Hi,
I fired up my QA400 for the first time today, tried to run the calibration procedure, but it'll fail unless I accept the default value of 1.29Vrms, is this normal?
Also, I run a loopback test and got the attached result, and it seemed the THD figure of the right channel is 3dB better than the left channel, again I'm not sure if it's normal.
BTW, Big-E's experience is really educational and helpful, incidentally I bought this device in order to measure a Pass F6 that I'm gonna build, and the F6 has some pots to tune the 2H and 3H also
.
Thanks and regards.
I fired up my QA400 for the first time today, tried to run the calibration procedure, but it'll fail unless I accept the default value of 1.29Vrms, is this normal?
Also, I run a loopback test and got the attached result, and it seemed the THD figure of the right channel is 3dB better than the left channel, again I'm not sure if it's normal.
BTW, Big-E's experience is really educational and helpful, incidentally I bought this device in order to measure a Pass F6 that I'm gonna build, and the F6 has some pots to tune the 2H and 3H also
.Thanks and regards.
Attachments
I think the trash can idea was mentioned because they're a little bit thicker, which can actually make a huge difference.
Window screen.
Solder the pieces together on seams, just enough to hold it together and make
electrical contact.
Around a box.
Use metal window screen, not fiberglass...
Great for RFI. Useless for LF magnetic fields.
A continuous ring of magnetically soft metal is best, a large overlap, even if not conductive will pass the magnetic force and effectively short circuit the magnetic field so it won't go inside. Even with the lig of the trash can could really reduce the magnetic hum. If it does the next step would be to make a magnetic probe and start looking for the source of the field.
Holy SMokes,
I've been drinking tea for months and still haven't
gotten down to the end so I can use the tins. Now
the post about IKEA tins....Had I only known!
@BigE some of your plots look similar to mine over on
the HP339A thread.
@Bear, I didn't know they still made metal screen do they
make steel or is it just aluminum? You didn't want us to
ask about soldering fiberglass?
@Richard, does it help if you put metal screen around
your florescent fixture?
Anyone know about the spacing of the screen? That is, can
we use something larger like rabbit wire maybe 1/8 inch,
lathe wire, or other and would it be help in reducing interference.
@Demian LF Magnetic field...wondering does it matter if it's electrically
created from a transformer, etc or from a magnet?
I've been drinking tea for months and still haven't
gotten down to the end so I can use the tins. Now
the post about IKEA tins....Had I only known!
@BigE some of your plots look similar to mine over on
the HP339A thread.
@Bear, I didn't know they still made metal screen do they
make steel or is it just aluminum? You didn't want us to
ask about soldering fiberglass?
@Richard, does it help if you put metal screen around
your florescent fixture?
Anyone know about the spacing of the screen? That is, can
we use something larger like rabbit wire maybe 1/8 inch,
lathe wire, or other and would it be help in reducing interference.
@Demian LF Magnetic field...wondering does it matter if it's electrically
created from a transformer, etc or from a magnet?
Yeah, Demian, right-o screen is NG vs. magnetic fields.
Guess I have to order up that Mu-metal dog house I have always dreamed of?
Maybe some chucked out industrial HVAC duct, galvanized would work? Good form factor! Cheap at the junque yard, and free from the dumpster.
Or you could convince your bank to let you in the vault for a bit??
_-_-
Guess I have to order up that Mu-metal dog house I have always dreamed of?
Maybe some chucked out industrial HVAC duct, galvanized would work? Good form factor! Cheap at the junque yard, and free from the dumpster.
Or you could convince your bank to let you in the vault for a bit??
_-_-
Yeah, Demian, right-o screen is NG vs. magnetic fields.
Guess I have to order up that Mu-metal dog house I have always dreamed of?
Maybe some chucked out industrial HVAC duct, galvanized would work? Good form factor! Cheap at the junque yard, and free from the dumpster.
Or you could convince your bank to let you in the vault for a bit??
_-_-
I like the bank idea. A very large safe deposit box. You can sit in there all day examining your belongings.
When I first opened up the unit and tested it, I was on the first floor of the house. The basement finds us sitting with a water meter transmitter.
My bet is that unit is responsible for the noise.
The noise you have seems to be 60 Hz and harmonics of this. I therefore doubt that it is related to the water meter transmitter. The water meter transmitter will probably transmit with very long intervals to save power. So perhaps intervals of several hours, at least if it is battery powered.
There are some cordless phones, which can generate 100 Hz and harmonics of this. But this does not seem to the problem here. I work with the design of such cordless phones and I have seen noise from them when working with sensitive analog circuits. And living in an area where the mains frequency is 50 Hz it can sometimes take a while to identify the source.
There are some cordless phones, which can generate 100 Hz and harmonics of this. But this does not seem to the problem here. I work with the design of such cordless phones and I have seen noise from them when working with sensitive analog circuits. And living in an area where the mains frequency is 50 Hz it can sometimes take a while to identify the source.
Hi,
I fired up my QA400 for the first time today, tried to run the calibration procedure, but it'll fail unless I accept the default value of 1.29Vrms, is this normal?
Also, I run a loopback test and got the attached result, and it seemed the THD figure of the right channel is 3dB better than the left channel, again I'm not sure if it's normal.
BTW, Big-E's experience is really educational and helpful, incidentally I bought this device in order to measure a Pass F6 that I'm gonna build, and the F6 has some pots to tune the 2H and 3H also
Thanks and regards.
Hi Cwtim01,
I understand you plan to use QA400 with Pmillet "frontend" is your graph with or without "frontend"
Thank You
That is a brilliant idea....will try that later. Sleepless night => mistakes can happen.... best to avoid poking about the amp today.
There is a difference in the house since the original loopback test was done... New LG dishwasher and New LG fridge. Perhaps it is one of those?
If you are on a concrete floor, it can induce some very nasty power junk. The rebar and the concrete itself are conductive and often have more than you would think, or want, ground noise. You MAY be able to reduce it by turning off the main breaker to the house, then again you may NOT. Harmonics in the power grid for your location may be there regardless of what you do. It's all fun and games!
If lifting the piece off the floor reduces the interference, then you have ground current flowing thru your building.
Cheers,
Alan Garren
If lifting the piece off the floor reduces the interference, then you have ground current flowing thru your building.
Cheers,
Alan Garren
You may have a wiring issue in the house. If the current was going around your space in a large loop instead of in paired wires like Romex you could have a strong field inside of it. This if the case would also imply a safety issue.
You could make a quick mag field probe out of a speaker inductor or wire around a magnetic iron rod or bolt and just explore with the QA400 to see where the field is strongest .
You could make a quick mag field probe out of a speaker inductor or wire around a magnetic iron rod or bolt and just explore with the QA400 to see where the field is strongest .
Try running the tests early on a Sunday morning. It's a pretty quiescent time for electrical devices.
What type electrolytics did you use in the amplifier power supply?
Is this why you're not supposed to store auto batteries on a concrete floor? For all i know that suggestion might be urban myth. Nevertheless, there seem to be quite a number of papers from engineering schools on the conductivity of concrete slab.