I managed to fry my last Ammo Can Amp by letting a little thermal paste drip onto the legs of one of the chips, causing a short. It was like the 4th of July in there.
This time I used a bigger can to have more surface area for stuff. On the front is a switch to select between the front and back RCA/TRS jacks, a High-Off-Low switch for the case fan, and the on-off. On the back is the switch for the USB charging ports and big cam switch to select between AC and DC sources. The voltage display on the front is so that I don't discharge my SLA too deeply.
AC power supply is 36V Meanwell. Amp board is Sure 4x100w (AA-AB33182).
One minor disappointment is that the USB power supply, which feeds off the same 30V output from the Meanwell, introduces a horrible whine in the speakers when turned on. I wasn't expecting perfection with this setup, but turning on the USB makes the thing completely unusable. Any ideas how to fix it?
This time I used a bigger can to have more surface area for stuff. On the front is a switch to select between the front and back RCA/TRS jacks, a High-Off-Low switch for the case fan, and the on-off. On the back is the switch for the USB charging ports and big cam switch to select between AC and DC sources. The voltage display on the front is so that I don't discharge my SLA too deeply.
AC power supply is 36V Meanwell. Amp board is Sure 4x100w (AA-AB33182).
One minor disappointment is that the USB power supply, which feeds off the same 30V output from the Meanwell, introduces a horrible whine in the speakers when turned on. I wasn't expecting perfection with this setup, but turning on the USB makes the thing completely unusable. Any ideas how to fix it?
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Saturnus, thanks again for the input. I ran the power to the USB regulator from the same source as the amplifier supply so that it would work whether I was using battery or AC power. I didn't think to check but I wonder if the whine is due to some interaction with the big SMPS, or with the amplifier board. I will check if it persists when powered by battery.
If the problem is only when running on AC power, will it solve anything to add a 120VAC-5VDC module in parallel to the current DC-DC one? I don't know enough how to make one, but I could easily steal one out of typical 2A phone charger.
If the problem is only when running on AC power, will it solve anything to add a 120VAC-5VDC module in parallel to the current DC-DC one? I don't know enough how to make one, but I could easily steal one out of typical 2A phone charger.
Some random thoughts - and I'm guessing here because not too much info to go on (apologies if I ,missed earlier posts), but assuming your USB regulator running from the Meanwell is a switching type, it might be drawing large AC currents at frequencies in excess of power supply rejection capabilities or regulator output tracking capability, or this could be a problem due to power distribution configuration (e.g. if you have a not-fat-enough/inductive bus bar and your ac load at one end, and some sensitive circuit half-way down), or simply due too high AC impedance (not enough/wrong sort of caps on the outputs of the Meanwell and/or input to the USB PSU). Try large decoupling cap (and possibly some series inductance) on the _input_ to the USB supply? Also watch the grounding - go for a 'star' ground (and supply) arrangement from the Meanwell, if you can and if haven't already. Add some AC impedance if you like in the form of some ferrites or even some series inductance, to decouple the two supplies.
If you have a scope/audio analyser, AC couple and take a look at the supply voltages to see if you can see any noise that relates to what you're hearing (be careful to get a really good local ground connection, or you will likely be seeing only ground differences between your target and your scope). If you have an AC current probe (or a diff probe and a small value resistor), take a look at the current being drawn from the Meanwell. (You can cook up a current sniffer, albeit without any amplitude accuracy), with a few turns of on a ferrite ring (i.e. make a little current transformer) - looking at the output from your secondary on that can be instructive (i.e. if you see noise on that which relates to what you're hearing, you also might conclude it's current related). It's also possible to build a pretty decent dif probe using a good differential input op amp (or good dif circuit). TI have some great op amps, including the OPA1632 (there are ones with better common mode rejection, but if you're just sensing a small voltage across a small resistor with one end grounded, the 1632 is pretty good).
Good luck!
If you have a scope/audio analyser, AC couple and take a look at the supply voltages to see if you can see any noise that relates to what you're hearing (be careful to get a really good local ground connection, or you will likely be seeing only ground differences between your target and your scope). If you have an AC current probe (or a diff probe and a small value resistor), take a look at the current being drawn from the Meanwell. (You can cook up a current sniffer, albeit without any amplitude accuracy), with a few turns of on a ferrite ring (i.e. make a little current transformer) - looking at the output from your secondary on that can be instructive (i.e. if you see noise on that which relates to what you're hearing, you also might conclude it's current related). It's also possible to build a pretty decent dif probe using a good differential input op amp (or good dif circuit). TI have some great op amps, including the OPA1632 (there are ones with better common mode rejection, but if you're just sensing a small voltage across a small resistor with one end grounded, the 1632 is pretty good).
Good luck!
Sounds like it’s the bypass line. I’m going to need a set of 30 weight ball bearings…
Sorry, that flew over my head so quickly I had to laugh. Makes me wonder how I get anything to make noise when my understanding barely scratches the surface. Thank you for the thorough and thoughtful response but I don’t think I will have the skills or the equipment to do the kind of diagnostics you describe in the near future. Baby steps for me…
Ground loops I somewhat understand. If that is my problem, is the loop created by the negative of the regulator connecting to frame ground, or is the loop created by having the charger going to and the signal coming from the same phone? With some difficulty I should be able to isolate the regulator from the case, but a loop of the second type would be inescapable, right?
Regulator is this one:
1pcs DC 9 40V 4 USB Car Charger Adjustable Power Supply Module for Phone New | eBay
Sorry, that flew over my head so quickly I had to laugh. Makes me wonder how I get anything to make noise when my understanding barely scratches the surface. Thank you for the thorough and thoughtful response but I don’t think I will have the skills or the equipment to do the kind of diagnostics you describe in the near future. Baby steps for me…
Ground loops I somewhat understand. If that is my problem, is the loop created by the negative of the regulator connecting to frame ground, or is the loop created by having the charger going to and the signal coming from the same phone? With some difficulty I should be able to isolate the regulator from the case, but a loop of the second type would be inescapable, right?
Regulator is this one:
1pcs DC 9 40V 4 USB Car Charger Adjustable Power Supply Module for Phone New | eBay
I believe some phones don't have a common ground between audio output and USB. If you can get by with charging the phone only when the box is plugged into AC, wire a wallwart charger to the USB socket or something.
Surelectronics has a Bluetooth receiver that allegedly supports high-quality aptX audio. $26 shipped, "APT-X Bluetooth 4.0 Audio Receiver Board Wireless Music Stereo for iphone PC" on eBay.
Surelectronics has a Bluetooth receiver that allegedly supports high-quality aptX audio. $26 shipped, "APT-X Bluetooth 4.0 Audio Receiver Board Wireless Music Stereo for iphone PC" on eBay.
I drilled out the rivets and took the regulator out of the case. The whine was greatly reduced, but not gone. Still get awful popping sound when turning the regulator on an off, and small pops at each step of the attenuator. I would try another regulator, but the field is pretty narrow when you need one that accepts both 12V from the SLA and 31V from the Meanwell, and fits into the hole I've already cut into the case. So, I think I'm calling this a loss. I will hack up a 120V cell phone charger and put it inside so at least I can charge while plugged into AC power. Better than nothing and far better than the whining popping situation. Will check out that Bluetooth idea as well. That sounds pretty cool.
Took a pic after extracting the USB regulator. The guts in the all their shameful and untidy horrors...
Took a pic after extracting the USB regulator. The guts in the all their shameful and untidy horrors...
An externally hosted image should be here but it was not working when we last tested it.
Small update. I tried a couple of different phones and got very different results. An old Blackberry, which is what I used for initial testing, causes a whine and a loud, rhythmic tapping sound. Samsung S3 caused a barely audible hum and no tapping. Loud pop happened turning on USB unit with both phones.
I doubt it will help, but I ordered another USB unit just to see if it makes any difference. Worth a shot for five bucks.
DC DC HRD 12V 24V 36V Step Down to DC 5V 3A Car Power Converter Regulator Module | eBay
I doubt it will help, but I ordered another USB unit just to see if it makes any difference. Worth a shot for five bucks.
DC DC HRD 12V 24V 36V Step Down to DC 5V 3A Car Power Converter Regulator Module | eBay
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.