I've got a couple normal bias Staxen I'd like to build an amp for, any ideas for any simple mods to make a normal bias KGST?

 

Edit: apologies if this is a simple mod, I've done searches but what comes up is for going the other direction (normal->pro)

Edited March 20, 201511 yr by Earspeakers

I guess this would be possible by implementing a voltage splitter von the +350 to get to +230? Should be easy.

 

Maybe some else can chime in.

You only need to alter the bias supply for the amp to work with normal bias phones.  See here:

 

 

That is the bias supply for the normal bias on the right hand side panel of the amp, just behind the front panel.  Just a voltage divider off the B+ with a small filter cap, two resistors to form the divider and a 4M7 ballast resistor.  

I think you can also just put a divider off the pro bias.

It is already a divider so it's better to use the regulated B+. 

^^^ I'd listen to this guy.

Yeah do what spritzer says... safer than my idea.

Thanks Spritz, of course a simple voltage divider. Nice bit with a filter cap. 

 

Like so?

 

 

 

 

 

I placed the filter cap before the divider and used 270K to ground but it really doesn't matter. 

You may need to tweak the values to get the right bias from your B+.

Tru dat.  For a 350V B+ and a 270K resistor to ground you need a 141K series resistor. 

Actually why not just tap off the Pro bias pin (assuming a dual output amp) with the network above? Two equal resistors will drop the voltage by half, and 230V is close enough to half of 480V, assuming the bias pin is correctly set to 480V or thereabouts. 

 

Different question, with multi output Stax amps, are the ports all simply wired in parallel? That'll double the capacitance if equal ear speakers are attached for one thing. 

Edited March 20, 201511 yr by Earspeakers

The reason I gave above and the Pro output is 580V, not 480V. 

 

How else would you wire them?  They are capacitors after all. 

The reason I gave above and the Pro output is 580V, not 480V. 

 

Right, I keep remembering the pro bias incorrectly

 

 

 

How else would you wire them?  They are capacitors after all. 

 

Separate output drive sections. 

 

So folks regularly hook up multiple headphones simultaneously with no issues?  Or, when would a amp not be able to handle multiple 'phones? 

Most Stax amplifiers have multiple sockets.......

Is there any chance to up a limited pro-bias output at 470v to near 580vdc? I'm getting some compression distortion on the lower-end regions in sub-bass if I up the volume too much.

Edited March 23, 201511 yr by DefQon

If you have access to raw AC then you can do what ever you want.  With just DC things get... complicated. 

what would be the downside of building the zener string from some values that have 280V and tap the NB from there using some r/c+r/c and a balast resistor?

 

130V + 150V + 150V + 150V = 580V

 

130V + 150V = 280V

 

100k/100nF + 100k/100nF + 5

4M7 as balast?

Why 280V?  Normal bias is 230V and resistors are far less noisy. 

actually i did one amp this way with multiple taps off the zeners...

worked fine and all the parts were already there, just add

one output resistor

caps in parallel with zeners usually is a bad thing

Like this? I wonder what PCB this fits into with a few right angle pins?

ok ok ... my bad .... if you build your zener string to get 580V from something that gives you 230 somewhere ....why not tap the NB from there using a few R/C's  before the balast resistor?

 

can't be more noisy than the 580V since is would be a dublicate of what is going on there ...or do I completely miss the point here?

@luvdunhill: nice little utility PCB ...

...could we get a PCB containing all the neat utilities?  ....XLR in/out combined with alps ....the Stax jacks PCBs ... on/off switch ....bla bla, and so forth ...if someone would do the gerbers I'd do a GB on that ;o)

Stumbled across this:

 

I guess you would be able to regulate the BIAS from 350-580V using this?

@luvdunhill: nice little utility PCB ...

...could we get a PCB containing all the neat utilities?  ....XLR in/out combined with alps ....the Stax jacks PCBs ... on/off switch ....bla bla, and so forth ...if someone would do the gerbers I'd do a GB on that ;o)

 

Not sure if you're kidding or not but on the off chance that you haven't seen - http://mjolnir-audio.com/?page_id=73- I'll post it.