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Old 11th February 2012, 08:04 PM   #11
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I'd guess the volume pots in the PAiA design are 100k linear types, with the inverting opamp circuit's 10k input resistance being used to make response approximately log... old trick (see ESP project 1). I wouldn't call 100 ohms of output impedance "low" either.

I'd suggest a nice symmetric power supply (maybe O2-style if you can't find a transformer with a center-tapped output), LM317/337 based low-noise regulators (with an electrolytic at the adjust pin), and then clone an Apheared-47 style circuit a few times (using reasonably beefy opamps - 5532s are kinda OK but JRC/NJR 4580s and especially 4556s can provide more current). If super-high input impedance isn't required, a 10k volume pot is just fine and actually preferred.

Assuming the space is there and the higher parts count isn't an issue, amplifiers using a discrete A/AB buffer also are worth considering.
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Old 11th February 2012, 09:16 PM   #12
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Location: Carlisle, England
Originally Posted by FREDtheDOG View Post
Sorry that circuit wont work with wall power, it depends on having 2 batteries to genertate the virtual ground

If you use a wall wart you'll need a voltage divider type circuit
If you buy an AC adaptor you can use one wire as ground and use the other wire for providing + and - volts via diodes.
Murton-Pike Systems PCBCAD51 pcb design software.
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Old 11th February 2012, 11:54 PM   #13
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I forgot to mention, low voltage capability would be a bonus for ocassional field use. Why would Paia talk about 8-600 Ohm compatability, they never heard of the 1:8 rule? I'm not skilled enough to follow through without a PCB or perf/stripboard layout. I'll look for Gyraf and SDS projects. sgrossklass, do you know of any projects that use the designs you mention?

Last edited by RoadToNever; 11th February 2012 at 11:58 PM.
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Old 14th February 2012, 10:14 AM   #14
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Couldn't find any board layouts for the Gyraf and SDS circuits as a HP distribution amp. This came up in a google search:
This is the circuit:
Does it look any good?
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Old 14th February 2012, 12:49 PM   #15
rondr is offline rondr  United States
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Originally Posted by RoadToNever View Post
Found this: PAiA - 9206KP Headphone Distribution Amp Kit (International version - ships without 110V power supply), Headphone Distribution Amplifier, 9206KP Looks perfect (low output impedance) except that it has twice more outputs then I need right now. Still looking....
This was published back in 1992 in Electronic Musician Magazine as "Build Your Own EM Headphone Distribution Amplifier." In the article there was the schematic as well as the circuit board layout. It was the first electronic project I decided to tackle and was simple enough to build. Using a wax pen to draw the traces on the board and etching it in the kitchen sink. I drilled all those holes by hand and stuffed it all from parts off the shelf from Radio Shack except the opamps. They had dual opamps but not NE5532s so I got them from Allied or some place like that. The 5532s is what the plan called for and not knowing any different that is what I used. Thing is it worked and it worked good. Placed in the middle of a room with a few mics setup and musicians gathered around, each had their own headphone level controller. MDR V6s were mostly used and the amp had no problem driving them.

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Old 14th February 2012, 04:32 PM   #16
jcx is online now jcx  United States
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how can these threads get to over a dozen posts without a pointer to the Headwize archive?

HeadWize Library - Projects

site is dead, but the archives are required reading for aspiring headphone amp diyers has a diy forum - beware the relative lack of engineering knowledge/discussion, excess fanboyism compared to here - but some info

Last edited by jcx; 14th February 2012 at 04:36 PM.
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Old 15th February 2012, 12:42 PM   #17
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Thanks, guys. It all leads me back to the Jaycar kit due to the low output impedance and ready-made board. BTW the schematic I posted in post #14 was incorrect, this should be the right one: Click the image to open in full size.
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Old 15th February 2012, 03:15 PM   #18
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Looks like a nice concept, but... no volume control?
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Old 15th February 2012, 03:50 PM   #19
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Damn it. Thanks for pointing that out.
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Old 15th February 2012, 06:21 PM   #20
Tajzmaj is offline Tajzmaj  Slovenia
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No layouts? Hm...
Regards, Taj
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