balanced headphone protector

[GrindingThud]

Thanks! I should have checked for a new version 1st.

[GrindingThud]

//edit// Found the 1N914 above.....never mind.

Very cool board, thanks!

-------

What are all those little diodes on the board? Jumpers?

gt

Edited December 29, 2014 by GrindingThud

[luvdunhill]

No, they are diodes.

[cetoole]

Diodes are diodes?  That is inconceivable!

[kevin gilmore]

diodes are there to protect the inputs from voltages > +/-12

on those amplifiers with high power output

[GrindingThud]

Did you have any luck locating a 47uf ceramic? I've been hunting and can't find one greater than 10V.

Old thread, sorry: Kevin, do you have a schematic for the current version of this board?

//UFN

EDIT: Oh, and some BoM-questions:

1) I assume the diodes are just standard 1N4148/1N914?

2) Is the 47uF cap supposed to be ceramic or similar since it hasn't got the same footprint as the electrolytics?

Edited December 29, 2014 by GrindingThud

[UFN]

Well, it seems the 25V part is backordered at Mouser until February. I haven't done anything yet, but maybe a 47uF bipolar electrolytic will work instead? Looks like you can get at least an 8mm part into the board (and maybe 10mm at a pinch).

 

//UFN

[GrindingThud]

Yea, that's what I'll probably do for test until they come in.

Well, it seems the 25V part is backordered at Mouser until February. I haven't done anything yet, but maybe a 47uF bipolar electrolytic will work instead? Looks like you can get at least an 8mm part into the board (and maybe 10mm at a pinch).

 

//UFN

[luvdunhill]

Perhaps check out "pos-cap"? I am not sure the generic non trademark name, but that's what I would use.

[kevin gilmore]

no matter what i order, or when, mouser is always backordered on something

[gepardcv]

1. For the 100uF cap, I measured the leads at 2.5mm, and thought to use 647-UMA1E101MDD from Mouser. Is that adequate?

 

2. There are 7 short components on the board labeled "100k" left of the terminal blocks, but they don't look like normal resistor silkscreen images (2 by the in block, 3 by the out block, 1 to the right of each row of 1uF caps). Are they just resistors I'm supposed to mount at an angle so they fit?

[kevin gilmore]

those are vertical mount resistors to keep the board size down

[gepardcv]

Thanks! Is there any reason to use something like this slightly pricey Ohmite part (SM101031003FE) which seems like a perfect fit, rather than just bend the leads of an ordinary axial resistor for a vertical mount?

[GrindingThud]

Ready for test. 1st install will be in my SuSy Dynalo.

[Pars]

I was going thru the schematic and the gerbers for this to do a layout including a muting switch and Molex KK connectors, which I like better than the terminal blocks. From what I am seeing in the gerbers, I had a couple of questions:

 

• It appears that the LM339s are powered by V+/V- rather than V+/GND?
• The LM339 has 4 comparators in it. It appears that 2 are being paralleled for each input signal?
• The input protection diodes run from V+/V-?

• There are a couple of 1uf capacitors (the yellow ones on GrindingThud's board above) that I am not sure where these go?

I attached a pdf of the Eagle schematic I have worked up so far.

 

 

Gilmore_protect3_schematic.png.pdf

Edited March 12, 2015 by Pars

[kevin gilmore]

• It appears that the LM339s are powered by V+/V- rather than V+/GND?

yes

• The LM339 has 4 comparators in it. It appears that 2 are being paralleled for each input signal?

yes, one for the + limit, the other for the - limit and then repeated 4 times for each of the signals

• The input protection diodes run from V+/V-?

to the inputs of the lm339, not as shown.

 

this should make it easier

 

http://gilmore.chem.northwestern.edu/protector3.jpg

Edited March 12, 2015 by kevin gilmore

[Pars]

Thanks Kevin. Yes, that is much easier to see than what the gerber viewer was showing me

[Pars]

This version should incorporate all of Kevin's corrections from my previous version.

 

One further question:

 

I know on Ti Kan's protection circuit, the relay drive requirements were pulling the + rail down, though he was using a virtual ground scheme on his. A user was the one who suggested the use of the 2N7000 and a 24V rather than a 12V relay, so that both rails were involved in supplying the relay drive.

 

I notice here the you are using a 12V relay and driving it with V+ / GND. In actual use, does this present any problems?

 

 

Gilmore_protect3_schematic.png.pdf

[kevin gilmore]

test circuit certainly worked, and I don't believe in virtual grounds for all sorts of reasons.

 

when you are running a dynahi with 400ma of bias, 25ma to turn on the relay seems tiny

[GrindingThud]

Its running happily in my SuSy Dynalo with no issues that I've noticed.

Provides a nice little startup delay and cuts out if I induce DC on the output.

Edited March 12, 2015 by GrindingThud

[kevin gilmore]

the 15 second startup delay is intentional.

 

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

[GrindingThud]

This circuit should work single ended with both negative inputs grounded, yes? I'm planning on putting it in the CFA2.

Edited April 7, 2015 by GrindingThud

[kevin gilmore]

yep

 

in fact you can delete a number of the parts.

 

2 sets of RCRC and then a jumper on the C to ground.

[gepardcv]

Pardon the ignorant question, but... does using this circuit make any sense with an electrostatic amp, like a KGSSHV or KGST?

[spritzer]

Nope, DC isn't a problem for electrostatics.