Alembic F-1X Preamp Direct Out No Output

[Thomasio]

Hello -

I have an Alembic F-1X preamplifier, and the direct out (XLR) on the front of the panel is not outputting any signal.

The preamp is in new condition, and I took the top off to have a look. All of the plus are in place, and the vacuum tube appears to be soldered in place (as opposed to being pressed into a connector). Is that how these came from the factory?

Any thoughts on what may be wrong, or how I could try to troubleshoot this? Would Alembic do a repair if I send it to the factory?

THANKS for any advice.

[gtrguy]

I think it should be in a tube socket. You can plug it in with the top off and see if it glows.

[Thomasio]

The tube is in a tube socket, but appears to be soldered in to the tube socket as opposed to just pressed in. I'm wondering if this is something the factory did. (Or, it is possible I am misunderstanding what I am looking at... but normally it is easy to remove a tube, this one does not budge.)

[jazzyvee]

If it is the same as mine i had problems getting the tube out until i found that the sleeve is in two parts with the top half needing to be slid down to expose the top of the tube. Once I did that the tube pulled out easy. phew.

[Thomasio]

That may be what I am seeing. I'll take another look, thank you.

[Thomasio]

Thank you for the suggestion. The metal cylinder slides back which releases the vacuum tube.

I verified that the vacuum tube is fully seated. No change in the direct output (still nothing).

Everything else functions great and sounds fine, just no output at the XLR.

Any ideas?

[JimmyJ]

Hey Thomas,

The first thing to do is exercise that "Pre" and "Post" switch near the XLR about 50 times.  It's self-cleaning and might need to be - woken up.  The next thing to try is exercising the Effects Loop "Return" jack on the rear panel = plug and un-plug a few times.  Sending a signal into that "Return" jack and having the front panel switch set to "Pre" should work like a simple passive DI box.  You could even try connecting a 1/4" cable from the Effects Loop "out" to the "return" and see if that does anything.  Just some ideas.

Jimmy J

[gtrguy]

Might be some dirty contacts on the jacks (inside the box). Some have sets of 'points' like an old time car. I will also use a 9mm gun cleaning brass brush on the jacks from the outside just to make sure where they contact the guitar cables is clean.

[Thomasio]

Great suggestions, I'll give those a try tonight.

ThAnK yOu!

[Thomasio]

Update - I exercised the switches, no change. Also said the effects loop cables in and out several times, no change. Still zero output from the 3 pin direct out.

[gtrguy]

Does the tube look normal? Do the heaters glow evenly? Do you have another tube to try out?

[Thomasio]

I'll try swapping the tube next.

[StephenR]

Not sure if this will help you but here is the schematic for the F1-X. The forum I found it on said it was drawn by Ron W but no way for me to confirm.


I know nothing about electronics but if everything else works as expected I doubt that the tube has anything directly to do with the output from the D.I. Maybe that can be determined from the schematic?

[JimmyJ]

... Everything else functions great and sounds fine, just no output at the XLR.

So there's no sense in changing the tubes or pursuing anything else deeper into the circuit if all is working EXCEPT the XLR out.  This almost has to be something you can see. 

The diagram (which does look like could be Ron's handwriting) shows "point A" on the return jack of the Effects Loop.  The other side of "point A" is the Pre/Post switch in the "pre" position.  So with the switch in that position the signal comes straight from the "return" jack, into the transformer and out of the transformer to the XLR.  There is very little that can go wrong with that simple circuit path.  If you've got the lid off, visually inspect the wire from the "return" jack to the Pre/Post switch, the wire from that switch to the transformer, the other transformer leads which connect to ground and the XLR, and that's all that is involved.

Tell us, what are you connecting that XLR to which is not showing any input?  The input of a mixing board or an external mic pre?  Have you tried another mic cable?

We'll figure this out!
Jimmy J

[Thomasio]

Thanks Jimmy. Everything looks perfect under inside the chassis.

I’m using the XLR out to go into my RCF mixer. I’m getting zero signal from the XLR.

I made sure each of the connectors was fully seated while I was inside the the chassis.

I’ve tried other XLR cables.

I’m out of ideas.