balanced headphone protector

[Satyrnine]

Alright, the vast majority of my noise issue is resolved, but I still have noise on whichever "side" I connect the protector board power to. If I use low sensitivity cans, like my HE6SE, I can't hear anything, but high sensitivity cans, like my LCD-X, there is still a persistent and annoying very high frequency noise. I'm more and more sure the protector board is causing it. I'm currently running no shield at all from outputs to headphones, just 4 wires. I've tried connecting the protector board ground to the star ground as well as "chassis". No change.

At this point I think I need a separate supply all together, or possibly a RC filter between the grlv and protector board, to both filter and drop the 30v down closer to 12v a bit. Bad idea?

EDIT: I added 1k resistors on the +30v and -30v inputs. Noise is gone! Getting about 13v on the + input after the added 1k, before the regulator, and about 25v on the - input. Probably only needed the resistor on the + side that drives the relay, but can't hurt I guess. Everything seems to be functioning properly, looks like that did it, unless anyone can think of a reason this is a bad idea? If anyone else has this problem with 30v rails, give it a shot!

Here's the wiring scheme and pics.

Edited January 20 by Satyrnine

[justin]

I made a SMD version of the Protector PCB for the CFA3, and after testing it this weekend I came up with some ideas for changes

#1 - add blocking diodes in series with the power supply inputs. first thing I did was fry the V+ regulator by hooking up power backwards. other protection diodes for the regulators could be added, but I think they're less important

#2 - add minimum load resistors for the regulators (R25, R26). I've previously noticed some 3-pin regulators can have an unstable output voltage if their load is too low. the resistors are so each regulator has at least a 5mA load

#3 - option of getting DC voltage reference from the +/-12 regulators or the external supply. In this case, the +/-12 regulators could have as much as a 0.5V imbalance which requires hand selecting resistors to set the voltage reference (the voltage across R8 + RV1). if powering the protector with LT1021 referenced GRLVs, the voltage is going to be within millivolts for both + and - references. You would install either R1 or R9, and R2 or R10. the PCB could also be designed to allow switching between the two for two different range options.

one feature of using the GRLV / higher voltage supplies for the reference is if those supplies were to become damaged and start outputting a different voltage, the reference will probably be thrown off more than enough to permanently disable the output jacks until the problem is found/fixed.

#4 - added RV1 pot, the purpose is to adjust the range of the protection if it is too sensitive or not enough

#5 - added dual indicator LEDs, for "Good" (D9/white) and "Protection On" (D10/orange). Not a bi-color LED, but 2 separate LEDs next to each other. The white "good" LED will be lit but very dim when the Protect LED is on, and the orange will overpower it.

#6 - changed relay from 12 to 24V for 1/2 the current and to use more equal current from the +/-12V regulators

#7 - added 4.4mm Pentaconn jack short protection. The 4.4mm jack has a switch in the back that only opens when the plug has been fully inserted. The relay keeps the L- and R- pins disconnected, which is every other pin on the jack, until the plug has been fully inserted + a .5 second delay, and then instant release of relay when the plug starts to be removed

SMD version & in CFA3

Edited January 23 by justin

[justin]

Tested the 4.4mm short protection today. The relay disengages if the plug is even .5mm from fully inserted, so i think it will work  

 

[justin]

almost but not quite

disconnecting the L- and R- with a relay didn't solve all the problems, I found 2 conditions that remain, depending on how far the plug is inserted:

1) R+ and GND becomes connected to L+, L- of the headphone

I think this is OK, but I'm considering disconnecting the GND pin of the 4.4mm jack. As a balanced headphone jack, I don't think the GND has any real purpose

2) R+ and L+ connect to L+, L- of the headphone

this is the condition just before the final push to get the plug fully inserted. I'm not thrilled with it, but it may be OK. adding a 2nd relay or using a 4 pole relay to switch all 4 pins would also fix both issues

[Pars]

The only purpose for 1) above would be if the user had an SE 4.4 adapter which would require GND.

[justin]

I'm going to try an electrostatic HP version of Kevin's balanced HP protector. I may keep all 4 outputs separate, using 1kV rated relays, which are usually single pole anyway. Plus this way each output could have its own status LED, which would show which of the 4 outputs (L+, L-, R+, R-) was triggered. Here is a preliminary idea:

 

Edited February 28 by justin

[arcanaking]

Hi, I am building the susy dynalo and cfa3 with the protector board. The protector board works fine unless the volume knob turn over 11 o clock.

If the volume knob is below 11 o clock, each pin's voltage is normal (Pin 1, 2, 13, 14 is 7.9v, pin 5 & 9 is 0.54 and pin 6 & 10 is -0.49).

If the volume knob is over 11 o clock, all the pins' voltage remain the same unless pin 1, 2, 13, 14 keep changing between negative and positive voltage. The switch will auto mute the output. 

When I change this protector board to the original protector 1.0, everything works fine even the volume knob is over 11 o clock.

What is the cause of this problem? Thanks.

[kevin gilmore]

need to see the whole board.  definitely missing the power supply caps at the lm339

[arcanaking]

Sorry for the inappropriate link. Here is the full board. I will later provide another full version of the board from altium designer. Here is the full board.

 

Edit:

Here is the board.

 

[kevin gilmore]

solder on some .1uf caps on the power supply lines on each chip close to the pins.

also no diodes that i see across the relay coils.

Edited September 16 by kevin gilmore

[arcanaking]

6 hours ago, kevin gilmore said:

solder on some .1uf caps on the power supply lines on each chip close to the pins.

also no diodes that i see across the relay coils.

Thanks for the advice. Does the distance of the 0.1uf cap affects the effect? I will try to solder the .1uf cap near the chips.

The relay coils have diodes. For the protector (2nd in the right hand side), it will pass through the 1n4007 like the original protector board. For other relay coils in the right hand side, the led act as diodes across the relay coils in the left hand side.

[kevin gilmore]

yes the distance matters. always put caps as close to the chips as possible.

probably need a scope to see whats happening to the power rails. possibly one of the diodes on the input lines is in the wrong direction.

[arcanaking]

20 hours ago, kevin gilmore said:

yes the distance matters. always put caps as close to the chips as possible.

probably need a scope to see whats happening to the power rails. possibly one of the diodes on the input lines is in the wrong direction.

I tried the following things.

1.) solder the protector part in the new board.

2.) add another 2 100uf and 0.1uf caps near the chips.

3.) put 7812 and 7912 near the chips.

4.) by pass all the unrelated relay and keep the protector relay only.

5.) by pass the lm339.

6.) check the components and circuit direction with the multi-meter.

 

All the new components in the new board with 1, 2, 3, 4 still cannot solve the problem. I also check the circuit with the multi-meter in comparison to the protector v1.0. It can make sure that the route has no problem. In 5, the bypass of lm339 has no problem, this ensure that other relays works fine. Therefore, I am curious that if the width of the route for power supply will also affect the performance of lm339 (all the width of route that related to lm339 is 1mm except the power supply route is currently 0.5mm).

[kevin gilmore]

super thin traces are never a good idea. just ask cavalli.

[arcanaking]

Hi Dr. Gilmore, I finally fix the problem. Sorry for giving you a wrong insight of the malfunction of lm339. After a few day, I attempt to change the mind to lm339 work fine in the circuit and I finally witness the problem. At the beginning, I focus on the circuit in lm339 but overlook the input signal part.

The reason that the output mute after 11 o clock is because the input signal bypass the 100kohm resistor and directly feed in the lm339. Therefore, the voltage will larger than the ref voltage and trigger the protector to mute.

My schematic is following JoaMat's version and the lm339 part is following the protect v1.0. In the input part, I follow the port label design and I think they are the same labels. Therefore, the altium designer will define it as the same and bypass the 100k and the input signal to the lm339 will over the ref voltage.

 

After I change the labels into two group, the new board works fine even the volume is over 11 o clock.

 

Again, Thanks for your opinions.