I am thinking you have 4 gyrator sections messed up.IanB said:Right. Swapped over the pot PCB’s. It’s not that. Have I screwed up the gyro circuits x 2?
https://groupdiy.com/index.php?topic=63983.msg814157#msg814157iamnotacowboy said:I finished my pair of LC40s. Upon applying power, both units smoked. (I did test them one at a time) When I looked at the circuit, PR4 and PR5 are the items that look cooked on each unit. Did I follow the directions wrong in the exact spot on two different units a couple days apart?! I s’pose that’s possible. These are the 10 ohm power damping resistors. Any ideas?
noiro said:Hi Jeff, do you think it would be possible to change the range on each frequency band, so instead of +/-15dB in each band only +/- 3.75dB. It would be use for mastering.
Blackdawg said:I talked to Jeff about this. It is possible, but due to the EQ resistor ladder setup it's not super simple. You'd have to trail and error resistor values yourself. I bought two resistor ladders to do this but just not enough time..
I see countless bad looking solder joints and overall cleanup needed.Atlesque said:Hi everyone, first time posting and also one of my first builds, so please think of me with kindness and forgive my beginner questions and possible forum etiquette breaches...
I've been troubleshooting this build for some time without results now and some kind people over at the Facebook 500 series DIY community suggested I'd ask you techno wizards for some advice.
I'm building the LC40 Litz with a SL-2520 Red Dot DOA.
After finishing the build, device powered up, bypass worked, but when engaged, there was practically just noise. After inspecting and help of other more knowledgeable people, we didn't find any problems with misconfigured resistor/gyrator values, misaligned diodes/capacitors, or other trivial problems. There were some messy solder traces on the switch PCB, but I cleaned those and redid all weak solder joints on all PCBs and components.
After more trial and error, I found that the noise changed when I moved the gain switches around. Putting them all at position 0 (no gain) made the noise disappear. This made me suspicious of the switch PCB. I also noticed that wiggling the switch PCB around while connected would also influence the noise. So I redid the pin header connections and strengthened some of the pins with solder for a better connection. This eventually got rid of the noise for 90% and I could finally hear some real music passing. Tweaking the switches also did not result in any noise.
Now I'm at the stage where there still is some low but perceivable noise happening when the unit is engaged, and the volume of the signal is about -12dB lower on output than on input. The quality of the sound is not very good. There seems to be quite some harmonic distortion happening.
Someone suggested to check the Litz transformer for shorts to ground, check switches being wrong orientation (but I don't see how this is possible) and check opamps or transistors (no clue how to do this).
One thing I tried was checking resistance values for all wire pairs of the Litz transformer, and also each wire's resistance to ground. I've made a spreadsheet comparing these values with another working device (VP312DI) that uses the same transformer:
I don't know if this makes any sense or how to interpret these values sadly... But I Googled how (audio) transformers work, and I found information indicating there should be no physical connection (and thus infinite resistance) between different sides (primary/secondary) of the transformer. However, as indicated in the spreadsheet, some sides do have resistance between them, and thus a physical connection, which makes no sense to me. I think I'm missing some essential fact of transformers here, but I tried Googling and I haven't found it yet.
Does anyone have any idea what else to check to get rid of the noise and fix the lower volume?
I have an oscilloscope but please mind I'm a total beginner so I will probably have to Google a lot and I might not understand all of your answers immediately.. Sorry guys and thanks a lot in regard. Quality wise I'm incredibly impressed of my VP312DI, but this build is definitely out of my league to troubleshoot right now.
Some more pictures of my build for reference: https://imgur.com/a/ADZADAZ
Please ignore the rainbow breadboard wire coming out of the DTO5 board, it was for testing as someone said it might've been the board (but this was not the case). I've already attached it back directly to the board as per spec and on first pictures.