Wayne's BA 2018 linestage

[myleftear]

next time, yes.

 

[myleftear]

Since the standoff is probably grounded, you also shorted the + rail to ground. It may not have hurt the circuit at all. Your issue may be the power supply.

...quick check would be to switch the power supply boards.

Thanks, Rick!

VRDN is "alone", but I have a spare second one I could try. [Ditched the dual-mono-fantasies]

If the standoff is grounded, there would be measurable continuity, not?
[And, when it's powered, touching the Aluminium-frame gives me that buzzing feeling...]

The numbers above have a mistake: R27 is 20.94 mV, seems good to me...

 

[myleftear]

Your issue may be the power supply.

What I don‘t understand is that everything measures almost perfect…

If the PSU was the problem, wouldn‘t both channels be affected? Since both + and – rails send current into both boards/channels… (and output looks perfect…

Well then—what is the method to check wether Q1/Q2 are fried?

 

[andynor]

Quick one: perfect measurements across R1/2 means JFETs are all good. If not I seriously understand nada.

 

[myleftear]

That's what my gut tells me the whole day...
Gotta snort into ZM's sleeve

(in the end, it's something too banal to be true, like a disconnected wire touching something it shouldn't be touching, although there aren't many connected wires left)

 

[RickRay]

If touching the case gives you a buzzing feeling when powered, yea, you have an issue. Measure the voltage from the case to the ground on the VRDN output. I bet you find your + rail voltage. The VRDN ground is not connected to earth ground unless you add a wire from VRDN output ground to the case.

 

[myleftear]

this sound plausible.
I have a wire from ground through a CL60 to the chassis, is that eventually... wrong?
(Can't since it worked until I went berserk with the cinemags, must've glitched then)

 

[myleftear]

At least, since I already pulled it apart, I will have the opportunity to make even more holes into the baseplate, hahaha.

(I don't even know if the error is there but am already relieved)

 

[andynor]

What about trying to bypass the CL60? I think it might be too beefy for the fault currents in a preamp anyways...

 

[myleftear]

Hm. Doesn‘t a beefy cl60 keep the ground floating unless „something“ (a short) happens?
I‘ll disconnect it and will see.

 

[myleftear]

Now worried about the cinemags

 

[andynor]

I am not sure. Just read some thread where someone said CL-60 was better suited for power amps than preamps. But I doubt that is the source of your problem.

You’ll crack this, I know you will =)

 

[myleftear]

[emoji1307]

 

[andynor]

Think I found the source of my Q1/4 issues on my preamp, turned test PCB. Damaged pads/a tiny bit visible copper from tough JFET replacement job after my miswiring. Luckily new boards are soon in the mailbox.

Struggling, but hanging in there.

 

[myleftear]

HA! [emoji3]

https://twitter.com/UniverCurious/status/1390333644737236992

 

[jdg123]

Timid about connecting finished board

Has anyone posted a diagram for connecting the finished board to volume (pot) controls? I think I know what to do but always appreciate a guide

 

[pfarrell]

Here's a little something. Might give you some SE ideas.

 

[jdg123]

Thank you pfarrell. It looks to me like all that is being done is a variable resistor from say CN2's pin one and pin two with pin two and three connected/jumpered?

 

[jdg123]

OK, I'm a moron, but in a classic tube amp build there is only one resistor creating a path to gound at the input. On this board that is R18 at 100k for CN2 and R39 at 100k for CN4. Adding in a pot it seems to operate with those resistors in parallel. Seems odd...

 

[pfarrell]

For SE, -IN is jumpered to GND in each channel, then Right +IN and Left +IN doing their thing coming out the other side to switching jack and/or outs... That was a pre-release (purple) board—final blue board has labels...