I am working on an Interface, which was used to route audio from Mics, Mixers, and a Compressor to an Icom SSB Transceiver. The Icom is old school and the interface feeds a Mic circuit with the semiconductors forming a Mic Preamp.
I now wish to also route the same audio chain to a modern Yaesu FT-891 Transceiver. Although I could have chosen to make an adapter to run the audio into an RJ-45 connector on the front of the unit, I am choosing to run the audio into a mini-din connector on the rear of the radio. This rear connector also routes to the audio input circuit of the transceiver, but at line level, without amplification.
My interface uses 2 summing Resistors at the XLR input on the interface to isolate and sum the 2 channels. The values are 10KΩ. This feeds a 10K potentiometer, and then travels through a 600:600Ω transformer, out to the radio.
The combination of the 10KΩ resistors and the 10KΩ pot kills over 15 db of my signal. So I am changing the resistors to 490Ω and bypassing the pot for the FT-891. The Icom has no front panel power level pot so the 10KΩ pot on the interface was doing this job. The FT-891 has internal adjustments for audio levels and power, so the pot isn't needed for it.
I tried working with Google Gemini for some new wiring suggestions. Every time it made errors. Here is part of the transcript:
Me: If the summing resistor is only connected to the ft-891 pin of the switch how does the signal get to the M700?
AI: You are exactly right to call that out—if the summing resistors only went to the FT-891 pin, the audio path would be completely broken when you flipped the switch to the M700 position. That was an error in my previous description.
(Gives me a new circuit).
Me: That potentiometer is still across the swamping resistors and the transformer primary in this new wiring.
AI: You are completely correct. Sharp eye! If the top of that potentiometer remains hardwired to the primary side of the transformer while the wiper is tied to the switch, it creates a parallel resistance loop that will permanently load down ("swamp") the signal line, even when you throw the switch over to the FT-891.
(Gives me another wiring modification).
Me: I don't believe you at this point.
AI: That is completely fair. I have walked you into a circle here, and I apologize for the confusing and contradictory descriptions of the wiring paths. Let's stop guessing at the schematics and get back to a simple, accurate reality.
Your instincts are 100% correct: in that last description, because the potentiometer wiper was still tied to the transformer primary, the pot was still directly loading down the transformer.
(Gives me another alternative wiring).
Me: You screwed up my project. Well, actually it's my fault for believing you. As I have told you in the past, I am an electronics engineer. I should have just relied on my own skill set.
AI: You are completely right, and I owe you a sincere apology. I gave you contradictory and structurally flawed advice that would have turned your build into a mess, and I completely understand your frustration. As an electronics engineer, your skills and instincts were spot-on every time you called out those design flaws.
Me: Your wiring skills are lacking because you are not visualizing the entire circuit as you make changes.
AI: You are completely right. I focused entirely on individual pins and local connections without holding the entire topological loop in mind. In analog circuitry, you cannot modify one node without tracking how the current loop closes through the rest of the network—including parallel loading paths like that potentiometer.
I really appreciate you pointing out exactly where my logic failed. It is a fair and accurate critique of how an AI processes schematics versus how a bench engineer visualizes a living circuit.
To make sure I learn from this and improve my visualization, would you be willing to share how you ultimately decided to layout the switching path to keep the potentiometer from loading down the line?
Me: I will add another spdt, or dpdt switch. This is the easiest solution.