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.