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That”s great to hear that everything is working well for you. Let me know if you have any more questions.
Most metal film resistors (usually blue in color) are specified to be within 1% tolerance of the given value. This is indicated by the brown stripe at the end of the colored bands. If you are using carbon film resistors (usually tan in color), they are usually 5% tolerance, indicated by the gold stripe at the end of the colored bands. If all you have is 5% resistors then you could hand match them. In practicality it’s really not that big of deal with the Cortado in your application. The weakest link in the chain by far will be how well you couple the disc to the floor boards. The audio fidelity of the system mostly hinges on that.
Attached is a circuit that I just drew up. It shows you how you could use your external power supply as phantom power for the Cortado. As you can see, pins 2 and 3 of the XLR jack are used for both signal and phantom power. The signal (an ac voltage) is superimposed on the DC phantom power. The signal is the separated from the DC via the two 47uF/63V capacitors. Make sure they are rated for a voltage higher than your phantom power. The XLR pins (2 and 3) are separated from each other via the two 6.8K resistors. The two 100K resistors are to give the caps a place to drain when nothing is plugged into the XLR cable. You may need to increase the value of these (to has high as 1M) if the Cortado has a hard time driving the signal past them (ie the output signal is lower than you want). Let me know if you need more explanation or if you have other questions.
It’s no problem. I like helping people get their products working right.
Here’s another edited photo that you sent me earlier…just to illustrate these points…
If it’s sparking, the sparks have to be going somewhere…usually a black spot on the board. Can you find out where they are going? It would helpful if you could try to take a couple more close up pics of R15, both sides of the board. Maybe i could see something.
The via isn’t a soldering point, just a tiny hole through the pcb with no blue solder mask on top of it, so they are easy to accidentally bridge solder to if it overhangs the pad much.
To answer your questions from earlier…
It might not be destroyed…resistors are often more resilient that we think. Measure it and see if it’s still close to 220 ohms. It’s a 220 ohm, 1/2W, 1% tolerance metal film resistor…but you can use any tolerance and type of resistor, as long as it’s 220 ohms and at least 1/2W.
It’s never good when the resistors glow. It means there is too much current going though it. How is it sparking? My guess is that it’s glowing because it’s sparking and not drawing current elsewhere. Does it still spark with the tube removed? Sparking is an indication that it’s shorted (to ground) somewhere, possibly the via between C10, C9, and one of the pads of R15. Make sure you only have enough solder on the resistor pads that you need, and it’s not spilling over to the copper ground plane (or vias) around the pads. It might help to use some electronics flux (not plumbers flux) to clean up your solder joints if necessary. If you can’t see anything obvious from the top side of the board, then you’ll have to take it out and look for shorts on the solder side. Look for black burn marks on the PCB where it was sparking as an indication of where the shot is. Try to refrain from turning it on until you think you’ve found and fixed the problem, otherwise you might blow the fuse.
Let me know what you find.
Thanks for pictures. I edited one of them for reference here…
You say that you have ~120VAC across pads A and B.
Are you getting no voltage across pads C and D?…I’m assuming you get no voltage.
Please test the AC voltage across pads A and D…you should have ~120V with the power switch on, is this correct?
Assuming you don’t have voltage across C and D, the trace from pad C to B must be broken.
With the IEC power cable unplugged and power switch off test for continuity between C and B. They should be connected, but if they are not then the trace is broken. If this is the problem then you need to jump those 2 pads together with some thick wire…use about 1/4″ of the extra transformer wire that you cut off…tin it first and remove the insulation.
Upon closer look at the photo, please add a little more solder to pad B and re-flow that joint. Make sure the wire is making good connection to the pad. Do this first, to make sure that is not the problem.
Keep me posted.
Thanks. I’ll be looking for the pictures.
Are you getting 120ish volts at the board, though (not at the jack)? I just want to be sure the problem is at the transformer input, not another place on the board.
That makes since. It seems that the power transformer isn’t getting any voltage…probably because of the damaged pad. Would it be possible to send me some photos of the board where the pad got damaged? If you can’t attach them to the forum post then email them to me…brach “at” zeppelindesignlabs “dot” com
Just to make sure…are you getting ~120vac at P5 (where the wires come in from the IEC jack)?
We’ll get this fixed.
If the trace from that pad broke then that would explain why you are not getting any voltage on most of the test points. See if you can make that repair and let me know the results. If you want any help or tips on that process let me know.
This Brach, the electrical designer here at ZDL.
I’m curious what voltage reading you are getting from your power transformer. What AC voltage do you get across the brown wires coming from the power transformer (not from ground, but across the wires)? What AC voltage do you get across the Red wires? What DC voltage do you get at testpont 1 (from ground)?…If you get nothing, are the bridge rectifiers (BR1, BR2) in the correct orientation?
The good thing is, the amp works…it’s got the correct voltages in the correct spots. The problem is some of the signal isn’t making it through somehow to the output. If I understand you correctly, every time you re-flow/re-solder some stuff on the board the amp gets louder. To me, that’s a sign that there’s some sort of connection issue…most likely it’s something that’s not making a good connection somewhere (as opposed to a short)….only letting a bit of the signal through. If you are at all un-confident about the solder joints then please check them again…look very closely at each joint. I know it’s a pain, but that seems to be what all signs are pointing toward.
Just checking, you are using an 8 ohm speaker, correct?
If all the tube voltages are correct then the tube is working correctly. Besides that, we test every tube before we send it out, so there’s very little chance that it’s a tube problem. Vacuum tubes contain a bunch of tiny parts, very close together, so often times they do rattle when they are shaken vigorously…unless you are talking about loose parts in the tube, but if that’s the case then it most likely wouldn’t have the correct voltages on the tube pins because something wouldn’t be making a connection in the tube.
Thanks for verifying that you tightened the tube socket pins. If you are pretty sure all the tube pins are making good connection then you don’t have to keep trying to tighten them. I just know in the past these symptoms have been caused by that.
You’ve probably already done this, but I wouldn’t hurt to double check the values of resistors in the signal path to make sure they are correct.
Please keep me posted with how things are going.
The fact that re-flowing the resistors from the top side changed something, tells me that you had another bad solder joint somewhere. Since your Percolator still isn’t working properly it makes me think that there is another bad solder joint somewhere. You may be at the point of taking the board out of the chassis again and reflowing all the joints and double checking for solder bridges (shorts).
Have you tightened the tube socket yet? If so, did you tighten the socket and re-flow the solder joints in the same step, or did you test the amp between each of those steps? I’m just wondering if it might have been fixed when you tightened the tube socket, but you didn’t notice it. If that might have been the issue or part of it then gently re-tighten the socket again…if that works it will keep you from having to remove the board from the chassis. When tightening the sockets focus on pins 3, 6, and 11 (next to R1, R6, and R11)…these are the grid pins. The “grid” is where the signal comes into the tube stage. If you have correct voltages on the other pins then it’s most likely that the signal is not making good connection to one of these pins…if it’s the tube socket at all.
I don’t know if you have one, but it really helps to get one of those solder sucker tools to remove the solder from the holes after you remove the wires. They are very helpful in putting the board back after you remove it and removing excess solder from around the pads if you have any big solder globs anywhere.
We are really close. Keep persevering!
Good luck and keep in touch.
The fact that all the tube voltages are correct is a good sign that the tube circuitry is functioning properly. The first thing to do is to tighten the tube socket. To do this you just need to get some sort of sharp, pointy tool and gently pry the tube socket contacts closer together to help them grip the tube pins better. Sometimes they get spread a little to far apart in the “loosening the tube socket” step, and they don’t make good contact with the tube pins.
If this doesn’t work then you probably need to re-flow (re-solder) the solder joints again. I know it’s a pain, but the fact that you had one bad solder joint is a sign that other’s could be bad as well. At first, just re-flow the resistors from the top (component side) of the board so you don’t have to take out the PCB. If that doesn’t work then you’ll have to take out the board and check really closely for solder bridges (shorts) and re-flow the capacitors and other components that you weren’t able to get to from the top of the board.
You really shouldn’t turn on your amp without a load (speaker) attached. It’s really bad for the tube. So make sure the speaker is plugged in when you test it. It’s not uncommon for properly working tube amps to behave like that when they don’t have the speaker plugged in…so i’m not worried about the buzzing with no load. The problem is that the signal is not making it through somehow. We’ll get it sorted out one way or another.