Hi,
I'm building a gainclone amp, and I need a rotary selector to switch between sources. I have three inputs to the amp, and I bought one of these:
Rotary Switches : Rotary Switches : Maplin Electronics
I got the 4-pole 3-way one and that's fine, but will this switch do for audio?
Can you recommend something else I can use for this purpose? This is my first attempt at something like this and I'm not sure if this switch will work or not, I'd like to be sure before I solder everything up.
Thanks,
I'm building a gainclone amp, and I need a rotary selector to switch between sources. I have three inputs to the amp, and I bought one of these:
Rotary Switches : Rotary Switches : Maplin Electronics
I got the 4-pole 3-way one and that's fine, but will this switch do for audio?
Can you recommend something else I can use for this purpose? This is my first attempt at something like this and I'm not sure if this switch will work or not, I'd like to be sure before I solder everything up.
Thanks,
It's fine to begin with. The downside is the risk of some "capacitive" breakthrough from the inputs you haven't selected when using simple switches. Relays have the same issue too.
That's being perfectionist though... in reality it will be just fine.
You can use the unused pole to add LED indication of selected source. 3 LED's and one resistor... easy
That's being perfectionist though... in reality it will be just fine.
You can use the unused pole to add LED indication of selected source. 3 LED's and one resistor... easy
It's fine to begin with. The downside is the risk of some "capacitive" breakthrough from the inputs you haven't selected when using simple switches. Relays have the same issue too.
That's being perfectionist though... in reality it will be just fine.
You can use the unused pole to add LED indication of selected source. 3 LED's and one resistor... easy
So, both left and right signal ground should both go into one pole?
Thanks for that piece of advice, that's the kind of thing I wouldn't know about.
Not exactly
The signal grounds all have to be common. They don't connect to the switch at all.
With your switch you are switching the "live" signal feed by applying all the inputs of one channel to the outer pins of one pole of the switch. You will have one pin left in the group as its a four pole switch.
The signal feed to the amp is taken from the centre pin applicable to that group.
You then do the same for the other channel using either of the remaining poles of the switch.
This might help, from post #5
Also look at post #7 and imagine the LED's are your three signal sources (just one channel). The feed to the amp would be terminal A on the switch.
http://www.diyaudio.com/forums/chip-amps/166618-couple-quick-questions-i-begin-my-lm886.html
"The signal grounds all have to be common. They don't connect to the switch at all. - Mooley"
Thats not always a good idea these days. If'your various sources use SMPS internally, there can be quite a lot of nasty high voltage AC at low current from the primary side of the SMPS to the secondary side, via the obligatory high voltage capacitor between them.Even plugging/unplugging one of those sources into a preamp and power amp[ where the P.A. is earthed, can give quite nasty little bites. The effect is additive unless you also switch the "earth" side of the inputs.A couple of days ago I measured 160V AC from the "earth" side of an Oppo 981HD's output RCA jacks to the earth side of the preamp's input socket.
This doesn't do wonders for S/N either.
SandyK
Thats not always a good idea these days. If'your various sources use SMPS internally, there can be quite a lot of nasty high voltage AC at low current from the primary side of the SMPS to the secondary side, via the obligatory high voltage capacitor between them.Even plugging/unplugging one of those sources into a preamp and power amp[ where the P.A. is earthed, can give quite nasty little bites. The effect is additive unless you also switch the "earth" side of the inputs.A couple of days ago I measured 160V AC from the "earth" side of an Oppo 981HD's output RCA jacks to the earth side of the preamp's input socket.
This doesn't do wonders for S/N either.
SandyK
Hi Sandy,
That's why I mentioned in post #2, "it's fine to begin with". Many commercial amps use nothing more than this too.
It's not always easy to gauge someones experience and ability.
Switching signal and ground is an ideal approach but needs care to be done correctly using suitable switches to ensure ground continuity is maintained at all times to avoid massive thumps/bangs/noise as the switch is operated.
That sounds a lot like the phantom voltage that often troubles inexperienced electricians when measuring unterminated power lines. Are you sure that those sockets had a path to earth or each other?
Kevin
As stated, there is a low value, high voltage capacitor (sometimes 2) between the primary and secondary sides of an SMPS.It has to meet a maximum leakage criteria though.
If you want more information, email me and I will send you a copy of an article detailing the problems that SMPS can cause in DVD-A /CD players which use SMPS.
Alex
This leakage is a well known "problem" in the TV trade. Take a rooftop aerial and with the downlead feeder coax plug in one hand and touching the equipment in the other can result in quite a shock, particularly with wet hands. You can even draw an arc from the coax plug to the aerial socket outer even though the equipment is not earthed. There is probably inductive leakage via the SMPS transformer operating at hf as well as via the small caps Sandy mentions.
That said I still think a simple switching arrangement will do all that the op requires on a gainclone.
That said I still think a simple switching arrangement will do all that the op requires on a gainclone.
Thanks for your responses everybody. The other thread helped a lot, but I'm not sure I understand what the best thing for me to do is, given the parts I have. Since I'm a visual kinda guy, I've made this great drawing . This is what I have understood from your comments. What I want to know is, can I do it like this? Again, apologies, but I'm a novice, first attempt at something like this.
Only one input
All the inputs (a bit messy)
. This is what I have understood from your comments. What I want to know is, can I do it like this? Again, apologies, but I'm a novice, first attempt at something like this.Only one input
All the inputs (a bit messy)
Hmmm... it's OK as long as you understand last paragraph in post #7
"Switching signal and ground is an ideal approach but needs care to be done correctly using suitable switches to ensure ground continuity is maintained at all times to avoid massive thumps/bangs/noise as the switch is operated. "
If the switch is not a make before break type and you really do want to switch grounds then you might get around the issue by bridging the all the "wiper to pole" points on the ground switch with something like 100 ohm resistor. That would provide some isolation for unused inputs and all the wanted input to have a zero ohm ground connection. I have never tried that approach although I think it would work.
"Switching signal and ground is an ideal approach but needs care to be done correctly using suitable switches to ensure ground continuity is maintained at all times to avoid massive thumps/bangs/noise as the switch is operated. "
If the switch is not a make before break type and you really do want to switch grounds then you might get around the issue by bridging the all the "wiper to pole" points on the ground switch with something like 100 ohm resistor. That would provide some isolation for unused inputs and all the wanted input to have a zero ohm ground connection. I have never tried that approach although I think it would work.
Hmm, no, I didn't fully understand that. The switch I have is a break before make switch.
So you would recommend a 100 ohm resistor, on the ground side, like this?
ground resistor
Also, it's not that I WANT to switch grounds, I merely want to do it the best way, since I'm trying to learn how to do it. If I can do it without switching the grounds and that's better, I'll do it that way. Because I don't have the right type of switch, is your recommended approach the best, or should I simply connect all grounds together, bypassing the switch?
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Well all the amps I have ever built use common grounding, and all the commercial amps I have owned have too.
Switching grounds probably is the ultimate way to do things but we have to be realistic about it. Get the amp silent first with the two inputs shorted... if this is the first amp you have built don't underestimate how difficult that can be (for a variety of reasons).
If you wire as per the diagram (that's correct as you have drawn it) you have the switched grounds and the resistors will isolate to a very large extent the de-selected inputs.
Switching grounds probably is the ultimate way to do things but we have to be realistic about it. Get the amp silent first with the two inputs shorted... if this is the first amp you have built don't underestimate how difficult that can be (for a variety of reasons).
If you wire as per the diagram (that's correct as you have drawn it) you have the switched grounds and the resistors will isolate to a very large extent the de-selected inputs.
Thanks Mooly,
I don't want to attempt anything that would be more complicated than it has to be. And I appreciate that it could get complicated. If I skipped the switching of the grounds, do I then just solder all the grounds together, including the volume pot, or can I skip the vol pot?
Grounding is where most DIY amps fail and the result is hum/buzzes and noise.
All the input grounds connect together and should go to a "nominated" common point or "star". The volume control grounds should go here too. The speaker ground returns should not contaminate this point.
Don't get to hung up on all this, just follow good practice.
This may help you understand some of the real problems... read it all though as the thread got more onto this kind of thing.
http://www.diyaudio.com/forums/solid-state/101321-3-stage-lin-topology-nfb-tappings.html
There are sure to be dedicated threads around on grounding and recommended procedures but just blindly following a "connect this here and that there" doesn't always work... you have to think about current flow in all the main ground leads and consisder every lead and PCB trace as a resistance that will develop a fault drop in relation to that current flow. You can then decide whether that is relevant to where and how you want to wire it up.
All the input grounds connect together and should go to a "nominated" common point or "star". The volume control grounds should go here too. The speaker ground returns should not contaminate this point.
Don't get to hung up on all this, just follow good practice.
This may help you understand some of the real problems... read it all though as the thread got more onto this kind of thing.
http://www.diyaudio.com/forums/solid-state/101321-3-stage-lin-topology-nfb-tappings.html
There are sure to be dedicated threads around on grounding and recommended procedures but just blindly following a "connect this here and that there" doesn't always work... you have to think about current flow in all the main ground leads and consisder every lead and PCB trace as a resistance that will develop a fault drop in relation to that current flow. You can then decide whether that is relevant to where and how you want to wire it up.
Thanks, I checked all kinds of threads on the forum, including the mega thread on gainclones and found some good advice. I think the grounding is ok now, but I'm not sure. I powered it up for the first time, and it works, only on one channel though.... Beeing a newbie is not good for these kind of things, since troubleshooting is difficult. I feel I'm very close now though. Perhaps my new problems are for a new thread!
I have used these in the past , never had a problem
TE CONNECTIVITY|MRJE3-404FN|SWITCH, 3 POLE 4 POS | CPC
- SWITCH, 3 POLE 4 POS
- No. of Poles: 3
- Contact Material: Gold over Nickel
- Contact Resistance: 100mohm
- Contact Voltage AC Nom: 20V
- Contact Voltage DC Nom: 20V
- DC Power: 0.4VA
- External Diameter: 12.5mm
- External Length / Height: 8mm
- Indexing Angle: 30°
- Insulation Resistance: 100Mohm
- No. of Positions: 4
- Output Power Max: 0.4W
- Series: MRJ
- Shaft Diameter: 3.2mm
- Shaft Length - Metric: 19mm