Adding analog input to a digital headphone amp Fiio K11  - Page 1
Forum section: electronics / beginners

author: spacesmurf
author_rank: Newbie
timestamp: July 16, 2024, 10:41:25 am
content: I purchased this device 2nd hand without paying attention (very good price), intending to also use it as a record player analog out to headphones amp. However, I've realized it only has optical and coaxial inputs, no analog input.And here is the newbie question: Is there a way to solder an analog connection between the DAC and amp section?(PS: I'm linking images from other forums. Apologies if this is not allowed.)

author: RoGeorge
author_rank: Super Contributor
timestamp: July 16, 2024, 11:40:23 am
content: Might be easier to buy an adapter for analog to SPDIF (or whatever digital format that headphones amp supports).

author: spacesmurf
author_rank: Newbie
timestamp: July 16, 2024, 12:14:24 pm
content: Absolutely, it would be more convenient to convert and utilize the existing inputs. I'll likely end up doing thisI was hoping to avoid digital conversion and instead listen directly to the analog output from the turntable.Also, since I'm learning about electronics and not too concerned about this particular item, I thought it could be a fun little project. I just needed some reassurance that it is possible in theory. However, after reading the datasheets of the different ICs, it doesn't seem very promising that any of the circuits would accept a line-level signal."

author: RoGeorge
author_rank: Super Contributor
timestamp: July 16, 2024, 12:28:05 pm
content: In this case, maybe look at the last 2 ICs near the RCA out (can't see in the picture what they are). By the arrangement of the capacitors, it looks like it might be an analog stereo amplifier IC. Maybe you can add there a line-in input, right before the line-out/headset amplifier IC.

author: Ian.M
author_rank: Super Contributor
timestamp: July 16, 2024, 12:30:13 pm
content: The Fiio K11 has a "multifunction knob" rather than a dedicated analog volume control and the CS43198 has internal digital volume control, so even if you manage to inject an analog signal just after the CS43198 outputs you wont have any volume control. Either "embrace the suck" and convert analog to SPDIF, or get or build an 'old-skool' analog headphone amp and either use the K11 elsewhere or sell it on.Note that for old-skool turntables with output direct from the pickup, you need a preamp withRIAA equalisationto even get up to line level with acceptable frequency response. Modern turntables (not intended for purists) typically have the preamp built-in.

author: RoGeorge
author_rank: Super Contributor
timestamp: July 16, 2024, 12:48:13 pm
content: Got once a "miracle" IC specifically designed for headphones, though never built a headphone amplifier, the soundcard headphones-out signal was loud enough for me even for 110ohms headphones (not sure if it was 110 or 80, but certainly much higher than the typical consumer headphones with 32 ohms).Found it:TPA6120A2High Fidelity Headphone Amplifierdatasheethttps://www.ti.com/lit/ds/symlink/tpa6120a2.pdfdev boardhttps://www.ti.com/lit/ug/slou169/slou169.pdf

author: spacesmurf
author_rank: Newbie
timestamp: July 16, 2024, 03:23:23 pm
content: RoGeorge and Ian, thank you very much for the information; it's all very valuable. I will use an oscilloscope to examine the Vpp signal on the board before the gain/amp ICs and see if I can figure something out. Perhaps I can drop the line level to match what comes out from the DAC, if this makes sense.(Record player has a switch for the output so I can choose between phono and line)