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Old 8th January 2011, 08:20 PM   #61
IanAS is offline IanAS  England
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Hi, that response was fast

I'm very much into avoiding parts in the signal path.

I recently tried again one of the Shallco switches with the Silver contacts that I bought from Michael Percy Audio many years ago. Maybe the best switches available. I intended to make an L pad attenuator and bought all the Vishay bulk foils to go with it. I used it up to maybe 5 years ago to toggle between two sources, the CD player and the AV receiver. I never changed the volume of the CD player on those days so didn't need a volume control or pre-amp. Just fed the mono blocks directly. When I moved over to a PC for the music source it has a software volume control I stopped using the Shallco and just have been changing the RCA plugs from soundcard to AVReceiver.

Anyway, a pal wanted to switch two inputs, so I made up the solid silver wires to and from it, ran them in for a few weeks, took it over to him and inserted it between his PC soundcard and stereo amp and we thought, Yuk! So I took the amp end RCA plugs off his solid silver leads (same as mine) soldered to the switch and soldered his plugs to the switch output wires. Still it was the same degradation. So I unsoldered the switch in and out wire and joined them together. Much better, but still not right. So I took out the 30cm silver from the join to the plugs and refitted the plugs to the original ends. Back to normal.

So, the very good switch just ruined the sound quality. That's without RCA plugs and sockets going into and out of the a box a switch is usually in.

And, assuming the 30cm silver sounded the same, which is should have as I cut it from the same reel and it was fairly well run in, it was just that one extra TRT Wonder Soldered solder joint that was having an easily audible bad effect.

So then, it's no to any switch, and pots, conductive plastic or cermet are MUCH worse sounding, and no to plugs and sockets, and the fewest solder joints possible.

Hence my plan to add chips to a bit of Vero and possibly glue it to the sound card. I need to remove the surface mount resistors and add the Vishay bulk foils to it anyway, and try and I have, there's just too little room there so I need to take the analogue stage off the card to another board anyway. It's not too difficult. I'll then also be able to give each chip it's own decoupling caps and I might even be able to give each chip it's own regulators instead of all sharing one pair of them. I planto solder the headphone lead on so as to delete that 1/8" stereo headphone socket and plug which can't be doing anything good.

I'll need a separate output for the monoblocks. Or I might for the first time try using balanced mode for those interconnects and see if it reduces the slight hum I get with the unscreened silver twisted pair leads I currently use.

The question is really about what circuit and chips to use.

The HD600 appear to be fine with the small current from the 49710HA, but there is that 200 ohms output resistor there. I wonder if a 200 ohm lower output impedance would sound better. No short circuit protection. That 49713 buffer chip might do for that, like the first one you made your friend who reported better bass.

Thanks.
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Old 10th January 2011, 09:38 PM   #62
IanAS is offline IanAS  England
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Something similar:

http://www.diyaudio.com/forums/headp...fier-pcbs.html
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Old 31st March 2011, 08:43 PM   #63
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Quote:
Originally Posted by IanAS View Post
I've added a post to end of the above thread about doing a new PCB of essentially the National LME49600 reference design and I'm trying to see of there's much interest from others? More here:

National LME49600 Reference Design Project
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Old 10th April 2013, 01:58 PM   #64
Piotr is offline Piotr  Poland
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Hi, do you think it is a good idea to take 10pcs of LME496 in parallel per channel to make a small 5W power amp for a desktop speakers? Using the same idea with LME49710? What gain and resistors should be used?
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Old 10th April 2013, 08:40 PM   #65
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You mean like this?
The Wire - Low Power Ultra High Perfromance (LPUHP) 16W Power Amplifier
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Old 10th April 2013, 09:07 PM   #66
Piotr is offline Piotr  Poland
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Quote:
Originally Posted by Redshift187 View Post
lol small world! thanks!
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Old 10th April 2013, 09:33 PM   #67
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Originally Posted by lengthuy View Post
Hello,
I've built the headphone amp according to the 1rst schematic. The sound is just fantastic with my Denon AH-D5000 and Sennheiser HD600.
+ : Very detailed (but not agressive) at every level, very dynamic (the attack is superb)
- : Very sensitive to RFI and EMI (keep if far from the transformer or use batteries). I can't keep my mobile phone to my pocket. I have to put the PCB in a shielded enclosure). Personnally, I prefer not to limit the bandwidth with filter caps, because I love the way it makes music.
- : a little bit noisy (floor noise) you can notice it slightly using closed headphone and without any signal input. I will try it with batteries to check if the problem comes from my PSU.

I brought the PCB on Ebay from JIMS_AUDIO. It is good quality but the routing is not optimized (grounding). I use FC caps and 0.1uF MKP decoupling cap.

Paralleling the AH-D5000 doesn't make hot the ICs. My Denon Headphones needs power drivers. I used to drive them with TPA6120, but now, I do prefer the double LME49600.

If I can't solve the RFI/EMI + white noise, I will try re-route the PCB.
I also use Jim's Audio PCB for this circuit. In fact, the first schematic is directly from them and is exactly what's on the board. I would prefer to do things differently now, like including a blending circuit. I think only 1 LME 49600 is required for driving most headphones also.
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Old 12th April 2013, 12:55 AM   #68
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Common headphone op-amp 4556 is capable of about 70mA of current. LME49600 is capable of 250mA. Using two per channel seems like massive overkill to me.
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