Newbee build: PA03 amp (LM4780)

Hey,

First of all: I'm not sure if it's OK to post my question in a thread this old. If not, please let me know and I'll start a separate thread for my question.

About two years ago I bought two Pavel Dudek PA03 PCB's in Peranders group buy. Now, after a closely reading the instructions on sjostromaudio.com and the hints in this thread I finally started on building my first amp!

I think I've soldered everything together correctly, but when I plug in the power I get no sound! As advised I build the dim bulb tester. When I use it the bulb flashes for a moment, and then dims down when relais click. Both relais work (I can feel them when I put my finger on them). I've bypassed the mute relais with a jumper. Voltages on the rails and test points seem to check out. I've also checked the zeners, they both work as expected. Because I didn't know what else to check, I've just replaced the amplifier chip, but still no sound.

Right now I'm not sure how I can further troubleshoot the amp, I'm only a beginner in DIY audio.. ;)

Is there anything else I can check? Or does anybody know what could be wrong?


iKOE8Fr.jpg



Thanks!
Christian
 
Clog is probably spot on. From the manual:

Using the mute function the PA03 module can be switched to a low power consumption mode, normally called as "Stand by". You do not have to switch the main switch off. A wide range of applications can be found, for example in subwoofer amplifiers or active boxes. The mute function can be activated by the relay RE 1. If the mute pin on the input connector is connected to the earth (through a mechanical contact or PNP transistor). In case you do not use this function, the relay RE 1 need not be mounted, you must use the pins JP4 with jumper. The mute function is now deactivated.

Sjostrom Audio - PA03 Pavel Dudek's deLuxe Gainclone

Unless you plan on using the mute function, I would jumper JP4, which is under the RE1 relay.
 
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Thank you clog and loafimus! :worship:

My amp works now. I had jumpered JP4, but with the relais still in place. Then I took a closer look a the pictures of other people that finished their board and saw that a jumper is also needed on the fifth pin of JP1. The moment I put a jumper there, the music started playing :) I feel stupid now for replacing that whole amp chip..

Besides I see a lot of what seems to be metal particles between the fins of your heat sink. Better to be careful and clean the board thoroughly.

Yes, I saw that too when I took the photo :eek: , it's been cleaned up now.

The only problem left is that one channel (the one on 'Out A' of the chip) doesn't sound as clear and loud as the other channel. Tomorrow I will try to clean up the board some more, maybe that helps.

Any other ideas why one channel could be distorted? :scratch:
 
Mmmmm, could be anything. I'm no expert in fault seeking. Some points.

- clean the board, both sides;
- correct components in correct places with correct orientation?;
- check for solder bridges;
- cold joints, when in doubt reflow soldering;
- wiring firmly attached?;
- you checked the test points, right ?. Nothing strange here?

Perhaps one of the other builders with more experience than me can chime in (@loafimus?)
 
Hello all. After a few years I start this buid. It was easy for me, I had most of the electrical components or I found them easy.
The biggest problem I had with the mechanical components like insulators connectors , binding post, but I hope I pass all issues :)
Big thanks for clog and the others for this very useful thread.
and P-A and Pavel for this great project.
Until now my first board look like below and I hope next week will sing :)
 

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Hello all. After a few years I start this buid. It was easy for me, I had most of the electrical components or I found them easy.
The biggest problem I had with the mechanical components like insulators connectors , binding post, but I hope I pass all issues :)
Big thanks for clog and the others for this very useful thread.
and P-A and Pavel for this great project.
Until now my first board look like below and I hope next week will sing :)
Looks good so far! :)
 
Last weekend I visit one of my good friend and we finish all remained work: drill holes in heat sink, fix IC’s to heat sink, solder the inductors and the big capacitors. Quick board check for bad soldering and all look ok. Time for fire! Connect the transformer via bulb tester and ignition. No magic smoke only silence. We measure voltage on TP1 and TP2 look OK, but no click of the relays. First issue…, but my more experienced friend, quickly measures the 4020 pins (+12V and RST pin) and he realize missing C35 from board. To be honest, I do not know how I forgot this part, but I remember I do not put R17, S1 and Q1 because I do not want to use Mute function and was not obvious for me to see a part in that space. Quick check of the junk box and he found a suitable component for C35 and back in business  .
Start again with bulb tester, now relays click, measure most of DC voltage, look OK, eliminate bulb from circuit and re-measure everything again OK. Next step, generator, scope and a load. Nice signal on resistive load, no parasite oscillations this mean we can test the amplifier with real music and speakers.
Listening session was long and comparison unfair… chip amp vs tube amp (my friend had only tube amps). Amplifier promising a good sound, but probably need some burn in time.
After first 100 hours of usage I will come back with some impressions regards PA03.