Line out from OT voltage ratio question and such

[Chuck H]

Top left is the front of the amp. It looks like the input is located there. I can't see the wiring on that end well enough because it's dark.

[Dave H]

Dave, pretty sure there is no L or C in there unless it is the capacitance of the wire running along the length of the chassis. I'll check again tomorrow just in case I missed

I'm out of sensible ideas. Perhaps the scope probe is open circuit and you are seeing capacitive coupling? Try swapping the probes.

[nsubulysses]

Yup, no capacitors or anything in this line out. Just 6.8K resistor and 470K resistor.

Seems like 510 ohms and 10K is a ratio that works good for this amp. I can get about 1V RMS at clipping and into heavy clipping is only about 1.2V. The signal looks way more like the signal at the speaker out and the phase difference is lessened.



Just for reference here is 510 ohm and 15K


510 ohm and 33K (or was it 47K?), starting to get distorted like the original 6.8K and 470K


I added a .047/630V cap across the load too. Thanks for your input y'all.

[Dave H]

I added a .047/630V cap across the load too. Thanks for your input y'all.

Is that across the 4 ohm dummy load or the line out? The scope traces all look like there is a cap across the lower resistor of the line out divider.

[nsubulysses]

actually in the pics there is no cap I should have been more clear. I only thought to add it after. I added it across the line out divider. I used an 8 ohm dummy load this time because that's how I had it set up from a previous amp.

Here is a pic of 8 ohm dummy load in yellow and line out in blue. 510 ohm/10K ratio with .047 cap across line out load. Tried to line it up a little better than the previous pic. Looks pretty similar with the two channels synced to the same size on the display. Clipping at about 30V into 8 ohms (112W) and line out voltage is about 1.2V. Seems way better right?

[Dave H]

Yup, no capacitors or anything in this line out. Just 6.8K resistor and 470K resistor.

But the ratio of the scope voltages is greater than 470/6.8 and it can't have phase shift with just two resistors. There has to be a hidden cap across the 6k8 which would also explain why the phase shift is less with lower resistor values.

Anyway, it's looking good now