Thanks, but I'm still not sure I understand the procedure here though.
The issue is that the output back to the SC (through the interface) is always scaled down. For example, if I generate a -3dbFS signal (which is 2.8V on my SC), then when I volume match the output of the amp to -3dbFS, the SC will receive 2.8V as well. Increasing volume above this always leads to worse distortion and clipping.
I do also have an analog oscilloscope though. Perhaps what I need to do is first use ARTA/STEPS to determine the position of the volume pot before clipping. Then using same signal, measure the output voltage directly with the oscilloscope? (as opposed to the SC?)
At that point output would be V^2/R ?
The issue is that the output back to the SC (through the interface) is always scaled down. For example, if I generate a -3dbFS signal (which is 2.8V on my SC), then when I volume match the output of the amp to -3dbFS, the SC will receive 2.8V as well. Increasing volume above this always leads to worse distortion and clipping.
I do also have an analog oscilloscope though. Perhaps what I need to do is first use ARTA/STEPS to determine the position of the volume pot before clipping. Then using same signal, measure the output voltage directly with the oscilloscope? (as opposed to the SC?)
At that point output would be V^2/R ?
You have to adjust the PC interface attenuator so that with the amp running at full power the soundcard input won't see more than it can take (2,8V in your case). But with only four steps it's not possible to achieve -3dB every time. Just make it fit somewhere within its range.
That is Vrms, conveniently read at the panel voltmeter.
Thanks, I think I got it now. I changed the interface to the 20V range and increased the volume until I was happy with the THD% numbers. I also connected the oscilloscope to the headphone output.
I compared the Vrms value on the panel meter with the pk values in the scope and they matched... so seems good!
I compared the Vrms value on the panel meter with the pk values in the scope and they matched... so seems good!
Hi BS,
It's an USB. I modified it to cure the noise in one of the channels (I think right?...). It's very clean now.
I'm currently using it to create FFT readings with my Audio Precision System One (which doesn't have a DSP module). Works great (and likely cleaner than what the DSP module would have generated). Also, given the 1V level at the monitor outputs, I found it easier to normalize the fundamental.
Radu.
It's an USB. I modified it to cure the noise in one of the channels (I think right?...). It's very clean now.
I'm currently using it to create FFT readings with my Audio Precision System One (which doesn't have a DSP module). Works great (and likely cleaner than what the DSP module would have generated). Also, given the 1V level at the monitor outputs, I found it easier to normalize the fundamental.
Radu.
Hi Rax, many thanks, very impressive! I'm revisiting this project after a long break. I completed filling the interface board but never tested it as wasn't happy with intermittent noise on my M-Audio M-Track 8. Im considering a few options now and the E-MUs look very interesting for the money.
Cheers
Cheers
The onset of clipping can be when all harmonics rise together. Only very symmetrical clipping lacks even harmonics at onset. Basically the total distortion suddenly starts to rise much faster at clipping onset.
The Red Lion MDMV0000 seems discontinued, however the MDMV0010 and MDMV0020 are still available - you'd just need to sort out the backlight which should be pretty easy to do.
The Polyfuse is certainly available from other suppliers - e.g. there are several in the UK with stock.
The Polyfuse is certainly available from other suppliers - e.g. there are several in the UK with stock.
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The datasheets look the same, I don't think there is a separate pin for the backlight.. unless I'm missing something..
Those little bastards are expensive too... haha.
So did I.... just now.. I thought I looked there earlier...guess not. Found the fuses at mouser as well, so I'm back in action.
Thanks all!
Soundcard again
Hi all,
I just bought the PCB from Pete, and have managed to source all the components, even the display.
What I need now is a recommendation for a US sound card, not too expensive that will have balance I/O's.
I know people have had suggestions before but this thread is so long, that it would be good to have an up to date answer.
John
Hi all,
I just bought the PCB from Pete, and have managed to source all the components, even the display.
What I need now is a recommendation for a US sound card, not too expensive that will have balance I/O's.
I know people have had suggestions before but this thread is so long, that it would be good to have an up to date answer.
John
Modern Sound Card Recommendations (Internal or External)?
Decided to build one of these and go down this path. Anyone got any modern sound card recommendations to give? I've seen a few post but nothing specific or a 'known quantity' that people are using successfully. Planning to run on a Windows 10 PC.
Thanks
Mark
Decided to build one of these and go down this path. Anyone got any modern sound card recommendations to give? I've seen a few post but nothing specific or a 'known quantity' that people are using successfully. Planning to run on a Windows 10 PC.
Thanks
Mark
I bought one for that purpose a long time ago. There were two problems with it. First is that the company stopped issuing drivers for it. The second is that most of the electrolytic capacitors on the card tested badly for high ESR (equivalent series resistance). I have a decent in circuit ESR tester that makes it easy to test. I was able to replace the capacitors but it was not an easy job and I wouldn't wish it on anyone. You have capacitor leads that are nearly the size of the hole and the leads were cut with a dull tool so they don't come out easy.
I too would like to find a better option.
For this kind of purpose, I got an EMU 0404, which an exceptionally good card for measurements (needs mods though, as there's a design flaw). It's unsupported at this point (drives are still available for download, but may be buggy), so running it under Windows 10 may be challenging. I'm using mine attached to an XP PC.