Something along these lines as -40dB.
This is just dialing in the oscillator on the HP339a.
Now I understand the comments you were discussing when you'd
changed the Osc level, the -db reading would initially fall then
rise again. Also, changing the frequency venier with the same
sort of stuff going on.
Check out the next post when I dropped the Osc output voltage
for the first time.
This is just dialing in the oscillator on the HP339a.
Now I understand the comments you were discussing when you'd
changed the Osc level, the -db reading would initially fall then
rise again. Also, changing the frequency venier with the same
sort of stuff going on.
Check out the next post when I dropped the Osc output voltage
for the first time.
Dropped sample packets.
If the averaging in on you have to reset when you make input change.
build yourself a simple twin T notch filter, nothing fancy, a peice of perf board with connectors will suffice. You'll probably end up with something like 40 to 50 db of fundamental suppression, plenty to play with and learn what you want to do and build later.
Cheers
Alan
twin T
http://www.radio-electronics.com/info/circuits/rc_notch_filter/twin_t_notch_filter.php
Cheers
Alan
twin T
http://www.radio-electronics.com/info/circuits/rc_notch_filter/twin_t_notch_filter.php
Last edited:
I just updated my Twin-T by Dick Moore. This is a great thread; my images are in post 220: http://www.diyaudio.com/forums/equi...ilter-distortion-analysis-22.html#post4001866
Almost made it, but no BNC to Banana or vice versa.
x 2. Have the easy parts.
This is the output of the HP339a to the left input of the
QA400.
x 2. Have the easy parts.
This is the output of the HP339a to the left input of the
QA400.
Had to develop the pics first.
The notch?
I didn't inhale. ; )
Here is stable state before notch:
Here it is after the notch:
Here's notch with out cable just just banana plugs & wire:
Here's the notch in linear mode:
Using standard wire for the notch, to Banana, then
banana to BNCs. I tried to twist the wire a bit too.
Noticed the 50/60 Hz noise and their harmonics.
Then when I changed views to linear, you sure can
see the two humps around 9K and 17K.
So, I need more instruments to meausre it. I have to
check the OSC output level. Also need frequency counter.
You have to change it all up to see what the notch does
then start tuning it, then stabilize and greater resolution etc.
Have to iso late the notch some how and I guess not use
standard wire....put it in a box?
Unless I wire it up wrong. The notch circuit ground
connects to both OSC ground (banana black) and
QA400 ground (banana black) tab on banana to BNC adapters.
So THD went to hell with the notch. I don't know why.
Notch was supposed to help.
Thanks for the link Alan.
Used this site for the values
at F 1000 Hz.
http://sim.okawa-denshi.jp/en/TwinTCRtool.php
The notch?
I didn't inhale. ; )
Here is stable state before notch:
Here it is after the notch:
Here's notch with out cable just just banana plugs & wire:
Here's the notch in linear mode:
Using standard wire for the notch, to Banana, then
banana to BNCs. I tried to twist the wire a bit too.
Noticed the 50/60 Hz noise and their harmonics.
Then when I changed views to linear, you sure can
see the two humps around 9K and 17K.
So, I need more instruments to meausre it. I have to
check the OSC output level. Also need frequency counter.
You have to change it all up to see what the notch does
then start tuning it, then stabilize and greater resolution etc.
Have to iso late the notch some how and I guess not use
standard wire....put it in a box?
Unless I wire it up wrong. The notch circuit ground
connects to both OSC ground (banana black) and
QA400 ground (banana black) tab on banana to BNC adapters.
So THD went to hell with the notch. I don't know why.
Notch was supposed to help.
Thanks for the link Alan.
Used this site for the values
at F 1000 Hz.
http://sim.okawa-denshi.jp/en/TwinTCRtool.php
Last edited:
Passive Twin T
Here is QA400 with Twin T in box,settled.
Still the annoying humps and noise.
OH, should be using cable with impendence.
Shame on me. Okay, well I didn't build twin t
that way but wonder what terminating at the QA400 input.
This is with 75 ohm termination.
Wondering now what kinds of things can the QA400
be used with?
Wondering what kinds of things can the HP339a be
used in conjunction with QA400 and passive notch?
Wondering what kinds of things can we do with the
HP339a, QA400 with active or passive notches?
In what ways could I measure tube amps with out
frying the QA400 box?
Thank you gentlemen for having the patience to
answer my questions and providing me with assistance
and guidance. I hope to be a good citizen DIYer and
help others...this has been a great learning experience.
I am blessed.
Have a great weekend!
Here is QA400 with Twin T in box,settled.
Still the annoying humps and noise.
OH, should be using cable with impendence.
Shame on me. Okay, well I didn't build twin t
that way but wonder what terminating at the QA400 input.
This is with 75 ohm termination.
Wondering now what kinds of things can the QA400
be used with?
Wondering what kinds of things can the HP339a be
used in conjunction with QA400 and passive notch?
Wondering what kinds of things can we do with the
HP339a, QA400 with active or passive notches?
In what ways could I measure tube amps with out
frying the QA400 box?
Thank you gentlemen for having the patience to
answer my questions and providing me with assistance
and guidance. I hope to be a good citizen DIYer and
help others...this has been a great learning experience.
I am blessed.
Have a great weekend!
You need to correct for the notch insertion loss on the fundamental and on the harmonics to have the real number. The reported number is only meaningful for what you see.
At these levels the notch needs to be in a can.
Measure some sources with higher distortion with and without the notch to see how it affects things.
At these levels the notch needs to be in a can.
Measure some sources with higher distortion with and without the notch to see how it affects things.
You can use the HP339 as a notch in front of the QA400 and it can also extend the dynamic range and max signal ability of the QA400.
Losses
First I do the fundamental mueasurement.
Then connect the notch and measure its output.
Then measure at the output of the cable.
This should give me the Vrms reading for input
into the QA400.
Finally I dial it in on the QA400.
I tried to see the Monitor Output and it was a mess.
A very wide band of noise.
How would I hook up the HP339a to just use it for the HP339a notch?
From my limited understanding, the output jacks for the HP339a are
from its oscillator. Yes. Can I also use those same outputs for the
HP339a notch?
Placed my homeade TT notch in a altoids tin. I wasn't sure if I should
use banana plugs or BNC for through put. The BNC I have
itsn't ground isolated.
That twin T sucks voltage. From about 4.9 volts in, from OSC
I only get 200mV out Something is sucking power and that doesn't
seem right. 3 caps, 3 pots and 2 resistors...?
First I do the fundamental mueasurement.
Then connect the notch and measure its output.
Then measure at the output of the cable.
This should give me the Vrms reading for input
into the QA400.
Finally I dial it in on the QA400.
I tried to see the Monitor Output and it was a mess.
A very wide band of noise.
How would I hook up the HP339a to just use it for the HP339a notch?
From my limited understanding, the output jacks for the HP339a are
from its oscillator. Yes. Can I also use those same outputs for the
HP339a notch?
Placed my homeade TT notch in a altoids tin. I wasn't sure if I should
use banana plugs or BNC for through put. The BNC I have
itsn't ground isolated.
That twin T sucks voltage. From about 4.9 volts in, from OSC
I only get 200mV out Something is sucking power and that doesn't
seem right. 3 caps, 3 pots and 2 resistors...?
The monitor output of the 339A has a 80dB gain on it. HP manipulates the gains a lot through the signal chain. It kicked up 10dB then attenuated, normalized to 1Vrms FS.
The is no monitor for the output of the notch filter. This would be a mod. it can be done. There is a test point for the notch output and this can routed to the AM input BNC replacing that input with an output. Best to replace the connector with an isolated type BNC and choose a better grounding point at the notch output test point. The input to the notch filter is at 3.162Vrms for a 1Vrms input so you'll have to compensate for this at the monitor point. It works but is no where near as good as using TT and sound card such as the EMU 0204 or similar. The distortion at the notch output is high and is much better with a 1Vrms input level. But this causes a 10dB error in level measurement. No easy solution here. The mods described in the Low distortion oscillator thread clean up a lot of the noise seen at the monitor output and and put the distortion into proportion reflecting that measured at the monitor output. However in terms of cost and effort the mods are not worth it. The analyzer's performance is limited by design. All the THD+N analyzers of that vintage were done the same way and had about the same performance. AP broke through that barrier in the mid 80's with the SYS1.
Ground the BNC's to the can. Its what you want to keep the noise out.
The notch is supposed to remove all of the fundamental leaving only harmonics which should be a small signal.
Here is QA400 with Twin T in box,settled.
Still the annoying humps and noise.
OH, should be using cable with impendence.
Shame on me. Okay, well I didn't build twin t
that way but wonder what terminating at the QA400 input.
This is with 75 ohm termination.
Wondering now what kinds of things can the QA400
be used with?
Wondering what kinds of things can the HP339a be
used in conjunction with QA400 and passive notch?
Wondering what kinds of things can we do with the
HP339a, QA400 with active or passive notches?
In what ways could I measure tube amps with out
frying the QA400 box?
Thank you gentlemen for having the patience to
answer my questions and providing me with assistance
and guidance. I hope to be a good citizen DIYer and
help others...this has been a great learning experience.
I am blessed.
Have a great weekend!
Lets go through your list. I tried earlier but the interwebs did not cooperate.
At these frequencies cable impedance does not matter. Be sure the cable is shielded. Do not terminate the notch. it will mess up the notch performance.
The notch removed the fundamental leaving the harmonics which is why the level is much lower with the notch in the circuit. You will also need to correct for the losses of the skirts of the notch. calculating the THD from the amplitude of the harmonics may be better than trying to let the QA400 do it.
The interface board I'm working on is designed to address the issues of interfacing with bigger signals. If you look at the details of the probes that is where the level matching happens.
Making small box...
I'm biginning to understand what you guys go through
just to make simple little things.
Here I am and I'm stuck at the Altoids box.
I have the parts around to finish it but not
the drill bits not the correct punch for the jacks.
Now I know what Richard doesn't want to fool
with building stuff and I'm just doing mini stuff
in a can.
I'm stuck at the HP339a OSC maxed out and can't
get enough signal though the notch to the QA400.
Full out I get 1.02mVrms.
3 orange drops, 3 pots, two resistors = 1. mV???
I'm biginning to understand what you guys go through
just to make simple little things.
Here I am and I'm stuck at the Altoids box.
I have the parts around to finish it but not
the drill bits not the correct punch for the jacks.
Now I know what Richard doesn't want to fool
with building stuff and I'm just doing mini stuff
in a can.
I'm stuck at the HP339a OSC maxed out and can't
get enough signal though the notch to the QA400.
Full out I get 1.02mVrms.
3 orange drops, 3 pots, two resistors = 1. mV???
Well it's not that bad right now. I got it running at 500mVrms from the
HP339a OSC 3V output with unboxed notch adn terminated into the QA400.
I'll remove the terminator and try to box the notch. BNCs input to it
and out from it.
David and Demian I appreciate the time you give and I struggel with this
stuff...I won't let it win though.
Demian, do you have a formula that I would use to crunch
the numbers or know where I can find the right one to use?
HP339a OSC 3V output with unboxed notch adn terminated into the QA400.
I'll remove the terminator and try to box the notch. BNCs input to it
and out from it.
David and Demian I appreciate the time you give and I struggel with this
stuff...I won't let it win though.
Demian, do you have a formula that I would use to crunch
the numbers or know where I can find the right one to use?
Which numbers? If you mean the loss through the notch, just measure it. The QA400 can do that and then note the levels at 2X and 3X the fundamental. I'm using a complex system with the measured response as a mike correction file in my software. Its working pretty well but took me an evening to figure out. It was never meant to do this.
That is pretty good Demian.
Okay here's the pics of my little notch:
Here is the open box:
Here is rev1 in the open box w Banana:
Sorry that some of these are fuzzy. Somethimes the iPhone cam
works and focuses and sometimes not.
I still have some good pics on the Sony cam, but can't
find the special interface cord. It takes a propriatary
interface cable. My favorite.
The thumbnail link doesn't work for somereason,
that's why I posted the bigger pics to begin with.
Okay here's the pics of my little notch:
Here is the open box:
Here is rev1 in the open box w Banana:
Sorry that some of these are fuzzy. Somethimes the iPhone cam
works and focuses and sometimes not.
I still have some good pics on the Sony cam, but can't
find the special interface cord. It takes a propriatary
interface cable. My favorite.
The thumbnail link doesn't work for somereason,
that's why I posted the bigger pics to begin with.