R
rex
Guest
On Sat, 09 Apr 2005 02:00:27 GMT, Fred Bloggs <nospam@nospam.com> wrote:
That must be one of the functions that the 4052 is doing. There is also
a mono recording mode where the left mic input is recorded in the left
channel but a 15 dB down version of the left mic is recorded on the
right channel. I forgot about all these complexities.
I just tried flipping the 20 dB atten on and it reduces the hiss. Maybe
that is telling me that something in the cap/transistor/switch region is
the source of the noise.
The line inputs come into the board away from where this 4052 is. I
think there may have been another 4052 closer to the line inputs but I'm
not sure and don't want to dismantle it agan now.
someone replaced 2086 with AD8066 or some other amps. No one in this
thread seems to think the 2086's are a problem, so I'll accept they are
probably ok.
I had a quick browse around the Zetex pages just now and didn't find any
SOT23 NPNs that match the marking code.
published and that one guy is improving S/N by 15 db with some kind of
mod. There are lots of posts various places around the net that say the
main flaw in this recorder is the mic preamps.
I do appreciate everone's comments here. It's helping me think about how
to look at it when I get to opening it up again.
I just remembered that this thing has a 20 dB mic attenuation switch.rex wrote:
I don't have any schematic, but I opened the thing up and had a look at
what is in the preamp area. Assuming the signal flows sensibly across
the board, there are (per channel) two largish electrolytics. Then a
couple sot-23 devices (transistors I assume) marked 62Z. Then an HC4052A
analog mux. Then a JRC 2068 op amp.
I was surprized to see that 4052 so close to the input. Not sure what
exactly it is doing.
The 4052 is most probably switching all those inputs XLR and LINE into
the preamplifier chain.
That must be one of the functions that the 4052 is doing. There is also
a mono recording mode where the left mic input is recorded in the left
channel but a 15 dB down version of the left mic is recorded on the
right channel. I forgot about all these complexities.
I just tried flipping the 20 dB atten on and it reduces the hiss. Maybe
that is telling me that something in the cap/transistor/switch region is
the source of the noise.
The line inputs come into the board away from where this 4052 is. I
think there may have been another 4052 closer to the line inputs but I'm
not sure and don't want to dismantle it agan now.
I saw a discussion somewhere on the net about audio circuits whereThe JRC2068 is a low noise wideband amplifier in
wide use in many designs, like a lot of Yamaha stuff- so they did not
skimp there.
someone replaced 2086 with AD8066 or some other amps. No one in this
thread seems to think the 2086's are a problem, so I'll accept they are
probably ok.
I have no reason to doubt that speculation on function.The 62Z SMD marking code most likely belongs to Zetex, and
if it's a simple 3-lead single transistor, it is probably a simple
emitter follower used to present a high (6.2K ohm they say) impedance to
the XLR input and a low impedance source for the JRC2068 for lowest
noise-and this does not preclude linearizing feedback from the 2068.
I had a quick browse around the Zetex pages just now and didn't find any
SOT23 NPNs that match the marking code.
Well as I said in another thread message, the specs aren't that good asFrom your description, the problem sounds like it is not that the
preamplifier noise floor is so high, but that your microphone signal
amplitude is so low- at least when loaded by the preamplifier- this is
borne out by your observation that the low-level dynamic mics are coming
in at lower amplitude than you are used to..
published and that one guy is improving S/N by 15 db with some kind of
mod. There are lots of posts various places around the net that say the
main flaw in this recorder is the mic preamps.
I do appreciate everone's comments here. It's helping me think about how
to look at it when I get to opening it up again.