Post by: ZoZo on November 29, 2025, 08:00:55 am
@zozo just one of your 1w driver boards into a dummy load
I am happy to hear how clean the board sounds in your demonstration
Post by: jvok on November 27, 2025, 11:22:07 pm
Post by: Albert H on November 27, 2025, 02:39:45 am
Note that the schematic shows 1uF coupling caps, but it was suggested to me by a user over on Radionecks (don't remember who now, sorry) that they should really be 10uF to reduce bass tilt.
It was me! I came unstuck that way back in the earliest days of me designing broadcast gear, and thought I should pass on the benefit of my foul-up! I was surprised to discover the problem when I had it described to me by one of the engineers I was working with.
There are a number of other "gotchas" as well, but your design has sidestepped them all. It's a very elegant design.
Post by: jvok on November 26, 2025, 09:31:39 pm
Post by: ZoZo on November 26, 2025, 12:44:30 pm
Just curious what was your set up was for the test, assuming it was just a transmitter into a dummy load?
Post by: jvok on November 25, 2025, 09:16:18 pm
https://www.youtube.com/watch?v=StL4rGQMXUA
Post by: Radioclick1fm on November 22, 2025, 09:16:15 pm
Post by: MonTaylor on November 19, 2025, 07:41:41 am
Post by: ZoZo on November 18, 2025, 12:24:31 pm
I have grabbed the attachment and will have a play in JLC later today.
Post by: jvok on November 17, 2025, 06:36:37 pm
Note that the schematic shows 1uF coupling caps, but it was suggested to me by a user over on Radionecks (don't remember who now, sorry) that they should really be 10uF to reduce bass tilt. 1uF gives a response down to <10Hz, but the phase shifts at the low end can become a problem and cause overshoots, and therefore overmodulation. This is especially a problem if you're using a compressor/limiter ahead of the coder, because you'll set your limiter up to limit to +/-75kHz deviation, but the overshoot will mean you're overmodulating still. The 10uF caps put the cut-off frequency way down <1Hz - excessive for audio bandwidth, but means the phase shifts at 20Hz and up aren't so bad.
To be clear, the affected caps are C1, C2, C9, C10 and C27 - these should all be 10uF not 1uF as shown. Increasing C16/C17 to 100uF is probably not a bad idea either. You can also make C19 10uF too - not required, but otherwise its the only 1uF left on the BoM, and increasing it won't hurt.
[attachimg=1]
Also like I said on the Radionecks thread, I'm working on an SMD version of the coder which hopefully I'll put back up on ebay when done. Might be a while though, I have way too many projects on the go right now.