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Black Box Analog Design - the secret files
Old 21st February 2016
  #1
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Black Box Analog Design - the secret files

Greetings,

With the success of the Black Box, the IMT, the Dynatron and the HG-2 under my belt, I decided that it was time for something new. After all, I've learned a lot these past few years and I'm ready to put it to the test and see what comes out of the other end. With that said, come along for the ride and watch a microphone preamp go from an idea to reality.

Step one: This is my humble little shop down by the beach in sunny Ventura, CA. which is about an hour North of Los Angeles.



It isn't much but it is enough to do what I wish to do.

So, a couple of tubes I've never worked with before have arrived in the mail and it was time to get busy. I found some old copper clad proto stuff from years back and put in new tube sockets. I dropped in a regulator for the heaters and some variable resistors to control plate and cathode.



Here you can see the power supply, suicide plug, and even the first sine wave appearing on the scope. Also, there seems to be more parts. How did that happen?



Gosh, why stop there? Lets just fill my desk with parts.



This, you should know, is happening over the course of days and here you can see a slightly neater desk and the addition of input and output transformers as I'm now looking at balanced inputs and outputs.



Now I've put this all on a heavy piece of cardboard so I can move it around and test it in my main Protools testing rig.



Ok, back from testing and I'm happy with what I am seeing so far. I need to build a prototype rig that I can take to a recording session on Monday. That gives me, what, two days? I'm screwed.



I ran around looking in old boxes for parts I would need. I need something that will work as a box. I need to build a power supply. I need to find three toroidals to juice up the power supply. I need an IEC input module. I need a fuse holder and fuse. I need wire and relays. I need nuts and bolts and a drill and and and and and and

First, I found enough parts to stuff this.



Next, I threw everything down in a big pile and looked at it for a while. This, need I remind you, is very very important.



I worked the drill for a bit and put in some stand-offs for the main power supply board, bolted in the output transformer, bolted in the xlr's, bolted in the hammond transformer (not sure if I'm going to use it or not at this point but 3.5 amps at 16v never hurts)



This is where I left it for the evening. Tomorrow will be a long day especially wiring in all the relays by hand. Stay Tuned.

Old 21st February 2016
  #2
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Secret Files - the faceplate

Greetings,

So, I've finished up stuffing the face plate in anticipation for all the wonderful things it will be controlling. I have an early version proto-face plate from a Black Box that I am using and some of the controls will be the same.

Variable Impedance
Volume Controls
Mic/Di Options
Phase
Phantom

The other options are still up in the air but I'm leaning towards a high headroom/low headroom input and switchable output tube. I have some other controls currently bolted in to the rear of the unit.

I do not know how but I found some needed items for the Face plate.



I'm planning on running the switches as 12 volt relay controllers so that a single switch may do numerous things.



Here you can see the addition of the buss wire which will carry the 12 volts. Also, this voltage and the voltage controlling the LEDs will come from a separate transformer so as to isolate my heaters.



Here is the front of the face plate. Now I have to go build relay circuits and do so by hand - oh boy.

Old 21st February 2016
  #3
Very nice job sir !
Old 22nd February 2016
  #4
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Secret Files - the beginning of the end

Greetings,

Somehow, I've been at this all day and this is what I have to show for it. There are always hundreds of little steps that I block out of my mind until I find myself sitting there thinking things like, "I need one switch to re-route signal to a different tube and have the output pot switch as well."

Here, I remember to wire up the toroidal to the power supply.



Even though this is in a box, it still has to work as a proto-type. Values need to be "fluid".



It is 8:30pm, here is how I left it.



Old 22nd February 2016
  #5
That is comming along quite nicely !

The thing left to the "circuit board" ... looks like a motor ? .... is it a really big potentiometer ?
Old 24th February 2016
  #6
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Secret Files - missed deadlines

First, that thing that looks like an electric motor is actually a Helipot 100k .25% tolerance multi-turn resistor. I'll use it to fine adjust plate resistance.

Next, I didn't finish things in time for my session because this came up. This is Serial Number 50. I've hand built and shipped 50 HG-2's - wow.



Anyway, this is where we are now. I went back to the faceplate and wired in a number of the circuits. Oh, if you are wondering why there are so many lugs on those switches it is because I used to do all the routing and switching and fun stuff on the switch itself but now I just use them to control a 12V relay. This way I can keep whatever I'm switching near the thing that needs switching. For example, the relay that sends 48V is glued right under the female XLR socket. Why run antennas everywhere if it isn't necessary? It makes for way way way more work because I have separate grounds for relays, LED's, heaters and signal.





Here you can see me testing that all the LED's n such work. I think they are a bit brite so I will probably hit them with 3k resistors and dim them back.



Here is where things stand now. Tomorrow - there is always tomorrow.

Old 24th February 2016
  #7
I really enjoy watcing these pics, thanks for this !
Old 24th February 2016
  #8
Thank you; very nice of you to share this 'making of' project with such great detailed photos. The front panel looks super. Impressed.
Old 26th February 2016
  #9
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Secret Files - as God is my witness. . . .

Greetings,

OK, so I'm still not done but, damn, I am getting closer. The problem seems to be that I get distracted, forget what I was doing and then just stare at it for minutes at a time. I'm sure the Saturn V was built the same way.

First, lets revisit the tube "circuit board". I've still got a bunch of stuff to wire up to it so I may as well start there. I've tested that the relays actually do what I want them to do.







Power supply is in place and is giving me 300 Volts, 48 volts, 6.3 volts, 12 volts for led's and switches and 12 volts for heater. Take special note as to how I glued the bridge rectifier to the Hammond Transformer. That zip tie and liquid gasket are holding in a smoothing cap. I'm sure that that is how the professionals do it.



The input section is all wired up and connected to phantom, phase, impedance selection, variable output load, input transformer & output transformer.



Now I just have to finish connecting everything.





Connecting everything makes my head hurt so I'm gonna call it quits for the day and go play some video games. Yeah, I play video games.

Tomorrow is another day and maybe I can actually run sound through this.

Last edited by rvwainscott; 26th February 2016 at 06:49 AM..
Old 26th February 2016
  #10
Don't worry, I sometimes stare at my stuff for hours, sometimes even days,... it's how they build the great piramid
Old 28th February 2016
  #11
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Secret Files - the first recording

Greetings,

Yes, something like the Pyramids could have only been built by a ridiculous amount of intense contemplation. This thing, by the way, has stared itself into a state where I can make a recording with it. For some reason the "air" feature isn't working and I did have to modify a plate, load & cathode resistor to get some more gain but for its first time out, I'm rather pleased and I can see the potential of where this is going.

I've included a Soundcloud link so you can hear what it did. There is no processing and I'm pushing buttons and turning knobs so, it is what it is.



Here I am, making the recording.







Old 29th February 2016
  #12
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The Secret Files - 2nd recording

Greetings,

OK, so I've tweaked a few settings and here is my second recording done both on a Blue Bottle and a SM58. I think this recording shows the range of this particular unit. I've done no processing.



Finally, I may up the plate voltage just to get a few more db out of this thing but I'm not too sure I want to do that just yet.
Old 2nd March 2016
  #13
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Secret Files - An image is worth 1000 words

Greetings,

I have some visuals of pink noise, some harmonics and a transient shaper. Lets start with a video showing the transient shaper. This is a square wave coming out of my function generator. The corners of the square are a bit rounded as everything responds and saturates in its own manner. This little transient bump will be perfect for drums.



Check out the 1K sine wave fundamental and its octave harmonic with an odd order harmonic just starting to appear.



Here is the same sine wave but look at the proportions between the fundamental and his buddies.



Finally, I've driven it into saturation. Notice how the odd order harmonics take center stage.



I've added some of my favorite tone shaping options. This pre, I should mention, does not have an eq per se but gain stages that can act like EQ's. Here, I just ramp this thing up like home values in SoCal.



Here, I am playing around with different gain stages and using the "air" feature to get a mid-scoup.



Here, I am attempting to bump the mids.



Finally, I try to drive the lows here.



For the time being, I'm not too sure what else I can add. Perhaps, I will gather up some legitimate recordings other than me talking into entry level mics. If there are any readers here in my area that would like to give it a spin then let me know. The more testing I can do the better off it will be.
Old 2nd March 2016
  #14
I applaud you ! .... great engineering !
That's a nice range you got on that pre, very nice.

I wish I was in your neighbourhood, I would definitely drop by for a coffee
Old 2nd March 2016
  #15
Yeah; great range of tone and timbre (on Soundcloud sample)....that would be very handy for positioning the source in the mix soundstage.
Old 2nd March 2016
  #16
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Quote:
Originally Posted by Arthur Stone View Post
Yeah; great range of tone and timbre (on Soundcloud sample)....that would be very handy for positioning the source in the mix soundstage.
First, @ COZMIK , coffee would be great. I like mine strong.

Second, when I first started out, reverb was really the tool to move things around in the mix but with the RMS wars underway, saturation, harmonics and subtle distortion are the better tools especially now that reverb gets totally lost in the mix.

Third, when I finally get this thing all tweaked in, I plan on making a bunch of them and offering them up for sale. My goal is for a pre that allows you to do more work and worry less about mic placement, microphone selection and preamp selection. After all, music production is the 2nd biggest hobby in the world outside of photography and when people came to my studio, the last thing in the world they wanted to see was me spending 45 minutes figuring out the best combination of mic, preamp, placement and compressor. When I go to the mechanic, I do not care one bit about the tools he uses - I just want my car to run.

Stay tuned because after the values get hammered out, the design has to be translated to work on a circuit board, a power supply has to be designed, a box and faceplate imagined as well as figuring out how the user will interact with the unit. My partner-in-crime, Eric Racy, has already presented some excellent mock-ups that will go beautifully with the HG-2.

I'm hoping for an actual release date ~90 days from now.

For giggles, this is what one of the 7 circuit boards in an HG-2 looks like. Keep in mind, Eric and myself have zero formal education in any of this but are just two guys building the tools we wish we had.




Last edited by rvwainscott; 2nd March 2016 at 06:46 PM.. Reason: Spelling.
Old 3rd March 2016
  #17
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Hey Robert,

I just stumbled upon this thread and I'm completely hooked! I am currently in the process of finishing my very first DIY project (a GSSL) and I'm totally digging the DIY audio electronics stuff. Actually, I might venture into designing some basic circuits myself, which leads me to the question; what software are you using to design your PCB's?


Dutchy
Old 3rd March 2016
  #18
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Quote:
Originally Posted by Dutchy15 View Post
Hey Robert,

I just stumbled upon this thread and I'm completely hooked! I am currently in the process of finishing my very first DIY project (a GSSL) and I'm totally digging the DIY audio electronics stuff. Actually, I might venture into designing some basic circuits myself, which leads me to the question; what software are you using to design your PCB's?


Dutchy
Greetings,

We use Eagle Freeware | Get the EAGLE Light Edition free | CadSoft EAGLE to design our circuit boards and then we use Silver Circuits for manufacturing. Small runs are very inexpensive.

Eagle is a bit clunky but not the worst thing you can imagine. The free version allows you to make small circuit boards but anything big requires the paid for version.
Old 3rd March 2016
  #19
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Thank you for sharing what you are working on with us, very interesting! I'm wondering if having different kinds of Output Transformers might yield even more sonic variety. Maybe not needed or cost prohibitive, but I thought of this ever since I first saw the HG.
Old 3rd March 2016
  #20
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Quote:
Originally Posted by euclid b View Post
Thank you for sharing what you are working on with us, very interesting! I'm wondering if having different kinds of Output Transformers might yield even more sonic variety. Maybe not needed or cost prohibitive, but I thought of this ever since I first saw the HG.
Greetings,

I first went with Cinemag because I really liked how some of the ADesigns performed and those used Cinemag. Cinemag is local to me and Dave from Cinemag was so patient with me as I tried to figure all this out that I owe him big time. Also, I work to get as much tone out of the tubes as possible and it is as if I need something "forgiving" on both the way in and the way out to anchor things.

The input and output transformers tolerate a lot of nonsense from me but I strongly suspect that an esoteric output transformer would demand that I work within tighter tolerances. Perhaps it would be more limiting - I just dont know.

I would be curious as to what you think would be a better transformer and why? With the HG2, I drive harmonics and saturation and I even have a parallel distortion circuit. At best, I could hope to saturate the output transformer but is it then overkill? What do I gain?

Last edited by rvwainscott; 3rd March 2016 at 08:36 AM.. Reason: Spelling
Old 3rd March 2016
  #21
Very inspiring ! .. please keep doing this

I'll check that software also as I'm in the middle of staring at things and bits myself at the moment
Old 21st March 2016
  #22
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Very cool to see in-depth details on projects like this, thanks for posting all of it and I look forward to more in the future.
Old 21st March 2016
  #23
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The Secret Files - getting ready for round two

Greetings,

Here is a quick update.

I do not quite have the output I wish with the 12BH7 driving the output transformer. The pentode works great getting whatever signal presented to it up to 3 volts or so. Consequently, I switched over to the 12AV7 which is an amazing triode but one that isn't made anymore. I want this design to work with tubes that are readily available so I'm going to try the AT7 next as its characteristics closely match that of the AV7 but with an additional gain of 20. I ordered that tube last week and it should be here any day now. Oh boy!

Since I am adding a bunch more gain, I decided that I'd put in a -20db pad. Here is what something like that looks like.

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