My First U47 Build Begins!

[MasterEvan07]

This will be my third mic build...it's much simpler and more cathartic than building guitar amps.

Hanging around this forum is like hanging around guitar forums where there is new builder subsection and everyone is building a Fender 5E3/Tweed Deluxe, except here it's the U47.

I'm going to build Vamisound PTP and a VMPCBKIT.com kits but starting with the VMPCBKIT.

Starting out, is there anything I should be aware of, or that's missing, or additional work that's typically overlooked?

It looks like the Hammond enclosure on the Mouser BOM for the D-EF47 is undrilled so I'm looking at Collective Cases as I don't want to deal with drilling an enclosure - things of that nature.

Thanks!

 

[ElSmurf]

Glad to hear you pulled the trigger on this. Will you be building Dany's D-EF47?

Like you said, I think sorting out the PSU is the least straightforward part of the build. But that collective cases PSU enclosure looks like it will make that a lot easier.

 

[MasterEvan07]

Glad to hear you pulled the trigger on this. Will you be building Dany's D-EF47?

Like you said, I think sorting out the PSU is the least straightforward part of the build. But that collective cases PSU enclosure looks like it will make that a lot easier.

That's the plan - seems to be the consensus of what's good, so I'm trusting the collective wisdom of the fine people here.

 

[ElSmurf]

FWIW I recently swapped out C2, R1 and R2 in the mic to be closer to the original U47 values, and it seems to have balanced out the mic and removed a bump from the 250-300Hz range. I used a 0.47uF cap in C2 and 100M resistors in R1 and R2. The cap is easy to swap out, even in a fully built mic, but the 2 resistors can be a bit of a pain since they're connected to the HiZ pins.

 

[Murdock]

I can second that. Found 0,47uF and 60Meg to be nicer sounding than 1uF and 200Meg.

 

[MasterEvan07]

FWIW I recently swapped out C2, R1 and R2 in the mic to be closer to the original U47 values, and it seems to have balanced out the mic and removed a bump from the 250-300Hz range. I used a 0.47uF cap in C2 and 100M resistors in R1 and R2. The cap is easy to swap out, even in a fully built mic, but the 2 resistors can be a bit of a pain since they're connected to the HiZ pins.

Maybe I can mount them creatively so as to leave the door open for easier experimentation...

 

[MasterEvan07]

Most of my parts are in, still need to grab some 100M resistors but right now everything but the @soliloqueen K47 (probably gonna get a flat and her normal K47 when it releases) is on the way.

I'm confused with the PSU and could use some guidance. I don't know why there's three transformers and could use some direction and recommendations on layout. My PSU board is built, and I think I still need a light for the chassis, but otherwise I'm ready to put it together. Will post pics soon!

 

[ElSmurf]

The PSU board wants to see 220V AC, so I added the 1:1 toroidal after the AC input, since I'm in Europe. The BOM also provides an option for a 110V-220V AC transformer. This transformer provides 220V to the board and to the transformer that delivers the 20V AC. The third transformer is a choke.

As for layout, depends on the PSU case you have. I suspect my layout isn't ideal since my choke has a slight hum. I read somewhere on the forum that this could be caused by the angle between the different transformers. I'm sure someone more knowledgeable has more to say about this.

 

[MasterEvan07]

The PSU board wants to see 220V AC, so I added the 1:1 toroidal after the AC input, since I'm in Europe. The BOM also provides an option for a 110V-220V AC transformer. This transformer provides 220V to the board and to the transformer that delivers the 20V AC. The third transformer is a choke.

As for layout, depends on the PSU case you have. I suspect my layout isn't ideal since my choke has a slight hum. I read somewhere on the forum that this could be caused by the angle between the different transformers. I'm sure someone more knowledgeable has more to say about this.

Ah, I believe I see. My AC input is feeding the Hammond 115VAC to get the 20V on its secondaries as well as the Triad toroidal for its secondaries to bump up to 220VAC. Forgive my transformer ignorance, but why isn't it one transformer with multiple taps - both 220VAC and 20VAC secondaries from either a 115VAC/230VAC primary? Clearly there's a rationale for why it's this way, I'm curious what it is. Size? Cost? Both and...?

Transformers tend to want to be 90 degrees offset from each other so that their magnetic fields don't interfere with each other and cause hum/phase issues. At least they do when it pertains to power and output transformers in an amplifier build.

 

[Khron]

Forgive my transformer ignorance, but why isn't it one transformers with multiple taps - both 220VAC and 20VAC secondaries from either a 115VAC/230VAC primary? Clearly there's a rationale for why it's this way, I'm curious what it is. Size? Cost? Both and...?

Cost and availability, mostly. Sure, you can get "tube mic PSU transformers", but they're either stupidly expensive and/or tough to find, or if you CAN get them easily (from the far east), the MOQ (minimum order quantity) is in the tens or hundreds, which is... not very helpful.

Since one only needs a heater voltage with a decent current, and only single-digit mA from a high-voltage rail, it's trivial to achieve that with two bog-standard (and consequently cheap!) transformers, as opposed to a single bespoke one. Of course, assuming you can spare the physical real-estate. But for our onesie-twosie quantities, that's a non-issue.

 

[MasterEvan07]

Cost and availability, mostly. Sure, you can get "tube mic PSU transformers", but they're either stupidly expensive and/or tough to find, or if you CAN get them easily (from the far east), the MOQ (minimum order quantity) is in the tens or hundreds, which is... not very helpful.

Since one only needs a heater voltage with a decent current, and only single-digit mA from a high-voltage rail, it's trivial to achieve that with two bog-standard (and consequently cheap!) transformers, as opposed to a single bespoke one. Of course, assuming you can spare the physical real-estate. But for our onesie-twosie quantities, that's a non-issue.

Makes sense, thanks for the reply!

 

[MasterEvan07]

I suppose something like this for a Collective Cases box, layout-wise.
Running into a couple issues with my U47 body - the spacing for the mounting holes isn't compatible with my PCB and the XLR insert is too small for the output.

 

[ElSmurf]

I had a similar issue with the mounting holes. Ended up making my own support frame with some brass bars and threaded L brackets. You can see what that looks in this post.

 

[Hibernate Audio]

I suppose something like this for a Collective Cases box, layout-wise.
Running into a couple issues with my U47 body - the spacing for the mounting holes isn't compatible with my PCB and the XLR insert is too small for the output.

Hi, I'm also building a D-EF47 right now. Looks like we maybe got the same body off aliexpress? I was planning to grind away the parts of the rails that make electrical contact with the pcb, and then use a combination of screws and zip ties to secure the board probably. Can you let me know which XLR insert you end up with?

 

[MasterEvan07]

Hi, I'm also building a D-EF47 right now. Looks like we maybe got the same body off aliexpress? I was planning to grind away the parts of the rails that make electrical contact with the pcb, and then use a combination of screws and zip ties to secure the board probably. Can you let me know which XLR insert you end up with?

I'm still unsure if I'm meant to cobble something from a more complete part or if there's the exact thing at Mouser. Studio 939/@chunger has some Chinese ones but I was hoping to consolidate at Mouser.

 

[Hibernate Audio]

I'm still unsure if I'm meant to cobble something from a more complete part or if there's the exact thing at Mouser. Studio 939/@chunger has some Chinese ones but I was hoping to consolidate at Mouser.

Pretty sure this is the usual: QG 7 Pin Male XLR Insert - Standard Latchlock | Switchcraft

But I've also seen folks talking about pulling the inserts out of panel mount XLR connectors (https://www.mouser.com/ProductDetail/Amphenol-Audio/AC7MPNZ?qs=XDP25vQyejQzX3W8y2ut%2BA==), but not positive about the amphenol part working out.

 

[Khron]

but not positive about the amphenol part working out.

I can confirm at least the insert of the Amphenol AC5MPNZ is not useable as a mic output connector. If possible, look up Neutrik NC_MP if you can find some NOS or used ones (they're discontinued), or the Cliff UK equivalents.

 

[MagnetoSound]

Yes, you usually want the Switchcraft type with the grub screw that tightens into a hole in the body.

I say type as there are often copies of Switchcraft connectors made to the same pattern available at much lower cost. (£14 is a bit eye-watering for just the 7-pin insert!)

It looks like the part you received is the Neutrik kind, smaller and with no grub screw as it just sits inside the plug shell under compression. There’s no way I can think of to fix this inside the connector barrel on the body tube.

 

[MasterEvan07]

Geez, of all the silly things to need to spend money on for this I'm held up on a ghastly overpriced 7-pin insert!

 

[Khron]

Geez, of all the silly things to need to spend money on for this I'm held up on a ghastly overpriced 7-pin insert!

Those Switchcraft inserts are indeed barefaced ripoffs. At least in the EU, TME in Poland carries Cliff UK connectors for pretty good prices, and as i mentioned, i can attest for the (re)usability of their panel-mount XLRs' inserts.