Royer MXL2001 build cont'd

[doorunrun]

Continuing the thread, https://groupdiy.com/threads/royer-mxl-2001-mod-p-s-redrawn-w-pbc-layout.86272/#post-1128091,
to show the microphone side of my build and completion & enclosure of the power supply.

So, after getting the power supply board done I started work on the microphone board. Photos of the finished product:


As you can see I followed the layout to some degree from other versions of this project. To help figure out how this layout was wired I used KiCAD to layout the schematic and PCB point-to-point wiring:

This isn't exactly how I finally laid out the board, connections to power, transformer and XLR had to change due to the space occupied by the 5840 pentode, but it certainly helped me achieve an efficient parts placement.

I wanted to use as many parts as I had on-hand. To mount the 5840 tube I used some cut-down Vector bifurcated wire-wrap pins (T-68-like) I had thinking it would help ease replacement down the road. Those Vector pins were also used for PCB I/O connections.


To keep costs down I'm using a Neutrik NTE10/3 audio transformer.

That's where I'm at with the microphone side of things. Wrapping up the power supply is next...

 

[rock soderstrom]

Yes, go ahead. The Neutrik transformer is good enough for your first attempts, as long as you work with moderate levels you will be amazed at the quality you can achieve.
If you have problems with background noise such as popping, cracking and hissing, you can optimize the high impedance node with an teflon insulated pin.

 

[doorunrun]

Here's the power supply all boxed up:



Yes, that's a PC power supply case from Seasonic. The original supply died some time ago and I thought the case would come in handy...and it did! This type of case allows for great air flow with the perforations on the switch side and exhaust fan grille in the top cover. It was also easy to mount a carrying handle up there. I used a surplus cabinet door handle for that.

When I laid out the PCB I didn't really think about what I would enclose it in. I got lucky and it fit this case perfectly.
I varied a couple of components, R1 is now 110R and R2 is 100R. This combination brought down the filament voltage closer to 6V. I also upped the voltage on C1 to 50V because I was initially getting something like 37V across it.

Another lucky break came with the XLR connectors. I have some old Shure M67/68 series gear and used two circular connectors from them. The great thing about those connector housings is the inserts are also used in the cable mounted versions. For the 5-pin socket I cannibalized a inexpensive DMX 3 to 5 pin adapter. (I also used the DMX adapter approach to get a 5-pin plug insert for the MXL2001).

The 24V transformer is an old one from Radio Shack I had.

For the "U" shaped cut-out to the left of the XLRs I plan on mounting a LED power indicator on a scrap piece of copper-clad FR4 board.

I'm very pleased how the whole thing worked out.

 

[rock soderstrom]

I'm very pleased how the whole thing worked out.

Hi doorunrun, how are you doing? I am interested in the original power supply design by David Royer, which you use with minor modifications.

Is it quiet enough or is the hum level too high? I am asking because I would like to design a PCB for it and in my experience the ripple filtering of B+ is a bit tight.

What is your impression? I would add an additional RC filter stage.

Does anyone have any experience with the original PSU design?

 

[Migs 31]

What is your impression? I would add an additional RC filter stage.

Does anyone have any experience with the original PSU design?

Hey Rock, is it this one you are referring to?
I was tempted to build it for a different purpose.
I'm curious about this voltage multiplier : D1-D2-D3 & C1-C4-C5.
He (Dave R.) uses something similar on his SDC-PSU.
M

 

[doorunrun]

Hi doorunrun, how are you doing? I am interested in the original power supply design by David Royer, which you use with minor modifications.

Is it quiet enough or is the hum level too high? I am asking because I would like to design a PCB for it and in my experience the ripple filtering of B+ is a bit tight.

What is your impression? I would add an additional RC filter stage.

Does anyone have any experience with the original PSU design?

Hello rock!

Doing well here! I've haven't done extensive testing of the supply or mic for that matter. The mic is operational. I used it yesterday to record a "teaser-introduction" for a ~1:30 rock 'n' roll birthday segment that airs over shortwave radio during the weekends.
I'm not too critical a user, and comparing it against my usual workflow, I'm very happy with it.

As an aside, here's my usual workflow. I record using OcenAudio at 44.1 kHz, 16-bit, stereo. I use a short section of "silence" to grab a noise reduction profile. I select-all and run the noise reduction effect. I edit the piece into something that makes sense. I then use a VST plug=in that does some EQ and compression. Make an MP3 of the file and email to the station.

Now, I'm just recording in a spare room in my house. It's sort of quiet. When I go to get the noise profile of the silent room 60 Hz is pretty far down; most of the LF area is flat. I could screen-grab that if you'd like.

I can and should have a look and see if there's much ripple on the DC and take a pic of the o'scope screen to post here.

The segment I produce is called "Digital Modes" and airs over The Mighty KBC, a Dutch broadcaster. The segment airs during Eric van Willegen's oldies music show "Giant Jukebox." It's an hour long program and my segment airs right around the 30 minute mark. My introduction is to transmission of a digital audio mode MFSK64 that can transmit text and images.
Here's a screen shot of this weekend's featured artist, text and image:

A link to their shortwave schedule: https://www.kbcradio.eu/index.php?dir=shows/6095
If you're still reading this you can tune in using on-line shortwave receivers, KiwiSDRs, from here: http://rx.linkfanel.net/ (hopefully you'll get the map view).

Hope that helps!!

 

[rock soderstrom]

Hey Rock, is it this one you are referring to?

Yes, right.

He (Dave R.) uses something similar on his SDC-PSU.

True, he used this design over a longer period. He knows what he is doing and I have respect for his work. I used a similar circuit for a SELA T12 inspired mic and had some hum issues with so little filtering, hence my question about 1st hand experience.

If in doubt, I would add an RC filter stage, as mentioned before.

I was tempted to build it for a different purpose.

I am currently tinkering with the PCB. Normally I use my designs for such tasks, but at the moment I'm supporting young bands with hardly any budget and the Royer PSU design is very attractive because it's very inexpensive. If you want you can use my PCB design when ready.

 

[rock soderstrom]

Doing well here! I've haven't done extensive testing of the supply or mic for that matter. The mic is operational. I used it yesterday to record a "teaser-introduction" for a ~30 second rock 'n' roll birthday segment that airs over shortwave radio during the weekends.
I'm not too critical a user, and comparing it against my usual workflow, I'm very happy with it.

Cool, interesting stuff you are doing here!

As an aside, here's my usual workflow. I record using OcenAudio at 44.1 kHz, 16-bit, stereo. I use a short section of "silence" to grab a noise reduction profile. I select-all and run the noise reduction effect. I edit the piece into something that makes sense. I then use a VST plug=in that does some EQ and compression. Make an MP3 of the file and email to the station.

Noise reduction is powerful these days, but wouldn't it be better to record as noise-free as possible? This would save you a work process and keep the original quality high.

I can and should have a look and see if there's much ripple on the DC and take a pic of the o'scope screen to post here.

That would actually interest me!

The segment I produce is called "Digital Modes" and airs over The Mighty KBC, a Dutch broadcaster. The segment airs during Eric van Willegen's oldies music show "Giant Jukebox." It's an hour long program and my segment airs right around the 30 minute mark. My introduction is to transmission of a digital audio mode MFSK64 that can transmit text and images.
Here's a screen shot of this weekend's featured artist, text and image:

Very interesting, totally new world for me!

A link to their shortwave schedule: https://www.kbcradio.eu/index.php?dir=shows/6095
If you're still reading this you can tune in using on-line shortwave receivers, SDRs, from here: http://rx.linkfanel.net/ (hopefully you'll get the map view).

I'll have to have a look/listen to that.

Thanks for your feedback!

 

[rock soderstrom]

If you're still reading this you can tune in using on-line shortwave receivers, KiwiSDRs, from here: http://rx.linkfanel.net/ (hopefully you'll get the map view).

Wow, it works! I am listing to short wave radio online!! They are playing Lana del Ray...

 

[doorunrun]

Wow, it works! I am listing to short wave radio online!! They are playing Lana del Ray...

Excellent!!
It's too bad a lot of the big guns are gone. BUT There are some commercial SW broadcasters in Europe.
One of the show I can get here in USA is PopShopRadio. I listen over WRMI, also in Florida. The show also airs on Channel 292 in the EU. Here's a link to his website: http://www.popshopradio.ca/ maybe you can get more info there.

There's also a very exciting technology for radio called DRM, Digital Radio Mondale. The KiwiSDR's can decode them! In Germany there's Funklust on 15785 kHz. Excellent sounding near FM quality. https://www.audioblog.iis.fraunhofer.com/funklust-drm-shortwave
I can get them here, but it's better using a KiwiSDR closer, like Sweden.

Oh, I could go on and on about it!

Cheers!

 

[doorunrun]

A video of the HV (104V) through a 10x probe into the oscilloscope, an old Tek 7603. 'Scope gain is wide open. I also took one of the LV (filament) voltage which is runs about 6V. Result was about the same...no 60Hz.

 

[rock soderstrom]

Thanks for the links! I'm surfing through the ether right now. Besides the music and speech stations, it's also very interesting what sounds you can discover. An incredible source of spooky, interesting and mysterious sound textures

 

[rock soderstrom]

A video of the HV (104V) through a 10x probe into the oscilloscope, an old Tek 7603. 'Scope gain is wide open. I also took one of the LV (filament) voltage which is runs about 6V. Result was about the same...no 60Hz.

Yep, looks clean Thanks

 

[terry setter]

Royer used the voltage multiplier configuration because he wanted to avoid legal liability issues. Therefore, he specified UL-approved wall warts as the device that would connect to the power outlet. The video (thank you, doorunrun) shows the B+ looking clean, but I, personally , have had issues with diode-based voltage multipliers creating RF and other junk that I had to take significant steps to eliminate. That is to say, there's no sonic advantage in using a voltage multiplier to reach your target B+. My advice it to pick a power transformer that has the right secondary voltages for your needs.

 

[rock soderstrom]

Royer used the voltage multiplier configuration because he wanted to avoid legal liability issues. Therefore, he specified UL-approved wall warts as the device that would connect to the power outlet.

That's not quite right, David Royer uses the Trippler because a suitable transformer was/is much easier (and probably cheaper) to find.

In his schematics (LDC and SDC) he always specifies a transformer, for an important reason. Wall warts have no PE, which is a problem with a metal microphone and DC voltage beyond 50 volts. Even in the "Country Boy's Condenser Microphone" PSU he uses a back-to-back solution with two 12V transformers.

 

[terry setter]

Yes. He does do that. But he told me that he went with the wall wart and voltage multiplier because he didn't want any possibility of liability, and specifying a UL-approved wall wart, at least according to him, got him around that. And, as we saw in doorunrun's video, audio frequency noise was not a significant problem.

 

[doorunrun]

Yes. He does do that. But he told me that he went with the wall wart and voltage multiplier because he didn't want any possibility of liability, and specifying a UL-approved wall wart, at least according to him, got him around that. And, as we saw in doorunrun's video, audio frequency noise was not a significant problem.

Lots of manufacturers felt the same way. In my case, this cartoon is not too far from the truth

 

[Khron]

Yes. He does do that. But he told me that he went with the wall wart and voltage multiplier because he didn't want any possibility of liability, and specifying a UL-approved wall wart, at least according to him, got him around that. And, as we saw in doorunrun's video, audio frequency noise was not a significant problem.

Odd thing is, wall warts are almost never earthed...

 

[Migs 31]

That is to say, there's no sonic advantage in using a voltage multiplier to reach your target B+. My advice it to pick a power transformer that has the right secondary voltages for your needs.

Hi Terry,

I was tempted to go with a Voltage Quadrupler to get to at least 290-300V dc. for a different project.
In the mean time, I found this in the "way back machine" OP is from Kev, he still around I'm sure.
What you all think, could his scheme work well and produce less noise for tubes/valves?
If not, I will have a go at the Voltage Quadrupler.
M

 

[Khron]

What you all think, could his scheme work well and produce less noise for tubes/valves?

https://www.gyraf.dk/gy_pd/g9/g9pd.htm