Topic: Greetings... my new mic preamp.

[sanaka]

Mighty sweet indeed 

Peace

[fivefishdiy]

Update:

My wires arrived today... yay!

I got the switchboard and motherboard working together... Schweeet!!! 

I haven't wired the phantom power yet, and of course, the VU meters don't fit.... new VU meter boards will be here next week.  But doing tests with a meter, all parts are functioning. (48V for phantom and 12V supply for VU). Phase reverse works too... if you toggle the switch to the middle, it's a mute (unintended consequence).

I also need to solder the mini-LEDs for the switchboard...



OF COURSE!... I had a stupid mistake on the board. Nothing major... but the output jacks are swapped.

So it's like
IN1, IN2, OUT2, OUT1

instead of
IN1, IN2, OUT1, OUT2

Will fix this on the next board revision. The important thing is everything is working.

[Phiegze]

Sweet torture ...

  ...I want one NOW!

           

[digifish_music]

Update:

My wires arrived today... yay!

Nice! I notice you must have the highest +T to post ratio of any Taperssection user, currently @ ~2:1

I forget what the power supply options will be. However it would be nice if you could make a AA battery sled for it. 8 AA batteries?

digifish 

[fivefishdiy]

Nice! I notice you must have the highest +T to post ratio of any Taperssection user, currently @ ~2:1 Smiley

Hehehe... I try not to post too much. It keeps my signal to noise ratio high. 

However it would be nice if you could make a AA battery sled for it. 8 AA batteries?

8 batteries? I think (3) will work... 4.5Volts. 

I have 1" extra real estate in the case. But no promises. Changing out batteries will be a pain. Not unless I can find an easy method for access. It probably wouldn't happen... but hey, I love a good challenge.


I forget what the power supply options will be.

In the original design, I used 12VDC input as my design criteria. But after the prototype preamp was built and tested, I found out it will work down to 4.5VDC input just fine.

HOWEVER... the Phantom power will not reach a full 48Volts if the pre is only given 4.5VDC input. This may or may not be an issue for you. If you're using dynamic mics, who cares. If you're using a typical condenser, it should work even with PP of 12V or 15V or 18V.  A certain few types of condenser mics though prefer a higher voltage and sound crap at a low phantom power voltage. I use a FET condenser mic as my test mic. This mic is picky with regards to phantom power. So if it will work even at 4.5V input to the preamp, I'll be happy.

Here's the table of input DC voltage and the phantom power voltage you'll have available at that corresponding voltage.
(Phantom voltages rounded up or down to nearest value.)

Battery voltage = Phantom power voltage available
----------------------------------------------------------
4.5V input = 28V phantom <---- Not bad for phantom power even at 4.5VDC input
5.0V input = 32V phantom
6.0V input = 41V phantom
7.5V input = 48V phantom <--- at 7.5VDC input and above, we get full 48V phantom
8.0V input = 48V phantom
9.0V input = 48V phantom
12V input  = 48V phantom
14V input  = 48V phantom


So there... since PP specs are 12V to 52V range, I *think* it won't be an issue. 28Volts is more than twice the minimum 12V spec. Once I get PP wired, I will do some real world testing with my FET condenser mic.

More pics...

Front View... I need to get proper 1" standoffs.


Wiring closeup... I'm using headers to simplify and speedup assembly. You can see at the lower right corner of the PCB some pads for hooking up Switchcraft locking DC jacks.

The DC inputs are protected with diodes too! So no danger of hooking up your battery backwards! I think that piece of mind is worth the $0.05 the diodes cost me 

[digifish_music]

Nice! I notice you must have the highest +T to post ratio of any Taperssection user, currently @ ~2:1 Smiley

Hehehe... I try not to post too much. It keeps my signal to noise ratio high. 

However it would be nice if you could make a AA battery sled for it. 8 AA batteries?

8 batteries? I think (3) will work... 4.5Volts. 

Thanks, I was thinking of running it at 6V but with 8 batteries for more serious mah. Just that AA batteries are everywhere, easy to manage and everything I own runs on them

digifish

[fivefishdiy]

Well, my LUCK ran out.... Murphy's Law strikes again!

Found a major mistake.... at the very last step!

So I wired the phantom power wires from the switchboard to the motherboard... then problems... I'm not detecting any phantom power on the XLR jacks.... Guess what?  I connected the phantom power resistors on the wrong side of the input transformers on the motherboard!  What a stupid mistake! I drew it wrong in the schematic. And of course, since I don't have a second set of eyes checking my work, it slipped through.

It's not a complete show stopper... I'd just have to solder the resistors at the bottom of the board and use some jumpers.

Soldered the (3) LEDs to the switchboard.... The 3rd LED (Power LED) wouldn't light up. I think I overheated it. The (2) phantom power LED indicators are working fine though.

I'm calling it a day... just when I'm at 99% complete, I'm making stupid, simple mistakes.

[stevetoney]

dear fivefishdiy:

First off, congratulations on such a fantastic design project and what's turning out to be a model success story for a product that's custom tailored to the target market.  How better to do it than you are?  I'll buy one of your preamps for that reason alone! 

I've read the input here and there as it's gone along, but I'm not really tech saavy enough to provide much input.  However, just today I spent that last three hours really reading and absorbing everything that's been offered up to this point.  I hope you don't mind at this late stage some new eyes on this project and maybe a couple of new thoughts...take the input for what it's worth and it's probaby too late to matter.  However, I do have some input that might be useful.

I have an Apogee Mini-MP preamp that I recently inadvertently toasted because I accidently applied reverse polarity to the power jack.  Actually, I am thinking (based on other threads that I've read on this same subject related to this preamp) that the whole preamp isn't cooked, but probably just an internal fuse that is located at the output jack as reverse polarity protection.  I don't know circuit design, but on the one hand, I'm glad that I probably have only a blown fuse.  However, on the other hand, my preamp is now DOA until I have it serviced which of course is a PITA. 

For pretty much every other electrical component I own, if reverse polarity is applied, the only thing that happens is...well, nothing.  In other words, the component doesn't power on, but it also doesn't fail.  So, maybe the fuse is an additional form of reverse polarity protection on the Mini-MP (in addition to a diode), but FWIW I don't like it because I still have a dead preamp.

So, I guess my input is:
a) make sure that your preamp is fully reverse polarity protected (you mentioned output diodes, so I guess you have that covered???), and
b) make the design respond passively if reverse polarity _IS_ applied.  Yeah the fuse might be an additional form of protection, but now that it blew, I still have a dead preamp that's gonna cost me $100 to get fixed by Apogee, so from my perspective, I'm not sure what's been saved with this design.

Of course, your final case design should indicate in the cover artwork at the power input what are the polarity and voltage requirements are...surprisingly, a good number of my electrical gadgets don't give polarity requirements at the jack.

A second input on the case design is that I REALLY like the idea of standoffs at the rear of the unit, but I understand and agree with your efforts at permanent installation and how they are be in the way.  A thought I had when I saw your pics was some sort of removable or screw-on standoffs.  Or maybe some brackets or something that's kinda 'C' shaped and snaps onto the back with some detents to snap into place.  Or maybe a bracket that swivels out of the way...say it swivels flush to the sides of the preamp when not in use, but then swivels out around the back so that it acts as a stand-off. 

Of course the goal of the stand-offs would be something that doesn't get in the way, but something that would provide stress relief on everything in the back (not only stress relief but 'movement' relief in the case of battery connectors becoming accidently disconnected) while also allowing the preamp sit in a gig-bag with the face upward so we can see easily see the lights and settings.  Of couse the problem with 100% of existing preamps is that in that position, everything is resting on the wires or the RA plug of the XLR.

Regardless, of my input, congratulations on the great job you've done.  Sorry for the latest mishap with board design, but from the looks of it, you're WELL on your way to having the one of the most significant success stories in net history (as for as TS.com is concerned anyway!).

[stevetoney]

Well, my LUCK ran out.... Murphy's Law strikes again!

BTW, I think that getting this far with so little going wrong is an INCREDIBLE feat and testament to simply excellent planning and such a careful, thoughtful and professional approach that you've used.  The fact that Murphy has waited this long to strike is simply the reality that nobody is immune to Murphys dastardly ways. 

Also, FWIW, I hope you still plan on using the vintage dial type knobs instead of the black ones in the pics at the top of this page.  It wouldn't be a big deal if they ended up being the blackies, but those vintage knobs are COOOL!

OH, as long as I'm rambling...it would be excellent if your end product had external artwork that doesn't wear off over time...or is maybe even lightly etched onto the aluminum case using your CNC machine...or maybe a combination.

[stevetoney]

Sorry I keep adding onto this thread, but like I said earlier, I read on this thread for a LOOOONG time earlier today so I keep comging back to things that I read along the way.

Back a few pages there was some discussion about noise when the Tekkeon battery was sitting on the top of the box.  FWIW, I read the following message a couple days ago...it took me awhile to find it, but I _KNEW_ I had just read on that subject.  Check the link...not a whole lot of detail, but seems to confirm that your noise issue was simply an issue with having the Tekkon battery in close prox to your preamp...

http://taperssection.com/index.php/topic,97621.msg1443192.html#msg1443192

[fivefishdiy]

So, I guess my input is:a) make sure that your preamp is fully reverse polarity protected (you mentioned output diodes, so I guess you have that covered???),

Yes, I have protection diodes on the DC input jack to protect against reverse polarity.

(Not to be confused with the diode protection I also have at the output XLRs, which is meant to protect my pre when for example you plugged the outputs of my pre to the inputs of another pre/console by mistake and turned on 48V phantom on the other pre, which then goes to my pre via the backend. Of course, this scenario wouldn't happen to tapers but more likely for someone in a studio.)

(And not to be confused also with the input diodes on my pre, meant to clamp down high input voltages (example: 48V discharge) that may damage the pre.)

I just did a quick check with my bench PSU powering the preamp both with correct and reverse polarity voltages, and going back to correct polarity.

No problems. Dead as a doornail when reverse polarity powered.

Comes back to life when correct polarity is applied.

Just don't apply a reverse polarity greater than 400VDC. Otherwise, all bets are off. That's the max. limit. 


b) make the design respond passively if reverse polarity _IS_ applied.  Yeah the fuse might be an additional form of protection, but now that it blew, I still have a dead preamp that's gonna cost me $100 to get fixed by Apogee, so from my perspective, I'm not sure what's been saved with this design.

You know of course with my DC input protection, I'm losing $100 everytime someone applied reverse polarity and NOTHING happens to my pre. 

A fuse is not meant for polarity protection but for current overload protection. If the current flowing exceeds the rating of the fuse, the fuse opens up. For example, there is a short inside the unit, you apply power, instead of the external PSU being damaged because of a short in the load, the unit fuse opens up. It's not a form of reverse polarity protection. A fuse doesn't care which way the current goes.


final case design should indicate in the cover artwork at the power input what are the polarity and voltage requirements are...surprisingly, a good number of my electrical gadgets don't give polarity requirements at the jack.

From a cost standpoint, (remember, I'm a very tiny small operation not a huge manufacturer with deep pockets)... that's one more expense for silkscreening or engraving the backplate.  Maybe I'll put a metal sticker.


A second input on the case design is that I REALLY like the idea of standoffs at the rear of the unit,

You mean the bracket I installed in the back?

If the user is using straight XLRs, they do not get in the way.  But the straight XLR is still longer than the bracket. So the bracket is useless. 

If I put in a rear bracket, and somebody tries to use a right angle XLR, the brackets get in the way... and again, the right angle XLR is still taller than the brackets so the XLRs provide stress relief for the DC plug. So the bracket is kinda useless.

The only time the rear brackets provide stress relief is if you don't have XLR jacks plugged into the back, and only the DC plug.  But who uses a unit like that? i.e. DC plugged in, but the XLR jacks not plugged in?

I will be using DC locking jacks, so there is no danger of the DC plug falling out. And if you use straight or rt-angle XLR jacks, they will provide stress relief to the DC plug. Somebody also mentioned locking right-angle DC plugs. That would be even better.


I hope you still plan on using the vintage dial type knobs instead of the black ones in the pics at the top of this page.  It wouldn't be a big deal if they ended up being the blackies, but those vintage knobs are COOOL!

Yes, I agree! They are cool looking. I like them.  Either way, the knobs will be easy to replace. I could offer both styles as an option.

Thanks for your inputs. Much appreciated.

[Church-Audio]

Your preamp looks really good.. I like the vintage neve style knobs Anyway you should be very proud of it it looks sweet. One comment maybe instead of using jumper wires to go from board to board you can once you get into production use a pin socket system much better and more reliable.

http://www.erni.com/DB/PDF/STL-BUL/ERNI-PinHeader-Socket-e.pdf

[fivefishdiy]

One comment maybe instead of using jumper wires to go from board to board you can once you get into production use a pin socket system much better and more reliable.

Thanks Chris. 

I've been looking at something similar. Mill-Max, etc... Some of them do cost a lot (but I guess that's recovered in the labor savings), and I'll need a free common area on both the top PCB and bottom PCB so the two will mate/align.  The nice things about those Erni ones is it's ability to bridge a 1" distance board-to-board.

Ive seen blue and red cases.  Is color of the enclosure at all something that can be selected on order without undue extra expense?  I'm thinking dark grey or black might have appeal... and the Busman folks would want school bus yellow of course.

The enclosure itself is untouched. Only the front and rear panels will need to be machined. So I guess you can have a red case with black panels, or black case with red panels. I have not totally decided on case color... but for sure, I'm not leaning towards black. I have too many black stuff already... not unless the market really wants black.

[Jhurlbs81]

Is color of the enclosure at all something that can be selected on order without undue extra expense?  I'm thinking dark grey or black might have appeal... and the Busman folks would want school bus yellow of course.

Nextel Grey!

[Church-Audio]

One comment maybe instead of using jumper wires to go from board to board you can once you get into production use a pin socket system much better and more reliable.

Thanks Chris. 

I've been looking at something similar. Mill-Max, etc... Some of them do cost a lot (but I guess that's recovered in the labor savings), and I'll need a free common area on both the top PCB and bottom PCB so the two will mate/align.  The nice things about those Erni ones is it's ability to bridge a 1" distance board-to-board.

Ive seen blue and red cases.  Is color of the enclosure at all something that can be selected on order without undue extra expense?  I'm thinking dark grey or black might have appeal... and the Busman folks would want school bus yellow of course.

The enclosure itself is untouched. Only the front and rear panels will need to be machined. So I guess you can have a red case with black panels, or black case with red panels. I have not totally decided on case color... but for sure, I'm not leaning towards black. I have too many black stuff already... not unless the market really wants black.

Getting custom colors is very expensive. Unless you can buy say 50 cases and take them to get powder coated... I would really decide on a color and stick with it. Because in the end I think you will find keeping all the colors in stock to keep everyone happy is very expensive. I use Hammond boxes my self they are well made and reasonably priced and always in stock. I have seen some pin connectors in the digikey catalog that were pretty well priced. Its more money then wire for sure but in the end its faster to assemble no wires to strip.

Chris