A/B switching?
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Blooze

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I'm really ,really new to the whole idea of headphones and their separate amps (planning on getting a set of cans for my 11th anniversary in July and then building a millet hybrid). I was wondering if it's a good idea to build a unit that your inputs go into, then you can switch the output between your headphone amp or main preamp/power amp, relieving the need to always unplug your sources from one amp to the next? I realize you can design the headphone amp to be a preamp, but I would like to stay seperate. Or would this introduction of just one more link in the chain cause enough signal degradation to not be worth it? I searched forever looking for something on this on the site, but didn't find anything (course I may have just been putting in the wrong search parameters!). Thanks...Shane
 
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amb

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You can insert your headphone amp into your preamp's tape monitor loop (i.e., connect from the "tape-out" jacks to your headphone amp's inputs), if you preamp has such an output. You then use the preamp's input selector to do all the source switching. Turn off the speaker power amp when you want to listen only to your headphones.

The other option is to have multiple inputs on your headphone amp and use it as the source selector. There are two ways to go about this, one is to have a "loop-out" connection, which you then connect to one of your regular preamp's inputs. Or, you could use the headphone output as the preamp output to drive a speaker power amp directly. For the latter option, if your headphone amp has active ground outputs you have to wire the ground in a special manner, but I won't belabor this point without knowing which headphone amp you'd be using.
 
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Blooze

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AMB- I was thinking of doing Paramours and a foreplay, or possibly the Millet Low Mu preamp and some monoblocks of one sort or another. Thanks for the advise.
 
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rickcr42

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run the millett hybrid amp from the rec out which if you use the forplay you will need to add.do this by attaching a new set of RCA jacks dirctly to the input selector switch through a new DPDT switch so you can defeat this output feed when listening to speakers.
Having the amp connected will not actually hurt anything but the input resistance of the Millett will be in parallel with the resistance of the foreplay volume control and can in some cases screw with the sound quality of the preamp.

the millett amp like most headphone amps already has a gain stage so hooking it up to the preamp output means you are amplifying any noise level of that gain stage by the gain of the headphone amp and with headphones ANY noise will be magnified by the close headphone/ear coupling unlike with speakers where you are at a distance and may get away with it.
 
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Blooze

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I noticed on Pete's website his Low-Mu preamp has a toggle to switch between poweramps (switch just powers the amps up) and headphone amp. This is somewhat along the lines I was thinking.
 
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rickcr42

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Quote:

I noticed on Pete's website his Low-Mu preamp has a toggle to switch between poweramps (switch just powers the amps up) and headphone amp. This is somewhat along the lines I was thinking.


low mu=low gain.The forplay is a very high gain preamp.

And I stand by my satatement on cascading gain stages.If a headphone amp has enough gain to be driven from the source (The CDP,Tuner,Phono Stage,etc) why would you want to add to the noise level of the headphone amp by putting an additional gain stage between the source and the amp ?

especially with tube stages.they do not have the noise floor of SS to begin with.

do what you want but I recommend straight from the selector switch as the best method.
 
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n_maher

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This question is somewhat related to this topic, so rather than start another thread I decided to post it here.

Given the switchable input idea, what would be required for a rotary switch to change between a couple sources and a loop out (3 options)? I know I should be able to figure this out on my own but back to back 15hr days after working the weekend has my brain on full fry and I'm second guessing myself.

Thx,

Nate
 
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Blooze

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Thanks for the input, Rickcr42. That was along my lines of thinking, but it's always better to get the point of view from someone more experienced.
 
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rickcr42

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look at the switching matrix of any commercial preamp (many many online) and just toos out the active sections and volume pots.
Think of what you want to do,break it down into sections and design each,the assembleit as one device.

keeping it simple usually saves headaches AND usually means a better performing device.

but again,never never never cascade gain stages unless you either need the extra gain or there is no way to avoid it.This last is usually out of lkack of desire or skills.There is no reason in 99.9% of cases where a simple extra set of jacks and a dpdt switch to control the on/off state of those jacks can not be weasled in some way.
If making extra holes in the chassis or top plate is not an option then just do a hardwired connection where the wires go fron the input selector through any available hole big enough in the chassis to RCA plugs.

these plugs then go to a small box with the actual RCA jacks for connection to both the new wire and the headphone amp output.The mute switch is not essential but it is recommended
 
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rickcr42

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BTW guys.i know it is really hard to step away from the computer sometimes but I make a serious amount of switching devices and in fact i make more "widgets" to do complicated switching patterns than I make any active devices and i have come to the realisation that doing these things on a computer is the worst of all possible ways.

what I do is take pen to paper and draw it out in way that follows how the signal will flow and make corrections with a red pen until I am satisfied it is what i want and all errors are corrected.
At this point I do the "final' wiring schematic and put it aside.

Next I actually draw (I have that ability
) or print out the actual switches as the look from behind and pen in the wiring and again make adjustments for what I consider a neat layout and once I get it right,again do the final draft.

I use these as my wiring guide as I build and always have a schematic to reference back to if i need to make changes or something goes screwy down the road or even if i sell or give away the device.Nothing worse than having a piece of gear built by someone else with zero documentation if it ever needs servicing.

Plus there is something soothing about doing a low tech low stress diagram sitting a a comfortable chair,cocktail by my diade,some nice music in the background,nekked wimmin dancing on the coffeee table...........
 
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