2nd Gen Build Started (that didn’t take long…)

[martin manning]

I would try a signal tracing approach. Put signal into the input with your Bluetooth receiver, say 200 mV, and use your DMM to look for that starting from the input jack and proceeding along the signal path to see where you lose it. You could set the DMM to read AC volts, or if it has a frequency measurement you could use that.

[Raoul Duke]

To do that I would use the load resistor and measure across it for the 200mV while sending the signal in through Normal; am I correct? Then just follow the signal until I’m getting no AC reading?

Actually just realized my newer DMM has a frequency measurement going from 10Hz - 20MHz. How would I use that?

[dbharris]

Yes, put your speaker output on a resistive load. Inject signal in the normal jack. I would just measure AC through the signal path as Martin suggested. Start on the solder tab of the input jack then to the terminal strip, etc. You will want to skip over the plates and measure the other side of the coupling caps so that they block DC. Just trace through the schematic or layout and see where it stops. DMM set to AC and black lead clipped to chassis ground. Red lead as your probe.

Also might try chop sticking around when you find where the signal drops.

-Dan

[Raoul Duke]

Thanks Dan!
This is all new territory for me and I’m ready to learn
What sort of reading indicates good? Is it a “go/no go” type of measurement or is there a range of weak vs strong?

[martin manning]

Connect one lead to ground and probe with the other. The signal level will change depending upon where you measure, so an auto-ranging meter is best. If you use the frequency measurement, you can detect the signal when the reading shows your input frequency. You were successful in setting the PI trimmer, so you know the power amp is ok.

[dbharris]

Generally you will see the AC signal get larger after each stage. Think of what each circuit block is doing while you probe. For instance the signal should be large after V1b. But before V2a, it will be divided down by the OD entrance resistor network.

Once you locate the area where the problem exists, it may be a bad solder joint or something wired wrong.

-Dan

[Raoul Duke]

Thank you both for the info!

Martin, I’ll use that schematic you posted as my guide to start with. I really hope I can track it down quickly. It’ll be tomorrow’s project

[martin manning]

You should get something like this if everything is working.

edit: see above

[Raoul Duke]

Ok, I’ve got signal going to pin 2 of V1, then it’s gone. Re-flow, change tube?

Oddly, when I use my “f Generator” app, when I touch pin 7 of V1, it shuts down and kicks my Apple Music on (with Siri sometimes).
Hope I’m not frying my I-Pad.

I should mention that I built a tracer probe and am just following the sound. I tried the AC route and can’t seem to get 200mV across the load resistor - so I went to the homemade probe before asking questions about what I might be doing wrong with the AC.

[martin manning]

Ok, I’ve got signal going to pin 2 of V1, then it’s gone. Re-flow, change tube?

Oddly, when I use my “f Generator” app, when I touch pin 7 of V1, it shuts down and kicks my Apple Music on (with Siri sometimes).
Hope I’m not frying my I-Pad.

I should mention that I built a tracer probe and am just following the sound. I tried the AC route and can’t seem to get 200mV across the load resistor - so I went to the homemade probe before asking questions about what I might be doing wrong with the AC.

It's a good idea to use your Bluetooth receiver if you are using your phone or iPad. That isolates it.

Following the sound is fine.

The 200mV is on the input jack tip.

I would make a careful check of the wiring after V1a. Maybe there is some error in the tone stack, or inadvertent grounding. You wouldn't be the first one to miss a bit of shield braid touching the core conductor.

[ijedouglas]

Ok, I’ve got signal going to pin 2 of V1, then it’s gone. Re-flow, change tube?

Oddly, when I use my “f Generator” app, when I touch pin 7 of V1, it shuts down and kicks my Apple Music on (with Siri sometimes).
Hope I’m not frying my I-Pad.

I should mention that I built a tracer probe and am just following the sound. I tried the AC route and can’t seem to get 200mV across the load resistor - so I went to the homemade probe before asking questions about what I might be doing wrong with the AC.

So nothing after the coupling caps of V1 pin1?

[Raoul Duke]

With 100Hz sine wave going into the normal jack, I’m still not getting 200 mV AC on the tip. Using the Bluetooth now.

Not sure what I’m doing wrong here.

[Raoul Duke]

Ian,
I have signal on pin 2, but get a wicked buzz when I probe pin 1.
Oddly, I have signal on pin 6.

[martin manning]

Plug a cable into the input jack leaving the other end free and measure resistance to ground. Should be 1Meg.

[Raoul Duke]

I’m getting.028 vac at the tip with the negative grounded to chassis.