These are above and beyond the conversion and talkback modification. Echo mod: R550, NOT R39 as previously posted, controls the delay of the cho (speed of the echo). By changing it to a lower value, the delay is decreased. Higher value (obviously) increases the delay. Values below 1k would be inadvisable. I've not experimented with a max value yet, but a couple hundred K would likely be the practical limit. If you want, you can put a 100K pot in place of R550, making sure to use a bit of hot glue to keep the wires from moving around too much. Keep a 1k fixed resistor in series with the POT. Mic Preamp Mods: (I haven't actually tried these yet, but the theory is sound) 1. R181 is the feedback resistor on the 4558 mic preamp IC. It is 150K stock. Change it to anything from 470k to 1M. This will allow much more effective use of a good noise cancelling mic on the radio. As with the talkback mods and echo mods, use hot glue on the parts you install to make sure they do not flex. Values above 1M will be problematic from a noise standpoint, and 470K is likely going to give more than enough added gain for practical purposes. 2. C158 controls the speed at which the AMC circuit responds. To speed up this circuit (and thereby give more even modulation at max levels), change this to 10uf. If you go lower than 10uf, you start to get a choppy sound. If you need a parts layout, visit cbtricks.com and look at the data for the Cobra 200 GTL These mods are also listed on my website.