Distributing signal from signal generator to multiple devices and impedance - Page 1
Forum section: electronics / beginners

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 21, 2025, 11:54:22 pm
content: I am wanting take my FG-200 signal generator and output a waveform to 3 devices. The FG-200 output is BNC, and I have a BNC-to-screw-terminal adapter. The first device is an TDA2050 mono amplifier(Class AB, connected by two wires), and the other two devices are AD831 mixer boards(connected by FG402 cable). The mixer boards are 50ohm terminated, but the TDA2050 has an input impedance at the terminals that is probably 50K ohm(I will receive the part tomorrow, so I can't measure it right this second).So what is the best way to split up this signal? If all three were 50ohm(by putting a matching transformer on the line to the amp) that would be split up to something like 16.6ohms right? So do I need a line transformer on every one of these outputs? Is there some better way to distribute the signal? It would be really nice if I could sometimes disconnect the amp without messing up the impedance for the mixers. How did old BNC network hubs handle this sort of problem?In a related question: the output of the AD831 will go to the input of a TDA2822M headphone amp. So I would assume that the amp has a similar impedance to the TDA2050. Do I need to put an impedance matching transformer on the line between the mixer and that amp?

author: Benta
author_rank: Super Contributor
timestamp: May 22, 2025, 12:06:55 am
content: From what you're describing, it's an audio frequency kind of application.The 50-ohm thing is irrelevant, just connect your circuits directly.When you get into the 10+ MHz range, it might begin to be an issue.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 22, 2025, 12:11:43 am
content: Thank you. It's all under 500KHz. Probably mostly under 100. Do I still need to impedance match the audio amp so it's not so different from the other two lines?

author: lakis70
author_rank: Contributor
timestamp: May 22, 2025, 12:51:31 am
content: one of the tl08x (i dont remember which) las an application for audio distribution

author: radiolistener
author_rank: Super Contributor
timestamp: May 22, 2025, 03:22:50 am
content: You're dealing with a few separate issues here, and it's good to approach each one systematically.1. Signal ReflectionsReflections due to impedance mismatch become relevant when cable length is a significant fraction of the signal wavelength. For frequencies below 100 kHz and cable lengths under 1-2 m, reflections are negligible. Above 1 MHz, they can cause signal degradation, especially in high-dynamic range systems.2. Load CombinationYou're connecting one high-impedance load (TDA2050, ~50 kΩ) and two 50 Ω loads (AD831 mixers). Direct parallel connection results in an overall load below 50 Ω, which may overload the FG-200 or distort its output, especially if it's not designed for such low-impedance loads. Passive splitters introduce power loss and may not fully solve the issue.3. Recommended Solution- Use individual cables from a central point near the generator to reduce reflection issues at lower frequencies.- Add buffer amplifiers: These should have high input impedance and low output impedance, ensuring proper loading and signal isolation. Buffers also prevent noise and interference leakage from one device affecting others.Summary- Reflections are negligible below 1 MHz with short cables.- Use star topology for connections near the generator.- Employ buffers to preserve signal integrity and avoid overloading the generator.Note: 600 Ω is standard for audio/telecom as it matches twisted-pair line impedance. RF systems use 50 Ω as it uses coax cables with 50 Ω impedance to balance power handling and loss at RF frequencies.

author: Zero999
author_rank: Super Contributor
timestamp: May 22, 2025, 08:19:09 am
content: How long are the cables? Don't worry about impedance unless they're over 75m or 25 feet long.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 22, 2025, 09:58:15 am
content: Quote from: radiolistener on May 22, 2025, 03:22:50 amThank you for the detailed and excellent response. I see that due to my inexperience I failed to communicate many important points about this project that would be good to know. All of the cables between the devices will be less than ~2 feet(~0.5meters), but the antenna leads will be 4-6 feet(1.2-1.9 meters?). Everything is very close together. I will look at buffer amps. The isolation sounds very useful!

author: Terry Bites
author_rank: Super Contributor
timestamp: May 22, 2025, 10:52:01 am
content: OPA3692?If you believe the DS:Drives low Z lines with ease.8V pk-pkTHD~.05%Noise 1.7nv/HzEasy gain selection of +1 or +2 gain error <1.7%.I've used them a few times and have had no regrets. Well ok, the £10 price tag.

author: radiolistener
author_rank: Super Contributor
timestamp: May 22, 2025, 12:17:35 pm
content: Regarding reflections, what's critical is matching the load impedance to the cable's characteristic impedance at the cable's end. If the termination is matched, impedance mismatch at the source side is generally tolerable - even at high frequencies.However, as noted earlier, your signal generator may not tolerate very low load impedance. This can lead to signal distortion or, in some cases, hardware damage. To prevent this, it's advisable to either use buffer amplifiers for each load or, if your generator supports it, use multiple synchronized output ports to drive each device independently. It also helps to improve isolation between receivers.

author: Amish_Fighter_Pilot
author_rank: Regular Contributor
timestamp: May 24, 2025, 09:31:13 am
content: Quote from: radiolistener on May 22, 2025, 12:17:35 pmI think that may be the term for what I am trying to find. How does one make multiple synchronized output ports? I remember BNC network hubs way back in the 90s and they must have load balanced somehow. I don't know all the terms though because I'm self taught.

author: tooki
author_rank: Super Contributor
timestamp: May 24, 2025, 10:33:22 am
content: Quote from: Zero999 on May 22, 2025, 08:19:09 amDid you mean “75 feet or 25m”, or “75m or 225 feet”?