Switch Advice - Page 1
Forum section: electronics / beginners

author: goldfinger
author_rank: Regular Contributor
timestamp: October 25, 2016, 07:13:13 am
content: Hi Guys,I'm hoping I might be able to get some advice on what is the best type of switch and how to solder to and wire a switch for adding loading to a cartridge in phono amp.I want to put some sort of rotary switch on case to enable me to switch the loading on cartridge externally to the case.I've attached a pic of the schematic and part of pcb board. "RL" is the load resistor and I want to omit it from the board and place some sort of switch between the RCA input and the input terminal +\- of the pcb board.I'm trying to work out what kind of rotary switch I should get and get an understanding of how I should solder the resistors and wire the switch.Seems the rl is between + and ground..If anyone could provide some advice and maybe talk to how I can achieve it that would be awesome!! I'm pretty much a nooby so apologies for what may seems a simple task.Thanks heaps guys appreciated

author: MattHollands
author_rank: Frequent Contributor
timestamp: October 25, 2016, 10:11:49 am
content: It looks like you forgot to add the picture of the PCB which is pretty crucial for deciding which switch to use and how to solder it!

author: goldfinger
author_rank: Regular Contributor
timestamp: October 25, 2016, 01:18:13 pm
content: Quote from: MattHollands on October 25, 2016, 10:11:49 amSorry Matt I tried attaching and kept getting error. I'll try again thanks heapsSent from my 486 IBM WIN 3.1x Desktop...

author: goldfinger
author_rank: Regular Contributor
timestamp: October 25, 2016, 01:24:27 pm
content: Had issues posting the picture from mobile, here is pic of the PCB.If anyone could give me some pointers on what switch and how to wire that would be really great!

author: MattHollands
author_rank: Frequent Contributor
timestamp: October 25, 2016, 01:32:45 pm
content: So, if I understand the question correctly you want to put a switch in between CL and RL.If it were me I would cut the trace between CL and RL with a knife and solder a wire onto CL and a wire onto RL and connect the two wires to a switch. The issue with this is that having 2 long wires will pick up noise. Therefore I would try to keep the wires as short as possible and use 2 core shielded wire and solder the shield to ground (the other side of CL or RL).If the wires are short, you can probably get away with just using normal wire...

author: goldfinger
author_rank: Regular Contributor
timestamp: October 25, 2016, 09:29:18 pm
content: Quote from: MattHollands on October 25, 2016, 01:32:45 pmHey Matt,Thanks for reply mate not worried about the capacitance for now but yup I want to place switch in path and omit RL. I thought about cable so yeh I would probably place it on back panel to keep cable short.Are you able to elaborate abit more on how to wire and solder it?Looking at the various types of rotary I'm struggling to work out one that would be suitable and then how I wire and solder the resistors to the switch and also ground them.If you could offer more info about how the wires could go in and out (noting your comment on keeping path short and going to board)and probably part that's for me stumped is how to attach the resistor to each throw and have the resistor in path but tied to ground.Thanks heaps appreciate you taking time to provide advice really appreciatedCheers

author: MattHollands
author_rank: Frequent Contributor
timestamp: October 25, 2016, 10:26:29 pm
content: Do you especially want a rotary switch? If so can you link me to an example.Would something likehttp://www.microminiatures.co.uk/acatalog/SLIDE-SWITCH-261.jpgbe fine?If you look at the image I have attached, you should cut the trace along the red line. This will disconnect RL. Solder the capacitor as usual between the orange and blue pads and solder the resistor as usual between the pink and green pads. Then solder a wire onto the orange pad and another wire onto the pink pad. These will be the wires that go to your switch.

author: mariush
author_rank: Super Contributor
timestamp: October 25, 2016, 10:57:45 pm
content: Won't give you any switch advice, but i just have to say that's one ugly layout.Why aren't you routing the traces at 90 degrees and 45 degrees ... all those weird angles for the traces.I would move thelarge C6 capacitor more to the right (put your branding inside the capacitor footprint), and that should make room to place that Q3 transistor (or whatever) by the other Q4 and Q5You'd probably also save yourself a whole lot of routing issues by rotating those C7 to C10 capacitors by 90 degrees to have the negatives all on one sideFlip the R220 resistor the other way around , no sense to have that Z thereWith a bit of care you could move the Q2 to the left under q1 ..It's just an ugly board...

author: MattHollands
author_rank: Frequent Contributor
timestamp: October 25, 2016, 11:53:55 pm
content: Quote from: mariush on October 25, 2016, 10:57:45 pmWhile I have to agree, I think it's a kit:https://boozhoundlabs.com/products/deluxe-phono-peramplifier

author: Audioguru
author_rank: Super Contributor
timestamp: October 26, 2016, 01:08:13 am
content: I have never seen an audio product like this kit that has no audio spec's, this is the first one.The manufacturer of the phono cartridge says what load resistance works best. The output level of a phono cartridge is very low so use a switch with gold-plated contacts that costs no more than silver contacts that corrode and are cleaned with a high voltage and high current.

author: goldfinger
author_rank: Regular Contributor
timestamp: October 26, 2016, 02:02:48 am
content: Quote from: MattHollands on October 25, 2016, 10:26:29 pmQuote from: MattHollands on October 25, 2016, 10:26:29 pmHey Matt,Thanks very much for taking the time to draw things up, it's really helpful and noobish as I am visual helpsI'm not apposed to using slide switch per say. Only requirements really is I want to be able to do it external to unit, two poles/channels, and choose minimum of 6 load settings (ideally 10-12). I suppose raising a rotary type switch was purely on basis of my own limited knowledge on how I thought it was best way to achieve.I hadn't really landed on a particular switch per say. But here is a pic of a switch two pole and link to another as examples of the sort of switch I've been looking at.If I was to either connect passing the RCA inputs through switch to either the audio input or as you suggested cut trace and wire to board how would I wire it and how would I solder resistors to contacts and ground them?Thanks heaps again, it's a great help cause I've been trying to find a similar example as a guide to help me but come up blank thus far! I owe you virtual beer for thishttp://www.hificollective.co.uk/sites/default/files/elma_01_1263_datasheet.pdfEdit I'll post the other pic from my PC shortly getting error from phone but basically it's a rotary with two common pole connection points in middle and throws on outside 1a/b 2a/b out etc etcSent from my 486 IBM WIN 3.1x Desktop...

author: goldfinger
author_rank: Regular Contributor
timestamp: October 26, 2016, 02:14:39 am
content: Yup correct it based on le pacific form booze. Personally don't know enough to comment on the pcb layout, although for a passive Pre it does sound nice despite challenges that passive RIAA poses from dynamic/headroom perspectiveSent from my 486 IBM WIN 3.1x Desktop...

author: Brumby
author_rank: Unknown
timestamp: October 26, 2016, 02:35:09 am
content: Quote from: goldfinger on October 26, 2016, 02:02:48 amAh. This is the first time you mentioned wanting several different load settings!A rotary switch is definitely the way to go. You can easily get single pole 12 position switches which will do the job.This does, however, mean you will need to be a little more hands on with the mod....The simplest way (which is a bit ugly, but should work) is to remove the resistor and run two wires from the PCB. Connect one of these wires directly to the common connection on the switch. You then get the resistors you want to use as loads and connect one end of each of them to the switched poles of the switch. You then join the other end of all of these resistors together and connect them to the other wire from the PCB.This is a bit rough - but you'll get the idea....

author: Brumby
author_rank: Unknown
timestamp: October 26, 2016, 02:54:07 am
content: As others have said - the signal levels involved are low. Magnetic cartridges get down around 3mV. All this extra circuitry could pick up spurious signals, so short leads and shielding may be necessary.See how it goes first.

author: goldfinger
author_rank: Regular Contributor
timestamp: October 26, 2016, 03:30:42 am
content: Quote from: Brumby on October 26, 2016, 02:35:09 amHey buddy thanks brumby appreciated mate. Sorry if I failed to mention multiple loadings!Ok think my mind is getting picture now (I hope) I have a fresh board mate so no need to desolder resistor.The pcb is mono design so hence I thought I would need two poles, is that correct.So based on what your saying and pic you provided (cheers) I would take the active end of RL into common on switch... Then solder first resistor to contact point of (let's say 1a or 1a/b or what ever corresponding number is for second pole if it was two poles) the other end of the resistors which are free I tie them all together with bear wire and solder, that becomes ground I then take wire from there to the other pad of RL which is connected to the ground plain of the pcb board, is that correct?Hopefully I've understood correctly?Now if I wanted to also experiment by playing the switch between the RCA in +/- and the pcb audio in what's thoughts on how to achieve that?Thanks for all the help guys!!! Been really helpful appreciate you taking time to give me guidance!Oh and yes I definitely take your point on the signal degradation that's a concern for sure I know it's no ideal especially with a small signal! I suppose it's important I get a decent quality switch and see how it goesSent from my 486 IBM WIN 3.1x Desktop...

author: Brumby
author_rank: Unknown
timestamp: October 26, 2016, 06:57:07 am
content: Quote from: goldfinger on October 26, 2016, 03:30:42 am(That's for me.)Yes.For stereo, you will need a two pole switch. (Can't believe I missed that one...)The common rotary switch designs offer 6 positions for 2 poles, but you might be able to find a double gang, which can give you 12 positions.

author: Ian.M
author_rank: Super Contributor
timestamp: October 26, 2016, 07:10:01 am
content: For ease of construction, its probably worth redesigning it so the resistors are a tapped series chain. That way for all except the first, both ends go to adjacent switch tags. As its handling a very low level signal, it will probably need a screening can. . . .

author: Brumby
author_rank: Unknown
timestamp: October 26, 2016, 07:12:16 am
content: Quote from: goldfinger on October 26, 2016, 03:30:42 amThat is how to wire the switch. When connecting to the PCB, it doesn't matter which wire goes to which pad as far as the loading function goes - but doing it as you have described would be the best way to reduce the potential for interference. So - yes - do it as you have described.

author: goldfinger
author_rank: Regular Contributor
timestamp: October 26, 2016, 07:19:27 am
content: Quote from: Brumby on October 26, 2016, 06:57:07 amRoger thanks mate!I'm assuming that if I was to try between the RCA input and input on board I should look at a option that has a separate in/out ? Or would It be better just to just tap in and solder into the input wire + and gnd

author: Brumby
author_rank: Unknown
timestamp: October 26, 2016, 07:50:45 am
content: If you want to take the loading switch circuit off the board, you can.Just leave the resistor off the PCB - and you can connect the switch to any two points that are electrically the same.One wire goes to anywhere on the red and the other to anywhere on the green. For minimal noise pickup, keep the wires short, close together and possibly shielded. Connecting directly on the back of the RCA connector would work fine.

author: Zero999
author_rank: Super Contributor
timestamp: October 26, 2016, 08:01:38 am
content: I'd be tempted to use small MOSFETs on the PCB controlled by the rotary switch, as there will be less noise pick up and the tiny signal, no longer has to pass through the switch contacts.

author: goldfinger
author_rank: Regular Contributor
timestamp: October 26, 2016, 09:36:59 am
content: Quote from: Brumby on October 26, 2016, 07:50:45 amThanks heaps brumby legend..And thanks to everyone for providing input been really helpful!!!! Great to see people taking the time to provide help. Hopefully can return the favour sometimeSent from my 486 IBM WIN 3.1x Desktop...