Multiple headphone amps in one chassis.

[Subsonic]

With the limited amount of desk space I have and this endless hobby of DIY amplifiers, I had the idea of combining my next project (Antness Gilmore) and my Meta42 in to a single chassis. My initial thoughts are to split the input(s) into both amps and have the Gilmore power supply power both amps. I would probably switch between amps via a switch of some sort (SPDT?). Now my question right now is how would I combine the volume pot and the headphone jack to work with both amps? Or do you think I just keep those seperate for simplicity?

Here are some enclosures I had in mind: Enclosures
So far, it looks like the PRAL-1c and PRAL-1hc would fit my needs (looks expensive

)

 

[eric343]

To give you an idea, the PRAL-1sc is about $50 and the PRAL-2 is about $75.

 

[rickcr42]

Not difficult to do but why would you want to ?

I understand headphone distribution but not entirely different designs in a single chassis.

If it is for using different headphones it would be far easier to add gain adjustment and output load resisitors to change the characteristics of one of the amps for multi-headphone use.

But if you insist-

1-simply splitting off the input and sending it off to both amps may be a bad idea.The best option is to use an input buffer and send the signal to both amp volume controls for individual level setting of each amp.
But you are adding another active stage.
Direct input to individual volume pots is not good.There can be an impedeance interaction between the two which cound be detrimental.
Single pot ? Go for it but follow it with a DPDT Amp-A/Amp-B switch

2-the power supply is a non-issue.Use a normal AC line on/off switch and feed both amps simultaneously for "dual use" or with individual on/off DPDT switches for each amp so no power is wastedfor an unused circuit.

3-Headphone jack switch-simple DPDT switch again

If you want a "one switch" approach use a four deck /two pole rotary switch to switch both the input and output simultaneously.
Six decks will give you power supply switching too.


But to be honest I would suggest a three box approach
Box-1 : external power supply with a amp A/OFF/B (center off DPDT) switch
Box-2 : Gilmore amp
Box-3 : META
If you look at the actual circuits of the amps they actually take up very little space individually so desktop room should not be an issue , especially if stacked

 

[eric343]

Quote:

Originally posted by rickcr42 Not difficult to do but why would you want to ?

As he said in his post, desk space. While the amps seem small, if you've got a desk crammed full with stuff, more than one amp per case is nice

 

[rickcr42]

point being,not two amps in one case but two entirely different amp DESIGNS in one case .

Headphone distribution amplifiers are common,multiple headphone amps in one chassis,this is not and seems to me a strange way to build an amp


but hey WTFDIK

 

[Subsonic]

Quote:

Not difficult to do but why would you want to ?

Oh just for the fun of it

. I'll probably won't use the Meta42 once the Gilmore is put together, but I would like to still have it as an option. I'm not going to be using both at the same time so I'll probably have a switch turn one or the other circuit off.

Would I still need to use an input buffer if one circuit is turned off?

 

[rickcr42]

not as long as the amps don't "see" each other. By that I mean no direct connection between the two inputs or the above mentioned impedance interaction could occur and have an effect on the sound.
the outputs -same thing . Even though one amp will be "undriven" (no input voltage) the output of one amp will try to drive the output of the other amp PLUS the headphone load.

You could put a series resistor inline with the output of the amps but this again has its own problems.

Best choice is total disconnect of the unused amp so you will need either a four pole rotary switch (expensive) , a 4PDT switch (also expensive) or two DPDT switches-one for input from the volume pot selection , one for amp out to headphone jack selection

 

[Subsonic]

Thanks rick for the information. So it would appear to be best to use a 6 pole rotary switch if I wanted to switch between circuits (input, output, and power). One last question for now, how do I separate the virtual grounds between circuits or does it even matter?

 

[rickcr42]

I would not use a virtual ground circuit,rather i would go with a true bipolar powersupply of -/+ 15 volts .

but if you must use the single polarity supply (with the gilmore ?) you wouldsimply treat the plus and minus legs (NOT the generaterd artificial ground ) as you would true dual polarity-switch each with a pole of the DPDT

o o
o o
o o

Top left is + to meta
top right is - to meta
center left is + from power supply
centerright is - from power supply
lower left is + to gilmore
lower right is - to gilmore

Use quasi star grounding approach-----each group with a star ground then tiedinturn to a central star ground.

In other words-each amp circuit grounded as if an entire circuit,the input and pot considered as another circuit and the output jack the same-all tied to the main ground oint,be it artifically generated or the junctionbetween the two power supplies

Rick

 

[eric343]

Quote:

Originally posted by rickcr42 I would not use a virtual ground circuit,rather i would go with a true bipolar powersupply of -/+ 15 volts .

Why?

 

[rickcr42]

performance . A true Bipolar regulated power supply will always out perform an artificially generated bipolar ps .
The proof is in the listening

 

[Subsonic]

I'm now realizing how new I am to this

. Isn't the Gilmore power supply Bi-Polar? The shematic shows a +-16.4V and a ground line.

 

[rickcr42]

hehehe,yes . that is why I was wondering where the virtual ground came in . Since you already have the dual supply you would run both amps off of it.

the only reason for a virtual ground is if you are either running the amp off batteries (single 9volt/single polarity battery pack)
or if you are using a DC adapter (wallwart) or even a cigarrette lighter plug