I just completed my first real amp. No RadioShack opamps or capacitors, or Planter's nut can enclosures this time. I built it basically to Tangent's instructions in his tutorial except I modified it somewhat like Apheared's 47 amp. Basically I added a second dual opamp right below the first one and connected the whole thing according to Apheared's schematic. When I first hooked it up I found out I miswired the headphone jacks, but once I corrected that the whole thing actually worked. The first thing I noticed is just how much more bass there is in this amp compared to the first amp I built. And this thing is a lot louder than the other one, too. It is powered by a single 9V battery. It is all enclosed in a Serpac H65 case.

I socketed the chips so I could experiment with different opamps. The unity gain opamps are both on the second chip, while the voltage gain opamps are on the first chip. I am using OPA2227PA chips right now. Anybody have suggestions for other chips I should try?

I've used ad8610/fet's in my cha47, with good results. Presently, I've been using ad843/browndog adaptors/fet class A. I'm powering it with a 24v reg. supply.

.

The 47 is a nice topography... the bass extension really is better with that second amp.

Congratulations on the build .

I'll second puppyslugg's recommendation on the chip roll.

Thanks Voodoochile. This second amp is just leaps and bounds better than my first both in sound quality and in build quality.

puppyslugg, will the AD8610 work properly with a 9V (±4.5V) supply? If so, I'll definately have to try it out to hear what kind of sound I'll get out of it.

I am also curious about the AD823. I keep reading that it works very well on low voltage and sounds quite good, but needs a buffer to perform well. Could I expect to hear any benefits from this chip if I were to put it as the voltage gain chip and leave an OPA2227 as the unity gain chip for the current boost?

Quote:



It'll work, but 2X9v's would be better, IMO.

As far as the ad823/opa2227 goes, you have but to try it. Should work. But why not try a real buffer like the el2001/2?

Thanks for the suggestions puppyslugg. Those AD8610's are a bit expensive at $20/chip and I can't find the AD8620 which is what I would actually need since they are dual opamps.

I am having a problem with hiss in this amp. My first amp had this problem too. But something new is the fact that when I turn the power switch on or off I hear a loud pop in my headphones. And for some reason I hear static when I insert my headphone jack when the power is off. I am thinking it is a ground problem, but I have checked the connections and there are no shorts or anything. I really don't know where I should be probing with my multimeter. The hiss is definately from the amp as I can hear it without any source connected and when the volume is all the way up it is quite loud. Anybody have any ideas?

Do you have a resostor inline with the output of the second stage?

Hardly required, but sometimes it helps quell hiss with low-impedance cans. What cans are you listening to?

Edit- ahhh- I see your signature now. The Sonys I'm not familiar with, but undoubtedly low-impedance.

Yes, I have a resistor (47 ohm) inline on the output of both stages. These Sony's are 63 ohms.

Try increasing it to 100 ohms.

You could add another 47 between the jack and the board, rather than replacing the board-mounted resistor, for testing purposes.

Additionally, you might consider increasing the value of the resistor between the two amps (maybe 100 or even 150)... but I'm not really qualified in the selection of that part. You have a 47 there, too?

Virtually all the values I used in the amp are the same as those shown on the A47 schematic, except at the input. I used a .33microfarad capacitor and a 1megaohm resistor there, instead of .47microfarad and 100Kohm respectively.

Are you using a 100k pot (assumed, as you have the 1meg in there)?

Maybe JMT will have some thoughts on this. Sounds like you have most everything in order .

I am actually using a 10K pot. puppyslugg suggested that I lower R2 a bit, since the 1M resistor may be a bit high. I'll try that later and see what happens. Thanks for your guys' help so far.

Quote:



Actually, Voodoochile picked up on it. Good observation, VC!

Quote:

I changed R2 to 100K and even tried removing C1 and it made no difference at all in the hiss. Now when I have it hooked to my computer and I turn the volume all the way up I hear a humming noise after a few seconds that qucikly gets louder and the amp just shuts off. I guess I definately need C1. I think I'll change R2 and C1 back to what I had them at previously tommorrow. I have checked, re-checked, and checked again that there are no solder bridges and the components are of the proper value. It sounds great except for that annoying hiss which makes it seem like I am listening to a cassette player. Any other ideas on what I could be doing wrong in this thing?

Edit: I should note that this hiss doesn't seem to be from interference from anything in my room. The hiss is present no matter whether my computer, monitor, or anything else is on or off.

Edit 2: I put C1 back in. I grounded the pot's metal chassis. I added an extra 47 ohm resistor to each side. Still some hiss. Oh well, I guess I should just be happy that I have an amp that works overall pretty well, despite my inexperience Thanks very much for your help puppyslugg and Voodoochile. I think I'm just gonna leave this amp as is and maybe try another (simpler, too) amp and see if I can eliminate that problem in that one.