Have a close look at the, IIRC, 100ohm resistors going to pins 4 and 11
on the IC. If one of those is bad it would make the whole works distort.
Likewise for the resistors that provide power to the 737's.
iz
On 1/26/2010 3:45 PM, Jared wrote:
Thanks Matt and Ike
I'll try to take a closer look at it within the next few days. The console was
recapped a little less than two year ago and has been functioning great ever
since. So I'm inclined to say that is is unlikely related to caps. But a bad
solder joint is definitely possible. I'll investigate that some more and
continue searching for some transistors to have on hand.
I'll report back with my findings,
Jared
-----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
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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
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or reply sent to the list will be automatically forwarded to all subscribers.
Vive Le Neotek!
Thanks.
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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
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