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.
