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Another PIMETA not working

post #1 of 17
12/27/07 at 10:16pm
Thread Starter 
This time around there are two problems: either the left channel is the only sound I'm getting, or I get a very faint signal on the right ear (read "I have to turn the volume knob all the way up to hear a whisper"). If I swap around the buffers and opamps, the situation changes from one to the other. I tried bypassing the ground channel altogether, but that didn't solve it. I don't see any bridges, and I've already put it through an alcohol rinsing. I realize the red wire can confuse me, but I ohmed them all and they check out. Currently only the left ear is giving me stuff. I have a couple opamps to roll in L/R and G, so you guys could give me some suggestions, I'll give them a shot. Here are some pics. I can take more if needed.





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post #2 of 17
12/27/07 at 10:23pm
Quote:
Originally Posted by joneeboi View Post
...If I swap around the buffers and opamps, the situation changes from one to the other...
that sounds like it might be the problem

try swapping in new opamps, see if it still occurs, if it does it might be a dead buffer

if the problem doesn't occur then it's a dead opamp
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post #3 of 17
12/28/07 at 12:15am
Thread Starter 
I just had some weird results.

First, I cut the ground channel bypass wire. Then I pulled out the ground buffer and I got music on both ears, but it was only of the right channel. I pulled out the right channel input and nothing played anymore. Putting it back in, I pulled out the ground opamp and music kept playing.
Checking offset (no ground buffer in), the right channel had a variable offset, between 1.9mV and 3.0mV. The left channel had a stable offset sitting at 2.3mV. Then I pulled out the ground opamp and the right channel went to varying between 7.8mV and 9.0mV while the left channel remained at at constant 2.3mV. Pulling out OPAG, BUFG and BUFL, music somehow was playing. Then with only OPALR and BUFR, music didn't play anymore.

I don't know what this all means. What does the changing DC offset mean? What does it all mean?
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post #4 of 17
12/28/07 at 1:46am
were is the left input connected?
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post #5 of 17
12/28/07 at 1:58am
Quote:
Originally Posted by MisterX View Post
were is the left input connected?
Nice catch!
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post #6 of 17
12/28/07 at 2:02am
Quote:
Originally Posted by MisterX View Post
were is the left input connected?
X2.

Your inputs appear to be to IR and IG, but there is no connection for IL. If you move the IG to IL, you'll still need an IG as well. This may also mean you won't need the connection from the Alps to the ground.
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post #7 of 17
12/28/07 at 2:29am
Quote:
Originally Posted by bhjazz View Post
X2.

Your inputs appear to be to IR and IG, but there is no connection for IL. If you move the IG to IL, you'll still need an IG as well. This may also mean you won't need the connection from the Alps to the ground.

See the wires connected to the IL2 and IG2 pads?
That leads me to believe the in grounds are fine and he just needs to move the left input over (IL2 does not connect to anything when you use the blew velvet pot but IG2 does connect to the ground "bus")
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post #8 of 17
12/28/07 at 5:54am
Thread Starter 


I appreciate the help, guys. I swapped out the 8066AR too and everything is working fine. Now all I need to do is case it up! And that will be the second time I wired the input incorrectly. I will add it to the checklist. Thanks again.
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post #9 of 17
12/28/07 at 6:28am
nice work.

this is a tangent, but just wanted to ask, how are you powering the pimeta? STEP (or THREAD) or just a wallwart? might get some noise from the powergrid... depending on what else you got plugged in to the outlet
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post #10 of 17
12/28/07 at 9:24am
Why did you choose to use those huge 10uf caps?
Better to use something that fits the board in my view.
Its not a good idea to get into the habit of long leads
when using caps for high frequency operation.
OK, in this circuit I doubt it will make any difference,
but in some situations the lead length can be critical
to cap performance.

Anyhow glad you sorted your amp, happy listening



.
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post #11 of 17
12/28/07 at 1:09pm
Thread Starter 
I used the Solens for two reasons: they were around, plus I didn't want to pay $10 for the ones in Tangent's shop. I probably wasn't thinking about it when I was ordering my parts from Mouser, but I could just as well have picked up Tangent's Wimas for much cheaper. Alas, your point is well noted, and I'll try to keep the leads short in the future.

I am powering this baby from a wallwart. I had a TREAD, but it unexpectedly exploded on me. It was weird. I was powering a CMoy for the entire day with that TREAD, then I went to take a shower and it just died and stunk up my room. This amp is going to be a home amp for my dad, so I probably won't need such a high quality power supply. I'm still juggling projects right now, but I'll get the TREAD done down the line.

Casework will be terribly annoying. I got a teabox from an auction at work, but the siding is all too thick for everything: RCA, mini, and DC jacks, switch, and the Alps Blue. I'll figure something out though. I hope it's still pretty.
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post #12 of 17
12/28/07 at 2:30pm
Quote:
Originally Posted by joneeboi View Post
It was weird. I was powering a CMoy for the entire day with that TREAD, then I went to take a shower and it just died and stunk up my room.
...you're not supposed to use it in the shower.





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post #13 of 17
12/28/07 at 3:30pm
Thread Starter 
I knew something was wrong when my hand turned all crispy black and smokey. Live and learn, right?
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post #14 of 17
12/28/07 at 9:46pm
Quote:
Originally Posted by joneeboi View Post
I didn't want to pay $10 for the ones in Tangent's shop....I'll try to keep the leads short in the future.
Not that I'm trying to talk you into getting the caps from me, but those Solens probably aren't doing anything for your PIMETA due to the lead length. The longer the wire, the more the inductance, and at HF, inductance directly opposes capacitance. This doesn't matter in signal coupling applications, which is where those Solens should be used.

If you want cheaper alternatives, just step down to a bog-standard 1uF polyester film. You can even get 'em at Radio Shack.
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post #15 of 17
12/28/07 at 10:26pm
Thread Starter 
So I should reduce the lead length if I want to keep the Solens...? I have some 1uF caps too, I just figured these were better because they're closer to the 6.8uF on the schematic.

edit: Also, Radio Shack is no more in Canada as of January 31 earlier this year, just to let you know. Its analogue would be Circuit City, but I get the point. It was nice when RS closed down cause I stocked up on KSC75s. Too bad Circuit City doesn't carry them. =T
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