Have you placed your system side by side with (parallel test paths) more expensive commercial analyzers to see if they agree in individual harmonic levels measured below -100dB?
Only when I added in a notch filter did the measured individual harmonic levels come close to one another.
Demian (1Audio) has got to within 5dB with his CPU based system. Which is amazing for the cost involved.
I picked up the 339A for 200-250 dollars each. Some like the wide range of selectable source freqs which are -120dB THD levels. I like to tune a circuit for lowest THD with an analog meter better than a digital system which you have to wait for refresh/update cycles. And, the 339A is harder to blow up with over voltage.
-RNM
Last edited:
RNMarsh,
That's good point! and I have a HP339A on hand.
Im wonder if it's possible to improve the analisys part og HP339. espectical for the noise floor, Distortion. So, feed the signal of under test device to the HP339A, then take out signal from after the Notch filter, feed it to a Specture analysiser or a ADC board. that my thought 2 years ago. But not achieve yet.
Am I right? or there is some limitation bloking me?
thanks.
Roger Wu.
HP 339A Process
Well I started, yeah.
Replaced Power Supply Caps with some Panasonic NHG...4700 microfarad
35V x 4.
Replaced the Level Pot...simple 20 minute job turned into hours.
Me thinks the original extension was hand made and someone
just stripped out one of the set screws for the pot.
Measured and cut the pot shaft and beveled it.
Tightening the set screw kept pushing the shaft out.
Set screws then kept falling out with one set screw disappearing
all together. Can't find it anywhere, in nor outside the
analyzer...which worries me it got lodged into something inside.
I ended up tapping it to 6-32 and used a brass set screw.
Replaced the 741 Quad opamp with socket & LME49740.
More to come as I can get to it.
Well I started, yeah.
Replaced Power Supply Caps with some Panasonic NHG...4700 microfarad
35V x 4.
Replaced the Level Pot...simple 20 minute job turned into hours.
Me thinks the original extension was hand made and someone
just stripped out one of the set screws for the pot.
Measured and cut the pot shaft and beveled it.
Tightening the set screw kept pushing the shaft out.
Set screws then kept falling out with one set screw disappearing
all together. Can't find it anywhere, in nor outside the
analyzer...which worries me it got lodged into something inside.
I ended up tapping it to 6-32 and used a brass set screw.
Replaced the 741 Quad opamp with socket & LME49740.
More to come as I can get to it.
@sky2city -- the residual of the 339A analyzer section is dominated by a large 2nd Harmonic spike in the output of the notch filter. Noise is not the biggest problem, but it will be after the harmonic is killed. So far, I have not found a way to get rid of the 2nd H. But I also have not worked on mine in a long time. Non-inverting gain stages have higher ditortion than inverting stages, so the solution may be an all-inverting topology. May be easier to start from scratch.
@ChrisA -- the reading will not be "0.0", but rather will be the residual of the analyzer, which in mine is about 0.001% or 10 parts per million at 1kHz. That is very low -- measuring ppm of anything is a challenge; sadly it's not low enough for modern amplifiers.
@ChrisA -- the reading will not be "0.0", but rather will be the residual of the analyzer, which in mine is about 0.001% or 10 parts per million at 1kHz. That is very low -- measuring ppm of anything is a challenge; sadly it's not low enough for modern amplifiers.
Hi Dick,
I don't have the experience why non-inverting gain stages have higher ditortion than inverting stages.
But I fonud that inside the in HP339 the preamps (U100,U101) is non-inverting gain stages. Maybe it the root cause, but I am not sure. is there any theory or paper prove that or talk about that the HD diff. b/w non-inverting gain stage and inverting gain stages?
I don't the manual of VP 7722. so check the schematic of Shibasoku AD-725B (Just got it from Demian, many thanks to him).the first amp (use discrete circuitry) is a non-inverting gain stage. and next amps: QA1(LM318N),QA2 (TL083N) are inverting gain stage. I am a little confused.
Correct me if I am wrong.
-Roger.
I don't have the experience why non-inverting gain stages have higher ditortion than inverting stages.
But I fonud that inside the in HP339 the preamps (U100,U101) is non-inverting gain stages. Maybe it the root cause, but I am not sure. is there any theory or paper prove that or talk about that the HD diff. b/w non-inverting gain stage and inverting gain stages?
I don't the manual of VP 7722. so check the schematic of Shibasoku AD-725B (Just got it from Demian, many thanks to him).the first amp (use discrete circuitry) is a non-inverting gain stage. and next amps: QA1(LM318N),QA2 (TL083N) are inverting gain stage. I am a little confused.
Correct me if I am wrong.
-Roger.
The usually increased distortion of noninverting opamp configurations is a result of common-mode effects. In a noninverting configuration, the input signal appears as common-mode signal to the opamp. Both the open-loop gain and input impedance of an opamp is (although only weakly) dependent on the applied common-mode voltage. The resulting gain modulation is observed as increased distortion. The effect increases at high frequencies and with source impedance.
You may want to check out my opamp measurement series for practical results: www.sg-acoustics.ch/analogue_audio/ic_opamps/
Samuel
You may want to check out my opamp measurement series for practical results: www.sg-acoustics.ch/analogue_audio/ic_opamps/
Samuel
I'm stuck at the OSC output.
Looking at the monitor output is useless, I think DDR (David/Demian/Richard)
did and I'll have to find a pick off point without having to take all the
pots and the face off the analyzer.
I have to go back through and find Davids notes for grounding also...
as a hand around the face of the meter changes readings.
Other question, who makes a good set of open end or wrenches that is
offordable that goes to at lease 3/8-inch, 7/16-inch, and 11mm?
Even my smaller stuff wouldn't fit the pot nut...old Craftman, Taiwan made,
Proto, nor Vulcan....I got lucky and didn't break off anything...did some
minor bending. PITA is right, thanks RichEEM for the heads up.
No wonder David was going to blow it off more than once.
Stay tuned for pics at 10 O'clock, (if developed and bicycled over), if you haven't heard the news I'm just a few blocks
away from EBOLA ground zero.
Kids exposed, also all the big retail chains, wally world, etc...
planning on driver a little bit farther away for a few weeks
until no one else show's up with it for 21 days or so.
Rather be safe than loose my little girl.
Looking at the monitor output is useless, I think DDR (David/Demian/Richard)
did and I'll have to find a pick off point without having to take all the
pots and the face off the analyzer.
I have to go back through and find Davids notes for grounding also...
as a hand around the face of the meter changes readings.
Other question, who makes a good set of open end or wrenches that is
offordable that goes to at lease 3/8-inch, 7/16-inch, and 11mm?
Even my smaller stuff wouldn't fit the pot nut...old Craftman, Taiwan made,
Proto, nor Vulcan....I got lucky and didn't break off anything...did some
minor bending. PITA is right, thanks RichEEM for the heads up.
No wonder David was going to blow it off more than once.
Stay tuned for pics at 10 O'clock, (if developed and bicycled over), if you haven't heard the news I'm just a few blocks
away from EBOLA ground zero.
Kids exposed, also all the big retail chains, wally world, etc...
planning on driver a little bit farther away for a few weeks
until no one else show's up with it for 21 days or so.
Rather be safe than loose my little girl.
Last edited:
Nope,
Just the first time someone in the Texas/US was walking around with
Ebola and didn't know it. Went to the ER they gave him antibiotics
and released him. A couple of days later, came back in...much worse.
Now, he went to four schools etc and we don't know where else he went
as he was infected, sick, and contagious.
Presbyterian Hospital Dallas - Used to be great. Now it's the same crappy
hospital I took my wife when she was miscarrying....
....I rush my wife in a wheelchair into the ER, dripping with blood
all over us, wheel chair and all then the fricking ER lady looks at us,
then ignores us and continues to chat it up with her home girls.
Looking at us now as we get to the desk she tells me I have to fill out
the forms before they can admit her and pushes over to me a clipboard
with paperwork to fill out.
I have to yell at them, that this is an emergency and my wife is dripping
blood from her womb and its all over the the chair, floor, etc.
After they started caring for her and things started settling down,
I moved the car to the corner of the parking lot. We ended up
losing the baby.
If that wasn't bad enough, as I went to get some personal things
for my wife, home girl started complaining to the valet as to where
I parked. It ended up taking a uniformed officer to tell them it was
fine where I parked.
I hate what that place has become, a selfless suction to take everyone
financial resources.
I gotta find an FFT to post here.
Just the first time someone in the Texas/US was walking around with
Ebola and didn't know it. Went to the ER they gave him antibiotics
and released him. A couple of days later, came back in...much worse.
Now, he went to four schools etc and we don't know where else he went
as he was infected, sick, and contagious.
Presbyterian Hospital Dallas - Used to be great. Now it's the same crappy
hospital I took my wife when she was miscarrying....
....I rush my wife in a wheelchair into the ER, dripping with blood
all over us, wheel chair and all then the fricking ER lady looks at us,
then ignores us and continues to chat it up with her home girls.
Looking at us now as we get to the desk she tells me I have to fill out
the forms before they can admit her and pushes over to me a clipboard
with paperwork to fill out.
I have to yell at them, that this is an emergency and my wife is dripping
blood from her womb and its all over the the chair, floor, etc.
After they started caring for her and things started settling down,
I moved the car to the corner of the parking lot. We ended up
losing the baby.
If that wasn't bad enough, as I went to get some personal things
for my wife, home girl started complaining to the valet as to where
I parked. It ended up taking a uniformed officer to tell them it was
fine where I parked.
I hate what that place has become, a selfless suction to take everyone
financial resources.
I gotta find an FFT to post here.
Last edited:
These are the result of three changes:
1. The LME49740
2. Level Pot
3. Electrolytics in the power supply.
I haven't even gone through and adjusted any pots yet
for low distortion, or H2, H3, etc. It sure did clean up
nicely though. More to come, no LT1468s yet.
I'm looking for some of the LME49710 metal cans
ya'll spoke of too.
1. The LME49740
2. Level Pot
3. Electrolytics in the power supply.
I haven't even gone through and adjusted any pots yet
for low distortion, or H2, H3, etc. It sure did clean up
nicely though. More to come, no LT1468s yet.
I'm looking for some of the LME49710 metal cans
ya'll spoke of too.
Last edited:
Monitor Output...
@RichEEM & David, what did you guys do to tame the monitor output?
Compared to what I posted above, the monitor output is like a distorted wave in the
middle of the FFT screen. Sorry I didn't capture it.
Also, at higher output levels towards -80dB etc, 3V output do your meters
start a slow type oscillation? Mine will usually be slow, but
sometimes it acts like a short and will start bouncing around.
I didn't know if that was the HP339a sputtering to try and maintain
output or if the auto-null was just trying to get a handle of the signal
at the upper end of its scale but cannot.
I'll go poke around in the manual and elsewhere and try and search for it.
Here a capture of the little Xmsn tester I found...
big difference between it and HP339a, it is handy
that it Displays Levels and Frequencies (kHz, dBm, dBrn, sent or
received. It's nothing fancy but works in a smaller
package. Maybe it is ripe to shove a victors osc
in it's little box for a better oscillator.
@RichEEM & David, what did you guys do to tame the monitor output?
Compared to what I posted above, the monitor output is like a distorted wave in the
middle of the FFT screen. Sorry I didn't capture it.
Also, at higher output levels towards -80dB etc, 3V output do your meters
start a slow type oscillation? Mine will usually be slow, but
sometimes it acts like a short and will start bouncing around.
I didn't know if that was the HP339a sputtering to try and maintain
output or if the auto-null was just trying to get a handle of the signal
at the upper end of its scale but cannot.
I'll go poke around in the manual and elsewhere and try and search for it.
Here a capture of the little Xmsn tester I found...
big difference between it and HP339a, it is handy
that it Displays Levels and Frequencies (kHz, dBm, dBrn, sent or
received. It's nothing fancy but works in a smaller
package. Maybe it is ripe to shove a victors osc
in it's little box for a better oscillator.
Last edited:
David,
Some were the uncompensated LT1468, if I recall.
I guess you had problems with the OPA1641 in the notch as well?
Or did it work okay there?
Something better to place in it?
I think I have much written down in the notes.
In various places.
How are you doing on your Oscillator?
Did you get your boards and it into production?
It should start to get chilly up there eh?
But then I guess it has to be less than -20 C for
it to start getting really cold up there.
cheers
Some were the uncompensated LT1468, if I recall.
I guess you had problems with the OPA1641 in the notch as well?
Or did it work okay there?
Something better to place in it?
I think I have much written down in the notes.
In various places.
How are you doing on your Oscillator?
Did you get your boards and it into production?
It should start to get chilly up there eh?
But then I guess it has to be less than -20 C for
it to start getting really cold up there.
cheers
Don't use the uncompensated 1468. The distortion is quite a bit higher the the compensated version. The opa1641 is a good op amp but I think there is better. I used it because filter require lest amount of loading at there output. The Jfet op amps are good in this way.