digitally controlled preamplifier - Page 1
Forum section: electronics / projects

author: dosensuppe
author_rank: Contributor
timestamp: August 08, 2025, 12:24:40 pm
content: Hello. I made an arduino controlled preamplifier.I did not route the board yet, but the schematic and layout of the board is pretty much complete.Please tell me your honest opinion and point out some mistakes I made.KiCAD files:https://files.catbox.moe/cy5e40.zipattached

author: moffy
author_rank: Super Contributor
timestamp: August 08, 2025, 11:14:57 pm
content: If you want people to comment on your design/schematic it would be helpful to post the schematic as a picture or pdf.

author: MariuszD
author_rank: Regular Contributor
timestamp: August 09, 2025, 06:05:37 am
content: The zip file is empty.

author: dosensuppe
author_rank: Contributor
timestamp: August 09, 2025, 12:55:38 pm
content: Sorry. I guess the retarded file sharing service messed up. the built in file attachment function of the forum complained that the file was too big (30mb). I don't have access to the computer right now. I'll update it monday.

author: dosensuppe
author_rank: Contributor
timestamp: August 11, 2025, 05:42:24 am
content: KiCAD saved backups into the same folder which took up a considerable amount of space.File is attached.

author: Zero999
author_rank: Super Contributor
timestamp: August 11, 2025, 08:46:31 am
content: Please post a PNG or PDF schematic of the schematic for those who don't have KiCAD installed.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 11, 2025, 09:47:11 am
content: you could have used ULN2003 driver, you would have lowered the part count and still do the job ?they do interface neatly with duino's

author: dosensuppe
author_rank: Contributor
timestamp: August 11, 2025, 12:59:09 pm
content: you're right. I changed it.

author: themadhippy
author_rank: Super Contributor
timestamp: August 11, 2025, 01:15:45 pm
content: you got nuffing connected to the coil of k3

author: dosensuppe
author_rank: Contributor
timestamp: August 12, 2025, 06:05:32 am
content: yup. already noticed that. other than that looks fine?

author: dosensuppe
author_rank: Contributor
timestamp: August 13, 2025, 01:20:32 pm
content: almost finished with routing. It's gotten more convoluted than I anticipated. I had to route the SPI lines over some signal lines. Though the digital potentiometer chips are only receiving SPI when the volume is adjusted, so I figure it isn't that bad...

author: cncjerry
author_rank: Unknown
timestamp: August 16, 2025, 04:05:23 pm
content: Are you going to use IR control?

author: dosensuppe
author_rank: Contributor
timestamp: August 25, 2025, 06:30:08 am
content: Yes. Why?

author: dosensuppe
author_rank: Contributor
timestamp: August 27, 2025, 08:33:00 am
content: I added some isolation distance to the AC input connector.Does this make sense?

author: dosensuppe
author_rank: Contributor
timestamp: August 27, 2025, 08:40:31 am
content: updated kicad files

author: fchk
author_rank: Frequent Contributor
timestamp: August 27, 2025, 09:10:15 am
content: Your choice of relays is not optimal.These relays are supposed to switch audio signals, right? Did you know that relays do have not only a maximum load but also a minimum load? The minimum load prevent the accumulation of oxides on the contacts over the time. Unfortunately most datasheets don't name this minimum load or minimum current.I'd suggest reed relays. The contacts are sealed in glass filled with a protective gas, so this should be a better option for very low currents.

author: dosensuppe
author_rank: Contributor
timestamp: August 27, 2025, 09:50:13 am
content: Does this really result in a significantly worse audio fidelity?I already have around 50 of those relays in storage and don't want to wait another 2 weeks or so for some new parts to arrive.

author: fchk
author_rank: Frequent Contributor
timestamp: August 27, 2025, 11:07:01 am
content: Quote from: dosensuppe on August 27, 2025, 09:50:13 amWhen they are new everything will be fine. The first signs of problems usually take months or years to come. Warranty will have expired by then, but your reputation ...

author: dosensuppe
author_rank: Contributor
timestamp: August 27, 2025, 12:35:26 pm
content: I'll keep it in mind with future designs. For now I don't think it's that vital. I'm mostly doing this project for myself.

author: dosensuppe
author_rank: Contributor
timestamp: August 27, 2025, 12:36:13 pm
content: updated kicad files