[einolu]

Well my first step outside the "cmoy" world and I mess up. I decided it would be fun to make a RA1 clone, even though it seems to be "frowned upon" on this forum. Anyway, I found that schematic online and pieced together everything I could find and went ahead with the build. Heres the board layout I thought up:

Im pretty sure its right, or at least it seems to match up to the schematic on this site....

Anyway, here is how it looks after some soldering (massive pictures so Im linking them):
1
2
3

Everything seems pretty good to me, except Im confused on how the ground works, so that could be the problem. Help me out if you see any problems. I think all my parts are in working order, but sadly I dont have a multimeter at the moment, so trouble shooting is a bit hard. I really think that its something amazingly simple that is wrong. When I turn on the amp, I get a loud pop and very quiet music for a few seconds and then nothing. Also, did I wire the pot correctly? I imagined that the signal would go something like this:

Its the $3 pot from radioshack (alps).

Maybe people can help me out!

~EO

 

[Earwax]

I think the pot is wired wrong, if I follow what you've done.

One row of 3 lugs is for the right side, the second is for the left channel. With the shaft towards you and the lugs sticking up, the left-most pair are the input, middle goes to the amp board and the right-most pair is for ground.

 

[einolu]

hah, that would explain a lot. im off to bed now, but i will rewire the pot tomorrow and report in. anyway, i wonder if the earsplitting pop when i turn the amp on will go away...

 

[einolu]

i wired up the pot and im getting sound, but its not working correctly. the pot doesnt seem to be doing much and i get a lot of random noise and crackling. im almost positive that i have a grounding problem, which would make sense since i dont fully understand how this grounding method works. can somebody explain this grounding method to me?

what im doing at the moment is using the 2 long rows of the radioshack protoboard as my grounds, all the ground wires go to that part of the board first, and then i have a wire coming off the protoboard and going to the place were the 2 9v batteries meet. is that right, i thought it was.

you neveknow, i could have something wrong with my design of the board layout in the first place.

i also looked at the soldering and everything is clean and there are no solder bridges anywhere (except where i need them which is to connect the 2 long rows on the protoboard for the ground). damn,

 

[Earwax]

Tangent's virtual ground article includes the 2 x 9V center split example. It sounds like you're on the right track. Are both the groung lugs on the pot connected to your ground bus on the board? If that's not it, post a picture of your battery setup.

 

[einolu]

thanks earwax, i got the thing to work! it was the pot all along and i fixed the grounding issues. i just had to bridge the two ground pins which seemed to make everything work, although i fooled around with other things too so it could be something else, but now that it works i will just accept that and relaxe. i will post some pictures when i box this thing in a cool wooden box i have.

the thing still pops very loudly when i turn it in, so loudly that it hurts my ears if i put my headphones on and then turn it on, from now on i will do it the other way around, but i was wondering if this is normal? if i did follow the directions, this should basically be exact clone, so does the real thing pop like that too?

thanks again!

 

[Excalibur]

If you use a DPDT power switch for both the V+ and V- rails, there should be no loud POP. Maybe a slight "click" sound but not loud. Connect the junction of the two 9V batteries (0 volts) to the circuit ground.

 

[einolu]

hah, Im dumb, I used a powerswitch with only 2 lugs, so that I put it in the V+ wire, soon I found out that my amp doesnt really run off, the loud pop must be from the opamp not being able to take the sudden messing up of the volume. Ill make my usual run over to radioshack tomorrow and everything should be good. Well now all the problems seem to be settled, this thing sounds great once its on though.

Also ive been playing around with another opamp, comparing it to the njr 4556. the opamp I got at mouser, the product number is ts922ain. It was mentioned on headwize as a good opamp for low impedance headphones. Ive been switching between the 4556 and the 922 and I think the 922 sounds better, specially in the highs and the lows. Cylibals dont sound as harsh, and deep base seems to be more tight and under control, but Im going to play around with it some more. Also while the 4556 would do the ear shattering pop when I turned it "off", the 922 seemed to handle it better, by still playing distorted music after the amp was turned "off". If the 922 has anything going for it, it should be that it can take stupidity of the owner in stride, hah.

Thanks for the help again!

 

[tangent]

Quote:

the 4556 would do the ear shattering pop when I turned it "off"

Um, did you measure DC offset at the output of the amp when trying that chip?

 

[einolu]

Im assuming that the offset would instantly become 9v, hah! I think the chip is fine though.

 

[einolu]

Hey, I got one of those dual switches from radioshack (what part of it costs $4 exactly?). Its the one with 2 rows or 3 lugs, Im just wondering how to wire it up since after I wired it it still pops quite loudly, I think it needs to be grounded but Im not sure. Radioshack doesnt seem to print anything about the product on the back. Currently I just have it wired like so:

| [V+ in] [V- in] |
| [V+ out] [V- out] |
| [empty] [empty] |

I can post a pic, but I dont feel like going through the hassle, my question is basically, how do I wire this switch. Or, why does the amp pop loudly with the way I wired the switch?

 

[einolu]

the dont-get-lost-in-the-commotion bump

 

[morsel]

You are well on your way to destroying your headphones from DC offset, if you have not already done so. Do not hook up any headphones until you have checked for DC offset at your outputs.

 

[einolu]

Im doing all the testing with some cheapo ear buds, once its on its fine though, so I hooked up my grados and everything seemed to be okay. Does anybody know why it pops so loudly when turning the amp on and off, like I said earlyer, I dont think I have wired the switch up correctly. Also, I dont have a multimeter, but I think I will have to get one pretty soon.

 

[Earwax]

Have you searched the archives here and headwize? I know there were a number of threads at one place or the other talking about power-on pops from the RA-1.