[Jose C]

  Question to all builders, is it true that I should never plug/unplug TRS while the amp is on?  Most of my phones are balanced but just want to make sure I do not do anything that will damage the amp.

 
Usually it's enough to turn the volume to minimum with TRS connectors. XLR are safe to plug/unplug. If you don't plan to drive speakers and want to use TRS just change the output resistors to 1R or 2R2.
 
Turning the volume to minimum is always a good practice with any amp when you use TRS connectors.

 

[jc9394]

   
Usually it's enough to turn the volume to minimum with TRS connectors. XLR are safe to plug/unplug. If you don't plan to drive speakers and want to use TRS just change the output resistors to 1R or 2R2.
 
Turning the volume to minimum is always a good practice with any amp when you use TRS connectors.

 
My beta22 build does not have speaker out.  

 

[naamanf]

The TRS shorts signal to ground when plugged/unplugged. If you like replacing MOSFETs go ahead and do it with the power on.

 

[jc9394]

thanks guys, i will keep in mind to power off the beta22 when plug/unplug trs.

 

[cfcubed]

The TRS shorts signal to ground when plugged/unplugged. If you like replacing MOSFETs go ahead and do it with the power on.

 
That statement, unqualified (e.g. as it stands), is utter BS & FUD.   Briskly inserting/removing TRS plug with power on & volume down, for a properly constructed / adjusted b22 (w/1R R34/R35s as recommended for TRS), will not/does not cause any problems whatsoever. 
I've used my b22(s) in this way, briskly inserting/removing headphone TRS plugs if/when necessary, dating back years (e.g. the "budget" b22 in sig - used most weekdays).
I've no qualms swapping headphones on it "hot", just turn volume down during the brisk insert/remove of TRS plug.  Once on I leave it on for the day, whether swapping cans or not, if not swapping cans I leave 'em plugged in period, even through power on/off cycles (most all my b22 builds have e12s to protect against any DC offset during power up or down).
To each his own here and this very topic has been discussed ad nauseam here & elsewhere.  People fail on each side of the fence on it. 
If I didn't have high confidence in my b22 build w/TRS, or its proper adjustment, or it lacked >= 1R R34/R35, then yeah I'd consider powering off during w/the process.

 

[naamanf]

Okay.

Missed the part about using the higher resistance output resistors. If using default .47 ohm resistors my statement stands.

 

[fishski13]

as long as the music is paused and the volume turned all the way down, i've never had an issue with my B22 and 0.47R output FET-Source resistors.  this should be habit for any HP amp though.  that being said, i do recommend 1 or 2R, and a mute switch is fail-safe if primarily rolling TRS without having to power down.  i also prefer a particular Switchcraft TRS jack since they're difficult to short, but they feel industrial and not "hIGH eND".  if you have other people playing with your B22, make sure they know "the rules".  powering down is easy and no big deal.  the B22 can crank out some power.  treat it like a speaker power amp.     

 

[jc9394]

as long as the music is paused and the volume turned all the way down, i've never had an issue with my B22 and 0.47R output FET-Source resistors.  this should be habit for any HP amp though.  that being said, i do recommend 1 or 2R, and a mute switch is fail-safe if primarily rolling TRS without having to power down.  i also prefer a particular Switchcraft TRS jack since they're difficult to short, but they feel industrial and not "hIGH eND".  if you have other people playing with your B22, make sure they know "the rules".  powering down is easy and no big deal.  the B22 can crank out some power.  treat it like a speaker power amp.     

Thanks Corey, I usually very careful with it and the headphones I have are balanced. I'm considering to bring it to a meet and want to make sure I got it right.

 

[fishski13]

Thanks Corey, I usually very careful with it and the headphones I have are balanced. I'm considering to bring it to a meet and want to make sure I got it right.

 
at the last meet i was at i placed a sign on top of my B22 with polite rules (please and thank yous).  requesting that members ask for assistance before interfacing is not improper either.  pushing the switch and hearing the relay click can be geekishly fun too. 

 

[cfcubed]

You make good points Corey esp. regarding meet conditions where much headphone swapping may be happening. 
And think I owe naamanf an apology for the harshness of my response above.
 
Had direct experience w/the meet thing @ the 2nd meet I attended.  I'd brought some amps, sources + cans & was talking to someone/working with one set of them when someone walked up & without asking pulled & inserted his cans into my budget b22 (it was power on/volume down).  This was back when it had 0.47R R34/35s (& no e12 btw).  Couldn't react quick enough but saw him insert his TRS plug into it as slowly as humanly possible, taking 2 seconds or so to do so!  As if purposely trying to cause smoke.  The amp was fine, perhaps because it had properly adjusted offset, the most important factor here (<= 3mv?).  Instructed him about this and have since been wary of exposing my gear to such abuse at future meets.
 
>  and a mute switch is fail-safe
 
Don't recall seeing any builds with that.... Is it a momentary switch that lifts ground on the TRS jack?
 
BTW here's a (good) thread were Ti among others discuss this point: http://www.amb.org/forum/blown-outputs-t2312.html

 

[fishski13]

a DP toggle mute switch could be placed between the outputs from the amp boards to the TRS, only switching the L and R, and effectively removing the TRS from the output. 

 

[cfcubed]

a DP toggle mute switch could be placed between the outputs from the amp boards to the TRS, only switching the L and R, and effectively removing the TRS from the output. 

Of course but yuk! Might as well use the power switch instead if you must, unless it was some sexy momentary DP

 

[Xovaan]

Hey guys,
 
I'm about to undertake building a 2 channel b22 with LCduino and an o1 from Glass Jar Audio. I'm interested in using a Par-20 case for the b22/lcduino/o1 setup and a separate enclosure for the o25, o22, and transformers.
 
1. For anybody who has gone this route, what is a proper way to gauge the dimensions of the LCDuino screen if I plan on having the front panel done with Front Panel Express?
2. What would you guys recommend for feet for the base of the case?
3. What is a good case size to fit both transformers, the o25, and o22? The Par-20 cases seem a bit large for something like this.
4. I have 22awg Belden shielded wiring. What parts of the circuit would benefit most from using this wiring? I've read that any wiring over several inches should be shielded. What's the guideline for hooking up the ground wire in this Belden cable?
5. Where should I purchase my non-shielded umbilical and board wiring?
 
Thanks in advance!

 

[Zashoomin]

Does anyone know if it will be ok if I just use 2 Sigma 22 boards supplied by 100VA transformers instead of using 4 in balanced configuration to power speakers.  If I read things correctly, if I set everything up correctly I can output 50W into 8ohms.  

 

[H22]

Does anyone know if it will be ok if I just use 2 Sigma 22 boards supplied by 100VA transformers instead of using 4 in balanced configuration to power speakers. If I read things correctly, if I set everything up correctly I can output 50W into 8ohms.

If I understand your question correctly, you want to build a 4 channel B22? And you are wondering if you will be ok using only 2 Sigma 22 power supply's with 100VA transformers for speaker use? Yes, I think that you would be fine, 4 sigma 22's would be overkill I think, but for speaker use you might want to upgrade the heatsinks on all the boards.