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Old 5th April 2007, 06:35 AM   #1
impsick is offline impsick  United States
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Default need critique, Mic pre amp

Ok this is my first layout design. So i would appreciate some input on this board. Its a mic pre using the INA217 and DRV134 for balanced out. It has phantom power, so it can be used for condensor or dynamic mics. the OPA134 is a DC output control loop.
I've etched a board and have done some listening. I've tested a SuperLux CH8, AudioTechnica 2020, oktava MK-219, and for dynamic i tested an SM7.
The SM7 really shined the best out of all the mics which surprised me but then again it is the most expensive of them. the AT2020 was the hottest of them. I dont know if the way i have the gain is set up has anything to do with it.

anyways any ideas? how would i implement a -10 or -20dB pad?

Click the image to open in full size.
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Old 5th April 2007, 07:39 AM   #2
lineup is offline lineup  Sweden
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Default Re: need critique, Mic pre amp

Quote:
Originally posted by impsick

Ok this is my first layout design.

Its a mic pre using the INA217 and DRV134 for balanced out.

It has phantom power, so it can be used for condensor or dynamic mics.

the OPA134 is a DC output control loop.

I've etched a board and have done some listening.

I've tested a SuperLux CH8, AudioTechnica 2020, oktava MK-219, and for dynamic i tested an SM7.
The SM7 really shined the best out of all the mics which surprised me but then again it is the most expensive of them. the AT2020 was the hottest of them.


I dont know if the way i have the gain is set up has anything to do with it.

anyways any ideas?
how would i implement a -10 or -20dB pad?

.

very nice 'your 1st layout' work, impsick

you use high quality IC: INA217, DRV134
in balanced configuration

this + very good 'pro' microphones, should make result be nothing but top class

at least if you can come very close to best possible values for supporting components ( resistors, gains, power supply etc. )


/Regards, lineup
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Old 5th April 2007, 08:50 AM   #3
impsick is offline impsick  United States
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Default Re: Re: need critique, Mic pre amp

Quote:
Originally posted by lineup



very nice 'your 1st layout' work, impsick

you use high quality IC: INA217, DRV134
in balanced configuration

this + very good 'pro' microphones, should make result be nothing but top class

at least if you can come very close to best possible values for supporting components ( resistors, gains, power supply etc. )


/Regards, lineup
thanks
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Old 8th April 2007, 06:03 AM   #4
impsick is offline impsick  United States
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so nothing to be said on my layout ?
i know it can be better, anyone have any ideas?

anyone know how to put a -10 or -20dB pad on the input?
i found a website a while ago but now i cant find it.
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Old 24th May 2007, 12:58 PM   #5
lineup is offline lineup  Sweden
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Quote:
Originally posted by impsick

Anyone know how to
put a -10 or -20dB pad on the input?

I found a website a while ago but now i cant find it.

.

impsick
our forgotten audio friend


1. How is it going - project status?

2. Generally, to make -10dB / -20dB, is no big problem. Attenuate a signal.
... can be done in a number of ways - all of them good

3. It is when providing gain, +10dB / +20dB etc., we should take care.
... and those op-amps you use in your setup will ensure very good quality



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lineup
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Old 24th May 2007, 01:14 PM   #6
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What are 10uF caps near output intended to do?
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Old 24th May 2007, 02:58 PM   #7
lineup is offline lineup  Sweden
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Default DRV134 Audio Balanced Line Drivers Burr Brown Texas

Quote:
Originally posted by darkfenriz
What are 10uF caps near output intended to do?

Yes, darkfenriz, Good observation!

Looks like some bug / error.
Such big caps from output pin to GND will kill the signal, close to 100%

My guess they are suppose to be output coupling caps for the balanced XLR out,
and so instead should be put in series with the signal
= from output pins to output pads, jack.
Value of 10uF makes very good sense for this.


I know this about Those two 10uF:
They are NOT intended to be supply bypass caps for DRV134, V+ V-.
Because two such 1uF are already added at V+ V- (pins 5 & 6).
This is perfectly good as recommended ( 2x1uF ) in Texas datasheet:
Burr Brown DRV134, Audio Balanced Line Drivers
http://focus.ti.com/lit/ds/symlink/drv134.pdf



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Old 24th May 2007, 04:09 PM   #8
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the 10uf caps on the out are called for in the drv134 data sheet. I actually just used some Wima 6.8uf caps and my results have been good. The data sheet says to use the 10uf BP caps to minimize Vocm. it states that they dont affect the performance. I just wanted to play it safe, but i also included the option to have an unbalanced output which would bypass the drv134.

The mic pre came out very good. I still havent made a 10-20db pad yet, i've been side tracked. But it needs one, some mics are hotter then others.

Ive been working on this compressor design if someone woould like to check it over. I havent been able to test it yet cause i burnt out my THAT2252 rms detector but i should be getting another one today or tomorrow.

Here it is. and the power supply that is currently powering the mic pre and will be used to power both.
Click the image to open in full size.
Click the image to open in full size.

YOU ARE TOTALLY RIGHT ABOUT THOSE CAPS!!!! Thank you, very much for catching that guys. They should be ran in series, not to ground. It still works to ground haha. Anything visible in my compressor layout? Thanks again.
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Old 24th May 2007, 04:17 PM   #9
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Click the image to open in full size.
here is the schematic
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Old 24th May 2007, 06:41 PM   #10
lineup is offline lineup  Sweden
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impsick

Good nice artwork
Thanks for publishing your layout and schematics


almost anybody can come a long way
in making such nice web presentation

Just by getting some nice freeware Schematic Drawing Tool and layout editor.
And some reading and looking at recommended circuit in Datasheets.
Make small adjustments to circuits, to match you own needs.


Maybe somebody else would like to build 'your project' .....
and maybe suggest some small clever changes.
We still need some good idea, where and how to put -10dB -20dB.

Have you considered to put this attenuation somewhere close to output?
Maybe BEFORE last output buffer IC ...


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lineup
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