Preamp Studio Projects VTB-1 - No signal, only hum.

[tempus]

Sorry then, I misunderstood earlier.

Looking at the 7812 problem, we can see that D8 should have more than 11.2v on it since it's feeding the input of the 7812. Not sure how we're going to address that at this point, but it's something to keep in mind. Can you verify the remaining connections at the diodes (esp. that purple ?). You can trace the connections by using your meter set for resistance. Put one probe on the + end of D6 and the other probe at the - end of D5. If they're connected, they should read 0 ohms (or close to it).

[stonerbox]

Hey man, I'm sorry for being a bit foggy in the first place, if that is grammatically correct to put it? But you'll probably get my point.

Great idea Tempus, why didn't I think of that.   I'll check right away...

D5 and D6 is connected, meter does not show any sign of drop in resistance.

[tempus]

Ya that makes it a lot easier to trace things. Thanks for the clarification on the diodes. The more of the schem we have the easier it'll be to troubleshoot.

Another thought came to mind: again, I'm no tube expert, but I would think that the 90v (if it is here somewhere) would be applied to the tube's plate. Since the 12AX7 is a dual triode, there will be 2 of them, on pins 1 and 6. So, if we're looking for 90v, it'll likely be on those 2 pins. Remember, I don't know this for sure, so use it as a guideline for now.
Also, when tracing with the meter, make sure that the power is off on the preamp. You can't use the ohmmeter with voltage applied.

[duck_arse]

orrright, I've been scratching around in my confusion, but some things are a bit clearer, rereading the whole thread helped.

the geezer that designed this says it has a starved plate 12ax7 at 90V, and the specs say 12V AC power supply, so it follows that there is a fair bit of doubling going on with all the diodes. so, yes, there should be 90V dc appearing somewhere between the diodes and the valve, if all the diodes are good. 90V would indicate that the supply is working and it is something attached to it that has gone wrong. does your meter have a "diode test" setting?

studio products ought to be shot if they are putting 100V caps on 90V supplies, and should be shot anyway for their total lack of support ie a circuit diagram.

[stonerbox]

Ya that makes it a lot easier to trace things. Thanks for the clarification on the diodes. The more of the schem we have the easier it'll be to troubleshoot.

Another thought came to mind: again, I'm no tube expert, but I would think that the 90v (if it is here somewhere) would be applied to the tube's plate. Since the 12AX7 is a dual triode, there will be 2 of them, on pins 1 and 6. So, if we're looking for 90v, it'll likely be on those 2 pins. Remember, I don't know this for sure, so use it as a guideline for now.
Also, when tracing with the meter, make sure that the power is off on the preamp. You can't use the ohmmeter with voltage applied.

Hey man no probs! I'm working like crazy on the layout, I am hopeful to have it ready tomorow.  

Ok, I'll check the tube pins every now and then from here on. As for right now, the tube pins have these voltages:
1. 18.5v
2. 0v
3. 0v
4. 8.5v
5. 0v
6. 49v
7. 18.5v
8. 19.5v
9. 4v.

Another question arose last night when I came across some "cross-like" connection points on the circuit board . I wonder how these are connected, in relations to each other. I marked three examples in the picture. Could it be possible that these are connected to each other?
/confused  

[stonerbox]

orrright, I've been scratching around in my confusion, but some things are a bit clearer, rereading the whole thread helped.

the geezer that designed this says it has a starved plate 12ax7 at 90V, and the specs say 12V AC power supply, so it follows that there is a fair bit of doubling going on with all the diodes. so, yes, there should be 90V dc appearing somewhere between the diodes and the valve, if all the diodes are good. 90V would indicate that the supply is working and it is something attached to it that has gone wrong. does your meter have a "diode test" setting?

studio products ought to be shot if they are putting 100V caps on 90V supplies, and should be shot anyway for their total lack of support ie a circuit diagram.

Yeah, Studio Projects are f-cking cheap bastards.

My inherited and tiered analog meter does unfortunately not have a diode setting, but I did a simple resistance check on them two days back. No read through negative side, only on positive.

[tempus]

Did you test these points with your meter? Also, have you tried swapping out the tube to see if that's the problem?
In your scem, have you accounted for all the caps connected to all the diodes? If we can get that part complete, and verified with the meter, I think I can redraw the voltage multiplication section and we can get a better idea of what voltages we should be seeing.

[slacker]

Another question arose last night when I came across some "cross-like" connection points on the circuit board . I wonder how these are connected, in relations to each other. I marked three examples in the picture. Could it be possible that these are connected to each other?
/confused 

Yes those are all connected together. It's what's called a ground plane, basically instead of have lots of individual traces that are ground you have big areas of the board that are connected to ground and when you want to connect a component to ground you connect them to that. The crosses make it easier to solder to, if you had the whole of the solder pad connected to the ground place then when you tried to solder to it your iron is trying to heat up all that copper meaning you either need more heat or you need to leave the iron there for longer both of which could damage components. The crosses mean the pad is only connected to the ground plane by a few thin tracks meaning the heat doesn't spread into the ground plane as much.

[stonerbox]

If I check the tube pins with my meter? If so, then yes!

I'm not sure I follow you on "accounted all the caps.." If they all are in place with the correct values, then yes!  
I tried changing the tube but without any notable changes.

This is how the "clean" HiZ input sound like..  
https://soundcloud.com/tropicalhippo/things-are-starving-vtb-1-di

D4
Positive: 0dcv/acv
Negative: 13+dcv
D5
Positive: 11.9+dcv
Negative: 22.5+dcv
D6
Positive: 22.5+dcv
Negative: 34.8+dcv
D7
Positive: 34.8+dcv
Negative: 46.8+dcv

D8
Positive: 12.5+acv / 0dcv
Negative: 10.2+dcv
D9
Positive: 11.5-dcv (-NEGATIVE READ-)
Negative: 11.8+acv / 0dcv
D10
Positive: 12+acv / 0dcv
Negative: 11.2+dcv

Here is a slightly update beta layout. The power part (top/left) should be 100%. Keep in mind that the diode values are outdated in this layout.

[duck_arse]

Tube Stage : 12AX7 vacuum tube with DC filament supply for minimum
hum and noise. 1st half of tube is operated as a high gain amplifier
stage, 2nd half operates as a cathode follower to minimize loading
of the first stage. A low-voltage plate supply is used to create a
"starved-tube" condition for enhanced sound.

from the manual.

I don't think your heater voltages look right, shouldn't they be 6-0-6 or 12-0?

[stonerbox]

Slacker, thanks! It makes defiantly sense.

Duck_arse, I haven't a clue..

[stonerbox]

This is escalating pretty fast into a studioprojects-cluster@#$%-sh*tstorm-of-the-century..

[tempus]

I concur with the voltages we should be seeing on the heaters. Also, we need to check the 2 5v regulators. Can you remove them and check them in a trial circuit (i.e., put 12v on the input of the 7805 and see if you get 5v on the output, and the same only negative with the 7905)?
If the 7905 is functioning properly, there should be a steady -5v on the output with -12.5v on the input - same goes for the 7805.

[stonerbox]

I'll try it!

Just checked the L7812CV (the large one) and got a 5v drop on the output pin, broken.

[stonerbox]

..and -12v on the -out of 7905, definently broken.

The meter reads a 2.5v drop on the output of the 7805, broken. YAY! PRAISED BE THY HOLY PROGRESS!

EDIT: hold on, the 7905 is a 7915 must have read it wrong when it was on the crowed board.

[tempus]

The question is why are they broken. These are usually fairly robust parts. Did you take them out of the circuit to test them? Also, what do you mean by 2.5v drop and 5v drop? Also, can you check C33 and 34 to make sure they aren't shorted?

[stonerbox]

Yes, did check them outside of the circuit. When I feed the voltage regulators with +12v (input) the output reads +7v or +9.5V (5v and 2.5v "drops"). Gonna check those caps asap.

[tempus]

I see now. Ya a 12v regulator means just that - you feed it with something more than 12v, and it puts out 12v and only 12v. If the 7905 is actually a 7915, it may be OK, since there's only -11.5 at the input. Can you try it with something like -20v to test? And what about the 7805, is it actually a 7805 or is it 7815 as well?

[stonerbox]

The 7805 is 100% correct. It's getting really late here, got to sleep.

[stonerbox]

Had to have a yesterday off from this thing, to keep sanity intact.

Today I order a bunch of new diodes, zeners, neg- and pos-voltage regulators, transistors, a 339n and some hi-quality op amps. So.. tomorrow the fun begins again.