JMSig Power Section Voltages - 50v+ High

[watchthedivers]

Hey everyone! Question about power supply section voltages in a JMSig/Wonderland build.

Real quick since this it my first post... thank you to everyone for all the amazing help here. I would never have been able to build this thing in a million years without the insane amount of knowledge you all openly share. I'm hooked now and already have another 3 amps I want to build next

I just finished my first amp build ever and after a few troubleshooting issues it's sounding pretty good!

The only weird thing left is that I'm still measuring around 50ish plus volts above the schematic at each of the listed power supply section voltages.

I'm likely missing something obvious but the only thing before the power section board is the rectifier board and the transform/choke... so I can't figure out what could cause these to be high. I double checked all the resistors in the power section and they're accurate.

Is there a reason could this be 50v higher than expected? I've double checked the amp a few times and think it is wired correctly but can't figure out why these could be high.

Here's a chart of the voltages:

Screen Shot 2022-09-01 at 11.03.55 PM.png

[ijedouglas]

Do you have the 220K dropper at the end of the string to ground? Based on your diagram it looks like you have omitted it. This is needed (it simulates the FET node) and may explain your higher voltages.

Cheers

[pdf64]

Key voltage measurements are the VAC across the mains and heaters.
That means across them, ie not with one probe tip connected to earth.
So live to neutral, and pin2 to pin7 of the first output valve along from the PT.

And what is the idle loading, how much cathode (or anode) current is each output valve drawing (bias setting)?

A full schematic, and transformer details, would be handy.

[watchthedivers]

Thank you! I wasn't with the amp yesterday so just got a change to look at it today.

The amp does have the extra 220k to ground. I don't know why it is crossed out in the schematic but the layout I used has it and I included it. I double checked just in case but it is there.

Thanks for the voltage check suggestions. In checking the heater and mains vac measurements I figured out at least one problem!

I had the center leads of the power transformer flipped on the output side. The 50v bias lead was going to ground and the center lead was going to where the 50v should have been.

I fixed that and it's a ton better but still doing this weird feedback thing at higher volumes or added gain from pedals. It's like a bloom effect but in a bad way and sounds kind of muddy. You hit the note and then it kind of oscillates and drones getting louder and vibrates with tons of extra bass... then it dies off. Again, I wish I had a reference for what was normal with this thing but it doesn't sound great when it does it. Low volume sounds awesome now just at higher volume or with gain pedals it still seems off.

Since I'm sure my terrible explanations of what it sounds like don't help much I took all the voltages as suggested. If anything stands out immediately as looking off it would be a huge help!

Thanks again,
Patrick

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[WhopperPlate]

Delete

[WhopperPlate]

68FAD523-D8EA-4580-8B5D-C73A87F6C4C2.jpeg

Center tap to bias supply …0 volts…tubes probably unhappy

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[martin manning]

I had the center leads of the power transformer flipped on the output side. The 50v bias lead was going to ground and the center lead was going to where the 50v should have been.

There would still be 60VAC available on the CT if the bias tap lead was grounded, but one leg of the HV would be 60V high and the other would be 60V low. Probably average DC would be high, but with a lot of 60Hz ripple.

[watchthedivers]

Thanks guys for all your help. I guess I’m going to look at lead dress since it’s a bit messy for my first build and check the solder joints. I poked around and found that one of the LNFB caps on V1 was making noise when I taped on it. The same thing was true for one of the tube lugs. I resoldered them and it doesn’t seem to make noise now when I tap it.

It’s still doing this weird distorted feedback thing when I turn the gain up. It’s sound pretty good now with the gain and master at noon but any gain pedal and it starts sounding weird again.

Also I noticed today that in videos online it looks like the reverb is a lot more wet at the noon positions. It is still very dry on mine at noon. Send needs to be past 3 and return needs to be near 4 o’clock for it to be very deep. I’m using an accutronics 3 spring long delay. Not sure if that’s just a difference in the Ceriatone JM100 since most clips I could find are of that amp.

[ijedouglas]

Have you tried swapping primaries on the OT? You may be getting positive feedback from your GNFB. Quick test is to disconnect the GNFB and see if you still get the distorted feedback. If this clears it up, reverse your primaries.

[WhopperPlate]

I had the center leads of the power transformer flipped on the output side. The 50v bias lead was going to ground and the center lead was going to where the 50v should have been.

There would still be 60VAC available on the CT if the bias tap lead was grounded, but one leg of the HV would be 60V high and the other would be 60V low. Probably average DC would be high, but with a lot of 60Hz ripple.

Good to know my assumption was incorrect. Thanks

Have you tried swapping primaries on the OT? You may be getting positive feedback from your GNFB. Quick test is to disconnect the GNFB and see if you still get the distorted feedback. If this clears it up, reverse your primaries.

He only gets the oscillation with the gain up . I find the primaries swapped won’t produce results that you would play, just instant and loud undesirable noise.

[WhopperPlate]

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I know I already brought it up to you boss, but those bias readings are very low and going to have very low power output . Does raising the bias current change anything for the better yet?