I finally had some more time to look at the mic pre. Replacing the diodes fixed the problem. It is now functioning as is should.
Thanks to everyone for all your help take care, Jared -----Original Message----- >From: Brian Strate <[email protected]> >Sent: Feb 9, 2010 3:01 PM >To: [email protected] >Subject: RE: NEOTEK: Mic pre transistors > >Fader buffer chip U7. >Brian > >-----Original Message----- >From: [email protected] [mailto:[email protected]] On >Behalf Of Jared >Sent: Friday, February 05, 2010 5:12 PM >To: [email protected] >Subject: Re: NEOTEK: Mic pre transistors > >Hi everyone > >Ok I finally had some time to look at my misbehaving mic pre, and now I'm >even more confused. > >So after digging in a bit deeper this is what I've discovered. > >Fist problem distorted noise with no input (peak light flashing) replacing >the TL074 seemed to make a slight improvement. But the signal was still >distorted but not as bad. So I reflowed some solder, I replaced the 100 ohm >resistors feeding the chip, and the ones feeding the transistors, no change. >Then I swapped the transistors from a spare channel no change. This was >about the time I realized that the gain pot was not affecting the signal. It >seemed to have fixed gain (It may have been this way I don't think swapping >the transistors did this). By turning the pot its full range it only mad a >slight change in sound the last 10% of its travel the sound got darker and >that was all that i could hear changing. All of my testing has been with me >talking into a 57 so not very scientific, and I may not be hearing something >more obvious. > >Looking at this circuit is confusing me so I think I need someone with some >real knowledge to help guide away from replacing every component in the mic >pre. > >I have attached a copy of the schematic. > >Sorry for the long post >thanks, >Jared >(612)802-3150 > > >-----Original Message----- >>From: Ike Zimbel <[email protected]> >>Sent: Jan 26, 2010 2:55 PM >>To: [email protected] >>Subject: Re: NEOTEK: Mic pre transistors >> >>Hi Matt, >> All of the documentation that I have seen says "factory selected" >>on the 2SB737's, which are the only one of these transistors that I >>have seen (or at least noticed) in a Neotek mic pre. Incidentally, I >>have never seen one fail in a mic pre yet. Jared, I agree with Matt >>that you should check all of the other components 1st, both for >>soldering issues and value. Have the caps been done? >>best, >>Ike >> >>On 1/26/2010 12:36 PM, Matt Syson wrote: >>> Hi Jared >>> All or some of these transistors are approaching obsolete but should >>> be obtainable by post from the internet. >>> I would suggest getting a bag of them (they are not expensive) then >>> you can match them using a multimeter for similar Hfe. >>> (note, don't hold them for long as the finger temperature affects gain!). >>> You could simply fit one and it will work but distortion would be >>> reduced by matching. I don't suppose Neotek matched them originally >>> though. >>> It may be worth running the multimeter over the whole circuit >>> comparing it to others (DC conditions) as there may be something else >>> amiss. >>> Matt S >>> >>> Jared wrote: >>>> Hello everyone >>>> >>>> I'm having a problem with a series 1 mic pre (just the mic pre, line >>>> in is fine). I'm getting a lot of noise and extremely distorted >>>> signal. Everything looks fine visually. I swapped the chip and that >>>> didn't fix it. My next thought was that it could be caused by a bad >>>> transistor on the front end of the circuit. So I did a little >>>> looking and now I'm a bit confused. >>>> It seems that I need either of these transistors: 2SAB737, 2SA991, >>>> or >>>> 2SA1084 >>>> >>>> I'm sure their are others but this is what is in my console and the >>>> 2SA1084 was written in some of the documentation that I have. Does >>>> anyone have a lead on where these can be sourced or other >>>> replacement options? Also what is the best way to match them? Can it >>>> be a simple DMM hFE test? >>>> >>>> Also maybe I'm going down the wrong path, any other thoughts about >>>> what could be causing this? >>>> >>>> Sorry for the long post, >>>> >>>> Thanks, >>>> Jared >>>> ------ >>>> >>>> View the list online at: >>>> http://www.mail-archive.com/[email protected] >>>> >>>> You can unsubscribe at anytime by sending an email to >>>> mailto:[email protected] with "unsubscribe neotek" in the >>>> message body. If you have any difficulties, or questions --please >>>> send an email to mailto:[email protected]. >>>> >>>> The Neotek list is lovingly hosted by Catapult Web. Remember that >>>> any message or reply sent to the list will be automatically >>>> forwarded to all subscribers. >>>> >>>> Vive Le Neotek! >>>> >>>> Thanks. >>>> >>> ------ >>> >>> View the list online at: >>> http://www.mail-archive.com/[email protected] >>> >>> You can unsubscribe at anytime by sending an email to >>> mailto:[email protected] with "unsubscribe neotek" in the >>> message body. If you have any difficulties, or questions --please >>> send an email to mailto:[email protected]. >>> >>> The Neotek list is lovingly hosted by Catapult Web. Remember that any >>> message or reply sent to the list will be automatically forwarded to >>> all subscribers. >>> >>> Vive Le Neotek! >>> >>> Thanks. >>> >>> >> >>-- >>Ike Zimbel >>Zimbel Audio Productions Ltd. >>Toronto >>416-720-0887 >> >>"Studio House Calls". Authorized Warranty service for Allen& Heath, >Clear-Com, Drawmer, Soundcraft, SPL and Yamaha. Repairs and upgrades to >analog audio equipment including: AMEK, dbx, Neve, Neotek, MCI, Soundcraft >and more. Ask about our RF Frequency co-ordination services! >>www.zimbelaudio.com >> >>------ >> >>View the list online at: >>http://www.mail-archive.com/[email protected] >> >>You can unsubscribe at anytime by sending an email to >mailto:[email protected] with "unsubscribe neotek" in the message >body. If you have any difficulties, or questions --please send an email to >mailto:[email protected]. >> >>The Neotek list is lovingly hosted by Catapult Web. Remember that any >message or reply sent to the list will be automatically forwarded to all >subscribers. >> >>Vive Le Neotek! >> >>Thanks. > >------ > >View the list online at: http://www.mail-archive.com/[email protected] > >You can unsubscribe at anytime by sending an email to >mailto:[email protected] with "unsubscribe neotek" in the message body. >If you have any difficulties, or questions --please send an email to >mailto:[email protected]. > >The Neotek list is lovingly hosted by Catapult Web. Remember that any message >or reply sent to the list will be automatically forwarded to all subscribers. > >Vive Le Neotek! > >Thanks. ------ View the list online at: http://www.mail-archive.com/[email protected] You can unsubscribe at anytime by sending an email to mailto:[email protected] with "unsubscribe neotek" in the message body. If you have any difficulties, or questions --please send an email to mailto:[email protected]. The Neotek list is lovingly hosted by Catapult Web. Remember that any message or reply sent to the list will be automatically forwarded to all subscribers. Vive Le Neotek! Thanks.
