Picked up a pair of LA3A's a while back, one was dead and one wasn't doing any compression. Did a full recap, replaced a few burned out components in a PSU and replaced the EL panels/opto cells in the T4B's (thanks to electrochronic for the parts! https://sites.google.com/site/diypartsstore/catalog/new-t4b-opto-el-panels )
Both are up and running now, sounding real nice. The bias test point read a bit out on each one, they're in the 14-15v range. Mine do not have a trim pot, just the resistor, R7 in this schematic: http://www.waltzingbear.com/Schematics/Urei/LA_3A.htm
Should I just straight swap the resistor for a 500k pot or is it maybe a better idea to do something like 250K resistor and 250K pot? How much of an adjustment range is necessary? Or should I bias it with a pot, then replace with a fixed resistor? Anything else to know?
The one that is closer to 12-13v seems to do more GR when both have the same input signal/settings (non stereo linked). Will this even out with the bias adjustment or do the units just vary? I purchased a matched quad of photocells.
I'd be happy to answer any other questions about the LA3A, am pretty familiar with it at this point. Thanks!
Both are up and running now, sounding real nice. The bias test point read a bit out on each one, they're in the 14-15v range. Mine do not have a trim pot, just the resistor, R7 in this schematic: http://www.waltzingbear.com/Schematics/Urei/LA_3A.htm
Should I just straight swap the resistor for a 500k pot or is it maybe a better idea to do something like 250K resistor and 250K pot? How much of an adjustment range is necessary? Or should I bias it with a pot, then replace with a fixed resistor? Anything else to know?
The one that is closer to 12-13v seems to do more GR when both have the same input signal/settings (non stereo linked). Will this even out with the bias adjustment or do the units just vary? I purchased a matched quad of photocells.
I'd be happy to answer any other questions about the LA3A, am pretty familiar with it at this point. Thanks!
