Barry Mishkind - The Eclectic Engineer
Frank Foti was the chief engineer at FM-100 in New York City when he began building audio processors.
The Dividend led to his collaboration with Steve Church and the Omnia. Today, Telos Systems produces the Omnia along with the Telos Zephyr, Axia consoles and other products.
Among the many modification popular with the Audimax, Burt Weiner shares his favorites:
I always thought that the Audimax was a pretty nifty device and still has its place. I will agree that a properly designed "multiband" system has more room for customizing and less of the bass poking holes in things.
But to pass along a couple of my favorite modifications for the Audimax I offer the following:
A little remembered fact is that the Audimax has a tube in it that must be replaced. The tube is an 8056 Nuvistor. When this tube goes flat the AGC action becomes poor at best. I've replaced the Nuvistor in mine with a general purpose N-Channel FET from Radio Shack. The difficult part of doing this is figuring out which pins of the Nuvistor socket are which and then getting the correct FET pins into the little holes. The "source" is the cathode, The "Gate" is the grid and the "Drain" is the plate. As they say, "This can be done by a four year old". The reason for that saying is that you will need the eyesight of a four year old! Once the FET has been installed the unit will easily re-calibrate without any further circuit changes. It wont know that you replaced the Nuvistor with a FET.
The Gated Gain Stage platform: I replaced both R-45 and R-45A (paralleled resistors) with a pot. As I recall I used a 10K pot. This allows you to set the sensitivity of the GGS, which is essentially the gating threshold. I found that this will allow you to drive it with less audio to get the desired action and greatly reduce the distortion although the vario-losser circuit which is a couple of biased diodes is not the easiest on distortion figures.
The infamous 10 meg recovery resistor has been changed to a POT. I used a 15 Meg pot with a 1 Meg series resistor. This allows me to change the recovery time and the series 1 Meg sets a limit on how fast you can set it to recover before really sounding bad.
It goes without saying, so I'll say it, that all capacitors should be replaced, particularly the original black electrolytics.
The pots can generally be cleaned and continue to work for a long time. it is necessary to remove the pots from their respective boards. You will see that these are three-section pots. Not all sections have three pins. However, the center pin of what would be the three pins in a section has an opening that goes up into the pot. You can spritz your favorite pot cleaner (not Brasso) up into the pot through that hole. I use WD-40 and have had pots working for over ten years and when I need to adjust them they are still quiet.
My favorite place to put an Audimax is on the back haul side of an ISDN, or whatever your favorite remote transmission scheme is, to control the levels of your typical "all over the place" send buss. Being a gated AGC device they still have a lot to offer. The Audimax makes a nifty addition to any Ham Repeater.