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

[martin manning]

462 mV on the free end of the 10n? Something between the volume pot and the output of that stage. Just for grins, check the resistance from the open end of the 10n to ground, Should be infinite, of course.

What about the coax from the volume pot to the V1b grid? Maybe that's open?

[Raoul Duke]

One probe on the open end, one probe to ground?

What’s the best way to test that coax? I’ve done basic continuity to ensure the center is isolated from the shield. Is that sufficient or is there another way?

[martin manning]

One probe on the open end, one probe to ground?

Correct, just to be sure there isn't something under the board shorting it to ground.

Then check the resistance from the volume wiper to the V1b grid.

I don't see coax connected to the V1b grid...

[Raoul Duke]

Ha! There isn’t. Truthfully, I didn’t catch it in the schematic and didn’t see it in the layout.
I know, “what a dumbass”.

What is the actual connection that needs to be made?

[martin manning]

Volume pot wiper to the terminal strip lug with the 56k connected to it.

And no, it's not shown in the layout, the only clue is the small note near the terminal strip.

[Raoul Duke]

That’s probably it. I went over every other thing at least 3 times.
Ugh! I’m on it!

FNGs!

Thanks Martin!

[Raoul Duke]

Ok,
Got that coax in and have it running. My apologies all - nothing stops a signal like the wire to carry it not being there, lol.

- The volume, tones to include the pull pot, level, and accent are all responding.

- The FET now has sound and the trimmer sweeps the signal strength - 1.5 at the top, 9.6 at the bottom of the drain. Doesn’t really do much boost and CCW on the trimmer really attenuates the output. Some tweaking to do there.

- The manual switch and OD pot don’t seem to do anything and the OD trimmer isn’t responding - but I tested the pot in circuit and it sweeps from 0 to 46 ohm’s resistance. Still not hearing any relay “clicks” like I did with my previous build. Maybe it’s not switching?

- 10n - NC1,NO2 is reading 17.8vac

- COM2 reads .42 mvac - something’s up there I suspect - should be 320mv. Signal obviously not getting to the trim pot?

- Lug 3 of the OD pot is 3.7; but the wiper sweeps upward until about 75% full - then starts sweeping downward.

- All B+ voltages are good, plate voltages are good and the clean sound is beautiful and strong.

I feel like we’re gaining ground…

[martin manning]

- The volume, tones to include the pull pot, level, and accent are all responding.
- The FET now has sound and the trimmer sweeps the signal strength - 1.5 at the top, 9.6 at the bottom.

Clean channel is working then.

- Odd part is that manual switch and OD pot don’t seem to do anything and the OD trimmer isn’t responding.
- 10n - NC1,NO2 is reading 17.8vac
- COM2 reads .42 mvac something’s up there, right?

The OD is not working. Let's see if the relay is getting energized.
With no signal applied,
OD switch set to pedal, resistance to ground from Com 2 and NC 2 should be zero ohms.
OD switch set to Manual, Com 2 resistance to ground should be ~180k.

[Raoul Duke]

Set to pedal - COM2 and NC2 resistance to ground is 0 ohms - voltage at relay board is 5.7 positive, 0 negative.
Set to manual - COM2 resistance to ground is 0 ohms - voltage at relay board is 11.8 to ground both positive and negative.

[martin manning]

The coil seems to be getting voltage when you switch to Manual, so I think you have a wiring error around the relay.
Look at the schematic I posted above:
In Pedal,
Clean output 10n goes to NC 1 and NO 2, and on to the Level pot (master volume) lug 3 via Com 1. OD input goes to Com 2, and is grounded via NC 2.
In Manual,
OD output goes to NO 1, and on to the Level pot lug 3 via Com 1. Clean output 10n goes to OD input via NO 2 and Com 2.

[Raoul Duke]

That looks like how I have it wired:

COM1- level pot lug 3 and power amp out
COM2- OD input on main board
NC1- jumper to NO2 to 10n on main board
NC2- ground
NO1- OD out from main board
NO2- jumper from NC1 to 10n

Puzzling. Is there a way to test the relay without ripping everything apart?
I’ll re-check the voltages IAW the schematic and report back.

Thanks!

[martin manning]

In standby,
Switch to Pedal, and see if the right connections are present, which you can check with resistance measurements. For example, is there zero resistance between Clean output and Level pot lug 3, and between OD input and ground.
Switch to Manual and see if there is there is zero resistance between the OD output and lug 3 of the Level, and between the Clean output and OD input.

[Raoul Duke]

Martin,
Here’s what I get from those four measurements:

Clean out @ 10n to Level lug 3 - 0 resistance
OD in at COM2 to ground - 0 resistance

OD out NO1 to Level lug 3 - 2.13M ohms resistance
Clean out @ 10n to OD in @ COM2 - .95M ohms resistance

[martin manning]

Clean out @ 10n to Level lug 3 - 0 resistance
OD in at COM2 to ground - 0 resistance

Good for Pedal setting.

OD out NO1 to Level lug 3 - 2.13M ohms resistance
Clean out @ 10n to OD in @ COM2 - .95M ohms resistance

This is not right. The spots you are measuring from are as shown below?

[Raoul Duke]

Yes Sir - exactly.