Author Topic: PU selector switch wiring shield (important) (Read 599 times)

lg71 · « **on:** October 30, 2006, 01:43:32 PM »

Hello Mica, I guess you'll probably be the only one that can answer that question. I was supposed to get my bass today, after I found an brought the Luthier a 3 poles 4 positions rotary switch...

But there is a problem, Chris said that he couldn't get it to work because the Alembic PUs are magnetically shielded, and it would require a 6 poles 4 position rotary switch to work, because of the shield.

In case you need to know, the wiring is like so; 3 PUs + 2 Filters + 2 Q-switches + 2 Volumes + 1 Pan, in this scenario 2 PUs are sharing 1 Filter + Q-switch (all this was done and worked fine) With a the newly added rotary switch, I'll be choosing which PU pair is sharing the Filter + Q-switch, as simple it sound.

I asked Chris how is the shield from the PUs wired on your switch then, he didn't know and though you were using different PUs, so he asked me to ask you, where does the shield from the PUs go when wiring a PU selector.

Tomorrow first thing in the morning, chris will be ordering a 6 poles 4 ways rotary switch for the task, but I wish I could hear from you before then, so I could get back to him before he place the order... That's what I would call doing it by the book, according to your instruction.

In case I kind of confused you or didn't make it clear enough, what we need to do is quite straight forward, 3 wires from the PUs going to the switch and come out of that switch, the different position simply swap their path, i.e;
1) bridge + mid PUs share a filter, neck PU has its own filter.
2) bridge PU has its own filter, mid + neck PUs share a filter.
3) bridge + neck PUs share a filter, mid PU has its own filter.
4) Standby or Off

Please note, I am not asking a detailed wiring, mainly were would the shield from the PU go in a scenario like that, in case we can avoid wasting time and money again ordering a 6 poles 4 positions switch.

Thanks,
LG

lg71 · « **Reply #1 on:** October 30, 2006, 04:28:34 PM »

Or in case someone has got an Alembic with the pickup selector, I would be very grateful if you had look inside and tell me where the shields from the PUs are connected to. A photo would be even easier.

Thanks, I know that you can do it

LG

mica · « **Reply #2 on:** October 30, 2006, 05:57:38 PM »

The three shields from the pickups and the two shields from the preamps (filters) all need to be connected together. But that common point cannot be connected to ground (it's running at half the battery voltage).

Then all your switching can just be in the hot leads of the pickups/filters. This should get Chris what he needs to know.

lg71 · « **Reply #3 on:** October 30, 2006, 07:30:14 PM »

Mica, thanks a lot for your help.

But, there is the PAN between one of the Filter, I enclose a diagram I just made, could you please have a look, I left the shield not connected, because I am not sure I understood the wiring properly.
I want to make sure that Chris does it the right way, this is the last crucial part of the project.

Thanks,
LG

mica · « **Reply #4 on:** October 30, 2006, 07:53:09 PM »

The only difference here is that you have 6 wires instead of the 5 I referred to in my earlier post. You should still connect all 6 wires to a common point that is not connected to ground. Should work fine.

lg71 · « **Reply #5 on:** October 30, 2006, 07:58:01 PM »

Well, I hope that he hasn't blown or short anything then, because he tried something that didn't work.

I enclose a newer diagram with my understanding of the wiring for the shield, please let me know if it's correct, so I can show it to Chris. As I said previously, there is a Pan pot between the filter and the switch, so I assume that some of the shield shouldn't go to that filter, but instead to the pot?

Thanks,
LG

dfung60 · « **Reply #6 on:** October 31, 2006, 11:52:40 AM »

Since it sounds like you derived the original design with guidance from Alembic, perhaps things are under control.

But it looks to me like what you need to do is look at this from a different perspective. You need to keep the signal positive and negative separate from the power positive and negative. On a passive instrument there's only a signal path. On most active instruments, the signal and power grounds are connected together.

For some reason, it sounds like you can't connect power ground to signal ground in your design. That's OK. What you need to do is wire up the pickups, switch, and the signal path through the filter boards so they properly switch the positive side and share a common ground which is connected to the signal out on the output jack. Then you need to wire the +V and power ground to the active boards using a separate ground. You'll need to switch battery power on and off with an independent switch on the output jack (e.g., you can't wire through the ring or second channel on a stereo jack). That's no big deal either, many Alembics (Series for sure) seem to use an output jack that has a dedicated switch which closes when a jack is inserted.

When you're getting this up and running, you may find it less complicated to just set up the power circuit without a switch initially so you can make sure everything is OK, then add it later. I have to admit that my brain is somewhat boggled at what you're trying to do with the alternate pickup routings through the switch.

David Fung

mica · « **Reply #7 on:** October 31, 2006, 04:08:55 PM »

Hi Louis-Gino,

We have redrawn your diagram showing explicitly how the shielded wires are the be connected:

Hopefully this will make complete sense. If not, please have your technicial person contact us directly for assistance.

lg71 · « **Reply #8 on:** October 31, 2006, 04:49:04 PM »

Hi Mica,

I think we managed to do it, I call early this morning and explain what you told me to tell Chris, and he understood.

Thanks for your updated diagram, I think that I did understand what you meant in the end, because when I explained it to Chris, he said that it made sense (I wanted to make sure I understood it).

On my previous diagram, the shield wire is going UNDER the switch, sorry, I forgot to make an angle, like you did, so by comparing the two, they look the same. Also the common ground as you named it in a first place, I did understand that it shouldn't touch the ground, but I just named it common ground, maybe I could have named it meeting point for the shield, I understood it's wasn't supposed to touch the ground.

Your second reply before I posted the second diagram, made me understand it more clearly, I am sorry if I made you update my last diagram, the mistake were not intentional. It's much appreciated indeed.

On the other hand, on your diagram, there is no shield from the volumes to the filters, I assume you simply forgot, right? Sorry if it sounds silly.

A quick simple question regarding the finish project; I chose a shorting type rotary switch, as you recommended, and when I switch positions there is a pop/click, is this unavoidable? or would a non shorting type rotary switch solve this problem, or maybe I read somewhere that resistors could be used to fix this problem?

----

Dave, thanks for your input. Although the project was already completed this morning, and it seems to work fine (apart from the annoying pops/clicks when I switch positions)... It's never too late for offering suggestions, much appreciated.

Many thanks,
LG

PS: I will post a photo of the finish project soon, it looks nice.

mica · « **Reply #9 on:** October 31, 2006, 07:42:23 PM »

The redrawn diagram is accurate: the wires from the volumes to the filters are not shielded. I'm glad you got the bass more or less working.

In order to give you advice about the switch, I need you to confirm with Chris that it is wired like this:

Also, please describe the volume/character of the pops and clicks. Are they equal in each position, or do different positions sound different?

(Message edited by mica on October 31, 2006)

bsee · « **Reply #10 on:** October 31, 2006, 10:24:18 PM »

Mica, did you study under Escher?

lg71 · « **Reply #11 on:** November 01, 2006, 09:21:02 AM »

Hello Mica,

Thanks again. For some reason I didn't receive your post in my mail box, I only got Bsee, thanks to him for making a comment, otherwise I would/could have missed it.

To avoid confusion, in case I didn't explain it properly, the shield connection from the volumes to filters I was referring to, is NOT going to the common point at all, it's been left the way it was before.

The wires from the Filters to the Volumes were untouched, meaning that they were left the way they were connected originally, grey wires and red plugs, so their shields are still connected (are we talking about the same wires?).

I have just called Chris and said that the shields (from filters to volumes) were supposed to be cut off/disconnected, he didn't know, as we've only find out now. I already have the bass back, so I sent your last diagram for him to have a look, he hasn't got a computer in the workshop, so he won't get it right away, also he will be off until Friday...

Regarding the pops/clicks, I am going to check again right know, so I can answer your question more accurately.

Many thanks again,
LG

lg71 · « **Reply #12 on:** November 01, 2006, 04:30:15 PM »

Amendment:

Hi just opened the back plate and had a look inside, it's not a grey wire that goes from the Filters to the volumes, sorry about further confusion, it's actually three wires going to the red plugs, a red, a black and a yellow, all are still connected, if this Fine? Thanks

mica · « **Reply #13 on:** November 01, 2006, 06:06:43 PM »

There isn't anything the cut from the volume control to the filter control - the original wiring is a non-shielded wire. Stated another way: leave the original wiring between the filters and the volumes intact.

I'll be interested to hear your report about the clicking situation.

Bob - I do like Escher of course! My dad taught me how to draw schematics, and he's a good teacher. Of course, I always want to redraw every one as soon as I'm done.

lg71 · « **Reply #14 on:** November 01, 2006, 06:54:58 PM »

Hello Mica,

Ah, understood, I'll re-explain it to Chris, and luckily the bass is with me, so nothing bad could have happened meanwhile.

I have to say, that looking at the wiring going in and out of the switch, is some kind of serious engineering, so, for anyone who has been looking at the diagrams, it's only part of the equation, and would recommend to not try this at home unless you have studied electronics. Personally, with all my fancy and limited talk, I couldn't have work it out myself. Even by trying to keep the cost down as low as one can possibly do, there are times when you need to get the experts to get things done properly.

well, once again, Thanks Mica and Chris, and Ron of course!

Regarding the noise, I thing that I am going to post a short MP3, it will be easier to demonstrate. It's hard to describe, but what I can say is that the pop/click is there even when I mute all the strings, and it's quite loud. It wouldn't be suitable/acceptable for the gigging musicians.