Hey guys sorry if this is the wrong forum but I have a simple pre amp using 2 ne5532s hooked up to a tda7498e 2 channel BTL board. The preamp works without the power ground connected I'm assuming because the audio signal ground and power ground are tied together on the preamp. I have run into this problem before but don't know what I can do about it? I actually blew up one of my tda7498e boards hooking up an accuphase 3850 clone preamp last week.
Not enough information. Do you have a schematic? The TDA chip is single ended power, I assume your op-amps are also single ended power with virtual ground? Need pictures and schematics.
Forgive my crude drawing but that's how it was hooked up when it fried the amp. As soon as I flipped the power switch the magic smoke and sparks started coming from the tda7498e. I turned it off immediately and upon inspection the outputs from the tda7498e were black and fried. I didn't have any audio signal input at the time and the amp board has 1uf caps on the input signal traces. There's 4 total 1 UF caps in series with the left, right, and 2 grounds of the audio signal.
So I can see that both the power amp and the pre-amp are floating with respect to each other, and need to have a common ground. The 16V transformer provides 100% isolation between the pre-amp board and the TDA board, so I am not sure what would have cooked it- I don't think that is related to the pre-amp. If it was the outputs that were fried, I would suspect an incorrect connection at the speaker outputs. Perhaps you crossed something there.
I recommend hooking a power type ground wire between the ground of the TDA board to the ground of the pre-amp board, and see how that works before hooking up any signal between them.
The power supply for the pre-amp is a little funky- instead of two diodes this should be a 4-diode bridge rectifier.
I recommend hooking a power type ground wire between the ground of the TDA board to the ground of the pre-amp board, and see how that works before hooking up any signal between them.
The power supply for the pre-amp is a little funky- instead of two diodes this should be a 4-diode bridge rectifier.
The preamp has a bridge rectifier and lm7815 and lm7915 on it. Also the preamps power and signal grounds are connected together. The diodes in the diagram were just being used to split the single power supply to make a virtual ground.
I have since ordered a SMPS that provides 12 0 12 dc that's isolated. I will have to modify it's feedback network to boost it's voltage to around 18 0 18 for it to work with the preamp since it has 15v linear regulators on it. I'm just concerned about frying another amp since it doesn't make sense to me how the first one fried. I figured it has something to do with the preamp sharing power and audio grounds and maybe the preamp somehow sent power into the amp via the audio input but it has DC blocking caps. I guess I must have hooked something up wrong in which case I'll never know what happened.
I have one of those accuphase clone kits. The power is supposed to be supplied with a 30VCT transformer (15V - 0 - 15V) with center tap tied to preamp ground. The pre-amp has a bridge rectifier already. The two diodes are not splitting the supply- as drawn, they are forming a half-wave rectifier. Assuming the 16V is an RMS reading, the result is 22V from the positive output to the negative output, and the two 10K resistors are forming a virtual ground putting +11V above and -11V below. You could eliminate all of that and just put the two resistors on the pre-amp board and run the two secondary wires to the + and - power inputs. This is not a really good solution though, as any imbalance in load between the two supplies will cause the virtual ground to not be centered. A much better solution is to use a center tapped transformer.
However, all of this is moot, because the pre-amp should not be what fried your amp board. What was connected to the amp speaker outputs when it fried? I'm not sure what amp board model you are using, and what it's speaker output connection requirements are.
However, all of this is moot, because the pre-amp should not be what fried your amp board. What was connected to the amp speaker outputs when it fried? I'm not sure what amp board model you are using, and what it's speaker output connection requirements are.
I'm using the Sanwu tda7498e board from Amazon, ebay, aliexpress etc. Micheal Beeny also reviewed this board a couple years ago. Its an almost identical copy to the datasheet layout. I didn't have any speakers connected at the time if I remember correctly. If I did they were my book shelf 2 ways that are 4ohm each and have been used with the amp for over a year. From what your saying I'm starting to think I made a mistake and hooked my speaker wires up wrong. I have never done that before and have banana connectors on the wires but there's a first time for everything! I was very surprised when I saw the output from the chip is what was fried, I was expecting to see something burnt on the power input.
No idea. That sucks. Given the amp's input coupling caps, and the transformer isolating the pre-amp and power-amp supplies, you should have been able to connect signal ground to power ground and connect the grounds between the pre-amp and power amp and had no problems. Since your new switching supply for the pre-amp is already putting out regulated DC (I assume it's +12V - 0 - -12V) it just needs filtering. The pre-amp will run just fine on that, no need to hack the SMPS, just remove each linear regulator, connect it's input to the output and put a 0.1uF ceramic from that to ground for good measure. Hacking the sense network in the SMPS should be easy too, and the extra regulation would be good since they do tend to put out a lot of ripple.
Thanks for your help. The SMPS is a +12 0 -12 and it will arrive in the mail tomorrow. It was recommended from a YouTube channel I watched where the author used one to replace a broken PSU for his mixer. He needed 18 0 18 and shows how to modify it and the math he used to figure out which resistor to use. His was a 15 0 15 which was available if I waited for shipping from china. I got the 12 0 12 because it shipped from NJ.
Here is the link to eBay for the SMPS I bought
Here is the link to eBay for the SMPS I bought
Looks more than adequate. Be careful, exposed line voltage, and you might want to put a shield or box around it as it will be kicking out EMI from the naked components and traces, but should work great. Good luck!
I'm mounting everything inside an old DVD player enclosure I gutted and made a new faceplate for. Right now I've been using the amp and SMPS adjusted to 34v for awhile now. Just when I went to add the preamp was when the trouble occurred. I've tried a lot of the Chinese amplifier boards using the tpa3116d2, tpa3255, and the tda7498e. Out of the ones I've tried I prefer the sanwu tda7498e(red board) the most. There's no opamps boosting the gain just the input caps, potentiometer, and strait into the chip. I also have a wondom(sure) bdm8 using the tpa3255 but I still prefer the tda7498e. Sounds much cleaner and gets just as loud.