aph47 amp

[nikongod]

hello headfi.

here is an aph47 mp i made up the other night. it has a ti railsplitter on the ground chanel, a whole load of caps, and it is set up so that the same chip amps both chanels, and the same chip functions as a "pseudo buffer" on the other half for both chanels. i set the amp up this way so that i could see if there was any wound improvement by using different chips in these positions.

the amp has a really crappy pot, and locking output jack. the switch is leftover from my automotive diy days.

click:looks your standard junk extruded aluminum enclosure

click: the innerbits

 

[chaostic]

post a schematic.

 

[nikongod]

just lik in the article here

except where he seems to indicate using the same chip for both "halves" of the left and a diferent chip for both halvs of the right chanel i used on chip for the actual "amp half" of both chanels, and a difernt chip for the "pseudo buffer" for both chanels.

edit: i suppose that that dosnt have the schematic of the ground chanel in it, but its a relativly simple one, with 3 330uf caps and 1 1uf from + and 3 and 1 from - to vitrual ground. simple. the single 1uf caps are polystyrene, and the 3 are electrolytics.

 

[dsavitsk]

Quote:

Originally Posted by nikongod except where he seems to indicate using the same chip for both "halves" of the left and a diferent chip for both halvs of the right chanel i used on chip for the actual "amp half" of both chanels, and a difernt chip for the "pseudo buffer" for both chanels.

My sense is that your design makes more sense as the opamps don't need to be matched, or even of the same type. This is probably more important in tubes, but also applies here.

-d

 

[mono]

Quote:

Originally Posted by dsavitsk My sense is that your design makes more sense as the opamps don't need to be matched, or even of the same type. This is probably more important in tubes, but also applies here. -d

On the one hand I wonder if there is greater crosstalk from using same opamp for both channels. On the other hand I too once built one similar to nikongod's except with only 2 x 1500uf rail caps and two .1uf ceramic decoupling.

The nice thing about the way nikongod & I did it is that the 2nd opamp (if socketed) can be removed entirely and amp still works with no mods (no jumpers in a socket). After initially putting mine together I noted that it did fairly well operating from a unregulated wall-wart, removing most of the 60/120Hz hum... not "great" but leaps and bounds better than a Cmoy did. Later I was "short" one buffer for a different project and removed the buffer from mine... still works audibly as well except now same wall-wart's noise gets into the audio, but AFAIK it still sounds as good from 9V NiMH pack.

That was one of my first amps after visiting Head-Fi, if I had to do it over again (looking backwards) I'd probably have gone for Morsel's 3-channel design instead... but you really CAN'T go backwards.

 

[blip]

I hadn't seen that three channel design before. Kind of neat... A super-CMOY! Might have to use that in a portable amp.

One of the things I love about headphone amp DIY is that the community is still small enough (and there few enough designs out there) that you can see how the designs have evolved over time.... From the simple CMOY to the MMM!

 

[Mr.Radar]

Quote:

Originally Posted by blip I hadn't seen that three channel design before. Kind of neat... A super-CMOY! Might have to use that in a portable amp.

Its design concept is very similar to the 2nd generation Headsave Classic (HSA3V1): 3-channel (L, R, G) un-buffered. I wonder how they would compare, especially if they were both built with similar components.

 

[chaostic]

Has anyone tried a 4 channel opamp with a a47?

 

[mono]

The one I made... with more planning I might've squeezed a POT onboard too but it was built in a hurry.

 

[chaostic]

What chip did you use, and how did it sound compared to a two chip (1 sound, 1 buffer), two chip (1 per channel) or four chip a47, mono? Or is that the only a47 you built?

 

[meat01]

Quote:

Originally Posted by chaostic Has anyone tried a 4 channel opamp with a a47?

I believe Erix did an A47 variation with a 4 channel op-amp. I believe it was his Forehead

 

[mono]

Quote:

Originally Posted by chaostic What chip did you use, and how did it sound compared to a two chip (1 sound, 1 buffer), two chip (1 per channel) or four chip a47, mono? Or is that the only a47 you built?

I only made the one A47 with both channels per each chip. I wouldn't go so far as to call the 2nd chip the buffer though, since their output is paralleled.

I noted little to no different between single and dual chip use, but it was driving 120 Ohm Senns, not 32 Ohm Grados. I first used a throwaway pair of 'phones @ 32 Ohm and couldn't tell any difference there either but the throwaway 'phones really were awful, I wouldn't ever use them to judge quality, only a final check that nothing is wrong before connecting better cans.

Right now I have only one OPA2107 in mine, but I mainly used it for rolling chips, first impressions. It seems a little more precise, less smooth than my Pimetas at lower volumes. At high volume it needs buffers, but again I wasn't using 32Ohm Grados. I haven't listened to it much recently though, most recently I used it for judging power supply noise, because it reveals more of it since I took the power buffer out.

I'd call the A47 a mission-specific CMOY, that it's simply able to put out more current as intended. It's only a tiny step above the CMOY though, ideally I (and I expect most people) will want real buffered output, a ground channel, and at least .1uf decoupling caps, something I think even a CMOY could use to increase detail (but I've never A/B'd one w/wo decoupling to be sure of this). Even so, CMOY is really best for first-time builders and anyone whose held an iron before would probably feel that building an A47 was worth the extra ~$8 for 2nd opamp and power buffer, IMO.

I don't usually listen to anything very loud so I may reconsider the Morsel 3-Channel and build one.

 

[tyre]

Quote:

Originally Posted by chaostic Has anyone tried a 4 channel opamp with a a47?

I realize the BUF634 in the virtual ground wasn't really necessary, but there seems to be some contention as to the actual output capabilities of the TLE2426, so I just threw it in anyways.

 

[jasonhanjk]

Here's my buffered Cmoy, uses LM6171 as ground.

 

[mono]

One question this design brings up is, "if you need a simple design to drivelow-z cans, why use only opamps instead of only buffers?" Or the opposite, if you don't need the current then why the two dual opamps? My thinking on this is that the A47 is simply the most flexible very-low-cost amp one can build since it supports a wider range of cans.

Edit: Except of course that there are op amps with higher current capability too.