OK, I'm listening to mine, and sounds downright awesome... none of that japanese amp overated symbals and highs... much more natural proportions to highs and lows than standard opa2132 cmoy... I think it may be ok to leave out the 10uf caps, as bass is abundant, and it may just make it even better... Listeing to Norah Jones - Not too late CD now... those acoustical instruments sound scary realistic... and that off one half flat 9v cell...
Very smoothe with a Z.... best out of the 15 or so headphone variations I built so far...background should be called blackground... it is but pitch black silent... even with ipod phones.
Re the PCB ... change package for R4 and R8 to one size smaller, or you wil have to drill a hole in the trace like me...
But guess what? it seems to be an impendance mismatch for my ipod, just like the cmoy is for my portable fm-radio, so there is a good chance it will mate perfectly with your source.... tommorow I will try to double the gain
Very smoothe with a Z.... best out of the 15 or so headphone variations I built so far...background should be called blackground... it is but pitch black silent... even with ipod phones.
Re the PCB ... change package for R4 and R8 to one size smaller, or you wil have to drill a hole in the trace like me...
But guess what? it seems to be an impendance mismatch for my ipod, just like the cmoy is for my portable fm-radio, so there is a good chance it will mate perfectly with your source.... tommorow I will try to double the gain
Paul Although you are not wrong... take for instance the rod elliot headphone amp with crossfeed... that thing plays phenominaly loudly... but is to heavy on the juice for one 9v cell. But it is why I will look at upping the gain... as long as I stay under 5 It will be great.
I have been so impressed I spent a few minutes fixing the files while listening to music... will test with opa2132 in the morning but that one resistor may cause mean offset, which at the moment measures 0 mv on one channel and 1mv on the other.. which explains the silent background.
I have been so impressed I spent a few minutes fixing the files while listening to music... will test with opa2132 in the morning but that one resistor may cause mean offset, which at the moment measures 0 mv on one channel and 1mv on the other.. which explains the silent background.
Off course it was a dc measurement... but I see what you are saying, which now gets me another step to understanding biasing.... I couldn't understand how an amp could be silent if it had a constant voltage added to the signal... dc has no sound, unless you count the crackle from the flames...
One channel lacks the small bypass caps... just got it going so long... this circuit is completely DC coupled with no caps appart from those in the PSU... I.e. you put DC in, you throw headset away...
I know you have alot of experience.. I so enjoy going over your dac circuits etc... but don't discount this one... try it... I got the chips for free as samples... I guess you could do the same...
One channel lacks the small bypass caps... just got it going so long... this circuit is completely DC coupled with no caps appart from those in the PSU... I.e. you put DC in, you throw headset away...
I know you have alot of experience.. I so enjoy going over your dac circuits etc... but don't discount this one... try it... I got the chips for free as samples... I guess you could do the same...
Nordic said:
This looks like what is known in the headphone circles as the A47 Amp (http://www.diyfactory.com/projects/headphoneamp/a47_assembly_and_schematic.pdf)
I have built it, and most other opamp headphone amp variations. It is a pretty good performer for low impedance phones considering its low cost. I do think a single LM6172 sounds a little better, but it is a chip prone to oscillations and needs some care in layout.
I can't imagine you'll need two.
Also, the 551 is a mono chip. There is the 552 which I think is dual, but you should check the datasheet.
The 552 is a single also. It has a 24V/µs slew rate and 12mhz bandwidth vs. 15V/µs and 3mhz for the 551. The 552 also requires a gain of at least 5.
I removed the 51R resistor in series with the output on my amp and it makes no difference. I also tried adjusting the gain and the amp just gets louder with a lower input signal and still distorts at the same output level. I also tried a +-14v 5A supply and while the bass seemed a lot more full it didn't really play any louder. I think it's just as simple as not enough current output.
I removed the 51R resistor in series with the output on my amp and it makes no difference. I also tried adjusting the gain and the amp just gets louder with a lower input signal and still distorts at the same output level. I also tried a +-14v 5A supply and while the bass seemed a lot more full it didn't really play any louder. I think it's just as simple as not enough current output.
OK, up to 2k now, so 2x gain... sounding just as good, only gets louder. I thought at first it was missing some top frequencies, but after a few hours of listeing (its very non-fatigueing), I would say its just because it is so much cleaner...
Spent lots of time listening to jazz etc, a few minutes ago I thought, heck lets try some digital music... synth ******* sounds almost analog.
I plan to build an all film caps version, and getting precision resistors, once I settle on a gain level.... with the low parts count, it is worthwile getting GOOOD components.
Spent lots of time listening to jazz etc, a few minutes ago I thought, heck lets try some digital music... synth ******* sounds almost analog.
I plan to build an all film caps version, and getting precision resistors, once I settle on a gain level.... with the low parts count, it is worthwile getting GOOOD components.
I finished drawing up the board for the OPA551. I have to connect two nets with jumper wire, but I think it came out pretty good considering it's single sided with the components so close together. Size is approximately 25mm x 25mm.
The OPA551 will be delivered on Thursday. I will post my results after it's all put together and tested. I think I'm also going to order an AD8397. It will fit on the board I already made and has pretty high output current.
The OPA551 will be delivered on Thursday. I will post my results after it's all put together and tested. I think I'm also going to order an AD8397. It will fit on the board I already made and has pretty high output current.
An externally hosted image should be here but it was not working when we last tested it.
I'm a bit of a nub when it comes to making boards. Eagle is a bit too much for me so I just use Pad2Pad. I connect all the nets manually, then route, then fix the traces manually.
Works fine for small boards like this.
I was still working on the trace placement in the above pic. Here is the final layout ready for laser printing......
Works fine for small boards like this.
I was still working on the trace placement in the above pic. Here is the final layout ready for laser printing......
An externally hosted image should be here but it was not working when we last tested it.
BWRX said:
Ermmmm.....
Pad2Pad actually makes all the traces bend at 45's when it can. I manually made them all 90's
. The 90's allow for better clearance between traces and components in some instances, and I like the way it looks for some reason. I know it technically makes the traces shorter, but the board is so small I'm not worried about it. Is there other reasons why 90's are no good?As far as a schematic, it's just the basic CMOY using single opamps and without the output resistor. I connected it all by hand using what's left of my brain. I use double sided PCB even thous it's a single sided layout. The other side will be used as a ground plain and 6 of the square pad will be connected to it through drilled holes.
Told you I'm nub.
90 degree bends in traces are not optimal from a manufacturing standpoint. It's just harder to maintain the integrity of a 90 degree bend than it is a 45 degree bend.
If you're going to make it on a double sided pcb you could use the other side to run a couple traces instead of using jumpers.
If you're going to make it on a double sided pcb you could use the other side to run a couple traces instead of using jumpers.
I use the "toner transfer" method of etching and putting traces on both sides of the board is a royal PITA. If I try to do both sides with one etch I have trouble ironing on the second side without messing up the first.
I could iron on the top, mask the bottom with tape, etch, iron on the bottom, mask the top, and then etch again. That's a whole lot of work. It's easier to just use two jumper wires this time around.
You are the board making King in my eyes Brian. I envy your skills.
I could iron on the top, mask the bottom with tape, etch, iron on the bottom, mask the top, and then etch again. That's a whole lot of work. It's easier to just use two jumper wires this time around.
You are the board making King in my eyes Brian. I envy your skills.
I'm a noob compared to a lot of PCB gurus out there 
but I like to think I half know what I'm doing
A good way to make sure both sides a DIY double sided PCB line up is to put a little cross in opposite corners of the layout. Mark where the center of the crosses are and drill through the board. Now you have references to line up both sides of your board to. As for transferring one side without messing up the other, you just have to be careful I guess.
but I like to think I half know what I'm doing A good way to make sure both sides a DIY double sided PCB line up is to put a little cross in opposite corners of the layout. Mark where the center of the crosses are and drill through the board. Now you have references to line up both sides of your board to. As for transferring one side without messing up the other, you just have to be careful I guess.
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