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DIY: Summer Projects

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Silou

Silou

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On the negative board the wires need to be connected to the other side of R17 and the other side R21 !
So the holes of those resistors being closest to the edge of the board.
Both Pin 1 & 7 from U1 are -5mV now
 

solderdude

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Seems like it is working.
Any idea what kind of LED indiction you want (see post #160)
 
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Silou

Silou

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Seems like it is working.
Any idea what kind of LED indiction you want (see post #160)
Listening test passed aswell. I did not work out the LEDs yet. I think it depends on the case I am going to buy. Before I am going to buy an expensive case I want to make sure everything is fine though.

That is the current test setup. I have got a lot of spare SC-Goblin and some other instrument cables here. Probably better to use them instead of the thin wire I currently use for testing.

Do you think I can trust the setup yet and plug my balanced DT770 in?
IMG_20190816_110824.jpg
 
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solderdude

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Keep the wiring between the PCB's as short as possible.

Looks like it is safe to plug in the balanced DT770.
 
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Silou

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R+ = 4 (P2Off Board Output) positive board -> (insert filters here later) -> pin-3 XLR
L+ = 3 (P2Off Board Output) positive board -> (insert filters here later) -> pin-1 XLR
R- = 4 (P2Off Board Output) negative board -> pin-4 XLR
L- = 3 (P2Off Board Output) negative board -> pin-2 XLR

The right chanel is muted and the left chanel is playing on the right earcup.
The DT770 is working as it should when driven SE on my other amps

Edit: Both sides are working after I redid some solder joints. Polarity is still reversed though
 
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solderdude

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What do you mean polarity is still reversed ?

Both channels working both in single ended and balanced but the stereo image on balanced is 'wrong' ?
 
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Silou

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That was probably the wrong term. The left chanel plays in the right earcup and the right chanel plays in the left earcup. Sounds like a wiring problem at the XLR socket, but I just checked it and I did it as you described
 

solderdude

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Is L-R incorrect in both SE and balanced ?

The sound is 'correct' though so it is not L+ combined with R- and R+ combined with L-

BAL-HEAD-ADAPT-pinout__80209.1540524069.jpg
 
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Silou

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Is L-R incorrect in both SE and balanced ?
It was correct when using the normal J3 output and is correct on my other amplifiers. I did not wire the SE output yet.

The sound is "correct" but chanels are swapped
 

solderdude

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When soldering the XLR please note that the numbering is from the front of a female headphone socket.
From the soldering side this is mirrored.
There should be small pin numbers on the solderside.

Is the DT770 balanced connector wired correctly ?
 
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Silou

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I just checked everything again and tried with the K712. Same result
I wired everything like this:
Pin 1 is L+
Pin 2 is L-
Pin 3 is R+
Pin 4 is R-

XLR cable is wired correctly
DT770 is wired correctly
K712 is wired correctly
XLR socket is wired correctly

Maybe the P2 output is not wired like I thought.
objective2_o2_headphone_amp_pcb_1552980364_feb4aa9c0 - Kopie (2).jpg
 

solderdude

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for the P2connector: (both boards have a P2 connector)
1(&2) are ground, so are only needed for the sleeve of the TRS socket.
3= Left
4= Right

P2 connector numbers are red here
TRS socket = blue
XLR = green


For the fully populated (+) board:
pin 1 = ground = connected to Sleeve of the TRS plug
pin 3 = L+ it goes to Tip TRS and pin-1 of the XLR
pin 4 = R+ it goes to Ring TRS and pin-3 of the XLR

for the negative board:
pin 3 = L- it goes to pin-2 of the XLR
pin 4 = R- it goes to pin-4 of the XLR
 
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Silou

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I checked all again, but the wiring is correct. I connected a TRS socket aswell, but the chanels are still swapped. Any ideas what else could cause it?

Edit: I did not even think about the input socket. Maybe it was all fine with the J2 output because I swapped L and R at the input and the output. Does that even make sense? I have to think about it and check the input socket.
 
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solderdude

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On P1 pin-1 = Left (Tip)
On P1 pin-2 = ground (Sleeve)
On P1 pin-3 = Right (Ring)
 
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Silou

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Yep I fixed it and it works now :facepalm: What a stupid mistake :mad:
 

solderdude

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You are not the only one to make that mistake.
I wired a headphone plug incorrectly once which made me think something sounded really different in that headphone compared to others.
When I put it on 'backwards' it sounded normal again.

Glad to hear it works well. Perhaps install the gain switch on the positive board and figure out what gains you need.
 
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Silou

Silou

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You are not the only one to make that mistake.
I wired a headphone plug incorrectly once which made me think something sounded really different in that headphone compared to others.
When I put it on 'backwards' it sounded normal again.

Glad to hear it works well. Perhaps install the gain switch on the positive board and figure out what gains you need.
I already installed the 680 Ohm resistors. Is the amplifier currently playing in high or low gain without a switch installed? The DT770 (80 Ohm) is easily powered by the amplifier with a lot of headroom.
 

solderdude

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It plays in neither mode when there is no switch installed.
For Single ended the gain is 1x (0dB), for balanced the gain is now 2x (+6dB)
When you like this mode all you need to do is remove the gain resistor for low gain or not connect the switch to the low gain position on the board.
 
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Silou

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Running on mains = max Uout: 14.4V
600 Ohm: 0.35W
300 Ohm: 0.7W
150 Ohm: 1.3W
60 Ohm: 1.1W
32 Ohm: 0.6W
Correct?
2V input, 1X Gain -> out 2V SE / 4V BAL --> matches Atom Low Gain SE and nearly matches Atom High Gain BAL
2V input, 2,25X Gain -> 4,5V SE / 9V BAL --> matches Atom High Gain SE
2V input, 3,5X Gain -> out 7V SE / 14V BAL
2V input, 3,6X Gain -> out 7,2V SE / 14,4V BAL --> High Gain for max output?
 
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solderdude

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correct
 
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