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Old 9th July 2018, 11:21 PM   #2021
Absolve is offline Absolve  United States
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Thanks, I will try that. I did try swapping the opamps before, but with the same results. I swapped the transistors also, but no difference. I'll get back with my results!
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Old 9th July 2018, 11:39 PM   #2022
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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As bolserst suggested, you need to start taking voltage measurements and comparing the "good" unit to the "bad unit". Randomly swapping parts is a tough way to troubleshoot, and eventually you'll damage the board with so many parts pulled and re-soldered.


I also suggest you check and compare the output of the wall transformer. I've seen them go bad.
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Old 13th July 2018, 01:11 AM   #2023
Audio Adrenaline is offline Audio Adrenaline  Australia
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Default Adjusting bias voltage on acoustat spectra 11s

Hi Andy, I've read both in this thread and also on on the Audio Circuit site about adjusting the bias voltage on the Spectra 11s I've looked around google and your site and can't find a procedure that describes how to safely do it-obviously you unplug the speakers adjust the potentiometer on the circuit board but do i need to discharge the panels first similar to when you take them apart to move them by touching the red wire on one of the other pin connectors or anything else I'm not worried about getting an exact match of level by using a multi-meter so im not going to have them plugged in when I do the adjustment- but I still want to make sure I am performing the procedure correctly.
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Old 13th July 2018, 01:36 AM   #2024
Absolve is offline Absolve  United States
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I tested pins 4 to 6 and I'm reading 10.77V for the good unit, 11.82V for the problem unit.
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Old 13th July 2018, 01:37 AM   #2025
Audio Adrenaline is offline Audio Adrenaline  Australia
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Default how do I adjust the Bias voltage on the spectra 11 model?

I'm not sure if my last post went up so im putting this up as well my apologies if I doubled up was wondering the procedure to do this ? i looked on the audio circuit site and any other sites I could find -obviously you adjust the potentiometer and could not find anything I'm not going to use a multimeter or anything but I would like to know whether I need to discharge the panel same as when you take them apart to move them? obviously you unplug them lol I've worked on a few different audio things before but not electrostatics so I want to make sure I do it right
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Old 23rd July 2018, 04:24 PM   #2026
Atom666 is offline Atom666  Canada
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Hi Andy
Just wondering how many panels can the MK2146 interface drive? I have enough panels to build an 8 panel speaker,
Thanks
Andrew
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Old 23rd July 2018, 04:39 PM   #2027
Atom666 is offline Atom666  Canada
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Hi Andy
Just wondering how many panels can the MK2146 interface drive? I have enough panels to build an 8 panel speaker,
Thanks
Andrew
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Old 24th July 2018, 01:40 AM   #2028
Absolve is offline Absolve  United States
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An update on the Spectra 11 with low bias. I did the diode bypass mod mentioned by Chamberman,
and I finally got the bias back up! Woo hoo! I was able to adjust the trim pots so both are stable at around 75V. I recapped the large crossover electrolytic caps while I had them opened up. Thanks for the help! They sound super, just like I remember from years ago. Has anyone tried a modern replacement woofer? Any links suitable 8 inch woofers would be great.
Quote:
Originally Posted by Chamberman View Post
I had a low bias issue with my Spectra 22's several years back. Here's a link to that thread, my summary is in post #34. Maybe something there will be of assistance to you.
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Old 26th July 2018, 07:29 PM   #2029
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by Atom666 View Post
Hi Andy
Just wondering how many panels can the MK2146 interface drive? I have enough panels to build an 8 panel speaker,
Thanks
Andrew

Since an 8-panel Spectra was never contemplated, I cannot say how suitable the MK-2146 would be at driving 8 panels. If you try it, the extra panels would be added to the low frequency segment only. You will likely end up with too much bass. You'd also want to change the LF sector resistor to compensate for the added panel capacitance, if you want to keep the transition frequency the same.


Sounds like a lot of work to me, with the potential for results you may not like. A six panel Spectra is already one awesome speaker.
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Old 26th July 2018, 07:31 PM   #2030
AcoustatAnswerMan is offline AcoustatAnswerMan  United States
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Quote:
Originally Posted by Audio Adrenaline View Post
I'm not sure if my last post went up so im putting this up as well my apologies if I doubled up was wondering the procedure to do this ? i looked on the audio circuit site and any other sites I could find -obviously you adjust the potentiometer and could not find anything I'm not going to use a multimeter or anything but I would like to know whether I need to discharge the panel same as when you take them apart to move them? obviously you unplug them lol I've worked on a few different audio things before but not electrostatics so I want to make sure I do it right

Do not attempt to adjust the bias without a means to measure the voltage. Yes, the panels must be discharged and disconnected from the interface before adjusting the bias. Instructions for adjusting the bias have been posted in this thread numerous times. See post #1999 for the most recent.

Last edited by AcoustatAnswerMan; 26th July 2018 at 07:38 PM. Reason: added info
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