D1080 Mk II 08 actives - XO mods
Posted 23rd December 2010 at 12:21 PM by abraxalito
Updated 5th March 2012 at 03:53 AM by abraxalito
Updated 5th March 2012 at 03:53 AM by abraxalito
Here's the schematic showing the component value tweaks I made to the tone control board. I'll list the changes in detail - only the first three are depicted in the schematic. The remainder aren't as they don't show up on the sim plots 
1) The original input stage has attenuation followed by gain. I have removed both, its now a unity gain stage and also no longer rolls off the HF response.
2) The low-end high-pass filter originally had a rather too high Q for my taste. It's been tamed.
3) The bass-mid low-pass filter was rather too low Q, so I've brought this up, making the response flatter across the band - now the hand over to the tweeter is tighter. The tweeter high-pass is left unchanged.
4) The decoupling regime has been changed so as not to contaminate the local ground. Thus the original 100nF ceramics to ground from either supply rail have been moved to decouple between the positive and negative rails. Ground is thereby preserved as signal reference only.
5) The input ground (RCA connector sleeves) no longer has a connection to the XO local ground. Instead its routed back along the power supply ground wire and from there direct to the star point. Orignally there was something of a ground loop, since ground was supplied from the amp board via two wire harnesses - one for power and the other with the signal outputs. Now the ground link between the boards is solely via the signal output harness - the power supply ground now carries the dirty ground signal from the input (and no power). This mod is implemented by track cuts isolating the two pins in question from 0V and a link between the input ground and power ground pins.
1) The original input stage has attenuation followed by gain. I have removed both, its now a unity gain stage and also no longer rolls off the HF response.
2) The low-end high-pass filter originally had a rather too high Q for my taste. It's been tamed.
3) The bass-mid low-pass filter was rather too low Q, so I've brought this up, making the response flatter across the band - now the hand over to the tweeter is tighter. The tweeter high-pass is left unchanged.
4) The decoupling regime has been changed so as not to contaminate the local ground. Thus the original 100nF ceramics to ground from either supply rail have been moved to decouple between the positive and negative rails. Ground is thereby preserved as signal reference only.
5) The input ground (RCA connector sleeves) no longer has a connection to the XO local ground. Instead its routed back along the power supply ground wire and from there direct to the star point. Orignally there was something of a ground loop, since ground was supplied from the amp board via two wire harnesses - one for power and the other with the signal outputs. Now the ground link between the boards is solely via the signal output harness - the power supply ground now carries the dirty ground signal from the input (and no power). This mod is implemented by track cuts isolating the two pins in question from 0V and a link between the input ground and power ground pins.
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