Become a Site Supporter and Never see Ads again!

Author Topic: small ic preamp  (Read 8910 times)

0 Members and 1 Guest are viewing this topic.

Offline MIQ

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 215
  • Gender: Male
    • Stereo Mic Tools
Re: small ic preamp
« Reply #15 on: October 17, 2015, 11:56:11 PM »
weroflu,

Could you possibly provide the schema in a PDF or JPEG format?  Screen shot?  Attaching zipped Eagle CAD files is really cumbersome. It's not free ware, and even if it was, I have no desire to download a CAD pkg I will never use, just to look at a schematic.  If you want more feedback on your designs, you should make the designs more accessible IMO.

Miq
« Last Edit: October 17, 2015, 11:59:41 PM by MIQ »

Offline weroflu

  • Trade Count: (6)
  • Taperssection Member
  • ***
  • Posts: 343
Re: small ic preamp
« Reply #16 on: October 18, 2015, 02:06:24 AM »
jpg schems added.

a few posts back is the same preamp with schematic, all that was added was the plug-in power.






Offline MIQ

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 215
  • Gender: Male
    • Stereo Mic Tools
Re: small ic preamp
« Reply #17 on: October 18, 2015, 04:42:58 AM »
Thanks!

On the DPA schema you are shorting the inputs to AC ground through the battery and C9.  The DC blocking caps C3 and C4 need to connect to the other side of R3 and R4.  As shown, you will not have any signal reaching the gain stages. 

You could also put some high impedance ground reference resistors after C12 and C13.  It would keep the outputs from flying up to 1/2 B+ and causing a pop when you plug into a recorder. 

Miq

Offline weroflu

  • Trade Count: (6)
  • Taperssection Member
  • ***
  • Posts: 343
Re: small ic preamp
« Reply #18 on: October 18, 2015, 05:49:01 AM »
Thanks...

schematic updated

not sure how to decouple the opamp and feed power at the same time. ??


Offline MIQ

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 215
  • Gender: Male
    • Stereo Mic Tools
Re: small ic preamp
« Reply #19 on: October 18, 2015, 10:29:01 PM »
Looks like you've got it sorted out now.  You have to imagine the capsules' FETs drains hanging off the input jack as the rest of the circuit.

At the 50dB gain setting you will have some droop in response at low frequencies.  Even with C7/C8 at 220uF there will be a breakpoint at 22Hz.  This along with the 15Hz breakpoint caused by C3/C4 R5/R6 will cause you to be more than 3 dB down at 20Hz.  Not a huge deal but thought I'd mention it. 

You could increase C10/11 by an order of magnitude (220pF) and the high freq break point would still be out at 72kHz.  It's set to 720kHz right now. 

Miq

Offline weroflu

  • Trade Count: (6)
  • Taperssection Member
  • ***
  • Posts: 343
Re: small ic preamp
« Reply #20 on: October 19, 2015, 02:47:01 AM »
Thanks for your help.

I think I'll try to get the response as flat as possible, change the filter values a bit and lower gain somewhat.

http://rec.arts.movies.production.sound.narkive.com/1JkB8l4H/dpa-mics

DPA microphones are not "hot" in the usual sense that the element is
very sensitive. The DPA mics can be high or low current outputs
depending on the applied voltage and series resistance. They require
different wiring than other two wire mics because of their output
stage. They use a compound transistor output rather than the
conventional FET (field effect transistor). They have to be wired
according to figure 3 on this wiring guide.
http://www.lectrosonics.com/service/ServoBiasWiring.pdf


Offline MIQ

  • Trade Count: (0)
  • Taperssection Regular
  • **
  • Posts: 215
  • Gender: Male
    • Stereo Mic Tools
Re: small ic preamp
« Reply #21 on: October 19, 2015, 03:52:15 AM »
They require different wiring than other two wire mics because of their output stage.

Mr Fisher is talking about specifically wiring to the Lectrosonic transmitters.  This is not true in general. You do not need a series resistor or "servo bias" circuit, whatever marketing babble that is.  DPA mics will work fine with the simple 10k bias resistors fed from 9V like you have in your schema. 

The PDF link in your re-post of Mr Fishers post is dead.  Did you even try following it?

Miq

Offline weroflu

  • Trade Count: (6)
  • Taperssection Member
  • ***
  • Posts: 343
Re: small ic preamp
« Reply #22 on: October 19, 2015, 04:49:04 AM »
Yes you're right nothing special there.

working link

http://www.visonomedia.com/assets/pdf/lectrosonics_servobiaswiring_tn.pdf

he's just feeding 4v through 4k - all the lectrosonics have regulated 4v supply.


 

RSS | Mobile
Page created in 0.081 seconds with 32 queries.
© 2002-2024 Taperssection.com
Powered by SMF