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Old 16th January 2012, 04:18 PM   #11
nsx51 is offline nsx51  United States
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I can find lots of toggle and rocker switches, but pushbuttons are difficult. I find a list of filters when doing searches that are beyond my knowledge. How do I specify beyond dpst? That's why I asked for a recommendation for this application. Thanks for any advice.
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Old 16th January 2012, 05:22 PM   #12
Mooly is offline Mooly  United Kingdom
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I'm losing the plot with this

Do you want to switch line level signals into the various amps and headphone amp, or, are you after switching speaker level signals to either/or speakers and 'phones ?

It probably isn't easy finding "nice" push buttons that are highly rated and toggles and rockers are a bit clunky and agricultural.

Many small pushbuttons are signal only and wouldn't survive switching speaker loads and currents. Fine for headphone feeds though. One way around that is to use the tiny switches to control relays but that means adding a power supply.

A DPDT covers most possiblities as it allows two channels (stereo) to be switched one of two way. DPST is just on/off.
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Old 16th January 2012, 05:37 PM   #13
nsx51 is offline nsx51  United States
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Sorry. In post 7 I responded to ethanolson "Can I build or buy a switch box that will connect to an output of my preamp and allow me to select amp (speakers), headphones, or both (A, B, A+B)?" He responded "The easy and cheap way is to wire up a bus box with two pushbutton switches for A and B which decide if they're on or not. Both in means both are on."
I would be switching the output from my preamp.
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Old 16th January 2012, 06:34 PM   #14
Mooly is offline Mooly  United Kingdom
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For preamp levels you want something like these. These should be universally available and tend to conform to a standard pin out,

Switches | Farnell United Kingdom | Results

Perhaps something like this from the above range,
ALPS|SPUJ190900|SWITCH, 2POLE, LATCHING | Farnell United Kingdom

the data sheet gives all the connection details.

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Just to complicate things...

in pursuit of best sound quality (and because switches in signal paths aren't always ideal long term... they have a tendency to go noisy over the years) I wonder whether this might be possible.

To feed the preamp to main amp via a low value resistor (value depends on drive ability of preamp) and use one switch to short the signal to ground rather than pass it through. That leaves the audio clean for normal listening. When you want just phones the switch mutes the main amp not by interuppting the signal but by shorting it out. Any preamp worth it's money will drive 600 ohms and Nelsons probably a whole lot lower than that. The tube one...hmmm

Minimal signal degradation, it passes only through a fixed resistor.

You could do the same for the h/phone feed too but use a higher value resistor so that impact on being shorted is minimal.

Just a thought...
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Old 16th January 2012, 08:03 PM   #15
nsx51 is offline nsx51  United States
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I just swapped out preamps and the tube AI doesn't like the headphones, so it's back to the Pass. It's gain is adjustable using a 6 position dip switch, and can be 0 dB, 6 dB (default), 12 dB, or 17 dB. I assume since a means to increase the gain is incorporated in the preamp, that there is no harm in doing so?
Would it be possible to send send me a sketch of the circuit you're describing? It sounds simple, and I can build things from schematics, but have a limited understanding of how circuits work.
When I just want the speakers, which is much of the time, can't I just unplug the headphones?
I really appreciate your help.
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Old 16th January 2012, 11:47 PM   #16
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I'd do it real simple like this until someone else comes along to shed some more light on the matter.
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Old 17th January 2012, 01:27 AM   #17
nsx51 is offline nsx51  United States
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Ethanolson, that will work with the Pass, but not the Modulus. The Modulus won't, or will barely, drive the headphones. They are 32 ohm. I guess I really need to get a headphone amp. Then it would work with either the Pass or Modulus? The only reason I'd like to use the Modulus is for the phono amp. With the Pass I have to use a discsaver phono amp, which works but is kind of cheesy. If I built or bought an O2 head amp I guess I could use either preamp and everything might work better.

Thanks for the schematic, but I understood your solution, and that's what I may do. I was asking Mooly for a schematic for what he was suggesting, which also sounds good, but as I said, I'm not sure how to build it.
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Old 17th January 2012, 02:06 AM   #18
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Well... if your Modulus isn't really driving the headphones well, then an amp is in order for that setup. As you suspect, the amp will work with the Pass as well. Until you get an amp (and they don't have to be expensive), I guess you'll be using the Pass, possibly wiring up a switch box to it.
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Old 17th January 2012, 12:15 PM   #19
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by nsx51 View Post
I was asking Mooly for a schematic for what he was suggesting, which also sounds good, but as I said, I'm not sure how to build it.
I'll post something later today hopefully
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Old 17th January 2012, 01:49 PM   #20
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Like this. One channel shown. R1 would be as low as is practical. I would say 600 ohm or lower. R2 is similar but see below. The output from either amp is silenced by the switch shorting the signal to ground rather than passing it through. This means the switch is out of circuit for listening.

R2... A h/phone amp probably has a highish input impedance and so it would make sense to make R2 a little higher. This is because for main listening the h/phone amp feed would be shorted and so making it say around 4K7 means it presents a light loading on the preamp.

I'm assuming that when the situation is reversed and h/phones are needed on there own that the "heavier" 600 ohm load will have no real impact. FOt the main amp we are thinking in audiophile terms to preserve the best possible feed to the main amp.
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