balanced headphone protector

[baggerbole]

Thanks JoaMat

but I can´t download this zip files. It´s marked as unsecure from Windows...

[JoaMat]

Seems windows don’t like us. Try click and rightclick you around until you find a way.

Alternative go direct to the Gilmore source on Google Drive, click on first link and scroll down to you find protect3.zip.. Lots of good stuff here.

Sometimes it’s tricky to find the information you need, but it’s there – somewhere.

Edited October 19, 2022 by JoaMat

[baggerbole]

Great sources, thanks Joa

[Satyrnine]

Any reason I can't use this with a 30v balanced CFA2 if I plan on driving small speakers with it? It's rated for 1A, 2A max, and 30w at 8ohm is right at 2A. Thoughts?

[Satyrnine]

I built a protector board up for my 30v CFA. When I connect it to a grlv set to 30v (also powering 2x CFA boards), it  causes pretty bad high frequency noise. Right now in SE mode, grounding negative inputs. Negative outputs not connected to anything.

I tried grounding two ways:

1) GRLV ground AND cfa output grounds all connected to protector board. (hf noise was present) 

2) Only GRLV ground connected to protector, cfa output grounds and protector input ground connected to star ground. (hf noise was worse)

When I remove the protector, cfa is dead quiet. 

Thoughts?

[Pars]

What are the voltage in pins on the LM339s (3 and 12) at? 30V inputs seem a bit excessive for the 12V regs, but not sure about that. And you have all unused inputs grounded it seems? You don't need to do anything with the unused outs I don't believe.

[Satyrnine]

Will have to check the pins tmrw, but fwiw, spec sheet says the regs used max input voltage is 35v, so it is cutting it close. And yes, all unused input pins grounded. On delay is only a few seconds too. I'll triple check everything again asap.

[Pars]

It almost sounds like something is oscillating. Do you have a bench supply you could power the protector with to see how it behaves in that situation?

I've only built one protector board and haven't used it yet in an application. I was saving it for a CFA3. On my DynaFET (30V GRLV), I use one of Amb's boards since it is SE only.

[Satyrnine]

I do have a bench supply, will def give that a shot and report back. I'll try it at 12v and 30v to see if there's any difference in behavior.

[Satyrnine]

I ended up using a spare 30v grlv to power the protector board separately. Same transformer. +/- 12v on pins 3/12, still had noise, but it was different sounding this time maybe. Less hf content?  Maybe imagination. That mostly (?) rules out that it's somehow injecting the noise back through the grlv and through the cfas, but solidifies that it's happening at the protector board. I think. Suspecting overworking the 12v regs w 30v at this point.

Wasn't able to test at lower input voltage because my bench supply isn't bipolar apparently. (I usually do tube stuff, rarely need a bipolar supply until now, hah!)

I'm going to go through it and triple check values and get some more detailed readings.

[Satyrnine]

Still  haven't been able to test at below 30v, BUT I did find that if I have no CFA boards connected, just the protector board powered, I don't get any hum from headphones. I also built up a second board, and had same symptoms as first, so I'm guessing it doesn't like 30v.

Edited June 8, 2023 by Satyrnine

[Pars]

My DynaFet isn't in a state that I could try my protector board w/30V GRLV (casing it). Maybe I could rig something up this weekend to try to see how it behaves?

[simmconn]

The protector board needs a solid ground, i.e. split +/-15V power with their common GND tied to the amp GND. A single floating 30V would not work, because the 12V relay only draws power from the +12V and will throw the GND off center and causes feedback to the comparators. You can share the +/-30v with the amp. Make sure the variety of 7812/7912 you use are rated for 35V or more, and the 7812 has sufficient heat sink for continued operation of the relay.

Edited June 8, 2023 by simmconn
Corrected the rail used by relay

[Satyrnine]

1 hour ago, simmconn said:

The protector board needs a solid ground, i.e. split +/-15V power with their common GND tied to the amp GND. A single floating 30V would not work, because the 12V relay only draws power from the +12V and will throw the GND off center and causes feedback to the comparators. You can share the +/-30v with the amp. Make sure the variety of 7812/7912 you use are rated for 35V or more, and the 7812 has sufficient heat sink for continued operation of the relay.

I'm using a +/-30v grlv with common ground to power it. Tried it shared with a CFA2 as well as on it's own GRLV. I still get the noise both ways. Only way I don't get the noise is disconnecting cfa2 boards, powering only the protector board and headphones connected to it's outputs.

I'm using onsemi 7812 and 7912, rated for 35v input and 1A. Relay is Omron G6A-234P-ST-US-DC12 which is 12v and ~17ma coil current. 

I'll check on heat, but seems if it was the issue, I'd get noise even without CFA boards connected, no?

Thanks!

Edited June 8, 2023 by Satyrnine

[Satyrnine]

Now that my CFA3 tube hybrid is nearing completion, I'm trying to get my protector boards working again. 

I chatted with Dukei/Miroslav who's used a number of these at +/-30v, and he says he's had no troubles, so it must be a problem with the boards. I have two built and both exhibit the same noise. Merely connecting power to the board, without using the ins/outs injects noise into the power supply.

Only changes from schem are the slightly higher rated G6A vs G5A relay (pulls less max current actually) and a 1n4004 vs a 1n4007, which shouldn't a problem I don't think. I'm getting +/-12v on the chip pins as expected. Regulators aren't getting hot either. My bench supply is only positive, so no easily accessible bipolar supply on hand.

Would it be inadvisable to use a voltage divider on a grlv 30v rail to bring down the 30v and add some isolation just to see if that resolves? 

Does anyone want to sell me a pre-made protector verified to work with 30v rails? I've just about had it with this, haha!

I also tried the board in a friends Dynahi at 30v, and experience the exact same noise injection as soon as power/ground is connected.

[Satyrnine]

Well I made progress on my noise issue. There is no noise present if I remove Q1, the mosfet that turns on the relay and instead connect the relay to ground directly, effectively hardwiring the relay on. That tells me that the noise likely (?) isn't from an over-taxed 7812 regulator being fed 30v. Narrows it down to Q1 or the comparator circuit driving it... right?

[jamesmking]

3 hours ago, Satyrnine said:

Well I made progress on my noise issue. There is no noise present if I remove Q1, the mosfet that turns on the relay and instead connect the relay to ground directly, effectively hardwiring the relay on. That tells me that the noise likely (?) isn't from an over-taxed 7812 regulator being fed 30v. Narrows it down to Q1 or the comparator circuit driving it... right?

its possible that Q1 is only just providing enough current for the replay contacts to just about close resulting in poor switch contact - that might lead to noise.

Also does the relay have a built in diode for transient protection when the relay switches state? If not the transients could be damaging Q1 and or the opamps.

[Satyrnine]

7 hours ago, jamesmking said:

its possible that Q1 is only just providing enough current for the replay contacts to just about close resulting in poor switch contact - that might lead to noise.

Also does the relay have a built in diode for transient protection when the relay switches state? If not the transients could be damaging Q1 and or the opamps.

Thanks for the reply! In my case the noise is on the 30v rails, not the protector board ins/outs. I have a dual mono CFA3. All I need to do is connect the board to a grlv also powering one channel of the CFA and it injects the noise into that side of the CFA3, audible in headphones that are connected directly to the CFA3 outs, nothing connected to protector board ins/outs. So it's adding the noise to the grlv, which is then audible in anything also connected to that grlv.

And yes, there's a number of caps and diodes on the board that aren't in the drawing. There's a diode across the relay coil.

Thank You!

[simmconn]

I bought this finished protector board on Taobao for about $12. The parts look reasonably good. It could use better cleaning off the flux residue on the bottom side. Totally worth the time I would otherwise have to spend soldering it.

[Satyrnine]

18 hours ago, simmconn said:

I bought this finished protector board on Taobao for about $12. The parts look reasonably good. It could use better cleaning off the flux residue on the bottom side. Totally worth the time I would otherwise have to spend soldering it.

 

Thanks! Yeah, impossible to beat that price! I had my boards made at oshpark. While I've had great luck with them, maybe something is up with the boards themselves.

[Satyrnine]

Well, right as I was about to give up and buy a pre-made board I figured my issue out. 4P XLR shield shouldn't be connected to protector board gnd apparently? If I disconnect the ground between 4pin XLR jack shield and the protector board, no noise. Also no noise if I ground the 4P XLR connector shield to star ground. Protector board itself is also connected to star ground of course. So, ground loop/shared ground return current issue? Sure was a high pitched noise...

What gave me the idea to try this was when I touched the barrel of the XLR jack, the noise lessened and then slowly went  completely away. Let go, noise came back. That told me "ground issue" and here we are. Fixed.

[audiostar]

2 minutes ago, Satyrnine said:

Well, right as I was about to give up and buy a pre-made board I figured my issue out. 4P XLR shield shouldn't be connected to protector board gnd apparently?

No, balanced headphones do not touch ground. That "ground" pin on the 4P XLR connector goes actually to chassis; that is if everything is implemented properly, and if not, to nowhere.

5 minutes ago, Satyrnine said:

Also no noise if I ground the 4P XLR connector shield to star ground. Protector board itself is also connected to star ground of course. 

Exactly. Or properly to chassis and it goes then to the star ground in the PSU.

You had introduced a ground loop.

[Satyrnine]

1 hour ago, audiostar said:

No, balanced headphones do not touch ground. That "ground" pin on the 4P XLR connector goes actually to chassis; that is if everything is implemented properly, and if not, to nowhere.

Exactly. Or properly to chassis and it goes then to the star ground in the PSU.

You had introduced a ground loop.

Yep, apparently. Didn't think just a floating shield could do that...  Thank you for all of your help here and elsewhere, I seriously appreciate it! 

Edited November 3, 2023 by Satyrnine

[Satyrnine]

On 3/12/2015 at 6:05 PM, kevin gilmore said:

the 15 second startup delay is intentional.

you can change the resistor string to make it more or less sensitive

Could anyone offer a starting point to lengthen delay? First 100k to 200k too big of a jump?

Edited November 3, 2023 by Satyrnine

[audiostar]

8 hours ago, Satyrnine said:

Yep, apparently. Didn't think just a floating shield could do that...  Thank you for all of your help here and elsewhere, I seriously appreciate it! 

As balanced audio do not touch ground at all, think of the „shield“ as shield only, which is not even necessary for differential signals (caried over twisted wires), but, if shielded balanced cables are used, that shield connects to chassis only and a (metallic) equipment chassis extends that shield to the electronics and connects input to output cable shields. In order not to introduce a ground loop, the shield connects only to the star ground at a single point (in the PSU chassis near the IEC inlet) and nowhere else. 
In case multiple chassis are used, chassis and ground connectios are caried separately to the PSU chassis.