And the results are not as good as I was hoping for. I don’t think I understand every thing I know about room EQ. So I will be at this for a while.
I’d really like a histogram display with bins aligned to the 31 band EQ. That way I could see the frequency that is hot and just turn down the EQ at that bin. I’ll keep looking for just the right thing.
The top trace is what a reference mic sees in the room. The next trace is what the preamp see’s and the bottom trace is what the ADA sees. The trace is a recording of a sweep from 10hz to 15khz.
As you can see, there is a lot of amplitude variation in the room. There a lots of things in the room that can resonate and block certain frequencies.
The other 2 traces are tests of the equipment to make sure its all working correctly.
This is the “not yet ready for prime time” version.
http://www.youtube.com/watch?v=NHSZfXBxh4Q
Enjoy.
There was this annoying switching sound that would show up on from the preamp channels. Its was associated with the leds switching on and off. The cause was the 5V regulator connected to +15V buss on the board. Bad idea that. So, I reworked the boards and added a seperate +5 supply to run the LEDS. Noise gone.
The other problem was a bit more vexing. I have some condenser mics that want about 2ma to run. But they where not working. Looking at the spec sheet for the mic says that it will work anywhere from 15 to 48 volts, and the current is 2ma. Wrong, 2.8ma and at least 40v to get the mic working. This required another rework, I replaced the 6.8k current limiters with 3.3k, end of problem.
We seem to be close to the final version of the cabinet for the preamp, but there are several things to fix. dang
I found that this was caused buy a problem in the ioboard on the back panel. Problem is that I can’t find any reason for the bug. There is no obvious flaw in the board. I will try to reflow the solder and see if that makes it work.
In any case, I made a new board and now all the channels work correctly.
I think I will run some wave forms through the amp and take pictures of the performance and post them. Maybe a sweep from DC to 1.5MHz ….
Took the remote gear to a piano duet and recorded about 2 hours of music. Really nice work. The preamp was on-board for the gig and did a good job. All but one channel…. I have this one board that has a kind of feed back issue. It makes a loud hiss that I can’t get around. So I think I need to build a new board for that channel. No biggie.
So there will be some rework on the chassis to fix a few problems. I will have to design a mounting pan for the boards. The plan for holding the boards in place is total crap. Next round of bending metal is scheduled for Jan.
After a few weeks of messing around, I got the chassis this morning. Looks good so far. I will start assembling the unit tonight, and we will see. There is no silk screen work on this chassis and that will have to be done since its non obvious how it works. I can look at that next week.
So, the audio card in my studio computer is showing signs of impending failure. I tried to buy another one, and they are not being made anymore. So, I looked at the RME Hammerfall board. I really like this board but its $700 for a custom asic, and its pci (another aging technology).
I got a PreSonus 48 port FireWire box that will handle four 8 port ADAT ADA’s. I hope they have a better driver for this than the one on the FireStudio ….