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Old 6th December 2013, 08:25 PM   #21
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Default Same principle here ?

Very interested in this discussion, but for a slightly different application. I want to be able to A-B test source components. Let's say I have two DACs installed into a grounded enclosure. The raw signal comes from a digital file, say from a NAS or PC. Can I split the input to feed both DACs, then use a simple switch as described to move between DAC outputs?

I want this simple and with the best audio quality (without going overboard). Simple switch or relay, plus coupling caps and resistors, as in:
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DF96: ... Switching noise comes if the switch sees some DC. Coupling caps and ground leak resistors prevent that.

East: use relays and shunt to ground the source that is not selected . Via resistor of 600R if you like...

Jean-Paul: Switches or simple electronics (i.e. without a clock signal) driving quality relays with correct termination is the way to go...

DF96: That will still click, unless the relay is (unusually) make-before-break. ... You need to ensure that everything is at the same DC potential before, during and after any switch transition. That means coupling caps and ground leaks, as I said.
- - - - - - - - - - - - - - - - - - -
So, in the example I gave, I could use a rotary make-before-break switch of the DAC signal out wires from both DACs, plus caps/resistors as described, and this would work (without damaging either DAC)?

Thanks for your thoughts.
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Old 9th December 2013, 04:20 PM   #22
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Today I was looking in the service manual for my old JVC stereo amplifier, to see if I found something intresting, and yes, indeed, I did!

somewhere on one of the PCBs in there, I found the CD4066 (datasheet from TI) a digital IC switch. the datasheet says it can be used for analog signal switching, and thats exactly what I'm looking for!

have anyone tried this? Pros, cons?

EDIT:
this IC is prodeced my many manufactors, and is called CD4066/HEF4066/74HC4066

Last edited by hansibull; 9th December 2013 at 04:29 PM.
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Old 9th December 2013, 06:24 PM   #23
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CD4066 for audio ? Noooooooo ! You can't be serious. This is one of the worst solutions for input switching the audio industry ever invented. Any solution is better that this one. Throw that amp away or replace the input switching circuit and enjoy good sound.

http://www.time-step.com/distribution/4066.html

Relays are the way too go if one wants quality (for those who don't know what app that is please use google). Plain and simple. No Arduino, no CPU, just good relays with gold clad contacts or plain rotary switches with silver gold clad contacts (Elma etc) that will switch your precious analog signals. Don't follow in the pit of "clicking of relays" as that is the standard line manufacturers of digital switching stuff use a bit too often. A bit the same like "small footprint" and "low cost". I never used otherwise and hear no clicks with relays or good switches. Relays and rotary switches are unwished babies as they simply cost too much money. Just a simple resistor to GND will prevent clicking almost completely. And if it bothers you then pull down volume when switching inputs. Don't bother with make before break and such. If quality is of no importance just like audio manufacturers do then follow the digipot/digiswitching route for MP3 (garbage in/garbage out) and please add an Arduino/PIC/AVR and be busy coding for some time as that is the new electronics. Also an app should be written so you can adjust volume with a smartphone. For Gods sake: who forces us mortals to use mobile phones for everything we do in life ?

Check the DCB1 "Mezmerize". No one complains about clicking noises. Sounds excellent too. Any part in the signal chain affects sound quality so keep that amount to a minimum and use quality parts, good power supplies and good switching material. This is what analog is about.
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Last edited by jean-paul; 9th December 2013 at 06:53 PM.
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Old 9th December 2013, 07:12 PM   #24
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Oh, I'm sorry :P I thought it might be a good (and compact) idea, but I later read that 4066 add a lot of distortion to the signal. I guess asking about the 4066 on an audio forum is like asking a car enthusiast why he dives an expensive car if he just goes from A to B.

Yes, I've understood that quality relays is the way to go. But what are quality relays actually? I saw some someone recommend tiny reed relays for input audio, since they are cheap, and only draw a couple of milliamps. You see, I'm still going to use a microcontroller in my amp (sorry about that), so the it would be best to use 5v relays that didn't draw more than 30 mA of current. However, if thats impossible, I could easily add a transistor to add more voltage and current to the relay.

I'm going to have four input channels. That means I'll need to buy 2*4 = 8 relays. Do you know where I can get great relays that doesn't cost a fortune?
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Old 9th December 2013, 07:41 PM   #25
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Hi you need sealed, low power relays with bifurcated gold clad or plated contacts for audio switching. So I take you want them to be affordable. Not expensive and just good (but certainly not the best):

Takamisawa RY5W-K 5VDC

For example:

TAKAMISAWA RY5W K 5V DPDT Signal Relay x20 Pcs | eBay

Also just good, different footprint. As you can see they are discontinued like many good but more costly parts. Silicium is cheaper than copper wire and silver/gold ! Still they are easy to find:

http://www.mouser.com/ds/2/307/G6H_0609-17141.pdf

Quality SMD relays for sale here on the forum:

FS: Omron G6K sealed gold relays mega deal 500 units = $499 (attenuators, switching)

I stock a large amount Finder 30.22SH low power 6 V DC relays in the same layout but the datasheet seems to have an error as it states a quite high minimum switching voltage and current (0.1 V 1 mA which normally is 10 mVDC 0.01 mA with telecom relays so maybe it got written down wrong as the difference is too much). They have gold clad contacts and I use them in audio with quite good results.

http://gfinder.findernet.com//assets...s/32/S30EN.pdf

Always use a driving transistor and a diode across relay coil....
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Last edited by jean-paul; 9th December 2013 at 08:10 PM.
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Old 9th December 2013, 08:15 PM   #26
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Better ones (harder to find) NAIS/Panasonic DS2E-M-DC5V:

http://pewa.panasonic.com/assets/pcs...ds-catalog.pdf

Real good ones cost serious money like the Teledyne relays:

http://www.farnell.com/datasheets/77219.pdf

BTW allow me to give some info/rule of thumb:

Gold contacts are used for voltage switching while silver contacts are used for current switching.

Just remember that, it will save you time when you want to repair a japanese amplifier with intermittently failing channels (so a failing output relay)...
Ask yourself why the relay fails in such amps...
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Last edited by jean-paul; 9th December 2013 at 08:34 PM.
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Old 9th December 2013, 11:32 PM   #27
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Thanks! I'll make sure I get se good quality relays that doesn't destroy the precious analog signal. Since you said that gold is used for voltage switching; does that mean gold relays should be used for the input switching, while silver relays should be used in speaker protection circuits where a lot of current passes through ?

But about the Japanese failing amps. Do they use silver or copper relays instead? Will silver fail because the surface is oxidizing and making a bad contact? That may happend to copper relays too if the copper isn't protected form the oxygen in some way.
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Old 10th December 2013, 06:22 AM   #28
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Quote:
Originally Posted by hansibull View Post
Does that mean gold relays should be used for the input switching, while silver relays should be used in speaker protection circuits where a lot of current passes through ?
Yes

Quote:
Originally Posted by hansibull View Post
But about the Japanese failing amps. Do they use silver or copper relays instead? Will silver fail because the surface is oxidizing and making a bad contact? That may happend to copper relays too if the copper isn't protected form the oxygen in some way.
They often use non sealed 2 A max. rated gold contact relays for switching outputs to speakers. For some reason this error continued for many years. Use sealed Schrack 8 or 10 A rated relays (silver contacts) with the same footprint and the amp won't fail anymore. They even use less power than the original ones.

* Silver oxide conducts current but we don't like oxides so..... use sealed relays to avoid oxides....
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Last edited by jean-paul; 10th December 2013 at 06:28 AM.
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Old 16th December 2013, 06:47 PM   #29
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Hi everybody, I want to add a few more questions to this excellent thread. This time I'll try to be more clear to explain my situation. Sorry from the OP

What I have is a 30 years old tube pre-amplifier and soon I'll have it serviced to change some old components and make a few modifications. It has a quite cheap rotary switch for line inputs without relays or so. At the modification process, I want to add a mechanical switch for two MM level phono inputs. It can either be a toggle or a rotary switch.

From this thread I understand that, relays must be used at switches. Should I use them even if I'm looking a mechanical switching action? When I want to change input, I'll take my a** to the system rack. Repeat that if I'm not happy with the volume level.

Regards

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Old 16th December 2013, 07:10 PM   #30
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Hi you can use a high quality rotary switch too. Why the use of relays ? They offer excellent performance at reasonable cost. A cheap rotary switch can drive relatively cheap but excellent performing relays. A very high quality rotary switch from let's say Elma costs a lot more. Just bought two of those today as a coincidence.

If you have some patience you can find Elma switches now and then for reasonable prices. Or Grayhill which are also very good.

It is the bad cheap switches that gave mechanical switches a bad name. The use of good switches with good cabling is nice but crosstalk might occur when wired the non optimal way. Relays offer better separation but again this is not always like that. It starts with good materials and then some craftsmanship. When using cheap materials all over even good craftsmanship can not help you

When using a rotary switch without relays it is best to place the switch as close as possible to the circuit. In a preamp it is best to place it right in the vicinity of the input RCA connectors and use an extension rod for the volume knob. All mechanical stuff and thus some (nice!) labour.

Digipots and digital input switches are only produced as they're cheap. There is really no alternative to classic metalwork if you are into quality. Just replace such a "digital" circuit once for quality (electro)mechanical stuff and you will know. Point is that switches are becoming more expensive and they're also harder to find. You will see the day that new ones are extinct !
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Last edited by jean-paul; 16th December 2013 at 07:17 PM.
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