INA217 Build... a problem

Hi, I simply just use ExpressPCB to design the PCB and then use a couple Graphics programs to draw out the actual curcuit board, It is a Bit tedius but It is the only way i know how to do it...

Yes , I can share the design....

Here is my 4ch version....

INA217-4ch-pcb-0004.jpg

The Values for each Channel are the same and each channel is Identicle so you should be able to figure out the values from looking at the Parts overlay, I haven"t done the Offboard connections yet but you should be able to figure it out at the Phantom power is labeled, and the +in/-In are labeled and the Output is labeled...I suggest that you run the Input/Output grounds right back to a star ground or back to 0v Power ground as opposed to useing the Ground plane on the Board......

I also have PCB designs for Regulated PSU"s that also put out 48v Phantom if you are interested.....

any questions?? Just ask....
 
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Wow, man. You rock!

Thanks for sharing this. Time to get the PnP blue out. :D I'll have to print it at work, though.

Yeah, man, I'd DEFINITELY be interested in a PCB for a PS. I've been using FiveFishStudio's power supply, which is extremely nice, but I'd be interested in doing my own as well.

Thanks much!

Brandon
 
Oh yeah... another question...

Anyone know how much current these circuits pull?

All I can find on the datasheet is 12ma on page 3 under the power supply requirements. Is that a max?

Also, how much current should I assume on phantom per mic?

I'm trying to figure out how many channels I can run on this PS. :)

Thanks!

Brandon
 
Hi, Here is a link to a Mic preamp PSU I have used on quite a few occations,

http://1176neve.tripod.com/id11.html

It is for the "Green Mic pre" but will work for any PRE that needs 2x15v-18v DC and 48v Phantom power....

This one uses LM78xx/79xx regulators for the Preamp voltage and a voltage Tripler and a LM317 regulator for the Phantom power.....

I have actually moved on to a PSU that used exclusively Lm317/337 regulators but I couldn"t find the design right off hand but this one woks just about as well.....Pluss it is really quite cheap to build (Maybe less than $10 in parts not includeing the Power transformer......


Cheers
 
Your Five fish studio"s power supply should be good enough to Power Several channels....I don"t know the exact current consumption of the INA217 but it shouldn"t be more than 20-30ma max which means you can power at least 50 channels (30ma x 50 =1.5amps, the LM317/337 regulator can put out a max of 1.5amps each with good heatsinking) ,So you can pretty much run as many channels you can fit inside your Chassis....

As for phantom power the Max current output for each channel will be 14mA but most Mics will draw maybe 4mA to 8mA so the Phantom supply should be able to keep up with as many channels as you like......


Cheers


PS: there was a small Mistake in the PCB is posted above but I fixed it so if you copied the PCB above copy it again as the mistake has been fixed ....
 
Very cool, man. Thanks for the posts. :)

Is that your site? Very nice, man.

If it is, I may try those LED meters. :) Not sure how much current they'd pull, tho. We'll see.

And thanks for the heads up on the mistake. I'll download the image again.

Brandon
 
Actually I just checked my uploaded image and for some reason the new image didn"t upload so here it is again....

The mistake was just a small piece of trace was missing from the Power rails to the positive of the Bypass cap on the channel second from the left ,very easy fix , that is when Photobucket is cooperateing...This one is fixed...sorry about that...

Cheers
 

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Minion said:
Hi, I simply just use ExpressPCB to design the PCB and then use a couple Graphics programs to draw out the actual curcuit board, It is a Bit tedius but It is the only way i know how to do it...

Yes , I can share the design....

Here is my 4ch version....

INA217-4ch-pcb-0004.jpg

The Values for each Channel are the same and each channel is Identicle so you should be able to figure out the values from looking at the Parts overlay, I haven"t done the Offboard connections yet but you should be able to figure it out at the Phantom power is labeled, and the +in/-In are labeled and the Output is labeled...I suggest that you run the Input/Output grounds right back to a star ground or back to 0v Power ground as opposed to useing the Ground plane on the Board......

I also have PCB designs for Regulated PSU"s that also put out 48v Phantom if you are interested.....

any questions?? Just ask....
Click to expand...


I was wondering if you had the actual circuit diagram that you used and could send me a copy or paste it here?

Maybe you even have PC boards for sale. Please let me know. Regards,
 
The "actual circuit" is from the INA217 datasheet. You can google it to get it. Its fairly easy to find. :)

Brandon
 
Yes it is pretty much a stripped down version from the Datasheet , pretty much the same minus the DC Servo and Hot plugging protection pluss an output cap added and a resistor for the Ouput RC Filter ... it isn"t the most ideal PCB but it works , could be made much smaller and layed out much better ....

Cheers
 
A few problems with that schemo:

- R1 is too high, it creates a noncompliant phantom rail. It will still work fine with most microphones, but why bother to build your own stuff wrong? Phantom resistors must be 6k8 +/-20%, such that the net supply resistance cannot exceed about 4K. With R1, it's 4.4K. That will create an excessive voltage drop under load versus spec. For example, a mic that draws 8mA will drop 35V with that schemo, versus 27V at spec, for a voltage at the mic of 13V vs. 21V (also see R4 discussion below). That difference could be material to some microphones. How about 100 instead, and a properly filtered +48V upstream?

- R4 is insanely small. Do we really need 8mA to drive an indicator LED? Especially when it will drop 8V across R1, meaning that our phantom supply is really only 40V at best? How about 22K, for 2mA, and only a 2V drop across R1 (much less once we fix it)! And if we really do want 8mA for a LED, that needs to be either mechanically switched separately or driven from its own transistor.

- C2 and C3 are much too small. I suspect this is a symptom of the desire to use film capacitors, but it will show measurable bass rolloff at 20Hz. Try 47uF instead.

- 1.5K reverse log pots are less than easy to find. Instead, here's an easy trick: get a 5K dual audio taper pot, disassemble, and swap the front and rear pins. Wire the two sides in parallel. Voila, a 2.5K reverse taper pot :)

- R8 is bigger than necessary. Why raise output impedance just for fun? Try 47 or 150.

- Again, C3 is way too small, unless you know you are only driving a 10K ohm load.

- Why not an impedance balanced output? Doesn't cost much, lots of benefits . . .

What isn't shown is the quality of the power supply, which is really critical for a good pre. Yes, these chips have lots of PSRR, but that's not always true of the phantom rail to the mic, and the method given to filter phantom is far less than desirable.
 
Ok, so... after a stinkin' year, I'm finally getting ready to put these PCBs to use. :)

I have a question, mshilarious. What is the 100uF cap that goes from (I think) pin 4 to ground, in addition to the .1uF cap?

I think I may start drilling the PCBs tonight. I'm pumped! I'm using the Five Fish DIY power supply, and the reason I got it was so that I could stick this thing in a 1 space rack. :) 8 channels, one rack. Love it!

Brandon
 
Also, I would love to add a peak LED to the channels.

Any thoughts on this? Would it be simple or a bit complicated to do, and how should it be done?

Brandon
 
For some reason I can't see the schemo right now, but those are probably both filter caps-100uF on the power supply, and 0.1uF right against the IC. This is required by the datasheet. I am usually doing parts on both sides of the PCB and using SMT parts, so my 0.1uF caps go right between the supply pins.

Basic way to do a peak LED: comparator. Low parts count, voltage divider off the output driving a BJT with a LED as the load to the collector. Set the voltage divider such that the on voltage of the transistor gets hit at whatever you want your peak voltage to be.
 
Looked up some Grayhill rotary switches like the ones in the FiveFish SC-1... holy crap... $160 for 10 of them... that more than doubles my project cost... don't think I can swing that for now. heh.

Looks like I'll be grabbing and trying a 10k reverse from Blue Bear and hope for the best. :) Maybe I'll add some Grayhills later... but good grief, I can't afford to right now.

Brandon
 
10K reverse log will work fine; probably better than the original 1.5K. The gain equation is G = 1 + (10000/R), so minimum gain with 1.5K is 7.6, or 17dB. That's not all that helpful, really. 10K gives you min gain of 2, or 6dB. On the minus side, the wider gain range gives you a somewhat less linear control.
 
Thanks!

As far as the peak value goes, how would I calculate this? Would I just check the max output and calculate the voltage divider to light the LED at about 3dB below this?

Brandon
 
NeveSSL said:
Thanks!

As far as the peak value goes, how would I calculate this? Would I just check the max output and calculate the voltage divider to light the LED at about 3dB below this?

Brandon
Click to expand...

Kinda. Just remember to convert RMS voltage to peak voltage. But you could simplify a bit--if you know your power supply is +/-15V*, set it at +13V as you know your amp can get closer to the rails than 2V.


* Note that you have to consider full-wave rectification of your audio signal if you want an absolutely accurate peak meter. This is so you can detect asymmetrical signals. That will require quite a few more parts, which a lot of cheaper meter circuits will skip.
 
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