Gi'day eh. Here is a preliminary placement for your review. Still got lots to do....
Great work!
It will be nice to see how this turns out. Hopefully that SSM2164 VCA won't be too hard for people to find if they were to build it on PCB. I do wonder if other VCAs might work as a drop-in replacement.
A few of the internal adjustment POTs might benefit from multi-turn precision types too but so far I have not had any issue with my initial prototype in use. Signal paths shouldn't be too worrisome as long as the ICs all have power rail decoupling capacitors to ground right next to the chip. If my design worked fine on perfboard with the mess of wires shown in my photos I am sure PCB would be much less trouble with any potential cross-talk or interference. The most sensitive audio paths are to the audio jacks and control POTs. The multiband audio limiter section might benefit from careful signal path precautions too because of the high gain.
Other than that the only real issue is the enclosure itself and having solid grounding there when used in strong RF environments. Power supply rail splitter could be completely optional. Only reason I designed it that way was to take a standard 30 volt wall plug to get the needed +15/-15 to ground ref. In a professionally built setup it would be smarter to use the proper split rail power from a regulated toroidal supply or such.
Signal paths shouldn't be too worrisome as long as the ICs all have power rail decoupling capacitors to ground right next to the chip. If my design worked fine on perfboard with the mess of wires shown in my photos I am sure PCB would be much less trouble with any potential cross-talk or interference.
I don't know, but I would expect kicad would have an automatic groundplane option. I use sprint layout and it has that with just a click of a button. Might not be necessary.
BTW Kage, I really recommend trying out sprint layout at some point if you've never done pro PCB work before. I didn't have the patience for cad or eagle. It's SOOOO easy, but elegant as well. Yeah kicad is probably better, but I just found sprint so easy to use. You literally just draw the traces like paint, but it snaps to grid.
You can do gerber export and then send to allpcb, jlcpcb, or pcbway. I like allpcb the best cause their staff is more helpful and has better English and the prices are still dirt cheap.
Gi'day eh. Here is a preliminary placement for your review. Still got lots to do....
Great work!
It will be nice to see how this turns out. Hopefully that SSM2164 VCA won't be too hard for people to find if they were to build it on PCB. I do wonder if other VCAs might work as a drop-in replacement.
A few of the internal adjustment POTs might benefit from multi-turn precision types too but so far I have not had any issue with my initial prototype in use. Signal paths shouldn't be too worrisome as long as the ICs all have power rail decoupling capacitors to ground right next to the chip. If my design worked fine on perfboard with the mess of wires shown in my photos I am sure PCB would be much less trouble with any potential cross-talk or interference. The most sensitive audio paths are to the audio jacks and control POTs. The multiband audio limiter section might benefit from careful signal path precautions too because of the high gain.
Other than that the only real issue is the enclosure itself and having solid grounding there when used in strong RF environments. Power supply rail splitter could be completely optional. Only reason I designed it that way was to take a standard 30 volt wall plug to get the needed +15/-15 to ground ref. In a professionally built setup it would be smarter to use the proper split rail power from a regulated toroidal supply or such.
Hello Kage. Thank you for your encouragement. :-) I trust you are happy with the schematic I created (no mistakes) I do have a couple questions, requests for you. Can you tell me the clockwise directions for the pots? On your schematic you show a polarized cap with a value of .047uF, is this correct? Yes the availability of the SSM2164 is a concern, but I did find some suppliers on ebay and some sources of clones that should work. Here are some links ssm 2164 Synth DIY
One thing I'd like to do is add your skull/tower logo you created onto the silkscreen and etched on the solder side. I took a copy of the banner on the forum and added onto the schematic title block. You can see it has a low resolution. Can you provide a high resolution copy of the skull tower on a white background bitmap? I should be able to import it into kicad. So far I am having a blast playing with Kicad. It is well supported and has a lot of cool features. It is lacking some things that I find annoying, but overall it works quite well.
It will be nice to see how this turns out. Hopefully that SSM2164 VCA won't be too hard for people to find if they were to build it on PCB. I do wonder if other VCAs might work as a drop-in replacement.
A few of the internal adjustment POTs might benefit from multi-turn precision types too but so far I have not had any issue with my initial prototype in use. Signal paths shouldn't be too worrisome as long as the ICs all have power rail decoupling capacitors to ground right next to the chip. If my design worked fine on perfboard with the mess of wires shown in my photos I am sure PCB would be much less trouble with any potential cross-talk or interference. The most sensitive audio paths are to the audio jacks and control POTs. The multiband audio limiter section might benefit from careful signal path precautions too because of the high gain.
Other than that the only real issue is the enclosure itself and having solid grounding there when used in strong RF environments. Power supply rail splitter could be completely optional. Only reason I designed it that way was to take a standard 30 volt wall plug to get the needed +15/-15 to ground ref. In a professionally built setup it would be smarter to use the proper split rail power from a regulated toroidal supply or such.
Hello Kage. Thank you for your encouragement. :-) I trust you are happy with the schematic I created (no mistakes) I do have a couple questions, requests for you. Can you tell me the clockwise directions for the pots? On your schematic you show a polarized cap with a value of .047uF, is this correct? Yes the availability of the SSM2164 is a concern, but I did find some suppliers on ebay and some sources of clones that should work. Here are some links ssm 2164 Synth DIY
One thing I'd like to do is add your skull/tower logo you created onto the silkscreen and etched on the solder side. I took a copy of the banner on the forum and added onto the schematic title block. You can see it has a low resolution. Can you provide a high resolution copy of the skull tower on a white background bitmap? I should be able to import it into kicad. So far I am having a blast playing with Kicad. It is well supported and has a lot of cool features. It is lacking some things that I find annoying, but overall it works quite well.
While pondering how to create an assembly drawing in Kicad, I came across this external plugin and was surprised with the results.
Finally looked at the accessory schematic.... Ya should of added the power supply circuit to the board. :-( Guess I will see how easy it is to do changes in Kicad. Cheers all
Here is some files for proof of concept or peer review. I've added the power rail splitter circuit to the main board. I am not familiar with this type of circuit. So I ended up doing some guessing. I think I am going to go back and change the layout of the pwr circuit once I get some more understanding of the layout issues. Overall I am confident with the results of kicad creating an accurate pcb database.
Hey Guys So I took the pcb databases and imported 3D models of them into Freecad. Using the sheet metal function in Freecad I created a basic 1RU sheet metal enclosure. I then created a proof of concept assembly model of the processor.front_view_lid.pdf (56.37 KB) rear_right_view2.pdf (108.88 KB)What is really cool is that you can change the assembly and pcb's to further refine the overall processor device before manufacture.
It seems there is little interest in the project due to lack of comment. Can you guys see the documents I've uploaded? Anywho I found that Kicad projects are not easily portable to other user's computers due to how the libraries are setup. There is a way to make it portable, but is cumbersome... I think (something I gotta figure one day, but I'm going to try it on a test/junk project first) If there is interest I will work on making the Kicad project files portable and available. I would try this circuit myself, unfortunately I don't have a space to gather all of my stuff from storage and set up a workshop. I dearly do miss having a workshop. Another thing that is holding me back, is that I don't have a transmitter to plug it into. Just for fun I am thinking of doing a pcb of Dave Martin's Corsair II. I have read all about it and am aware of it's shortcomings. But what the hey, I'm sitting here unemployed, currently in government lockdown due to covid and bored as heck.
Hey Guys So I took the pcb databases and imported 3D models of them into Freecad. Using the sheet metal function in Freecad I created a basic 1RU sheet metal enclosure. I then created a proof of concept assembly model of the processor.View Attachment View AttachmentWhat is really cool is that you can change the assembly and pcb's to further refine the overall processor device before manufacture.
It seems there is little interest in the project due to lack of comment. Can you guys see the documents I've uploaded? Anywho I found that Kicad projects are not easily portable to other user's computers due to how the libraries are setup. There is a way to make it portable, but is cumbersome... I think (something I gotta figure one day, but I'm going to try it on a test/junk project first) If there is interest I will work on making the Kicad project files portable and available. I would try this circuit myself, unfortunately I don't have a space to gather all of my stuff from storage and set up a workshop. I dearly do miss having a workshop. Another thing that is holding me back, is that I don't have a transmitter to plug it into. Just for fun I am thinking of doing a pcb of Dave Martin's Corsair II. I have read all about it and am aware of it's shortcomings. But what the hey, I'm sitting here unemployed, currently in government lockdown due to covid and bored as heck.
Cheers All
Yes I was able to see your files and did download them for safe keeping
Sorry I haven't replied more to your effort. I very much appreciate that you took the time to do this since PCB design is one area I know nothing about yet. I can assure you that others are interested too and eventually an etched board would be awesome when I get the means to.
Even had the idea to build two of them if sometime down the road money and time permits, so that I can stereo link them and change the brick wall filter values to be useful for FM broadcasting too! Much like some stations did with a pair of DAP 310 processors made for AM converted to FM stereo service, which is after all what I based my design criteria around to begin with. Either way I am still using my original prototype processor as depicted in earlier posts above and it has yet to fail me. Had a few friends comment that our stations audio sounds great with it and gives us that big station sound.
I've been so busy with other things that I haven't had the time yet to deeply evaluate your layout and double check for any potential errors but from what I saw so far it looks perfect to my eyes.
As you know I used your circuit as a learning exercise for Kicad and Freecad. When I first posted I did not know how to use them both. I will say I was impressed with the results.
Let me thank you, for the availability of your circuit. I had a little advantage learning the programs as the first cad system I trained on, was in 1989.. lol I had to chuckle when I was laying out the LM3914 circuit. It was the test circuit I used to learn on that first cad program. (Daisy/Cadnetix, I remember our company paid over 400 grand for that cad system)
To make it clear I am a pcb layout designer and passionate radio hobbyist, not an Eng or Tech, they were my customers
Anywho when I assigned footprints to the schematic, The most concern I have for accuracy is the capacitors. I believe all of the values are available in the 200mil ceramic packages that I’ve assigned to most of them. At this point if I was to build this circuit, I would be kitting the caps and adjusting the footprints to suit. Can you tell me more about the power circuit? I want to redo the placement, Is the power transistor a good choice? Do they get hot?
As a seasoned pcb layout guy, I have a high level of confidence in the kicad database. If the schematic and the footprints assigned are correct and if my placement is ok, it should work on power up.
Anyone feel free to comment good or bad. This is the stage where corrections or improvements on my layout must be considered and made.
Hello, it is the first time that I write in the forum.
Excellent contribution, thank you very much for sharing such an excellent circuit. My query is, by modifying the output filter, can I use it in fm?
Thanks!
No reason you can't but it will take a little modification. Filter values will have to be calculated for 15kHz instead of 10kHz stop point and the overshoot filter adjustments calibrated to compensate. I might have the 15kHz values scratched down here somewhere but not sure if I have all my old notes. Other option is using those online filter calculators. Either way a scope and signal generator to sweep test it would be needed.
For stereo the AGC stages would benefit from being linked so that the stereo platform doesn't move around with some types of music. Never tried this myself as I only made a mono AM unit, but it should be fairly easy to implement with some experimenting. 19kHz stereo pilot might need further filtering for professional compliance.
Hello, it is the first time that I write in the forum.
Excellent contribution, thank you very much for sharing such an excellent circuit. My query is, by modifying the output filter, can I use it in fm?
Thanks!
No reason you can't but it will take a little modification. Filter values will have to be calculated for 15kHz instead of 10kHz stop point and the overshoot filter adjustments calibrated to compensate. I might have the 15kHz values scratched down here somewhere but not sure if I have all my old notes. Other option is using those online filter calculators. Either way a scope and signal generator to sweep test it would be needed.
For stereo the AGC stages would benefit from being linked so that the stereo platform doesn't move around with some types of music. Never tried this myself as I only made a mono AM unit, but it should be fairly easy to implement with some experimenting. 19kHz stereo pilot might need further filtering for professional compliance.
I've given this the "once over" and it looks like a superb design (much better than my old two-band design). Your overshoot compensator works flawlessly, and this is about as good an AM processor as you can build without delay-line processing.
I've been considering an FM / internet streaming version of this design, and have started to look at the stereo coupling issue, and the option of including pre-emphasis (50µs for this side of the pond, and 75µs for over there).
I've recently been experimenting with some Maxim switched-capacitor filter ICs for the 15kHz lowpass for FM use, and these can give a true brickwall response and precise turnover frequencies with minimal components. I'll put the filter details up here shortly. My original filters used twelve op-amps per channel, and gave an "elliptic" response using gyrators to simulate inductors. The op-amp based filters were a nightmare, because they needed 1% (or better) capacitors and resistors (expensive) and the constructor would still have to hand-select some of the more critical parts to ensure channel matching and response accuracy. The switched-capacitor filters eliminated these issues by using a crystal-derived clock signal fed to two filter ICs in each channel, and the turnover point on my prototype was exactly 15,006 Hz! Using two of the ICs cascaded in each channel, I was able to get the response down to -68dB by 19 kHz - significantly better than the usual broadcast specification.
Once again, well done with your AM design. I'm going to build one shortly, and put it to work on my little AM low-power station here in the Netherlands. I'd be interested in a few PCBs if you're going to make them available.
Great news for everyone - The VCA chips are available from Small Bear as Cool Audio V2164D. If you're in Europe, they're available as "Alfa" parts AS2164D. These work just as well as the originals, and are about 1/10th of the price of the ones from the dodgy Chinese sellers on Ebay!
I've been working on an FM 3-band stereo limiter with AGC and using delay lines to "see the peaks coming" to prevent overshoots and pumping. The delay ICs I'm using are (genuine) Panasonic MN3007s, which I'm clocking fast enough to give me 512µs to 1ms delay - the fastest attack time I can achieve with my compressor circuits is about 600µs. The '3007s aren't meant to go that fast, but if you clock them with a couple of BS170 FETs (to discharge the capacitances) fed from a CMOS bi-phase clock, you can really "overclock" them! I can omit the clippers that are usually used in broadcast processors - after all, who wants a "fuzz box" as part of their airchain?
I used the "Alfa" equivalents of the '2164, and they worked well.
I've been playing with the turn over frequencies for the three-way crossovers - I used "state-variable" stages to make them tunable - and have found that crossing over at 210 Hz and 2800 Hz is about right. I found that I needed a fairly long decay time for the bass compression to prevent "modulation distortion" of the audio. The huge advantage of this approach is that the heavy bass used these days doesn't affect the midrange and top end as it would with a single channel limiter, making the compression and limiting much less audibly obvious.
The results I'm getting sound noticeably better than the old Inovonics 255 that I used for years, and the processor will cost around £85 to build (plus a 19" box to house it). The power input to the board is at 18V AC, which is half-wave rectified each way to give dual rails, which are then filtered by a crude gyrator stage on each side and then regulated by a 7815 and a 7915. I've designed for balanced 600Ω input and output, to make it compatible with the rest of my gear.
There's a little more to be done to the design, but I'm close to finished. One of the prototypes is being used on a web radio station at the moment, and the quality sounds as good as an MP3 stream can, with the somewhat variable levels of some of the contributed programmes being corrected by the slow AGC. The one on the web doesn't have the delay lines in it, but doesn't seem to overshoot too much. I think that adding delay lines might improve the overall sound a bit further, but I'm not sure.....
I can omit the clippers that are usually used in broadcast processors - after all, who wants a "fuzz box" as part of their airchain?
Keep in mind the clipper stages at the end of the circuit are for transients and are not normally audible. They are overshoots that the previous limiter stages did not catch.
In fact this is one reason I wasn't excited about the asymmetrical clipper option. It's there for prosperity and does the same exact job as the professional units, but I find the transients that overshoot and unbalanced clipping to accommodate higher percentage modulation really don't make any audible difference but they do look nice on a scope I guess. They happen so seldom in the frame of audio reproduction as to not be detrimental to the overall sound.
Sure you can drive clipper stages hard to get peaked brick wall audio but in my circuit that was never the purpose since they were to catch transients, and on top of that they were softly driven so to round out rather than sheer peaks as the previous stages should have buttered up. Omitting them is fine but realize that the audible difference is so tiny compared to the potential band splatter of the transmitter modulation on adjacent channels.
Are clipping stages needed? Proper adjustment assumed, take a look at a scope and listen to the audio through the circuit chain and determine for yourself. I don't claim to have a golden ear, but I appreciate the little more tight spectrum it gives when properly filtered using overshoot compensation so not to annoy listeners who tune into stations next to mine.
FM is a different beast and there you might get away with lack of clippers because the deviation margin is so large. Not trying to be pedantic lol, I just tried to build this around known ideas to comply if ever used in a professional situation. You're welcome to modify as wished with full permission for other purposes.