| Author | Message | ||
| lg71
Intermediate Member Username: lg71 Post Number: 182 Registered: 3-2006 |
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
Intermediate Member Username: lg71 Post Number: 184 Registered: 3-2006 |
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
Moderator Username: mica Post Number: 3716 Registered: 6-2000 |
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
Intermediate Member Username: lg71 Post Number: 185 Registered: 3-2006 |
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
Moderator Username: mica Post Number: 3719 Registered: 6-2000 |
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
Intermediate Member Username: lg71 Post Number: 186 Registered: 3-2006 |
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
Advanced Member Username: dfung60 Post Number: 208 Registered: 5-2002 |
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
Moderator Username: mica Post Number: 3723 Registered: 6-2000 |
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
Intermediate Member Username: lg71 Post Number: 187 Registered: 3-2006 |
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
Moderator Username: mica Post Number: 3734 Registered: 6-2000 |
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
Senior Member Username: bsee Post Number: 1370 Registered: 3-2004 |
Mica, did you study under Escher?  | ||
| lg71
Intermediate Member Username: lg71 Post Number: 190 Registered: 3-2006 |
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
Intermediate Member Username: lg71 Post Number: 191 Registered: 3-2006 |
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
Moderator Username: mica Post Number: 3738 Registered: 6-2000 |
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
Intermediate Member Username: lg71 Post Number: 192 Registered: 3-2006 |
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. | ||
| lg71
Intermediate Member Username: lg71 Post Number: 193 Registered: 3-2006 |
I have recorded the pops/clicks and reduced the volume to avoid damage to the speakers, in case it comes loud in your system. I'll describe the symptoms as good as I can: 1) It's the same noise in any positions, 1, 2, 3 or 4 2) If I toggle "very slowly", I can virtually stop the noise! That should give some clues (at least there is this option for now). Chris suggested that "maybe" using a better switch, with silver/gold plated contacts my help, but it's not sure, he said 50% chances? I suggested a non shorting type switch (break before make), Chris said he didn't know if that would help, again 50%? Now that I realize that if toggle very slowly I can avoid the pop, it makes me wonder, why would a better switch (silver/gold) take care of it? It might last longer, yes, but would it fix this? I am not sure... http://www.topfloormix.com/bits/pops_clicks.mp3 Well, at the moment, I have to be extremely careful when I toggle the switch, because it could damage something (headphones, speakers...) | ||
| lg71
Advanced Member Username: lg71 Post Number: 204 Registered: 3-2006 |
Hello Mica, Thanks for being interested in the "clicking/poping" issue. Could you please advise or help me? Thanks, LG | ||
| mica
Moderator Username: mica Post Number: 3745 Registered: 6-2000 |
Hi Louis-Gino, I'm waiting to find out if the switch is wired as shown in the diagram I posted on October 31 before I can offer any meaningful advice. Let me know when Chris gets a chance to look at the diagram, thanks. | ||
| lg71
Advanced Member Username: lg71 Post Number: 206 Registered: 3-2006 |
Hello Mica, I am going to call him again tomorrow, I hope that he will be able to check the picture, I did send it to him last week though. Many thanks. | ||
| lg71
Advanced Member Username: lg71 Post Number: 217 Registered: 3-2006 |
Hello Mica, I just spoke to Chris, he confirmed that it is wired like on the diagram. As I explained, the click/pops are quite loud (unsafe for speakers/headphones...) and it is equal in each positions. Thanks for your help, LG | ||
| inthelows
Junior Username: inthelows Post Number: 18 Registered: 11-2006 |
Sounds like the contacts are loose or the contact point is off. Moving from point to point fast or slowly shouldn't matter. If the sound is similar to when you pull out the guitar cable, (contact for the battery), it sounds like the circuit isn't isolated. I've had switches that worked fine out of chassis only to ground out when assembled. Something with the wiper arm and collar. Is it possible to try another switch?..NLP | ||
| lg71
Advanced Member Username: lg71 Post Number: 225 Registered: 3-2006 |
Well, first, thanks for your input. But, second, unfortunately I have been having an extremely hard time getting a 3 poles 4 ways (shorting/make before break) rotary switch. I had to get the first and only one available in London/Maplin, the only other type they have is non shorting/break before make. http://www.maplin.co.uk/Module.aspx?ModuleNo=2417&criteria=rotary%20switch&doy=7m11 | ||
| inthelows
Junior Username: inthelows Post Number: 20 Registered: 11-2006 |
I googled 3 pole 4 way rotary switch and got a tons of hits including doctronics.co.uk and rs-components.co.nz. On some of the sites they post wiring FAQs. Perhaps its worth a look. I'm sure the Alembic staff will have a handle on this soon enough! NLP | ||
| lg71
Advanced Member Username: lg71 Post Number: 226 Registered: 3-2006 |
We checked RS UK (not NZ) they didn't have anything suitable. The thing is, I had to get it quick, otherwise it could have taken ages to get one from abroad, and both Chris and I, wanted to get this project out the way. I'll check doctronics as well, thanks. | ||
| lg71
Advanced Member Username: lg71 Post Number: 246 Registered: 3-2006 |
Hello Mica, Do you have any suggestion/ideas please? Would bigger resistors on the output help, maybe...? | ||
| dfung60
Advanced Member Username: dfung60 Post Number: 215 Registered: 5-2002 |
Here's a couple of things you should check - first, confirm the exact part number on the switch. You'll momentarily lose all output when you have the break-before-make switch instead of the make-before-break switch that you want which you may perceive as a "pop". If you turn a switch like this very slowly, you may be manually forcing both the before and after positions into contact at the same time, which makes it into the "right" kind of switch. Second, when you get a loud popping noise in a system with active EQ, it's because you interrupted power to the preamp circuit while switching. It sounds like your plan had a pair of filter circuits, which are active preamps powered from the batteries. They have a DC power supply wire that's coming from the batteries (however many there are). The +V power must not be interrupted at any time and shouldn't be routed through the switch. The trickier part is that the -V or power ground from the batteries can't be routed through the switch either. Interrupt either line and you'll get an enormous thump at the signal output. In one of her early responses, Mica noted that only the hot leads (center of the coax) from the pickups go through the switch. Also, all the pickup grounds (the mesh shield from each pickup) join at a common point which is separate from the battery -V or battery ground. The "output" pole of the big switch is the +signal input to the filter board. The pickup common ground is the -signal input to the filter board (and doesn't pass through the switch). In your design pictorial, you're doing something a little bit unusual which may also be part of the problem. In most instruments, the volume controls are wired immediately after the pickups and before any EQ or filter boards. In your case (because of the pan pot, I guess) the volume controls are wired after the EQ board. There's nothing wrong with that, but it does make things a little trickier. The same rule about what gets switched and what gets grounded together applies here, but you have to remember that the post-filter volume pots need to be grounded together, but not together with the pre-filter pickup grounds! The pan pot is pre-filter, so it needs to be grounded in the same common group as the pickups and switch, but not with the other volumes. As an adjunct to this, on most instruments this means the resistance value of the pan pot and volume pots will be different. Because the panpot is living on the passive side of the circuit, there may be some interaction effects (like treble loss) when you treat it like a blend. Fixing this would require a change in the circuit design (you need to have linear preamps immediately after the pickups and before the switching matrix to eliminate the passive interactions). Although you may not enjoy the tech bill, you might consider working through the wiring incrementally to assure that everything really is working OK. For instance, you can wire up the pickups and panpot, then take that output directly to the output jack. This is a totally passive setup, so there's no battery, power switching, or grounding weirdness (of course, no filters or volume knobs either). Next, add in the filter boards with the power wired directly to the boards (no switching in the jack). After that, add the post-filter volumes. Finally, add the power switching. You'll at least be able to get a sense of how it will sound at each step along the way. To properly maintain power separate, you really want to create a pre-filter common ground for the pickups, switch, panpot, and instrument shielding. For the power side, you want to wire the filter power supply boards point-to-point from the V+ and V- lines to the batteries, and use a special output jack (like a Series jack) which has dedicated independent power switching. This will keep power separate from signal and also keep you from interrupting the active EQ power. The reason that you get a big thump if you interrupt power is that the active preamps offset the signal zero point to half the supply voltage. For instance, if you have a 9VDC power supply, the preamp will amplify it's input signal over a range of +4.5V to -4.5V. When you aren't playing (no output signal) the zero point is +4.5V relative to the input signal. If you interrupt the power supply, the output drops from zero being at +4.5V to zero really being at zero. That is an enormous "thump", basically as loud as your amplifier can produce. You want to solve the thump problem by making sure the power is not interrupted. You can reduce the problem with a big capacitor between filter output and ground which filters out the big thump, but this is a low-pass filter which will affect your tone as well. The more I think about this, the more I think you probably will need to re-examine the circuit to get what you want out of it. In particular, I think it's unlikely that the pan pot will do what you want it to do without buffering the signal from all three pickups before the switch with a set of linear preamps. Doing this will mean that all the wiring in the control cavity will be back to common ground and simpler to understand and debug. Good luck, David Fung | ||
| lg71
Advanced Member Username: lg71 Post Number: 252 Registered: 3-2006 |
Hi David, While I am still waiting for Mica's advice... I thank you for you input, and it is a valuable post, it will be saved with my other valuable archived emails, BUT: I want to stress a few points here; by reading you post, it seems that you don't realize that the order of the circuit(s) is the original Alembic path, The PU goes to the Filter, then to the Volume, on dual PUs, the PUs go the the Pan, then to the Filter, then to the Volume... I haven't change anything here. Then, a PU selector would be exactly were it situated now in the chain, in place of my switch. Further, reading you post and your theory, the original Anniversary circuit with the PU selector should pop/click as well, but I don't think it does, no? To sum it again, it's simply two complete Alembic harness, one of them has a Pan/dual PUs and the other one doesn't, nothing as been altered or changed, apart for adding the Matrix switch (thanks for mentioning the word matrix, it seems to be the appropriate one). A last word, I haven't studied electronics, and I am very far from your knowledge, although I can solder. ;) Thanks, LG | ||
| dfung60
Advanced Member Username: dfung60 Post Number: 216 Registered: 5-2002 |
LG - Thanks for the clarification in your last post. I only have Series basses, which have dedicated preamps on each pickup (as well as the dummy coil), so the topology of the circuit is pretty different. This did come up in an earlier thread regarding the difference between individual volumes and a pan pot, so I should have known this! The effect of having the pan pot (or individual volume pots for that matter) before the preamp is that turning the pot down to decrease the output level will have an effect on the tone as well, usually a loss of treble. You probably don't notice this on panpot Alembics because the other pickup is full volume and full tone as well, but you might notice this on an instrument with individual volumes if you turned off one pickup and reduced the volume on the other. If the volume pot is located after the preamp, then there's no tonal effect from turning the volume down. This is what I meant when I mentioned that that the panpot might not work the way that you expected, but you are correct in that it should be no different than a panpot Alembic. I think the other observations in my post are correct though. You need to be careful to make sure that signal and power grounds are kept separate, but this should be straightforward if you follow the normal wiring of the filter boards. You also need to be careful that the switching system doesn't interrupt the power to the filter boards. You mentioned that the pops are equal in all positions and very high in level, which still leads me to believe that there's an interruption of sorts as you switch. Improper combining of grounds might possibly be involved although it seems somewhat unlikely (I guess you might suspect that a short between the two grounds might be part of the problem). And I do continue to think that the best way to start debugging this is wire things up without the filter boards first. You would route the outputs that would normally connect to the filter board inputs directly to the output jack (I guess all summed together) and see whether you can switch without noise, then add the active circuits afterwards. Good luck, David Fung |
