RichEEM, that is the bias for the oh wait. That IS R30 adjustment.
Left off the decimal point.
It's actuall something like -.416mV.
That is what is listed in the HP manual. So it should be less than that? As listed.
Left off the decimal point.
It's actuall something like -.416mV.
That is what is listed in the HP manual. So it should be less than that? As listed.
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Somehow I had 623469 characters too many and needed to cut them down
to only 30,000 characters. Even I'm not verbose. That works well if you
are getting paid by the inch (for publishing) but not here at DIY.
wondering how to get that down.
It's about to go into clipping. Heck the output is 6.2 volts. This is
QAs Low Noise Differential probe were looking at it though,
Demian recommended I purchase. I didn't fry my QA400 yet
looking at the power supply rails. : )
This is with the trace cut and 105 ohm resistor at pin6.
I guess it would like 200 ohms or more?
Add more feedback to it?
Larger Cap?
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Which cap? The cap around the U1 feedback R (fixed resistor+pot) should be no larger than 150pF if you want the oscillator to work over its full range. This cap must be a C0G or NPO or silver-mica or polystyrene -- do NOT use an ordinary ceramic cap.
Ok, where is where I am.
Nothing I do makes a bit of difference.
Turning C30 makes no difference other than to set bias,
I presume. It just varies voltage from +2or 3 Volts to -600mV.
I checked and reset R51 pot to 2K.
I checked and reset R50 pot to 2K.
C47 is now1000pf silver mica.
Just to check I also removed the LME49740 from socket
and replaced it back with original 741quad op amp?
All signal RCA are disconnected.
the A4 board is removed.
The power supply looks fine now. That was to meter.
The QA190 Low Noise Differential Probe is noisy
and compounds the problem.
Also note, the oscillator level pot and level control
have no affect on A1U1 output.
Could any of these be attributable to a fried Q2 JFET?
Frequency adjust knobs seem to work fine as I've seen
the fundamental move, along with all the harmonics.
I've also replaced a1u1 when trying to removed
pin six scope probe cause half of it to come up and
disfigure it.
I've got some AVX Multilayer Ceramic Cap, MLCC .1uf 50V
and some TDK Multilayer Ceramic Caps, MLCC .1uf 50V.
They are supposed to be of the C0G & NP0 types.
Also the white box cap that I was using was of
stacked poly Carbonate/poly styrene.
the brown blob caps polycarbonate/polystryene.
Nothing I do makes a bit of difference.
Turning C30 makes no difference other than to set bias,
I presume. It just varies voltage from +2or 3 Volts to -600mV.
I checked and reset R51 pot to 2K.
I checked and reset R50 pot to 2K.
C47 is now1000pf silver mica.
Just to check I also removed the LME49740 from socket
and replaced it back with original 741quad op amp?
All signal RCA are disconnected.
the A4 board is removed.
The power supply looks fine now. That was to meter.
The QA190 Low Noise Differential Probe is noisy
and compounds the problem.
Also note, the oscillator level pot and level control
have no affect on A1U1 output.
Could any of these be attributable to a fried Q2 JFET?
Frequency adjust knobs seem to work fine as I've seen
the fundamental move, along with all the harmonics.
I've also replaced a1u1 when trying to removed
pin six scope probe cause half of it to come up and
disfigure it.
I've got some AVX Multilayer Ceramic Cap, MLCC .1uf 50V
and some TDK Multilayer Ceramic Caps, MLCC .1uf 50V.
They are supposed to be of the C0G & NP0 types.
Also the white box cap that I was using was of
stacked poly Carbonate/poly styrene.
the brown blob caps polycarbonate/polystryene.
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Nope, center position. If R30 isn't changinganything, then a bad FET is a good hunch. You want one with Rdson of about 30 ohms or less. Try a PN3091 or 3092, or a J105. You can put the scope probe on the junction of the FET drain and R53 -- if there is effectively no signal, the the fET could be shorted; if there is a lot of signal, then the FET could be open. The gate voltage in operatgion wants to be about 0.5VDC at 1kHz, and you set that with R30, the gain control. Then the AVC circuits adjust the output voltage to around 6.3VRMS -- mine is actually about 6.65VRMS when distortion is very low. RE C47, try 220pF and see what hapens at 10kHz or more.
Dick did you mean PN4091/92. I tried a J105. It didn't work very well.
You might also try a PN4391/92.
If you don't like those I still have a bunch of the original part number. Not the HP select though.
Now this is real interesting:
That plot was taken at the front panel oscillator output, the level control works
there, for that output location.
Along with that, I still have my mini gator hooked up to the
pin 6 of A1U1, that we are discussing. That looks like this:
That plot was taken at the front panel oscillator output, the level control works
there, for that output location.
Along with that, I still have my mini gator hooked up to the
pin 6 of A1U1, that we are discussing. That looks like this:
Just for grins, I wanted to see what it looked like at the output
of the buffer amp too. That is shown here:
of the buffer amp too. That is shown here:
Finally, here at the output of the Buffer amp as shown below:
So, clearly we can deduce that buffer amp is kind of important.
I'm using an OPA134. With this new adventure I won't what
the LME49710 metal can will do in this position?
I still have concerns over the A1U1 in this position,
that buffer really cleans up a lot of hash, but how?
How much better would this be with the LT1468 not
being driving into near clipping?
Also, how much better would it be to use LT own buffer for
the LT1468? The LTC1605?
Wondering what to do to clear up the A1u1 currently the
LT1468. Any ideas?
So, clearly we can deduce that buffer amp is kind of important.
I'm using an OPA134. With this new adventure I won't what
the LME49710 metal can will do in this position?
I still have concerns over the A1U1 in this position,
that buffer really cleans up a lot of hash, but how?
How much better would this be with the LT1468 not
being driving into near clipping?
Also, how much better would it be to use LT own buffer for
the LT1468? The LTC1605?
Wondering what to do to clear up the A1u1 currently the
LT1468. Any ideas?
Finally, here at the output of the Buffer amp as shown below:
So, clearly we can deduce that buffer amp is kind of important.
I'm using an OPA134. With this new adventure I won't what
the LME49710 metal can will do in this position?
I still have concerns over the A1U1 in this position,
that buffer really cleans up a lot of hash, but how?
How much better would this be with the LT1468 not
being driving into near clipping?
Also, how much better would it be to use LT own buffer for
the LT1468? The LTC1605?
Wondering what to do to clear up the A1u1 currently the
LT1468. Any ideas?
You didn't by any chance happen to buy the LT1468-2 did you?
Now hows that sentence for double negatives.
David, Nope no 1468-2s. But I almost did based on old posts.
for the non compensated opamps.
UNLESS the lot of these are mis marked?
Thank you for the offer of some JFETS.
RichEEM, did you mean R52 (100 ohm)? That is where
the FET, C30, and Drain would all go together.
Now I know why you quit modding yours and got pissed off at it.
I'd fling mine across the room but I'd cause much more damage
to fix that, then fiddle with this boat anchor. Heck with my luck
this thing would float and my boat would drift off.
for the non compensated opamps.
UNLESS the lot of these are mis marked?
Thank you for the offer of some JFETS.
RichEEM, did you mean R52 (100 ohm)? That is where
the FET, C30, and Drain would all go together.
Now I know why you quit modding yours and got pissed off at it.
I'd fling mine across the room but I'd cause much more damage
to fix that, then fiddle with this boat anchor. Heck with my luck
this thing would float and my boat would drift off.
I didn't get pissed off it. I stopped modding it because I wasn't getting any further results.
The monitor output is far cleaner, lower noise and lower distortion that it was.
It now agrees with my measurement right off the notch filter. Gain scaled of course.
The monitor output is far cleaner, lower noise and lower distortion that it was.
It now agrees with my measurement right off the notch filter. Gain scaled of course.
David,
Yes, I also want mind to do that as well.
I've got to get through this first.
It was U10, U4 and maybe U6 over at the Meter board?
Did you change the filters OpAmp Quad?
Yes, I also want mind to do that as well.
I've got to get through this first.
It was U10, U4 and maybe U6 over at the Meter board?
Did you change the filters OpAmp Quad?