I spent a little more time looking at the mic pre. The Pot seems to be working correctly and the traces are all good. The Line in and EQ cicuit are all working as they should be. The mixer was recapped a about two years ago, I looked at the electrolytic caps and replaced a few and reflowed some suspect solder. Nothing is changing the operation of the mic pre.
My next plan is to try swapping the ceramic caps or the diodes. I'll report back after I try that. thanks, Jared -----Original Message----- >From: Adam Manoucheri <[email protected]> >Sent: Feb 8, 2010 11:21 AM >To: [email protected] >Subject: Re: NEOTEK: Mic pre transistors > >Hey Jared- > >Like Jim, I had a channel that was doing exactly the same thing, and >didn't think about it until just now reading his post... It may be >completely unrelated to yours, but thought I would mention it at >least. Has your console been re-capped recently? I had a channel in >my Series II that suddenly started acting that way not long after a >re-cap. It drove me nuts, I poured over that channel strip for hours >at a time, to no avail... Eventually I found a spot at one of the >new caps (I don't recall exactly where it was, it was near the eq >section I think) where the traces looked to be shorted by solder, but >it was awful close, enough that I wasn't sure if it really was or >not. So, I decided to go ahead and remove the solder and reflow and >see if it made a difference...and it certainly did! It fixed the >problem completely. Apparently it was making just enough contact to >cause a problem; curious that it worked ok for a while, but then >started acting just like yours... > >Anyway, don't know if it'll help but thought I'd throw it in just in >case! > >Adam > >On Feb 8, 2010, at 11:05 AM, Jim wrote: > >> >> >> Hi Jared, >> >> I had a channel with a very similar problem that drove me nuts for >> a while. Try replacing both of the diodes and see what happens. I >> didn't analyze the circuit to determine the failure mode of one of >> them failing, but it fixed the problem. Give it a shot and let me >> know. Good luck! >> >> Best, Jim >> >> >> >> At 08:11 PM 2/5/2010, you wrote: >>> 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. ------ 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.
