Weird problem with a preamp with 3 band EQ module - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th July 2013, 12:40 PM   #11
diyAudio Member
 
csom's Avatar
 
Join Date: Dec 2012
Location: Homeless, sweet homeless.
Quote:
Originally Posted by Mooly View Post
Pleased to hear its working

I wouldn't have thought you needed a pre amp as well as this because this tone control has gain. The microphone input is high gain (100) but has a really low input impedance (1K) so will not suit all mics.
I removed the Rod's preamp and connected this directly to LM3886.
Now this module is working nicely.

So a big thank you again

At present I'm using a 600 Ohm Mic, the response is very satisfactory as I have checked.
But in future I might purchase a professional mic.

So could you kindly suggest some modification to make the microphone work with all types of dynamic microphones?
Or is there any better professional easy to build circuit that is endorsed by you that I can build?
__________________
Warm regards, Som
  Reply With Quote
Old 6th July 2013, 12:46 PM   #12
diyAudio Member
 
csom's Avatar
 
Join Date: Dec 2012
Location: Homeless, sweet homeless.
Quote:
Originally Posted by gfiandy View Post
Hi, this circuit should be Ok to drive power amp directly so you can remove preamp.

Is the microphone input working ok on this design as it has no phantom power supply. If you have a fairly good microphone it is likely it expects a phantom supply, even most PC microphones expect a bias voltage to work.

Regards,
Andrew
Thank you Andrew, I've connected the preamp directly to the Power amp now. Working good.

The 600 Ohm mic I bought some days ago came with a 2 pin jack.
http://www.diyaudio.com/forums/attac...2-pin-jack.jpg

The performance of this mic when connected to this module is not too bad.

But I want to build a professional circuit to record voice with computer.

If you could kindly suggest some circuits with PCB layout that is easy to make it would be great.

Thank you.
__________________
Warm regards, Som
  Reply With Quote
Old 6th July 2013, 02:00 PM   #13
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
You are best looking at building a separate mic preamp that suits the actual mic you end up buying. You need to look at the impedance the mic is designed to work into and also how much gain you need. A simple opamp circuit isn't always ideal in terms of noise etc when matching to a mic. A simple discrete circuit could be better.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 6th July 2013, 02:37 PM   #14
diyAudio Member
 
csom's Avatar
 
Join Date: Dec 2012
Location: Homeless, sweet homeless.
Quote:
Originally Posted by Mooly View Post
You are best looking at building a separate mic preamp that suits the actual mic you end up buying. You need to look at the impedance the mic is designed to work into and also how much gain you need. A simple opamp circuit isn't always ideal in terms of noise etc when matching to a mic. A simple discrete circuit could be better.
Oh, thank you Mooly.
Could you please recommend such a discrete circuit for me to build?
__________________
Warm regards, Som
  Reply With Quote
Old 6th July 2013, 02:42 PM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
It's not something I have ever built or looked into so you would have to search but some quick examples,


Low Noise Microphone Preamp
Low Noise Balanced Microphone Preamp
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 6th July 2013, 03:02 PM   #16
diyAudio Member
 
csom's Avatar
 
Join Date: Dec 2012
Location: Homeless, sweet homeless.
Quote:
Originally Posted by Mooly View Post
It's not something I have ever built or looked into so you would have to search but some quick examples,


Low Noise Microphone Preamp
Low Noise Balanced Microphone Preamp
Thank you so much Mooly
I will try those and ask for help if needed.
__________________
Warm regards, Som
  Reply With Quote
Old 7th July 2013, 07:39 AM   #17
diyAudio Member
 
csom's Avatar
 
Join Date: Dec 2012
Location: Homeless, sweet homeless.
Mooly, could you kindly tell me if this circuit biasing is okay or not?
http://construyasuvideorockola.com/d_preamp_tonos.php

Here is the PDF
http://construyasuvideorockola.com/downloads/preamp_tonos_st.pdf

Should there be any difference sound wise between this one and the earlier one that you helped me fix?
__________________
Warm regards, Som
  Reply With Quote
Old 7th July 2013, 09:54 AM   #18
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Similar problem, the 100K at the input is on the wrong side of the cap. The opamp has no bias. 500K volume pot is poor choice too. 10 or 22K would be better with larger coupling cap.

All these circuits obviously haven't been checked.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote
Old 7th July 2013, 10:36 AM   #19
diyAudio Member
 
csom's Avatar
 
Join Date: Dec 2012
Location: Homeless, sweet homeless.
Quote:
Originally Posted by Mooly View Post
Similar problem, the 100K at the input is on the wrong side of the cap. The opamp has no bias. 500K volume pot is poor choice too. 10 or 22K would be better with larger coupling cap.

All these circuits obviously haven't been checked.
Thank you so much Sire.

1. Should I increase the value of 100K to 470K ( on the right side ) here too?
or add another 470K to the GND like you advised me earlier?

2. 500K pot is hard to find here. I will use a 22K.

3. It's very unfortunate that the circuits have not been checked properly before posting though the instruction/diy spirit of the site is really good.
I am following the site only because they offer PCB layout in PDF format.

But thank God, you are there to help me correct the problems.
I might attempt some more projects from that site and ask your guidance to rectify them.
Kindly keep an eye on this thread.
__________________
Warm regards, Som
  Reply With Quote
Old 7th July 2013, 10:46 AM   #20
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
The total resistance seen at the input will determine the input impedance. A 470K is fine for the opamp bias. If you leave the 100K then the input impedance will be around 82K (470K and 100K in parallel at AC). If you omit the 100K then the input impedance is just 470K if that is the value you use.

Either option is fine for modern source components.
__________________
-------------------------------------------------------
A simulation free zone. Design it, build it, test it.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
10 Band EQ Fiddlesticks Instruments and Amps 5 28th February 2012 01:18 AM
3 band eq with paramertic kendarmstat Analog Line Level 0 7th June 2011 03:20 AM
mec 3 band eq kendarmstat Instruments and Amps 3 2nd May 2011 01:59 AM
EQ band components ianmgreen Construction Tips 2 23rd April 2011 12:41 PM
3 band eq kendarmstat Analog Line Level 0 3rd April 2011 02:56 PM


New To Site? Need Help?

All times are GMT. The time now is 01:21 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2