MK47 PCB tube mic kit - build thread

[Sredna]

The U47N uses 2 X 8Hy.

 

[ioaudio]

I've been meaning to update the assembly instructions but could'nt get to it - i hopefully will get some spare time tonight.

 

[tommypiper]

yes:
1. the choke helps filtering crap from the mains and is a better solution for "poluted" places.
2. unloaded voltage does'nt rise as high as with the resistor-only circuit.

-max

Is this referring to a PSU schematic or discussion that exists somewhere?  If so, can you point me to it, please?

Are there any PSU schematics or discussions for this project?  What kind of PS and voltage is needed for the relay?  Etc.

 

[zayance]

yes:
1. the choke helps filtering crap from the mains and is a better solution for "poluted" places.
2. unloaded voltage does'nt rise as high as with the resistor-only circuit.

-max

Is this referring to a PSU schematic or discussion that exists somewhere?  If so, can you point me to it, please?

Are there any PSU schematics or discussions for this project?  What kind of PS and voltage is needed for the relay?  Etc.

Speaking in base of this one i think:

http://www.groupdiy.com/index.php?topic=35667.220

 

[ioaudio]

I just up-ed the PSU schematics to the first post.
Since the triad choke's are very cost-effective you can use two of them in series.

 

[Skylar]

Thanks Max. I'm looking forward to getting mine built here pretty soon.
I will share photos when it's done.


This is also a test post, as I'm getting a database error when I try to post in the White Market.

 

[horvitz]

Thanks for the updated drawing.  I'm actually working on my PSU layout right now, too.  A question on the 500R/5W trimmer.  Would something like one of those adjustable wirewound chassis mount things work here?  Like this:

http://www.mouser.com/ProductDetail/Ohmite/D25K500E/?qs=sGAEpiMZZMvNd0dY0KymzrlSPm%2fRXd%252bpQI%252bBTbFMc34%3d

I'd certainly prefer something pcb mountable, but I'm not seeing anything like that in the 5W+ range.

  Brian

 

[Kingston]

Thanks for the updated drawing.  I'm actually working on my PSU layout right now, too.  A question on the 500R/5W trimmer.  Would something like one of those adjustable wirewound chassis mount things work here?  Like this:

http://www.mouser.com/ProductDetail/Ohmite/D25K500E/?qs=sGAEpiMZZMvNd0dY0KymzrlSPm%2fRXd%252bpQI%252bBTbFMc34%3d

I'd certainly prefer something pcb mountable, but I'm not seeing anything like that in the 5W+ range.

  Brian

smaller, cheaper:

http://fi.mouser.com/ProductDetail/Alpha-Taiwan/VW24F-10-195K-B1K/?qs=sGAEpiMZZMtxdMMi52izynF7ZLtMY%252bzpmAcDgBFEwt4%3d

can be easily modified to be PCB mountable. Not 500ohm, but 1K. It's close enough for this task, and accuracy won't suffer. I've used them for this exact task in the past and they work well.

 

[horvitz]

Ahh.  Good idea with the pot, Kingston.  Thanks.

 

[Matthew Jacobs]

Talking about PSU... I wanna build mine out of wood...

Any things I got to watch out for? Should I line the interior in metal? to protect against hum, fire, health and safety, etc?

JD

 

[Kingston]

Should I line the interior in metal?

Yes.

consider wood a decoration only. You still need a fully enclosed metal case inside for electrical safety, and for shielding electromagnetic and especially radio frequency fields.

 

[Matthew Jacobs]

Thanks Kingston 

 

[horvitz]

As much as I don't like their stuff, Hammond has some wood bracketed metal cases now.. At least from the pictures, they don't look too bad.

 

[ioaudio]

Pictures for the constuction / heat transfer added.

 

[baadc0de]

FWIW, UPS and FedEx can have nasty "duty handling fee" surcharges into europe, never had these problems with USPS.

 

[Denyle Guitars]

Anyone know the min diameter for the mic body?

 

[tommypiper]

Max, thanks for the PSU schematic.  Can you please explain the test switch, and the pattern switch on that schematic?  How will patterns be selected, and which patterns?  What is the test switch?

Also, I don't understand the two parrallel resistors, 680 and 330.

Finally, the 500R pot?  Is that simply to adjust the 105v?

Thanks.

 

[grantlack]

FWIW, UPS and FedEx can have nasty "duty handling fee" surcharges into europe, never had these problems with USPS.

not to mention that they're outrageously more expensive (2-3x cost) than usps for international.

 

[ioaudio]

tommy,

the test switch connects a test-load to check the ballbark - voltage before connecting the mic to the psu.
the 680 330 resistor is either / or - to pre-adjust the voltage depending on your mains transformer's output.
500R is for final adjustments.

Patterns are like on a original U47 - omni and cardioid - switched via relais. The actual pattern switch is located in the PSU.

-max

 

[nashkato]

  Anyone know the min diameter for the mic body?

im going to go with 50mm diameter , cause thats what i have got anyway.
i put the assembled pcb in to check if it might fit , and yes , though theres not much of a space left.