Earspeakers Posted March 20, 2015 Report Posted March 20, 2015 (edited) 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, 2015 by Earspeakers
insanity Posted March 20, 2015 Report Posted March 20, 2015 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.
spritzer Posted March 20, 2015 Report Posted March 20, 2015 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. 1
n_maher Posted March 20, 2015 Report Posted March 20, 2015 I think you can also just put a divider off the pro bias.
spritzer Posted March 20, 2015 Report Posted March 20, 2015 It is already a divider so it's better to use the regulated B+.
insanity Posted March 20, 2015 Report Posted March 20, 2015 Yeah do what spritzer says... safer than my idea.
Earspeakers Posted March 20, 2015 Author Report Posted March 20, 2015 Thanks Spritz, of course a simple voltage divider. Nice bit with a filter cap. Like so?
spritzer Posted March 20, 2015 Report Posted March 20, 2015 I placed the filter cap before the divider and used 270K to ground but it really doesn't matter.
nikongod Posted March 20, 2015 Report Posted March 20, 2015 You may need to tweak the values to get the right bias from your B+.
spritzer Posted March 20, 2015 Report Posted March 20, 2015 Tru dat. For a 350V B+ and a 270K resistor to ground you need a 141K series resistor.
Earspeakers Posted March 20, 2015 Author Report Posted March 20, 2015 (edited) 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, 2015 by Earspeakers
spritzer Posted March 20, 2015 Report Posted March 20, 2015 The reason I gave above and the Pro output is 580V, not 480V. How else would you wire them? They are capacitors after all.
Earspeakers Posted March 21, 2015 Author Report Posted March 21, 2015 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?
mypasswordis Posted March 21, 2015 Report Posted March 21, 2015 Most Stax amplifiers have multiple sockets.......
DefQon Posted March 23, 2015 Report Posted March 23, 2015 (edited) 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, 2015 by DefQon
spritzer Posted March 24, 2015 Report Posted March 24, 2015 If you have access to raw AC then you can do what ever you want. With just DC things get... complicated.
sorenb Posted May 14, 2015 Report Posted May 14, 2015 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?
spritzer Posted May 14, 2015 Report Posted May 14, 2015 Why 280V? Normal bias is 230V and resistors are far less noisy.
kevin gilmore Posted May 14, 2015 Report Posted May 14, 2015 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
luvdunhill Posted May 14, 2015 Report Posted May 14, 2015 Like this? I wonder what PCB this fits into with a few right angle pins?
sorenb Posted May 15, 2015 Report Posted May 15, 2015 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?
sorenb Posted May 15, 2015 Report Posted May 15, 2015 @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)
sorenb Posted May 15, 2015 Report Posted May 15, 2015 Stumbled across this: I guess you would be able to regulate the BIAS from 350-580V using this?
n_maher Posted May 15, 2015 Report Posted May 15, 2015 @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.
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now