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QuantAsylum QA400 and QA401
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Old 26th July 2014, 07:59 AM   #1171
1audio is offline 1audio  United States
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QuantAsylum QA400 and QA401
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.
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Old 26th July 2014, 08:01 AM   #1172
1audio is offline 1audio  United States
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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.
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Old 26th July 2014, 03:54 PM   #1173
SyncTronX is offline SyncTronX  United States
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Default 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...?
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Old 26th July 2014, 07:35 PM   #1174
davada is offline davada  Canada
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Quote:
Originally Posted by SyncTronX View Post
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.
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Old 26th July 2014, 10:16 PM   #1175
1audio is offline 1audio  United States
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Quote:
Originally Posted by SyncTronX View Post
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...?
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.
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Old 27th July 2014, 12:00 AM   #1176
1audio is offline 1audio  United States
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Quote:
Originally Posted by SyncTronX View Post
Here is QA400 with Twin T in box,settled.

Click the image to open in full size.

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.

Click the image to open in full size.

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.
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Old 27th July 2014, 01:08 AM   #1177
SyncTronX is offline SyncTronX  United States
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Default 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???
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Old 27th July 2014, 01:41 AM   #1178
SyncTronX is offline SyncTronX  United States
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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?
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Old 27th July 2014, 02:14 AM   #1179
1audio is offline 1audio  United States
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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.
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Old 28th July 2014, 05:02 AM   #1180
SyncTronX is offline SyncTronX  United States
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That is pretty good Demian.

Okay here's the pics of my little notch:

Click the image to open in full size.

Here is the open box:
Click the image to open in full size.


Here is rev1 in the open box w Banana:
Click the image to open in full size.

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.
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