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Old 25th June 2013, 02:51 PM   #141
agdr is offline agdr  United States
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decayed.cell - I may very well do another run at some point and post them over in the vendor's bazaar subforum if all continues to go well with testing. I'll let you know if I do. I agree, it would be good to have the panels available as a set with the PCB. One of the big plusses of this amp - as with the O2 - is the matching case and that isn't of much use without the drilled panels.

It also turns out that Seeed Studio has a 5 board option (quantity) for the 4 layer PCB fab service if anyone wants to fab some of their own with those 4-layers Gerbers I posted Their selector comes up with a default quantity of 10, but there is a 5 qty option in the pulldown menu. I think that worked out to be around $100 for 5 PCBs plus $20 DHL express, vs. $120 or so for 10 PCBs with $30 DHL express. The 10 are the lower cost-per-board, but 5 shaves $30 off the total cost.

Erik - the outfit is Proto Panel:

http://protopanel.com/products-servi..._discount.aspx (opens web page)

They claim to have the discount going on through the end of the month.

Last edited by agdr; 25th June 2013 at 02:58 PM.
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Old 25th June 2013, 07:15 PM   #142
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Default What PCB Board Software do you use to create your PCB's

What PCB Board Software do you use to create your PCB's. I want to
start doing this myself. Nice work and take care.
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Old 26th June 2013, 02:50 AM   #143
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mrsavage - I'm using Cadsoft Eagle, here:

CadSoft EAGLE PCB Design Software - EAGLE Support, Tutorials, Shop

https://www.cadsoftusa.com/buy-eagle/?language=en

The free (for non commercial DIY only) "light" version goes up to 80mm x 100mm, the size of the O2 amplifier, with 2 layers maximum.. The other for-pay versions allow more layers and bigger boards.

Definitely recommended to give it a try! Essentially you build up a schematic first using the schematic editor, then hit a button and it brings up the PCB editor with all the parts sitting in a pile at the bottom that then have to be placed. From then on any changes to the schematic - adding or deleting parts - track on the PCB board. Moving stuff around on the PCB editor has no effect on the schematic editor.

Probably the best way to get started learning is do a search on You Tube for "CADSOFT EAGLE". A few outfits have done very good multi-part videos explaining all the basics. Eventually you will need to create and add parts to the stock libraries. That turns out to be easy.

I'm having a lot of fun with Eagle. It is really amazing this level of computer power just sits on the desk in a laptop now. When I last laid out integrated circuits and microwave stuff a long time ago it was on ComputerVision CAD machines, early Sun Workstations, and Mentor Graphics Workstations that probably had about the same compute power as a pocket calculator today. I managed some engineering groups later on but didn't get hands on with the more recent design tools, just signed the checks.

Last edited by agdr; 26th June 2013 at 02:57 AM.
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Old 26th June 2013, 08:09 PM   #144
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Default How do I import one of your files into Eagle?

How do I import your files into Eagle? I tried importing one of your designs, just to try out Eagle, but it does not work? Any ideas? Or am I something? I really new
to the PCB board building process. Take care.
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Old 26th June 2013, 08:25 PM   #145
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You can open any eagle file as long as you have the same or a higher version, no matter
what version (free, student, pro,etc...) created it. You might not be able to edit it, but you can view it. Just download the files to a directory on your computer, open EAGLE and
do File>open>schematic and navigate to where you put the downloaded files.
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Old 27th June 2013, 12:03 AM   #146
agdr is offline agdr  United States
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You will need two more files that I haven't posted, the schematic (.sch) and PC board (.brd) files. The Gerber files that go out to fab (the ones I posted) are something that you can tell Eagle to create. You can even view those with a Gerber viewer like this one:

Online Gerber Viewer

If you are using the free version of Eagle it would choke on the 80x160mm size and 4 layers of this "ODA" amp design. Go on over to the parallel LME49990 amp thread and I'll post the .sch and .brd files for the 2 layer version of that one. It is just 80x100mm and should work with the free Eagle.

You will probably get some complaints from Eagle upon loading the files due to missing libraries. I had to create the library parts for LME49990, the jacks, the rotary switch, and a few other things. But at least it should load what it can and let you mess around with it. Creating those parts from the data sheet information and adding them back into Eagle is a good way to learn how the libraries work.

Last edited by agdr; 27th June 2013 at 12:24 AM.
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Old 27th June 2013, 01:14 AM   #147
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Quote:
Originally Posted by agdr View Post
You will need two more files that I haven't posted, the schematic (.sch) and PC board (.brd) files. The Gerber files that go out to fab (the ones I posted) are something that you can tell Eagle to create. You can even view those with a Gerber viewer like this one:

Online Gerber Viewer

If you are using the free version of Eagle it would choke on the 80x160mm size and 4 layers of this "ODA" amp design. Go on over to the parallel LME49990 amp thread and I'll post the .sch and .brd files for the 2 layer version of that one. It is just 80x100mm and should work with the free Eagle.

You will probably get some complaints from Eagle upon loading the files due to missing libraries. I had to create the library parts for LME49990, the jacks, the rotary switch, and a few other things. But at least it should load what it can and let you mess around with it. Creating those parts from the data sheet information and adding them back into Eagle is a good way to learn how the libraries work.
He could view them no problem. He just wouldn't be able to edit them.
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Old 27th June 2013, 02:03 AM   #148
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Avro Arrow - interesting! Good to know.
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Old 28th June 2013, 04:36 AM   #149
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Here are the waveforms from some testing of this amp project, both for the first (gain) stage and the output stage powering headphones.

The first photo is the test setup. A function generator going into one channel and a scope on the output. The gain stage waveforms are taken off the input to the 1K attenuation resistor, which is the output of one channel's LME49990 gain chip. The output stage waveforms are taken off the amp output with a fairly sensitive 110dB/V set of test headphones (100mV for full volume, approximately).

The next photos are checking for clipping behavior. I increased a sine wave's amplitude until one of the rails clipped at 1kHz, then ran it down to 10Hz and up to 20Khz to see how consistant everything is. The result: extremely consistent vs. frequency! Almost nil change in amplitude or clipping level from 10Hz to 20kHz.

The clipping first occurs at -5.6Vdc on the negative rail, because the gain stage will have a small amount of DC offset from the chip's input offset voltage, the 10K input resistor (times the op amp input bias current) and then increased by the closed loop gain of the stage. All of this is the same for RocketScientist's O2 amp, which is one of the reasons he included that coupling cap in the middle to isolate gain stage offset from the output stage. If the signal amplitude is run up further (as shown in one photo) until the positive rail clips, it is also at +5.6Vdc. So no lack of symmetry in the amp per se, just the normal DC offset.

One of the outcomes here is to verify where I have the clipping indicator reference voltage levels set. The blue LEDs set the clipping points at about 2V below (positive rail) or above (negative rail). The results here show that for +/-7Vdc rails the clipping is at 7Vdc - 5.6Vdc = 1.4Vdc below the rail, and with the +/-16Vdc rails the clipping in the photos is 16Vdc - 14.5Vdc = 1.5Vdc. So for either rail voltage the clipping indicator LED will light about 1/2 volt *before* clipping actually occurs, which is exactly what I want it to do, to be an alert that signal levels are getting too high before they actually hit clipping. So I'm probably going to keep the internal blue LEDs, just tone then down a bit by increasing the series resistor so it doesn't glow blue through the end panel cracks.

Photos:
1-8 are all done with the power supply rails set to +/-7Vdc
1. test setup.
2. 1kHz gain stage output, showing neg half clipping onset at -5.6Vdc
3. 10Hz gain stage output, showing neg half clipping onset at -5.6Vdc
4. 20kHz gain stage output, showing neg half clipping onset at -5.6Vdc
5. 1kHz gain stage output, amplitude increased until both rails clip at +/-5.6Vdc
The next three have the amplitude backed down about a volt to stay away from clipping, to look at square wave waveshapes.
6. 1kHz gain stage output square wave.
7. 10Hz gain stage output square wave.
8. 20kHz gain stage output square wave.

9 and 10 are done with the power supply rails set to +/-16Vdc
9. 1kHz gain stage output, amplitude run up to show clipping on both wave haves, clipping onset on both wave halves at 14.5Vdc
10. 10Hz gain stage output, clipping onset on both wave halves at 14.5Vdc
Attached Images
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File Type: jpg IMG_1948.JPG (115.6 KB, 20 views)

Last edited by agdr; 28th June 2013 at 04:57 AM.
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Old 28th June 2013, 04:47 AM   #150
agdr is offline agdr  United States
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Default ...testing continued

I ran out of attachments. Here is part 2...

All using the +/-16Vdc power supply rail setting now. Amplitude backed down to about +/-12.6Vdc to avoid clipping to show the square wave shapes.

1. gain stage output square waves at 20kHz.
2. gain stage output square waves at 10Hz.
Attached Images
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File Type: jpg IMG_1951.JPG (115.4 KB, 27 views)
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