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Old 7th February 2006, 09:20 PM   #1
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Default $5 mic pre

Hey all, I have been reading about this $5 mic pre online.
http://www.record-producer.com/learn.cfm?a=3062
and then here http://www.record-producer.com/learn.cfm?a=3071

and finally here http://www.record-producer.com/learn.cfm?a=3080

it costs more that $5 to build, but whatever, I am jonesing for a new project to experiment with!
I can't find the 47uf 60v caps for which the schematic calls. any suggestions for substitutes? here is the pdf data sheet and schematic towards the bottom.
I can't find those caps anywhere. Anyway, take a look and thanks everybody!
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Old 7th February 2006, 09:46 PM   #2
Nisbeth is offline Nisbeth  Denmark
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I have been eyeing that design as well (well, in fact the original one from the DS) and although I haven't prototyped it yet, I have read good things about the INA217 in a couple of places. For this price I think its impossible to beat although I think I would upgrade it to a $7-pre and leave the diodes, the opamp and the RC on the phantom-supply in


/U.
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Old 7th February 2006, 09:49 PM   #3
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'Evening,
The capacitor ratings are both minimums in this case: fitting a cap larger than 47uF will improve the deep bass response of the amp and going higher than 60v will increase safety margin ie it should improve the working lifetime of the amplifier.

Nice one.
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Old 8th February 2006, 01:10 AM   #4
testlab is offline testlab  United States
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Interesting, although I cannot agree with the author about some of the component ommissions.

The protection diodes should be kept to clamp transients from 'hot plugging'. These can easily destroy the front end of the device. I would also add ferrite beads to choke off RFI and EMI.

The BB chip is not much different from the Analog Devices SSM2017/8 or the THAT1510/12. I have some AD pieces if you are interested. Also, check the app notes here http://www.thatcorp.com/icprod.html For other circuit delicacies.
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Old 8th February 2006, 10:57 AM   #5
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Default Re: $5 mic pre

Quote:
Originally posted by rockstudio

I can't find the 47uf 60v caps for which the schematic calls. any suggestions for substitutes?
I can't find those caps anywhere. Anyway, take a look and thanks everybody!
60V isn't a normal capacitor rating, a normal voltage would be 63V, and you should find those easily. As already suggested, the voltage specified is a MINIMUM and not a requirement.
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Old 8th February 2006, 05:50 PM   #6
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Thanks everyone! I figured that 60v wasn't a realistic cap rating, but I am a newb. Actually, I have a few more questions about the schematic, the gain pot at R7 (right?) should I eliminate R6 if I use a 10k pot, or should I use a 1k pot and keep R6? What about an inexpensive transformer on the output, is it necessary? The cable runs in my studio are merely 15ft.
I am kind of getting the hang of some of the basics now, and I'm getting really pumped!
Thanks again everyone!
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Old 8th February 2006, 05:53 PM   #7
Nisbeth is offline Nisbeth  Denmark
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I think the problem is in getting 63V bipolar caps(?)

Elfa in Scandinavia (my primary source for parts) has a suitable series of bipolars, but a quick look at digikey's website yields no results for the US members here.


/U.
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Old 8th February 2006, 05:58 PM   #8
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Since the caps in question C1 and C2 are in the audio path, shouldn't they be poly or metalized poly? I found some on ce distribution for $13.80 (47uf 630v) and the price keeps getting higher as the ufs increase. It seems like mouser doesn't stock too many caps above 1uf. Am I going the right way, or am I freaking myself out? I want to find some non polarized caps for less that $13.80!


here is the schematic again INA217 mic pre
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Old 8th February 2006, 06:03 PM   #9
Nisbeth is offline Nisbeth  Denmark
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Of course the most ideal would be if you can find PP or MKP caps, but as you've discovered it is no longer a $5-micamp If this was a commercial product I have no doubt the choice would be bipolar electrolytics, maybe bypassed with some small MKPs



/U.
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Old 8th February 2006, 06:08 PM   #10
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Thanks Nisbeth! I think I'll try some non polarized electrolytics!
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