Looking through past notes and posts -
for BAL in, change
R20 to 10K
R18 to 27K
XLR
Pin 1 GND
Pin 2 +IN
Pin 3 - IN
for BAL in, change
R20 to 10K
R18 to 27K
XLR
Pin 1 GND
Pin 2 +IN
Pin 3 - IN
First try the boards in single ended configuration with a SE stereo source see if they work fine without hum.
... the cap across R16 is feedback compensation, so would a similar be doing anything across R18? 😕
That may explain why when using XLR output cables, the gain was lower than when I was using RCA outputs.
I'll change those resistors tomorrow while I'm searching for the hum and let you know the results. Hope I have the parts in stock.
I'll change those resistors tomorrow while I'm searching for the hum and let you know the results. Hope I have the parts in stock.
I don't have enough of those values, I'll order the resistors and the 10pF caps, just in case. Let you know next week.
Not sure what configuration you are using.
Some people on this board they use 2 stereo boards to make a fully balanced version of the preamp. It means balanced input balanced output. In that case you don't need to change those values. You just use 2 single ended boards with a common ground. One for IN- one for IN+.
If you use a single stereo board with balanced input and SE output, then you need to change those resistors.
There are two different things and people on this thread are confused.
Some people on this board they use 2 stereo boards to make a fully balanced version of the preamp. It means balanced input balanced output. In that case you don't need to change those values. You just use 2 single ended boards with a common ground. One for IN- one for IN+.
If you use a single stereo board with balanced input and SE output, then you need to change those resistors.
There are two different things and people on this thread are confused.
I have two boards I built for balanced operation. Where XLR Pin 1 = ground, Pin 2 =IN +, Pin 3 = IN -.
On each channel the inputs are wired:
IN + to pin 2, IN - to pin 1
The other side is IN + to pin 1, IN - to pin 3.
Gain is poor, just not as poor as when I had the ground jumped to IN + and IN - respective.
I still think both sides of the schematic should be symmetrical with the change in resistor values like you suggest. If not, won't the gain be different IN + to IN -?
On each channel the inputs are wired:
IN + to pin 2, IN - to pin 1
The other side is IN + to pin 1, IN - to pin 3.
Gain is poor, just not as poor as when I had the ground jumped to IN + and IN - respective.
I still think both sides of the schematic should be symmetrical with the change in resistor values like you suggest. If not, won't the gain be different IN + to IN -?
You are doing it wrong for the other side.
For fully balanced operation you use only IN+ on each side. IN- is grounded on both sides. That is why you don't need to change the resistors values.
I attached connection diagram.
For fully balanced operation you use only IN+ on each side. IN- is grounded on both sides. That is why you don't need to change the resistors values.
I attached connection diagram.
XLR pin 1 goes to chassis ground, and PCB (preamp) ground to IN-?
Pin 2 and pin 3 to IN+, each side, this part I understand.
As usual, I struggle with the grounds, I'm using a bridge rectifier for the chassis ground to P/S ground.
Pin 2 and pin 3 to IN+, each side, this part I understand.
As usual, I struggle with the grounds, I'm using a bridge rectifier for the chassis ground to P/S ground.
Yes XLR pin 1 goes to chassis ground. Pin 1 of XLR is for shielding only, doesn't carry any return signal. You can experiment by connect it to preamp GND sometimes works better.
And yes both IN- of the preamps are connected to PS ground. First make ground connection between both sides then a wire from this connection to PS ground.
And yes both IN- of the preamps are connected to PS ground. First make ground connection between both sides then a wire from this connection to PS ground.
There is a jumper to connect the two sides of the board to the P/S ground. The ground pads on the inputs are connected to P/S ground.
I'll need to change pin 3 to IN+ and then jumper ground to IN -.
Easier than ordering parts, and swapping them out.
I'll need to change pin 3 to IN+ and then jumper ground to IN -.
Easier than ordering parts, and swapping them out.
BA 2018 Balanced and SE
Apart from all the soldering sagas mentioned above, the BA18 boards that did work I have used to make a balanced pre and a balanced to SE converter. The former uses both sides of a Stereo board for each channel with XLR Pin 2 input to + input , with -input jumpered to ground, pin 3 XLR input to + input on the other channel. The board grounds are jumpered together on the board and all grounds connected to a single point on the chassis including PS ground. Outputs from the + out of each board are connected to XLR pins 2 and 3 respectively of each output XLR. This works fine with the original resistor values and using a VRDN wallwart version there seems to be no hum that makes it past my tinnitus
For the Balanced to SE converter I used a stereo board with the changed resistor values, pin 2 XLR input to +input on the board, pin 3 input to - input on the same channel, output from the board to RCA socket. Grounds same as above . This board uses a Silent switcher to make a very compact and useful unit
In both cases I can use pots or stepped attenuators for volume control, with two pots for combined volume / balance if needed. I am thinking of building the Bal/SE converter into my Passdiy M2x and F6 amps to provide XLR inputs compatible with the DAC I use as well as some Integrated amp functionality
Apart from all the soldering sagas mentioned above, the BA18 boards that did work I have used to make a balanced pre and a balanced to SE converter. The former uses both sides of a Stereo board for each channel with XLR Pin 2 input to + input , with -input jumpered to ground, pin 3 XLR input to + input on the other channel. The board grounds are jumpered together on the board and all grounds connected to a single point on the chassis including PS ground. Outputs from the + out of each board are connected to XLR pins 2 and 3 respectively of each output XLR. This works fine with the original resistor values and using a VRDN wallwart version there seems to be no hum that makes it past my tinnitus
For the Balanced to SE converter I used a stereo board with the changed resistor values, pin 2 XLR input to +input on the board, pin 3 input to - input on the same channel, output from the board to RCA socket. Grounds same as above . This board uses a Silent switcher to make a very compact and useful unit
In both cases I can use pots or stepped attenuators for volume control, with two pots for combined volume / balance if needed. I am thinking of building the Bal/SE converter into my Passdiy M2x and F6 amps to provide XLR inputs compatible with the DAC I use as well as some Integrated amp functionality
I just bought two sets to make a balanced in balanced out preamp. Good to see the recent exchange that give me helpful hints!
Questions:
1. Can I use KSA1381/KSC3503 instead of A1220/C2690 and should I use the same component changes?
2. If I have +/- 12V regulated supply in the chassis I have for it, would that work?
Thanks in advance!
Questions:
1. Can I use KSA1381/KSC3503 instead of A1220/C2690 and should I use the same component changes?
2. If I have +/- 12V regulated supply in the chassis I have for it, would that work?
Thanks in advance!
Hey guys, what did you all use for potentiometer?
I built mine with as a mono with separate supply and it is staggeringly good. 🙂
JT
I built mine with as a mono with separate supply and it is staggeringly good. 🙂
JT
Precision Electronics Corporation 25K (KKA2531S28)
I will experiment with autoformer, and will also implement ESP - A Better Volume Control just to see...
I think this is a weak point... I have a 10k TKD and it has way to low R, but more than that; I connected direct before I found this TKD in the bin. I dropped the TKD in and I noticed, it took a moment, and replaying a few songs, but yes, there was a definite change.
I like this one enough to look at other options for controlling the input levels.
@Z Does the 50k give you smooth transitions?
@My thanks.🙂
I like this one enough to look at other options for controlling the input levels.
@Z Does the 50k give you smooth transitions?
@My thanks.🙂
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