Kent Armstrong question

bunker · #1 05-17-2011, 11:11 AM

Hi all. I'm looking for some info on the Kent Armstrong KSBT unit which has been incorrectly installed in my Aria Pro II SB 1000. Whoever did the job originally used a SPST switch in the output wire to the jack for some reason, presumably because they didn't want/ couldn't be bothered utilizing the Active/Passive feature.

I have seen a diagram on here which shows the 'switch' wire from the KSBT across the bottom pair of contacts of a DPDT switch. The common 'in' from the PU and the common 'out' to the volume pot. The top set of contacts go to the KSBT 'in' and 'out' respectively. So in the up position the PU feeds the KSBT in. Signal comes out of the KSBT onto the contact to the volume pot. In the down position the PU signal goes across the bottom contacts, as they are connected, and then onto the volume pot. So far, so good.

Connected to these bottom contacts is the 'switch' wire. As this connection carries signal in the Passive (down) position or is just left floating in the Active (up) position I can't work out what its doing? In my guitar the 'switch' wire is tied to ground permanently via the jack socket. In mine the connection isnt even broken via the jack.

I wasn't sure whether a ground on this connection might be part of a FET based bypass circuit or something similar within the KSBT but in the diagram I have described above this wire only sees signal or nothing but never ground.

Any help greatly appreciated. I wasn't sure whether posting the diagram would be the done thing. It is on this forum and can be found here..Instraling a Kent Armstrong Preamp

SGD Lutherie · #2 05-17-2011, 03:54 PM

I've wired up some of those (because I carry them), and the switch does work, and I'm not sure why either.

bunker · #3 05-17-2011, 06:34 PM

Hey David, thanks for the reply. I guess that makes two of us! I take it there is no explanation in the documentation as to its function? I might disconnect mine from ground and see what the result is..Maybe its a 'future use' thing and it doesn't actually do anything! My initial guess was that it was to 'turn off' the KSBT when in passive mode but I just cant see how that would work from the diagram? Could it sense a signal and switch the KSBT off and thats why mine is tied to ground, hence keeping it on? Why are we here?

bunker · #4 05-20-2011, 10:16 AM

No reply to the email sent to Armstrong so I picked up a 4PCO switch today and as soon as I as my mate gets here with my solder station I shall hopefully have Active/Passive switching with LED indication. Come on Dave, hurry up...

bunker · #5 05-20-2011, 01:39 PM

Done. I hadn't heard it in passive mode before, I like it though!

SGD Lutherie · #6 05-20-2011, 02:09 PM

I believe passive is passing the preamp. So it should sound like the bass without the preamp.

One thing about those preamps, they use a passive tone stack, so the controls are interactive. But that's a very musical way to do EQ.

bunker · #7 05-21-2011, 02:54 AM

Quote:

Originally Posted by SGD Lutherie

I believe passive is passing the preamp. So it should sound like the bass without the preamp.

One thing about those preamps, they use a passive tone stack, so the controls are interactive. But that's a very musical way to do EQ.

Yeah the passive mode just bypasses the pre amp and treble/bass controls. There isn't a tone pot on mine, it was sacrificed when the preamp was fitted. I might swap the two preamp pots in favour of a dual concentric pot, freeing up one hole in the body to fit a 500k tone pot. Its a shame the electronics aren't original but hey ho.

SGD Lutherie · #8 05-21-2011, 11:52 AM

Quote:

Originally Posted by bunker

I might swap the two preamp pots in favour of a dual concentric pot, freeing up one hole in the body to fit a 500k tone pot. Its a shame the electronics aren't original but hey ho.

I did that on one of those not too long ago. I used one of the concentric EMG pots from Best Bass Gear. The values are slightly different, but it worked fine.

Those are nice sounding preamps. I just started carrying them myself.

One thing I remembered is there are mistakes in that wiring diagram at the link you posted. They show the ground connected to the blend pot in two locations, and it should be one. Also the ground from the jack is not shown connected to the volume pot/blend/pickups.

Here's the corrected diagram. Also make sure the blend is wired up the right way. They are all different.