Need advise on DC/DC isolated converter - Page 1
Forum section: electronics / beginners

author: DefinitivVair0
author_rank: Contributor
timestamp: November 23, 2024, 07:53:45 am
content: Hi there,I recently bought a Bluetooth receiver (https://amzn.eu/d/f2wNUXt) to "Bluetooth-ify" my old GoldStar GSM-6330 (I tied the 3pin audio out to the AUX in).-> Sadly I had to realize that there is a lot of noise because of the common ground of the receiver and amplifier (noise was gone after using 2nd power supply for reciever)After researching a bit, it was advised to use a DC/DC isolated converter to isolate the ground. Now since I have not really a clue of what I'm doing, I wanted to ask what to use. The converter has to be 12V to 5-35V but I have no clue how many amps or output power I need since there is no information anywhere. Also, since the reciever is a standalone board, how can I hook it up best? Until now I only fo und through-hole components but will that be a problem or can I just directly solder to the legs?

author: iMo
author_rank: Super Contributor
timestamp: November 23, 2024, 08:09:37 am
content: I would estimate the power consumption of the module will be less than 200mA when feeding a headset (but you are not going to use speakers, imho, so it will be much less).Btw the "noise" you see - are you sure the noise is coming off your GoldStar? Such kind of audio device usually possesses clean linear supply. A DC/DC converter may introduce a noise too..How did you wire the module into the GoldStar?

author: DefinitivVair0
author_rank: Contributor
timestamp: November 23, 2024, 08:23:34 am
content: I think I measured the power consumption on 12V and if I remember correctly it was about 320mA but tbh I don't remember. I will measure again in a few days, since I can't access it right now.I took the ±12V from the old phonograph, wired the + to a switch and then to the receiver and the minus over the switch (for lights) to the receiver.-> note that even if I wire it without the switch it still happensAfter that I soldered the 3pin cable, that came with the receiver to the aux in (I also tried the phono 3pin input but same problem)Now once the reveiver has power there is noise and you can also hear some "beeping" when it searches for a connection.The noise goes away once I disconnect the 3pin or the power from the module and decreases when I increase the volume until it gets louder again after 50%Also when I ran the receiver from an external cable the noise was completely gone, wich proves to me, that the power supply must be the problem...[I can also add some images later but I can't until monday]

author: iMo
author_rank: Super Contributor
timestamp: November 23, 2024, 08:28:40 am
content: Quote from: DefinitivVair0 on November 23, 2024, 08:23:34 am320mA is definitely wrong current when not using low impedance speakers connected to the BT module..On Monday do not switch the BT module on (there is an issue with the wiring, imho), but rather do draw a small wiring diagram and post it here, such we may help you..

author: DefinitivVair0
author_rank: Contributor
timestamp: November 23, 2024, 08:36:13 am
content: Quote from: iMo on November 23, 2024, 08:28:40 amSince I'm not connecting the module to a speaker but the amplifier of the GoldStar who knows. Since i soldered the 3pin in front of the resistors at the aux input board maby that is the cause of the high power draw?! (It was easier to solder so I did not really think about it)Sadly I don't have any schematics of the GoldStar because I would have to buy the manual since there are no free downloads.I will draw up a little wiring diagram but I cant really say a lot about the power supply or what happens after the aux in...

author: iMo
author_rank: Super Contributor
timestamp: November 23, 2024, 08:42:43 am
content: I would wire the BT module into the GoldStar and power it from there (there is a clean 12V available, my bet).When you wire the L and R pins from that white BT connector via capacitors (as the first attempt) to the GoldStar Audio L/R inputs on the pcb ( it needs to be elaborated where exactly), and the G pin to the ground of the GoldStar near the L/R inputs on the pcb, and the power input and power GND of the BT module to the +12V and ground of the GoldStar on the pcb (it needs to be elaborated where exactly to wire the power ground in order to avoid ground loops generating noise), it should work fine, and the BT module's power consumption should be around 20mA (+/-10mA) my guess..

author: DefinitivVair0
author_rank: Contributor
timestamp: November 23, 2024, 01:28:26 pm
content: Quote from: iMo on November 23, 2024, 08:42:43 amThis is the current wiring of the receiver (since EdrawMax is a ...... "wonderful" software I can't export or screenshot the diagram so i could only upload a photo.)

author: iMo
author_rank: Super Contributor
timestamp: November 23, 2024, 01:40:26 pm
content: I would try this as the first step..12V or 9V could be taken from a battery for the first experiments..Later on you may install it into the GoldStar..

author: DefinitivVair0
author_rank: Contributor
timestamp: November 23, 2024, 01:53:05 pm
content: Quote from: iMo on November 23, 2024, 01:40:26 pmI mean, if I use a 12V battery, I won't get any noise.I read that a lot of people had the exact same problem and solved it using an isolated converter to prevent ground loops. I would have bought one but I wasn't sure because the high power draw exceeds the rating of most of them. I'm gonna try wiring the 3pin output differently to try to get a lower power draw.Btw you said I should wire the 3pin out to the pcb (so behind the resistors?) with capacitors. Can you maby explain why? Becuase the sound itself works fine except the (probably) ground loop and works perfectly with a second power supply...

author: iMo
author_rank: Super Contributor
timestamp: November 23, 2024, 02:06:37 pm
content: Do you want to have the BT module outside the GoldStar connected to the BT module via the L and R cinch cables? If so, I would use a small transformer with small linear supply. I would not mess with DC/DC converters around an Audio/Receiver box as they are noisy (especially those $1 from ebay).If you want to put the BT module inside the GoldStar (as many people do these days) then you do not need a power supply, because there is the power supply inside the GoldStar already.The ground loops - when you wire all the stuff properly you will not have there the ground loops.

author: DefinitivVair0
author_rank: Contributor
timestamp: November 23, 2024, 02:25:59 pm
content: Quote from: iMo on November 23, 2024, 02:06:37 pmI guess I should have said that but I want to have the BT module INSIDE the GoldStar connected to the power supply of the GoldStarI only use the aux input as a way to get the audio signal into the amplifier (i could also probably use the phono 3pin but that is way harder to solder to).This way I can inject audio over the BT module into the aux input but can still use the chinch plugs for normal aux in from a TV or somewhere else. This works fine! (Except maby the power draw but I'm gonna check on that)For power I branched off of the ±12V cables of the phonograph wich is connected to the transformer and whatever (tomorrow I can send some pictures of the power supply). Only once I use those 12V cables for power, I get noise. If I give the module power from any other souce I don't get noise.Also, it is noteworthy, that the GoldStar GSM 6330 is very old (at least from 1988, if not earlier)I hope this clarifies some things.