Author |
Message |
JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
|
Posted: Thu Mar 21, 2019 7:39 am Post subject:
|
|
|
Unless there is a build error, that looks like half-wave rectification of a potentially AC signal. This is often the result of trying to do something intended for dual supply with a single supply. It can be corrected for single supply by adding a positive bias.
Personally, I prefer a true dual supply. They really don't cost that much and make analog synthesis a lot easier. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
|
|
Back to top
|
|
|
gabbagabi
Joined: Nov 29, 2008 Posts: 651 Location: Berlin by n8
Audio files: 23
|
Posted: Thu Mar 21, 2019 7:49 am Post subject:
|
|
|
you are totally rigth!
it makes the life so much easy-er! |
|
Back to top
|
|
|
Tchidu
Joined: Mar 20, 2019 Posts: 6 Location: Terra
|
|
Back to top
|
|
|
Tchidu
Joined: Mar 20, 2019 Posts: 6 Location: Terra
|
|
Back to top
|
|
|
JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
|
Posted: Thu Mar 21, 2019 1:51 pm Post subject:
|
|
|
I understand, but really the positive bias stuff is, IMO, harder to understand than a dual supply. In fact, when you get done with the bias, I see an extreme similarity to creating a fake dual supply anyway - and a real dual supply is a lot better in the long run. Think of a dual supply as a single supply (the extreme + and extreme - rails) with a "bias" (the ground) in between. Except that with the single supply and bias, the bais is a weak current supplier whereas the dual supply has a super current capable "bias" so there's no funky drooping as you add stuff - and believe me - most people start small and go "I wonder if I could add..." and that's where the feature creep starts. This is not an issue with a real dual supply, but slowly but surely the single supply with bias point(s) turns to crap and then you start the cross-eyed head scratch.
If this sounds like the voice of experience - you nailed it. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
|
|
Back to top
|
|
|
Tchidu
Joined: Mar 20, 2019 Posts: 6 Location: Terra
|
|
Back to top
|
|
|
JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
|
Posted: Thu Mar 21, 2019 2:44 pm Post subject:
|
|
|
I've used 9vac transformer (wall-wart) for +/- 8v supply, so 15vac for +/- 12 should work, but there might be a bit of heat though I doubt it would be "too much", just might benefit from somewhat larger heatsinks.
So I think the answer is "yes".
EDIT ADDED:
Hmm. I just saw the note about 12V WALL WART ONLY... My assumption is that relates to my comment about regulator heat. I've had no trouble with 9vac (1000mA) and +/- 8 but that's only 1 vac above the DC regulated output. I think the real issue is going to be heat dissipation and unfortunately I really don't know how to calculte the regulator heat sink size. I just go with "big"... sorry... _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
|
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
Posted: Thu Mar 21, 2019 3:09 pm Post subject:
|
|
|
yep, 15VAC does work but could indeed get pretty hot. If my calculations are correct than there is voltage drop of about 8.5V across the regulators.
I usually don't calculate heatsinks either but if you can't keep your finger on it (because it is too hot) you'll need a bigger one. Be careful though
they can get pretty damn hot before they shutdown. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
SoundCloud BandCamp MixCloud Stickney Synthyards Captain Collider Twitch YouTube |
|
Back to top
|
|
|
JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
|
Posted: Thu Mar 21, 2019 3:41 pm Post subject:
|
|
|
Yeah, I use the "too hot to keep good pressure with finger for 10 seconds" rule too.
So for +/- 12v it's really a better idea to get a 12 volt wallwart that's beefy enough for the job.
The reason the lower VAC is better is that when rectified and filtered, the raw DC voltage that feeds the regulators is the square root of 2 times the VAC or or simpler yet Code: | 1.414 * 12 = 16.9 VDC | for a 12 VAC xfmr. For 15VAC it would be 21.2 VDC raw into the regs which is a lot for the regs to "get rid of".
Of course, there's other things that get in the way that reduce the VDC raw a bit, so what I wrote is just the theory that computes an RMS voltage from the peak voltage. RMS will be close to the RAW DC output before the regulators, but with no load (and the regulator is a load). _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
|
|
Back to top
|
|
|
PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
|
|
Back to top
|
|
|
JovianPyx
Joined: Nov 20, 2007 Posts: 1988 Location: West Red Spot, Jupiter
Audio files: 224
|
Posted: Thu Mar 21, 2019 4:01 pm Post subject:
|
|
|
Yeah, the theoretical calculation is just a starting point. All kinds of stuff drops it including the rectifier diode drop you mentioned and the actual application circuit load because as the reg starts to demand current, the transformer output voltage drops. _________________ FPGA, dsPIC and Fatman Synth Stuff
Time flies like a banana. Fruit flies when you're having fun. BTW, Do these genes make my ass look fat? corruptio optimi pessima
|
|
Back to top
|
|
|
Tchidu
Joined: Mar 20, 2019 Posts: 6 Location: Terra
|
Posted: Fri Mar 22, 2019 3:36 pm Post subject:
|
|
|
So I might better get a 12vac instead 15!
I 'll get that saved, but for now, I told myself I'll get everything on 9v.
I'm having hard times finding a way to build a cv/gate to make a keyboard for oscilator!
Thanks buddies!!!! |
|
Back to top
|
|
|
|