I would say the black wire is going in at one end and screen coming out the other. But its hard to tell. Bets are it's around the green blocks. China stuff can be very good I've used JLCPCB a few times and they are first class. I've also bought stuff from China and its cheap and does what it says.
The two green wires should be going to the same place on the main PCB. The picture is not the clearest. I would also expect to see a ground from the headphone connector to the main PCB too. Oddly I only see it go to one side of the headphone jack it should go to both and this is the diagram on the WEB. From memory all 3 contacts break so that would leave the headphones with no ground.
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The heat-shrinked black is screen braided with negative RCA wire. Red that comes out of the same sleeve is RCA positive. 2 green wires ultimately lead to star ground on the PCB. Wiper red and black wires lead to the 2 grids at the tube socket.
Not much progress on this one. Signal seems to be in phase between L and R all along the signal path.
The strongest clue remains that level is higher and FR appears correct when only 1 RCA input is connected. It doesn’t matter which one.
Next, I think I’ll compare key voltages when 1 RCA is connected and when 2 RCAs are connected.
The strongest clue remains that level is higher and FR appears correct when only 1 RCA input is connected. It doesn’t matter which one.
Next, I think I’ll compare key voltages when 1 RCA is connected and when 2 RCAs are connected.
This should be testable with an Ohmmeter. Ask yourself: what kind of wiring issue could cause this symptom? One where hots and grounds are reversed on both channels. Should be visible with an Ohmmeter from the outside of the box, including the location. If swapped before the volume control, continuity from one channel's hot to the other's ground will be independent of volume control position; if after, will vary with pot position; assuming common-grounding at the pot.
All good fortune,
Chris
All good fortune,
Chris
And of course…you all win and I am a dummy…
The problem was on the output side!
2 things, but only 1 big thing:
L and R wires were connected reversed to the output jack.
The headphones jack was faulty and didn’t make contact with the sleeve of the male jack.
I only had to play with jumper cables to figure this out, but I was so keen on the problem being on the input side or the circuit, I missed the obvious.
May I learn from this!
I take it this thing has no global feedback? That’s the only way you can accidentally swap OPT phase and not have other, much larger, problems.
No feedback of any kind.
It’s a simple circuit, but there are many things I don’t understand about it and don’t like, probably due to my ignorance.
For instance, I don’t like that the power supply side is not isolated from the amp side. (having the center tap of the HT secondary connected to the star ground, along with signal ground…seems weird, but I have seen it done in plenty of designs and it’s valid…apparently it’s called a “virtual DC ground”?)
The lack of symmetry on that PCB is also jarring, particularly since this circuit screams for it.
Many things and many books to reads.
Post #68 is the first mention of a headphone jack, despite several (mistaken - try it yourself) posts about speaker phasing. Good survival tip: never lie to your doctor or lawyer.
All good fortune in your future endeavors,
Chris
All good fortune in your future endeavors,
Chris
Tying the wire from the trafo secondary center tap directly to the star ground is generally a bad idea. Tie the transformer center tap to the negative terminal of the cap through its own path directly, then tie the negative terminal of the cap to star ground through another wire. This isolates the “power supply section” from the “audio amplifier section” to the best of your ability. The currents in the wire going to the trafo are full of power line frequency ripple, the one going to the amplifier is not.
Thank you for your patience.
In the mind of the beginner, there is this fallacy that ground is 0V, but of course it's a fallacy.
As I have learned it doesn't really matter that electrons don't flow in the direction of conventional current.
And positive and negative voltages are just a matter of viewpoint.
Etc.
@wg_ski Now, that makes a lot of sense!