You mean this one?HP 350D Attenuator Set 5W 55V 600ohm DC 1MC | eBay
So this just an attenuator. So I need a load resistor to terminate the amp, then feed the signal into this? Then drive the output into the QA400?
thanks
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Recommendations for cable/probe/clamp to go along with QA400?
My $5 gator clips raised noise floor by at least 7db.
My $5 gator clips raised noise floor by at least 7db.
No I mean you need to add more zeros for the Shibasoku 725.
They are way too conservative. Your calculation is correct.
Maybe not at 16kHz. It measures -109.9dBV (0.00032%).
They are way too conservative. Your calculation is correct.
Maybe not at 16kHz. It measures -109.9dBV (0.00032%).
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Use the shortest lead possible, I have some I made with RG175/U BNC to Pomona Maxi-Grabber that are only 6 inches long.
Off the shelf the Pomona 4648-C-36 are decently quiet, the maxi-grabber clips seem to work better than the mini or micro-grabber.
30 years ago, if you work on audio, you can be sloppy in grounding of the probe. Today, you have all sort of high speed digital circuit, 802.11i, Blue Tooth and all the others that I am too old to even know!!! Then you have all sort of florescent lights and switching supplies that spray noise all over. It's noise everywhere.
I remember when I was playing guitar in the 70s, single coil is not that bad. Now, you can hardly play a guitar with single coil as it hum and buzz like anything.
Point is you need to treat it as RF circuit like in the older days even you are working with audio. The ground lead of the probe is the SINGLE most dominant source of noise problem. Always use ground less than 1" on the ground plane to measure. get into a habbit that if you don't see what you expect, check the ground connection before starting to blame the caps, the circuit, or anything else.
Remember RF might be high frequency, but when a few sources of RF in the air, they mixed down and form IM that f1-f2 can well be in the audio frequency range.
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Hi David,
Thanks for that clarification. Is that 16kHz measurement THD or THD+N?
If the latter, what was the residual measurement bandwidth?
Cheers,
Bob
I bought it.
ENDEDHP Hewlett Packard 350D Attenuator Set T56814
I paid $25+$13 shipping. It supposed to be working as intended. I am crossing my finger.
Thanks, it's a good one. I would have to put more effort than it's worth to build it myself. Now I have to buy the QA400.
I bought it.
HP Hewlett Packard 350D Attenuator Set T56814
I paid $25+$13 shipping. It supposed to be working as intended. I am crossing my finger.
Thanks, it's a good one. I would have to put more effort than it's worth to build it myself. Now I have to buy the QA400.
I got a 350D as well just for the QA400. Mine needed some contact cleaning by exercising the switches. I'll go in and clean the contacts of any oxide junk. Just simple Q-Tip and alcohol wipe on the contacts. Maybe some Cramolin contact preservative, too.
THx-RNMarsh
Received both, the QA400 is TINY!!! Not that it's important, but the picture make it looked a lot bigger and substantial. It's not any bigger than my Personus USB and the Personus chassis looks a studier and more expensive. Hope this works better than it looks.
I am surprised there is not CD or anything. am I supposed to download on their website? what to download?
Attached are pictures of my new babies to show the relative size with the HP which is quite small already.
I should be in business!!!😀
I am surprised there is not CD or anything. am I supposed to download on their website? what to download?
Attached are pictures of my new babies to show the relative size with the HP which is quite small already.
I should be in business!!!😀
Attachments
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Thanks
Installed the software, now is to read the manual.😱
Too lazy right now, just play with the program blind, very similar to spectrum analyze, but I just don't get use to the mouse control of the turn knobs. I don't see how to set start and stop frequency, seems like it is running full BW all the time. I guess it's not important as you want to see the full audio BW.
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Alan,
You will get used to it. It is pretty easy. The biggest problem I've had with mine
is the lack of UNDO command. If you click on my handle here and go to my blog,
I put up some screen captures that will help you and other DIYers out in using the QA400.
First thing though is to do the QA400 calibration.
Cheers,
You will get used to it. It is pretty easy. The biggest problem I've had with mine
is the lack of UNDO command. If you click on my handle here and go to my blog,
I put up some screen captures that will help you and other DIYers out in using the QA400.
First thing though is to do the QA400 calibration.
Cheers,
Hold the Ctrl key down and click on the controls to bring up pop ups. In these pop ups are tables to set the BW and other properties etc. Also click on the graph in the same manner.
Read the help provided within the software, it's very complete.
Sent from my Nexus 7 using Tapatalk
Sent from my Nexus 7 using Tapatalk
Thanks guys, I have to read it. But I managed to get it going by just monkeying around. I feed the output into input and read the spectrum. I notice, I put in a 1KHz and read back. I see a small peak at 2KHz about 100dBV down from the main peak. I try using both gen1 and gen2 and see the same thing.
I tried raising and lowering the output level of the generator, the 2nd harmonic follows at -100dB down.
Is it something to be concern? I thought the sine wave should be pure from the generator, or else how am I going to judge? 100dB is not that good, I got better in LTSpice with the IPS and VAS.
I tried higher frequencies, like 4KHz and 3KHz, it got better.
I tried raising and lowering the output level of the generator, the 2nd harmonic follows at -100dB down.
Is it something to be concern? I thought the sine wave should be pure from the generator, or else how am I going to judge? 100dB is not that good, I got better in LTSpice with the IPS and VAS.
I tried higher frequencies, like 4KHz and 3KHz, it got better.
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I also have a QA400, it's spec states that at 0 dBV, loop back THD is -102dB. At -10 dBV, loop back THD improves to -106 dB.
QA400 Specifications
In actual use, I wouldn't count on the QA400 for anything less than 10 ppm. If you want better than that, may need to build a notch filter.
QA400 Specifications
In actual use, I wouldn't count on the QA400 for anything less than 10 ppm. If you want better than that, may need to build a notch filter.