So I am designing a line driver with 5532 opamps. The PCB I'm trying to make is for 12x buffer stages to drive 12x 600ohm vintage line transformers, simply to add colour to a signal straight from a modern rack digital audio interface. All of the boards and transformers will be mounted in a 19" rack unit.
I opted to try and make the signal fully differential going in and out of the device, so its balanced going back into the analog inputs on the audio interface.
This is my first build of this type and I guess I just wanted some reassurance before I make this PCB design.
I need it to amplify 6dB and be adjustable via trimmer.
Ive put together a linear regulated power supply that I intend to have on a seperate board and connect to the buffer boards with connectors. ERC is just pointing at the Mains AC earth that will go to unit chassis, and the regulator inputs , i guess because i havent specified any actual voltage sources:
Here is two channels of my balanced line driver circuit. I plan to have 6 per board ( 2 boards ) Let me know if theres anything I could change or improve. I created it on breadboard today and it seemed to work well. I had to play around with resistor values to get the gain trimmer values in good ranges:
I didnt add any caps to GND or inductors on the opamp outputs, which I still might.
The output 3 pin connectors will go to 2 core shielded wire to the audio transformers. The secondaries on the audio transformers will go to the back panel TRS sockets of the unit. I understand the Shields on the output TRS need to be grounded to chassis.
I might run a simulation to make sure everything is ok
Any input really helps 🙂
I opted to try and make the signal fully differential going in and out of the device, so its balanced going back into the analog inputs on the audio interface.
This is my first build of this type and I guess I just wanted some reassurance before I make this PCB design.
I need it to amplify 6dB and be adjustable via trimmer.
Ive put together a linear regulated power supply that I intend to have on a seperate board and connect to the buffer boards with connectors. ERC is just pointing at the Mains AC earth that will go to unit chassis, and the regulator inputs , i guess because i havent specified any actual voltage sources:
Here is two channels of my balanced line driver circuit. I plan to have 6 per board ( 2 boards ) Let me know if theres anything I could change or improve. I created it on breadboard today and it seemed to work well. I had to play around with resistor values to get the gain trimmer values in good ranges:
I didnt add any caps to GND or inductors on the opamp outputs, which I still might.
The output 3 pin connectors will go to 2 core shielded wire to the audio transformers. The secondaries on the audio transformers will go to the back panel TRS sockets of the unit. I understand the Shields on the output TRS need to be grounded to chassis.
I might run a simulation to make sure everything is ok
Any input really helps 🙂
Hi. If you are using a bipolar power supply, both opamp inputs must be dc biased to ground. I see + inputs are currently floating dc and connected just to 100uf capacitors. What will be when those capacitors finish charging? You will get full dc at output, you don't want that. Just add a resistor to gnd , similar value as you have from negative input to gnd now.
About kicad errors - just add ground and connect a power node to it. From erc in kicad to work, you need to specify where power is coming, if any pin of any part has a pin ,specified as power input, like opamp pin 4 and 8. Also this power node breaks if you add a RC filter, add power node again after a resistor. I'm stopped doing those erc checks long time ago, for routung tracks they are useless and just wastes time for me.
About kicad errors - just add ground and connect a power node to it. From erc in kicad to work, you need to specify where power is coming, if any pin of any part has a pin ,specified as power input, like opamp pin 4 and 8. Also this power node breaks if you add a RC filter, add power node again after a resistor. I'm stopped doing those erc checks long time ago, for routung tracks they are useless and just wastes time for me.
I used topology below, several times.
Take for R34 a trimmer for adjustable gain.
And you can use ne5532.
I have gerber to share.
Take for R34 a trimmer for adjustable gain.
And you can use ne5532.
I have gerber to share.
Yes of course, this explains why I'm getting a big DC offset on my output! thanks!
And Monstercore thanks so much for this topology. I think instead of using your gerber, I wil adapt mine as I need 12x channels worth. Having the electrolytics on the board like that and one trimmer instead of two makes more sense. I did notice the the cold ring on the TRS seems to go to GND though? instead of shield?
OK how about this? adapted Monstercores' design to my own.
Im going to make two boards of 6. Is it better to have your voltage regulators and filter caps on the board with the buffers? Or should I make a seperate board for that? I guess its cheaper just to double them up on two boards? Originally I was going to do the power supply as pictured in my first post as a seperate board and connect them to the buffer boards with plastic connectors.
I already factored that in to my PSU board.
Also epicyclic , Im not using XLR, its to be TRS, and ignore that pin numbering, it was just to show that im using a 3 pin connector from the panel cut jacks (shielded 2 core). and also on the outputs going to the transformers
yes but I thought it was normal protocol to connect the GND of your balanced input to hte circuit GND? Output balanced GND just goes to the chassis.
Nope, there is no ground in a balanced input, it's a shield.
You attach the input XLR pin 1 to the metal chassis at it's connector, Then you attach the audio circuit common to the metal chassis near the input connector.
You attach the output XLR pin 1 to the metal chassis at it's connector.
* * * * * * * * * * * * * *
a] all cable shields should be attached to the metal chassis at their connectors.
b] Safety Ground/Protective Earth wires should attach to the metal chassis near where the power cord enters the metal chassis.
You attach the input XLR pin 1 to the metal chassis at it's connector, Then you attach the audio circuit common to the metal chassis near the input connector.
You attach the output XLR pin 1 to the metal chassis at it's connector.
* * * * * * * * * * * * * *
a] all cable shields should be attached to the metal chassis at their connectors.
b] Safety Ground/Protective Earth wires should attach to the metal chassis near where the power cord enters the metal chassis.
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My schematic was not meant for trs but for balanced/ unbalanced(rca) input.
But is also used by Purifi and Hypex.
But is also used by Purifi and Hypex.
R14 and R17 will drop a lot of voltage as the NE5532 is bipolar with significant bias currents. Can you make them smaller? 470k ?
Also the circuit lets common-mode signal straight through to C49/50/51/??, so you can't choose correctly which orientation they need to be.
How about putting the capacitors on the input so there's no common-mode injection from the input? Then the cap values can be much smaller too (film caps?).
yeah i mean personally thats what i was going to do, Monstercore's design differed in that regard. I was worried it would turn into an RC filter and affect frequency response though. I didn't do the calculations. I'll do some maths and report back
hey, so i started doing the PCB in kicad. any critique is helpful. i did a ground plane underneath and a plus and minus 15v power plane (thin rectangles) on top layer. tried to make tracks short as possible and made sure bypass caps close to power pins. laid out pretty much same as schema. connectors for input and output. this is only one channel on the board i plan to copy the traces 5 times so theres 6 channels on two boards , obvs ill get 5? boards when i get it printed so that should work out fine, ill drill two sets of standoffs in the rack unit to make 12 channels total, 6 stereo pairs.
yes if any one has any critique feel free but im happy with it. the shields for the cables will be screwed to chassis via solder screw lugs etc, output on right side will go to the audio line transformers
yes if any one has any critique feel free but im happy with it. the shields for the cables will be screwed to chassis via solder screw lugs etc, output on right side will go to the audio line transformers
Why are you killing high frequenciee with c3 c4 to gnd , so large 10nf ?? Or these channels would be just for bass?
i did the RC calc and the rolloff is like 100khz. you think its too low? i wanted to clean up any unwanted noise before it went through the opamp.
and to confirm- no, I want a flat, transparent frequency response. To be honest im not bothered about component values as i can change this easily when i get the boards , more wanted to critique the PCB design
and to confirm- no, I want a flat, transparent frequency response. To be honest im not bothered about component values as i can change this easily when i get the boards , more wanted to critique the PCB design
Better try to simulate input stage in tool like ltspice or microcap, and watch frequency response. Personally I'm using 1k and 8uf in series with signal, then 33k and 220pf to ground. If values are higher , you may see rolloff on 20khz and very small on lower frequencies too, so ...