[lostspyder]

I just got done soldering, assembling and testing my PIMETA. It was my first time soldering so I was terrified of burning something up. Its an AD843/823 based amp and instead of BUF634, there are HA3-5002's (cause BUF634 can't be sampled). My DT-880s sound great on it, it really 'smooths' everything out while still preserving detail.

Anyhow to the point - one question: It starts to crackle as I turn the volume up (not as it's going up, but when it is up - it's not the pot), It's only running on 16v, and when I unplug the wallwart it fades off and the crackling gets worse. I assume it's clipping because 16v isn't enough?


I must post pics (I know there is a thread but I'm damn proud):


That's not it's permanent home. When I get money I will buy it a case.

 

[gnychis]

bad-ass case!!

maybe i'll swap that hard outer tomahawk shell for one of those bad boys

 

[Fitz]

Quote:

Originally Posted by lostspyder /img/forum/go_quote.gif Anyhow to the point - one question: It starts to crackle as I turn the volume up (not as it's going up, but when it is up - it's not the pot), It's only running on 16v, and when I unplug the wallwart it fades off and the crackling gets worse. I assume it's clipping because 16v isn't enough?

I ran into a similar issue when I plugged the AD843 in an amp I'm designing (running at 24V)... it seems to be a little bit on the finicky side. I had to tweak some of the values in the buffers and feedback loop to get it to work properly.

 

[lostspyder]

Quote:

Originally Posted by Fitz /img/forum/go_quote.gif I ran into a similar issue when I plugged the AD843 in an amp I'm designing (running at 24V)... it seems to be a little bit on the finicky side. I had to tweak some of the values in the buffers and feedback loop to get it to work properly.

Hrmm. I swapped out AD823 for OPA2132 and still had the same problem. Mabie AD843 for the ground is causing it still?

 

[tomb]

I always had big offset problems with the AD843 in the PIMETA in L/R. If you've put one in the Ground channel, it's probably more likely that it's causing problems. In my experience, the PIMETA is not totally compatible with every opamp. The AD843 is a particularly aggressive opamp, too.

 

[lostspyder]

Ok. I tried the following:

1) opa134 + opa2134 and still have the problem.

2) varying the input resistors to the buffer from 220 to 5k and still no improvement. (they are run from the input pad for BUF634 to a 1kohm resistor to the input of the HA3-5002 and the ouput of HA3-5002 is run to the output of BUF634. I modeled it after )

3) adjusted the gain to 5 from the default and it still hasn't improved.


It's kind of weird too. It only happens during particular songs. Songs that are mostly low frequency, but bass thumps don't do it. It's particularly bad during Jimi Hendrix's Electric Lady Land, but isn't present in any random techno at the same volumes. It seems to be deep guitars that are the root of it.

It seems like a supply issue - would a bad "Wima" cause this?

 

[tomb]

I've never heard of a bad Wima.

As for your problem, I've sometimes experienced what you describe with a grounding issue. It drove me crazy once and then discovered the signal ground wire on the input connectors was loose.

Other than that:
1. maybe some problem implementing the Intersils since they're non-standard PIMETA design
2. pot issues
3. over-driving the input stage - this can cause intermittent hard clipping - don't know if it would be a "crackle" though
4. intermittent short somewhere?

Pics might help someone spot something obvious ...

 

[lostspyder]

I figured out what it is. I left V2+ and V2- unconnected on the HA-5002. Thank you tomb and fitz for trying to help

Does anyone know how V2 and V1 differ?

 

[tangent]

Quote:

Originally Posted by lostspyder /img/forum/go_quote.gif Does anyone know how V2 and V1 differ?

They're separate supplies for the input and output stages of the buffer. It would allow you, for instance, to supply the input stage from a separate source than the output stage, so that current-modulated ripple caused by the output stage wouldn't affect the input. It could also be used to add current limiting to this buffer's output stage without affecting the input stage.

 

[lostspyder]

In that case, it has a silly pinout, assuming that for most tasks you don't need a separate power supply. Does it generate that much ripple?

Quote:

Originally Posted by tangent /img/forum/go_quote.gif They're separate supplies for the input and output stages of the buffer. It would allow you, for instance, to supply the input stage from a separate source than the output stage, so that current-modulated ripple caused by the output stage wouldn't affect the input. It could also be used to add current limiting to this buffer's output stage without affecting the input stage.

 

[NelsonVandal]

Try using isolating JFETs or any other CCS to the opamps, it has improved my LISAIII clone, and I'm very happy with the sound of PPAS. I'm not sure it's more silly than anything else we do in quest of the perfect sound

.

 

[tangent]

Quote:

Originally Posted by lostspyder /img/forum/go_quote.gif it has a silly pinout

If by "silly" you mean "uncommonly featureful", then yes, I agree.

Quote:

Does it generate that much ripple?

Er, "generating" isn't quite the right way to think about it. That implies that it's actively putting out a signal. It's just Ohm's Law: the impedance of the supply lines is not zero, so any current variation causes voltage variation in direct proportion to the supply impedance. V=IR.

 

[lostspyder]

I was referring to how the two different supply are crisscross/kiddy corner in the DIP and SOIC. The can version looks nice, it has the V+'s and V-'s right next to eachother.

Quote:

Originally Posted by tangent /img/forum/go_quote.gif If by "silly" you mean "uncommonly featureful", then yes, I agree.