all the way to get an useable level. other miks need (maximal) a 45 o clock setting. but perhaps a new cable does the job...

Good to hear it is not the capsule!
So you should get your build cleared up first(talking about grounding of course).
19 ohms is waaaayyyyyyyyyyyy toooooooo much,hahaha.......
A good cable should do it,correctly hooked up!
About low level again:what other microphones did you compare it to-condenser or dynamic types?
Anyway,get propper grounding first,then you can talk or write about the "real" signal much better since the noise level you have at the moment can be pretty high!

Cheers,

Udo.

[Volume11]

PSU gut shot

Hi James,
 Is your transformer wired for 115v? I bought the same one and was about to wire it up using a single red and single black lead for 115v, until I noticed yours. Do I need both red and both black to achieve 115v. I'm not sure what your standard is in Canada. (noobie here)

Thanks

[wave]

PSU gut shot

Hi James,
 Is your transformer wired for 115v? I bought the same one and was about to wire it up using a single red and single black lead for 115v, until I noticed yours. Do I need both red and both black to achieve 115v. I'm not sure what your standard is in Canada. (noobie here)

Thanks

If you are using the Antek transformer you wire both red wires together and both black wires together then wire the reds to the switch and the blacks to the -V in from the power inllet for 115V operation.
Wire one red to one black then wire the other red to the switch and the other black to the -V in from the power inlet for 230V operation.
In both cases you use another wire from the +V in from the power inlet to the other pole of the SPST switch
So looking at James's pic he is wired for 115V operation (through a fuse)
Make sense?

Dave

[Volume11]

PSU gut shot

Hi James,
 Is your transformer wired for 115v? I bought the same one and was about to wire it up using a single red and single black lead for 115v, until I noticed yours. Do I need both red and both black to achieve 115v. I'm not sure what your standard is in Canada. (noobie here)

Thanks

If you are using the Antek transformer you wire both red wires together and both black wires together then wire the reds to the switch and the blacks to the -V in from the power inllet for 115V operation.
Wire one red to one black then wire the other red to the switch and the other black to the -V in from the power inlet for 230V operation.
In both cases you use another wire from the +V in from the power inlet to the other pole of the SPST switch
So looking at James's pic he is wired for 115V operation (through a fuse)
Make sense?

Dave

That all makes perfect sense! Thanks again for the help, I really appreciate it.

Chad

[LHS]

I spoke to the folks at Tab-Funkenwerk recently about buying the Thiersch blue line capsule as well as having them make my power supply and got this response:

"When using a relay for switching, the relay will kick back voltage in the circuit anywhere from 5-7 times the amount that is needed to switch it in the first place.  So a 48V relay can kick back over 300V if not properly shunted within the circuit.  In this layout most of that kick back will hit the capsule and some may go all the way back to the tube.  A spike in voltage of this size can damage both the capsule and the tube over time"

Is this a real danger in this mic circuit? Has anyone experience damage to the capsule/tube thus far?

[kante1603]

I spoke to the folks at Tab-Funkenwerk recently about buying the Thiersch blue line capsule as well as having them make my power supply and got this response:

"When using a relay for switching, the relay will kick back voltage in the circuit anywhere from 5-7 times the amount that is needed to switch it in the first place.  So a 48V relay can kick back over 300V if not properly shunted within the circuit.  In this layout most of that kick back will hit the capsule and some may go all the way back to the tube.  A spike in voltage of this size can damage both the capsule and the tube over time"

Is this a real danger in this mic circuit? Has anyone experience damage to the capsule/tube thus far?

Hi,

looking at the schemo there is a diode strapped over relais coil,so all good.

Cheers,

Udo.

[mrvision]

My finished unit... I took my time to carefully build the project and it worked without mayor problems at first. The only problem I had was the noisy tubes, but I had some tested spare tubes that I got from a trusted source just in case I had the same problem that a lot of people were having with the tubes included with the kit. I replaced them with tested ones and the problem was gone. My next build I will probably experiment a mod to use 6AK5 tubes (same electrical properties/different heater). There are more options and brands to try than the 6028.

I will post some pictures to share some ideas, thank you to the others that have already contributed with some good DIY ideas about this project.

The capsule is the Beezneez from the group buy, very happy with it.

Thanks to ioaudio (mk-47 circuit) and skylar (Mic body) for making this happen.

[mrvision]

more pictures...

[mrvision]

Mic:

[mrvision]

PSU:

[david-p]

My finished unit... I took my time to carefully build the project and it worked without mayor problems at first. The only problem I had was the noisy tubes, but I had some tested spare tubes that I got from a trusted source just in case I had the same problem that a lot of people were having with the tubes included with the kit. I replaced them with tested ones and the problem was gone. My next build I will probably experiment a mod to use 6AK5 tubes (same electrical properties/different heater). There are more options and brands to try than the 6028.

It looks magnificent!

Where did you get the shock mount and PSU box with the handle?

David

[mrvision]

Thank you David, The Box is a Recycled SONY CMA Camera PSU, I Paid about $35 shipped on ebay, removed the guts (it has a nice 50V transformer btw) I just did some holes with my bench drill and repainted it with hammered finish spray paint. The handle is a 4-3/8 In. Senna Leather with Satin Nickel and the Shockmount is a Beezneez from the group buy.

Marv

[Volume11]

Need opinions of mounting the 1k5 resistor 'heater' from MK47 kit.
 

Thanks

Jason

Here is a pic of my mounting I've used it twice now worked great

Anyone have a part number for this resistor?

Thanks

[zayance]

Need opinions of mounting the 1k5 resistor 'heater' from MK47 kit.
 

Thanks

Jason

Here is a pic of my mounting I've used it twice now worked great

Anyone have a part number for this resistor?

Thanks

I think it would be this one.

http://fr.mouser.com/ProductDetail/Arcol/HS10-1K5-1/?qs=sGAEpiMZZMtlubZbdhIBIKR5oQtBrv7qwqZcsowM%252bXM%3d

Or RS 252-2530

Be sure to fit the treated bolt that locks the Male binder in place before poiting where to drill holes for it. Never know.