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| Help with 10MHz Distribution Amplifier |
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| MadMax01:
Greetings, I'm trying to create a 7 channel distribution amplifier by modifying an existing 4 channel amp available on github. I had a prototype board and soldered it up but when I power it on, the op-amps get really hot instantly, so I know I messed something up (Be gentle, I'm pretty new to this and still learning). My circuit is shown below. I'm guessing there is current feeding back into the op-amp thru the RF circuit but I've seen single channel op-amps wired in other designs the same way so that doesn't make sense to me but that's the only thing I can think of. If you could examine the circuit and point out any obvious flaws, I'd greatly appreciate it. |
| RFDx:
The schematic would be helpful. The non-inverting inputs of the buffers are not biased with VCC/2 and are floating because you put DC-blocking caps in front of the inputs. The inverting inputs need DC-blocking caps and shoudn't be tied directly to ground. The VCC/2 bias voltage generator doesn't work as intended. The 10MHz lowpass filter is shunted twice with 49.9 Ohm, at the input as well as at the ouput. The 49.9 Ohm isolation resistors should be placed close to the outputs of the buffers. |
| 807:
I assume it's the amp from this post:- https://www.eevblog.com/forum/projects/my-10mhz-distribution-amplifier/ As RFDx says, you have removed the bias on the non-inverting inputs of the chips by adding a 100n capacitor in series. Have you checked the supply on pin 4? As both chips are affected, it may be a PSU problem. Have you double checked that the chips haven't been connected the wrong way round? Was this board designed by yourself, or was it designed by someone else? |
| MadMax01:
Thanks for the great feedback... yes, that is the design I used initially and modified to double the output channels. I designed the board myself but yes, the circuit is derived from the one in your link. I think I got it exactly the same as their circuit other than splitting the RF signal into two paths (one for each op-amp), maintaining the 50 ohm impedance by going thru two 24 ohm resistors for each path, and splitting the supply voltage in parallel, one to each op-amp. Those are the only two changes from the original circuit. I will go back thru and double-check everything to be sure. I am sure the op-amps are connected the right way and I am also sure my supply is ok. I checked it and it's outputting 12v to the 9V LVR. When powered up, it was outputting 12V and drawing 0.35A which is too much for the design as intended. I didn't check the pin 4 output as I immediately disconnected power when I noticed how hot the op-amps were getting. They are $7US a pop and I really didn't want to fry them by taking any time to try to troubleshoot the circuit. |
| coromonadalix:
can you post your "enhanced" version schematics ?? maybe you added an error while expanding the design ? |
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