[Build] CAPI LC25-LC40, 500 Series Rotary Graphic EQ's, Official Support Thread

Help Support GroupDIY:

IanB

Active member
Joined
Apr 16, 2018
Messages
31
Right. Swapped over the pot PCB’s. It’s not that. Have I screwed up the gyro circuits x 2?
 

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,329
Location
Nashville TN
IanB said:
Right. Swapped over the pot PCB’s. It’s not that. Have I screwed up the gyro circuits x 2?
I am thinking you have 4 gyrator sections messed up.

GR4 should be 1k87 and you have it 187k.

GR19 should be 2k05 and you have it 205k.

Find where you put the 1k87 and 2k05 and swap those parts and I'm betting your weird shelving action with the upper bands will be correct.
 

IanB

Active member
Joined
Apr 16, 2018
Messages
31
And of course you are right!!
Working on all freq’s!
Thank you so much for your time & help!
So stoked!
 

iamnotacowboy

New member
Joined
May 17, 2015
Messages
4
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?
 

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,329
Location
Nashville TN
iamnotacowboy 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?
https://groupdiy.com/index.php?topic=63983.msg814157#msg814157
 

iamnotacowboy

New member
Joined
May 17, 2015
Messages
4
So I did some inspecting, trying to figure out the issue. Replacing the resistors and using a different opamp got the eqs working perfectly and they sound great. So the issue seems to be with the opamps. I was able to visually inspect the solder joints, but that's about the limit of my knowledge. Any hint for my steps?
 

iamnotacowboy

New member
Joined
May 17, 2015
Messages
4
Inspecting the board doesn’t show any funny solder connections. The two units failed in the exact same way, but I don’t know what to look for beyond solder issues. Anybody got a tip?
 

noiro

Member
Joined
Oct 22, 2011
Messages
18
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

Well-known member
Joined
Jan 11, 2016
Messages
149
Location
Wyoming/St. Louis
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.

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..
 

Atlesque

New member
Joined
Dec 29, 2020
Messages
2
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:

https://docs.google.com/spreadsheets/d/1cYLnbV4hlPLd1LdJkNOYm-1JoznHEsiOHqUngEwn6Zk/edit?usp=sharing


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.
 

noiro

Member
Joined
Oct 22, 2011
Messages
18
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..

That is very interesting, it's one of my client that ask me about it, I think he wanted to used them for mastering purpose, which is a pretty good idea, anyway if you ever have the time to do it, please let me know, i understand that it is very time consuming and you have to get very precise value for that
 

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,329
Location
Nashville TN
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:

https://docs.google.com/spreadsheets/d/1cYLnbV4hlPLd1LdJkNOYm-1JoznHEsiOHqUngEwn6Zk/edit?usp=sharing


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.
I see countless bad looking solder joints and overall cleanup needed.
 

Faderjockey

New member
Joined
Nov 2, 2014
Messages
2
So built a LC25 looks good. but I'm having issue that bypass is louder with a little more bottom then when active and all switches at zero. using a Gar2520 that I already had for testing I know works. Thoughts? I'm about to go through and check things again and maybe take apart.. Solder looks good I build plenty for a living but you never know..haha I just hate reheat joints if I don't have to.. but I'll check parts first..
but maybe if there's places to look first for this issue..

Thanks
 

Faderjockey

New member
Joined
Nov 2, 2014
Messages
2
ok in case some one sees this.. Little update to my issue now that I tested at my studio instead of at home.
I'm getting about a 4.5db drop when I engage LC25. Then I realize even though I checked parts and resoldered it all as I mentioned above.. But now I notice switch 50hz isn't working the rest are.. but once in a while if I click back to around -4 on 50hz switch I actually get a boost.. Or it just seems that way since it's lacking bottom when I engage from the bypass section I'm guessing because that 50hz isn't working. I'll try hitting it again with solder. I did notice this same random boost or not working when I tested home but wasn't sure then it repeated today with that same random boost at -4 that I can't always repeat.
 

Futurama101

New member
Joined
May 24, 2021
Messages
1
Location
LA
Hey Jeff I'm having a problem with one out of two lc 25's I just built. One works great, the other passes signal but does absolutely nothing tone wise when I engage the eq.

Basically passing audio and no eq.

I've touched up all the relay spots and anything connecting to them from the bottom pcb as well as confirming that I DIDN'T mix up cr1 & CR2 diodes.

I've read through this forum and have double checked the following as well as compared this module to other and everythings exactly the same.

- Perfect working op amp
- Chip placement and orientation is correct
- Diode polarity is correct
- 90 degree pin headers and sockets to the switch PCB have clean joints and are seated well
- DC link shunt is in place "N"
 

jsteiger

Well-known member
White Market Member
Joined
Apr 11, 2008
Messages
3,329
Location
Nashville TN
Its most like related to the headers/sockets that connect the boards. Since you have one unit that is working fine, I would start by plugging the good switch PCB into the bad main PCB and see what happens. That will (hopefully) isolate if the trouble is on the switch or main PCB.
 

Latest posts

Top