Dx Blame ST together Dx Super A

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#1,204
AndrewT said:
He has confirmed that the +ve half overshoot is also in the input signal.

That is why I suggested he compare the input and output using his two channel scope.
Click to expand...
Yes AndrewT is on the right side.
I don't know what happens but this is the first time that happens with this test configuration .
Generators output is ok without any overshoot but when connected to amplifier input then overshoot (oscillation)? apears.
It seems like ground loop.
Dear Carlos this is a diy forum ,these troubles isn't unknown even in factory designers.
Murphy's rules "Anything that can possibly go wrong, does"
Thanks AndewT
Thanks Carlos.
Thimios.
 
#1,205
For what it's worth. I had a similar experience with my Honey Badger. There was an oscillation on only the positive side of the wave, and when It would start it affected the input signal too. You can see it in one of the pictures in this post. OS seemed to think it was something "sticking" at high output.

Might be worth reading about what he found.

Blessings, Terry
 
#1,206
dx super A

New test.
+/-35V
I idle=10mV/R22=45mA
Voffset=28mV
I LTP=151.8mV/39R=3.8mA
I VAS=1.121V/180R=6.2mA
V OUT=19V RMS just before clipping
R DUMMY=8R
P OUT=45W sinusoidal JUST before clipping.
-3db at 5Hz doun
-3db at 181KHz up
overshot is still here.
I can't upload photos.
I don't know why.
overshot is present on input and output signal if the dummy is connected
overshot is present only in out signal if no load is connected,in this case input signal is absolutely clear.
If other RL (about 5uH4)is used overshot is smaller.
 
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#1,207
No overshot in any of my amplifiers tested at my home

Several videos shows several waveforms, all them without overshot.

Why this is happening at your home thimios, i cannot know...but for sure is an effect that is happening your place ...not my place.

Over shot if appear i would not release the amplifier this way....so...if was released, then had no errors in waveforms.

See the series of videos of BBC about electricity...the third movie shows an interesting effect... a block of silicon generating naturally waveform...and a fan was obstructing and not obstructing light that was into the silicon block...and there you could see an interference...this is interesting..and reminds me a possible cause of your problem...if your overshot has a frequecy inserted on it..them it may be RFI (Radio Frequency Interference)

Video is here...the third and last of the Electricity series.... see 40:59
http://www.youtube.com/watch?v=MT8yeMzHvKY

regards,

Carlos
 
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#1,208
dx super A

Thanks for reply dear Carlos.
I want to know if other builders (same pcb and parts values) can shows scopes.
I repeat that in same place with same configuration i had test many amplifiers without any problem in the past
This time i use two generators for comparison .
Results are same.
Unfortunately i can't upload pictures and i don't know why.
Best Recards.
Thimios.
 
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#1,209
Overshoot of the input squarewave is because the Source is expecting a correctly terminated transmission line as a load.
If your Source is a 50ohm BNC, it expects a 50ohm coax and the far end of the coax to be terminated with 50r. This becomes the input signal loading of the amplifier. 100k here is no good for squarewave testing.
Else the VHF portion of the squarewave sees an incorrect termination and reflects back to the source. This roughly doubles the VHF content relative to the LF (squarewave fundamental) level. You see overshoot on the leading edge.
I can't explain why the leading edge of the -ve half pulse does not show overshoot.

I said 3days ago
AndrewT said:
..............If the overshoot is in the input signal, see if you can use the probe adjustment to trim it out and/or use appropriate loading on the cable to suppress the reflection.
Click to expand...

If the RF gurus don't like my explanation, please feel free to post a rewording of it, so that all can read and/or understand the correct explanation.
 
#1,210
dx super A

AndrewT said:
Overshoot of the input squarewave is because the Source is expecting a correctly terminated transmission line as a load.
If your Source is a 50ohm BNC, it expects a 50ohm coax and the far end of the coax to be terminated with 50r. This becomes the input signal loading of the amplifier. 100k here is no good for squarewave testing.
Else the VHF portion of the squarewave sees an incorrect termination and reflects back to the source. This roughly doubles the VHF content relative to the LF (squarewave fundamental) level. You see overshoot on the leading edge.
I can't explain why the leading edge of the -ve half pulse does not show overshoot.

I said 3days ago

If the RF gurus don't like my explanation, please feel free to post a rewording of it, so that all can read and/or understand the correct explanation.
Click to expand...
Dear AndrewT has you see this please?
''overshot is present on input and output signal if the dummy is connected
overshot is present only in out signal if no load is connected,in this case input signal is absolutely clear.
Overhot is visible all over frequency width....from 5hz up to 180kz
If other RL (about 5uH4)is used overshot is smaller.
Thanks .
 
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#1,220
dx super A

here are pictures with and without load.
Overshot is present from 5Hz up to 180Khz and from 1W to max.
Now i must change emitters resistors in ltp from 39R to 10R and try again.
 

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