Yeah the amp shown in the pictures is built as A/C only, as described on the blog site. It will live on my desk and stay plugged in so I didn't see a reason to have batteries. It's amazing how cheap you can build one of these for in this configuration!
Also- it's built with gains 1X/2.5X, which is why you don't see R17 and R21. I'll be using this with pretty efficient headphones.
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Try changing the resistors to get a gain of 1. Since the amp doesn't have a clipping indicator / LED you have no way, without a scope, to know if you are actually clipping at high volume with the minimum gain switch setting. You could also do a DMM measurement of your input signal and multiply by 2.5 to see if it is less than 7V, but that is a little dicey since your DMM has to be good to 20kHz and has to have a fast peak-hold function.
If you want to try a better op amp try the LM4562 which is the same as the LME49720
LM4562NA/NOPB National Semiconductor (TI) Op Amps
But like RocketScientist said somewhere along the way the distortion figures of the output stage would exceed any improvements in the gain stage, so better gain stage op amps are probably wasted money. But can't hurt to try.
EDIT: just saw Anonanimal's post. I forgot about that - a gain of 1x doesn't need any resistors.
A 1x/2.5x combo is a really good idea unless someone is sure they need the higher gain.
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I always see stuffed boards as cities. This one looks like a tiny, ordered town with an big empty terrain. Where two gigantic hangars will be constructed
Ha ha! That's awesome. But instead of hangers, those spots are reserved for the power plants that "light up" the city.
Got my boards in today, just finished putting together one, took me about 2 hours. Listening to it right now through my gamma1/2 DAC with my Grado SR325is, sounds good.
Going to have to run it for awhile to let it burn in before I test it against the Mini^3 I've been using for the last year.
Can't wait for the front panels from the GB to come in so I can finish one of these up.
Thanks to NwAvGuy, olli and jktam.
Going to have to run it for awhile to let it burn in before I test it against the Mini^3 I've been using for the last year.
Can't wait for the front panels from the GB to come in so I can finish one of these up.
Thanks to NwAvGuy, olli and jktam.
I honestly don't know, as I have no basis of comparison. I only chose them because they had a slightly better tolerance than the recommended part, and because I had some on-hand. I'm not sure I'd be able to resolve a difference in output caps w/o measuring equipment that I will never be able to afford...
Hey Olli,
could it be that there's something wrong with my order? I'm just curious, seeing that others from Austria already got their boards well over a week ago, whilst mine haven't arrived so far.
Please, I don't want to press. I just want to make sure, that everything's alright.
Cheers Olli, and again thanks for your great effort!
could it be that there's something wrong with my order? I'm just curious, seeing that others from Austria already got their boards well over a week ago, whilst mine haven't arrived so far.
Please, I don't want to press. I just want to make sure, that everything's alright.
Cheers Olli, and again thanks for your great effort!
Yes, I am selling some more boards in the 'O2 PCB group buy (round 2)' thread.
Glad to hear it!
Hey Olli,
could it be that there's something wrong with my order? I'm just curious, seeing that others from Austria already got their boards well over a week ago, whilst mine haven't arrived so far.
Please, I don't want to press. I just want to make sure, that everything's alright.
Cheers Olli, and again thanks for your great effort!
Hmm... It is a bit dodgy. When the next batch of boards arrive I'll be in touch and we can sort something out.
Second batch was shipped to me yesterday so should be with me early next week.
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