Very similar to my findings on srpp pre. Offcourse different circuit, but the same conclusion. I built four pre kits, 6n11 chinese sounded best, most linear. 6n1p russian were second best, chinese 6n1p has higher distortion. 6n6p inspite running hot were not better than 6n1p.
6n2p were worst, even after lowering the voltage to optimum.
https://www.diyaudio.com/community/threads/6n1-6n2-6n11-6dj8-in-pre.380485/page-2
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The bench tonight is packed: modules for my custom PSU, the UMC202HD, the laptop for tests with R.E.W. tonight, a second breadboard with a Reg., a box containing parts of my experiments with USB isolation and the usual Lab Desk 1 gear.
Spent a lot of time yesterday looking for the isolation modules. Of course, couldn't find them, until the very last box I opened. This happens to me when we have guests: I have to put all the components out of sight and then they're hard to find again.
But, I found a few interesting things in my stash...
Remember the Panasonic MOSFET amplifier which had one channel go kaput after reflow? I had found another one on the street and I really thought I had chucked the MOSFET modules away. Well, while searching yesterday, I found two of them, open. I had kept them for some reason, so have a look. People call these 'chips' but they are really a PCB with components in them:
I have unfortunately broken the pins off. I could unsolder the remains and solder new pins and test them. I'll keep that in mind. At least examining it doesn't require me to unsolder the module in my amplifier and opening it.
Another part I found comes from a Klipsch subwoofer. I looked up the sub online for repairs and what not and found people showing the large transformer inside, and so I thought 'Great! A linear PSU!', but when I opened it, they had sneakily replaced it with a SMPS... Bummer.
So here is the amplifier module:
TDA7265B.
I'll most probably recuperate that and re-build my subwoofer amplifier around it, using a custom PSU when comes the time.
There are a few other TDA chips and other amplifier chips I gathered here and there, so it will be a good set of experiments to power them cleanly and listen to what they deliver when the PSUs are ready.
Spent a lot of time yesterday looking for the isolation modules. Of course, couldn't find them, until the very last box I opened. This happens to me when we have guests: I have to put all the components out of sight and then they're hard to find again.
But, I found a few interesting things in my stash...
Remember the Panasonic MOSFET amplifier which had one channel go kaput after reflow? I had found another one on the street and I really thought I had chucked the MOSFET modules away. Well, while searching yesterday, I found two of them, open. I had kept them for some reason, so have a look. People call these 'chips' but they are really a PCB with components in them:
I have unfortunately broken the pins off. I could unsolder the remains and solder new pins and test them. I'll keep that in mind. At least examining it doesn't require me to unsolder the module in my amplifier and opening it.
Another part I found comes from a Klipsch subwoofer. I looked up the sub online for repairs and what not and found people showing the large transformer inside, and so I thought 'Great! A linear PSU!', but when I opened it, they had sneakily replaced it with a SMPS... Bummer.
So here is the amplifier module:
TDA7265B.
I'll most probably recuperate that and re-build my subwoofer amplifier around it, using a custom PSU when comes the time.
There are a few other TDA chips and other amplifier chips I gathered here and there, so it will be a good set of experiments to power them cleanly and listen to what they deliver when the PSUs are ready.
On the bench tonight are some BTSB Lite boards. These are passive panel mount XLR/TRS and RCA input boards that provide automatic switchover between RCA and XLR using relays and an isolated 12v DCDC converter to power the relay coil in order to prevent ground loops. This will be used in the rear panel of the upcoming Emerald Physics 600.2SE amp. XLR has priority and RCA is disconnected when an XLR is inserted.
You measure in close proximity, foot or so.
It eliminates room to significant degree.
Other option is meassure outdoors. On tall ladder. Or put your speaker in ground facing up the sky.
Many options, like build youself small chamber out of an old closet.
Main thing is not to worry too much about it, since you are going to listen in the room after all. Anechoic chamber is an awfull place to listen to music.
It eliminates room to significant degree.
Other option is meassure outdoors. On tall ladder. Or put your speaker in ground facing up the sky.
Many options, like build youself small chamber out of an old closet.
Main thing is not to worry too much about it, since you are going to listen in the room after all. Anechoic chamber is an awfull place to listen to music.
I measure at 0.5m or 19in on a tall stool so away from ground or ceiling or rear wall. There are fancy Klippel auto measurement systems that subtract out the effect of the room. But I find that in room is pretty good as that’s where we listen. Just need to understand what response is intrinsic and what is room induced. Port measurements for bass from reflex or TLs need to be done at the exit plane and scaled with driver membrane area. I usually don’t measure that and just leave it up to good TL or reflex box design.
It's the Behringer UMC202HD with the box removed. The MIDAS preamp is off. I haven't calibrated using ARTA.
It can double up as a pretty good mains interference detector:
The shielding when it is in the box might be deficient, so there will be some investigations around that. I also want to have a look at how the power rails are and I'll probably do that first.
It can double up as a pretty good mains interference detector:
The shielding when it is in the box might be deficient, so there will be some investigations around that. I also want to have a look at how the power rails are and I'll probably do that first.
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They look quite good, especially their THD and dynamic range figures compared to what I have. Did you manage to get your new one working with R.E.W.?
With the Behringer, there might also be an issue with pick-up at the inputs. I was also using a jack adapter at the input and that might also play a role.
With previous tests, I was using a rather long HOSA cable, with loops, and no adapter. The latest tests were done with a much shorter cable with small jacks and so I have to use adapters at each end for the loopback. At least now the loopback is a single loop.
I find the proximity of the DC Booster and the codec to be a bit shady.
With the Behringer, there might also be an issue with pick-up at the inputs. I was also using a jack adapter at the input and that might also play a role.
With previous tests, I was using a rather long HOSA cable, with loops, and no adapter. The latest tests were done with a much shorter cable with small jacks and so I have to use adapters at each end for the loopback. At least now the loopback is a single loop.
I find the proximity of the DC Booster and the codec to be a bit shady.
I have been working with JohnPM (author of REW) on this problem, and no - apparently, the new ASIO driver from Focusrite is goofy and shows up as two USB ASIO interfaces when I plug it in. So it appears REW is confused and doesn't know which one to use. I probabaly need to uninstall, and wipe registry and reinstall. The joys of software drivers...
The data I have above is Java driver with old Solo 2nd gen.
The new 4i4 works fine with Audacity and Windows media etc.
The data I have above is Java driver with old Solo 2nd gen.
The new 4i4 works fine with Audacity and Windows media etc.
Ah cool. So there was indeed something going on between the audio interface and R.E.W. + ASIO.
I also found something today with R.E.W. and ASIO. Sometimes I get an error message that the soundcard can't provide data, etc...
I need to disconnect the USB cable, re-connect, change to Java, change back to ASIO and set it up again, and then it works again.
I have not re-tested this on a repeatable basis but I think I got that kind of thing again when I tried quite large values for FFT size.
I also found something today with R.E.W. and ASIO. Sometimes I get an error message that the soundcard can't provide data, etc...
I need to disconnect the USB cable, re-connect, change to Java, change back to ASIO and set it up again, and then it works again.
I have not re-tested this on a repeatable basis but I think I got that kind of thing again when I tried quite large values for FFT size.
I'll give this a try. I might not have calibrated the Volts properly - I have a little Fluke DMM but it's not true RMS. I suppose I need to multiply the measured AC Volts by a factor to calibrate R.E.W. properly.
Here are some measurements tonight, still unshielded, small cable with two adapters. First in non-calibrated ARTA with Output at around 2 o'clock and input gain zeroed, second is both zeroed. Third is R.E.W. with both at approximately 2 o'clock.
I think the high-freq spikes will definitely mess up the specs. I haven't seen any THD figures lower than around 0.017%.
This seems way too high to me.
You have 26kHz spike messing things up. Probably something in the USB or DCDC of the Behringer. Try limiting your window to 20kHz. You might want to take this up in the REW or ARTA thread.
Measure the signal with your Fluke. Doesn’t have to be true RMS if you have sine wave. Set it to 0.20Vrms. Then adjust input buffer/preamp gain to get -10dBFs. That leaves some headroom and uses your full dynamic range.
Measure the signal with your Fluke. Doesn’t have to be true RMS if you have sine wave. Set it to 0.20Vrms. Then adjust input buffer/preamp gain to get -10dBFs. That leaves some headroom and uses your full dynamic range.