"SHAKA TUBE" - almost working ??

[puretube]

http://diystompboxes.com/sboxforum/viewtopic.php?t=35100&start=15

[Paul Marossy]

I know for a fact that my power supply layout works. It's the opamp PCB that may have a problem. I don't know for sure, though.

[puretube]

imho ,it`s the offboard wiring between the 2 PCBs (no ground reference).

[transient]

It probably shouldn't make a difference, but i left the pins 5,6,7 of the opamp (tl072) unconnected on my working ShakaT.

...
emre

[Paul Marossy]

imho ,it`s the offboard wiring between the 2 PCBs (no ground reference).

Sounds like a strong possibility.

[aron]

Yes, Paul I didn't mean "the" layout, I meant their particular layout. You never know if there's a solder bridge or broken connection... Puretube could be right. It could be a simple missing ground.

[Paul Marossy]

Yes, Paul I didn't mean "the" layout, I meant their particular layout. You never know if there's a solder bridge or broken connection... Puretube could be right. It could be a simple missing ground.

Thanks Aron, I'm not getting defensive - I'm just trying to get to the bottom of the issue.  :wink:

[puretube]

aron (and those who missed the other thread):
http://diystompboxes.com/sboxforum/viewtopic.php?t=35100&start=15

in markr04`s case, that was it...

[aron]

show off  :lol:

[MartyMart]

http://diystompboxes.com/sboxforum/viewtopic.php?p=246248&highlight=#246248

I'm posting in both places now  :roll:
I did ask about "grounding both boards" yesterday, its in the link above.

..... SO .....
I now have both boards grounded together and have NO SIGNAL AT ALL
.. !!! ++ ****  ETC

Tried a "new" TL071 just in case the other two were damaged .. no go

So what is going on here ... ?
Very strange behaviour, the ground connection has made things much
worse ...
Thanks chaps,

Marty.

[puretube]

SCHEMO
PCBs
just to see what`s the fuss all about  :wink:

Circuit boards built as per Pauls layout, but on vero.

mmmhh...

btw, what voltage rating do (did?) your PSU caps have?

For around 10 seconds ( while I got my meter on it ) I had 15.7 volts
going to the board/valve !!

what is "board" here? (Pauls layout has 2 boards);
no matter if it was 12 or 15.7... did/does it show "+12V DC" and "-12V DC" (or ~15) simultaneously, measured from the "V+" and "V-" to "IN GND" respectively (as per Paul`s layout), while it showed 12 or 15.7V AC at the pins of the tube at the same time?

[MartyMart]

Ton, Hi .... OK I'll clear up  a little - sorry if I've been "sketchy" and not
provided enough information :

2 x Boards, power and op-amp i/o  I followed the schemo/layout quite
closely, ie: all the "nodes" check fine, there's no errors or "mis-wires" or
solder bridges.
It means that my vero version is 90% the SAME layout as Pauls is.

I'm using a Peavey 16.5 volt AC adaptor ( no it's not DC !)
Unloaded it measures 18.3 volts AC, so I have a tiny "extra board" with a
680 Ohm 1 watt resistor on it.
Other side of this resistor is now 12 volts AC  :-)
This connects to the "power board" 12v in, which links to the tube pin 4
all other pin/board/pot connections are fine and seem to work correctly.

The Power board caps are all 470uf 16 volt - they are recieving 12v so
should be fine right ? ... or the  + & - voltage to the op amp board means
they should be rated higher ??
The ONLY point that shows 24.1 volts, is pin 7 of the opamp ..!
So I seem to have +12 and -12 working correctly ( V+ & V- )

The 22uf caps on the opamp board to the tube are also 16v
The 2.2uf to ground is a 35 volt

The "Grounding both boards" did not work ... however this does :

Extra lead from "power ground" is now "floating" so if I play gtr, with this
"floating" lead between my bare "toes"  it works fine after a couple of
seconds of "st  st  st  stuttering" ......  ?? so there is a "ground" issue, but
not a "direct between the boards"   issue    .. Now I need to understand
why my "Toes" are causing this to work !!

Regards,
Marty.

[puretube]

"pin7 24.1V" measured against which reference point? ground?

btw: V+ should be +12V DC against tube-pin5;*
V- should be -12V DC against tube-pin5;
tube-pin4 should be 12V AC against tube-pin5;

*and all those little triangles pointing down in Aron`s schemo.
(This IS ground!... V- is not! );

V+ should be at the PS+pin of the IC;
V- should be at the PS-pin of the IC;


I was afraid, that before you put in the series resistor, the voltage might have been too high for the caps/IC...

ps: the bias trimpot probably (?) is best set close to V-

[puretube]

BTW: a general thought:
add a pulldown resistor (1M) on the "outside" of the input-cap...


I wonder how the behaviour (sound/gain) of the circuit changes, :

when you put a bleeder cap (0.1µ) between biastrimpot-wiper and GND;

And/or increase the 10k resistors between wiper and the respective grids
to 100k or more;

combine both mods;

[MartyMart]

"pin7 24.1V" measured against which reference point? ground?

<< yes measured against input/output ground >>

btw: V+ should be +12V DC against tube-pin5;*
V- should be -12V DC against tube-pin5;
tube-pin4 should be 12V AC against tube-pin5;

<< yes correct >>

*and all those little triangles pointing down in Aron`s schemo.
(This IS ground!... V- is not! );

<< yes "of course" !! I know what a "little triangle pointing down" means  !!! >>

V+ should be at the PS+pin of the IC;   << yes pin 7 >>
V- should be at the PS-pin of the IC;     << yes pin 4 >>


I was afraid, that before you put in the series resistor, the voltage might have been too high for the caps/IC...

<< possibly, but nothing "blew up" and the circuit "can work" normally
when I use my toe !!  I've replaced the ic anyway with no change >>

ps: the bias trimpot probably (?) is best set close to V-

Thanks Ton, still got my "thinking cap" on   :wink:

Marty.

[MartyMart]

BTW: a general thought:
add a pulldown resistor (1M) on the "outside" of the input-cap...


I wonder how the behaviour (sound/gain) of the circuit changes, :

when you put a bleeder cap (0.1µ) between biastrimpot-wiper and GND;

And/or increase the 10k resistors between wiper and the respective grids
to 100k or more;

combine both mods;

I've had a 1M "pulldown resistor" there from the start
The "gain" control doesn't seem to do anything, its just a general "mild"
overdrive ( nice BTW ) without "cleaning up" or getting "dirtier" - moving
the gain pot just brings on the "stuttering/Splatty" sound .....?
But that is intermittent anyway, so hard to tell until we solve the problem
the pot is wired correctly .....
It looks like a "ground" issue ......  :roll:  ??

Marty.

[puretube]

BINGO:

"pin7 24.1V" measured against which reference point? ground?

<< yes measured against input/output ground >>

should be half of 24.1V versus ground (24.1V only against IC`s V-);

You got a Power-Supply/ground flaw...

What I do in such cases: forget the schems and layouts for a while,
and redraw a schem by re-tracing/tracking the actual build wire by wire...

and then: compare! (to the original schem).



sorry - gotta go outside into the sun...
SUCCESS!

[MartyMart]

BINGO:

"pin7 24.1V" measured against which reference point? ground?

<< yes measured against input/output ground >>

should be half of 24.1V versus ground (24.1V only against IC`s V-);

You got a Power-Supply/ground flaw...

What I do in such cases: forget the schems and layouts for a while,
and redraw a schem by re-tracing/tracking the actual build wire by wire...

and then: compare! (to the original schem).



sorry - gotta go outside into the sun...
SUCCESS!

OK catch you later, that was an "AC" value against power "ground"
"DC" reads 12v against ground and -12v against ground for pin 4

Thanks Ton.

[Paul Marossy]

Just a quick question MartyMart, you do have Pin 4 of the opamp connected to V-, right?

Unfortunately, I'm going to be out of town for the next three days, so I probably won't be able to keep up on this during that time. I'll try to find a computer somewhere and check in if I can. I hope you get it straightened out!

[MartyMart]

Just a quick question MartyMart, you do have Pin 4 of the opamp connected to V-, right?

Unfortunately, I'm going to be out of town for the next three days, so I probably won't be able to keep up on this during that time. I'll try to find a computer somewhere and check in if I can. I hope you get it straightened out!

Yes thats correct.
I had one connection in the 4x470uf's that didn't seem right, on the middle
connection both + & - were connected together, they actualy do connect at
the left side of the cluster to ground, so it looked "circular" to me, however it
made no difference at all .....
Just ran down the power a bit more to 10.5 volts entering power board
and tube, that seems even more prone to "splattyness" ... !!
I also tried another PSU - 16.5 volts AC and 1.2 amps ... NADA ....

I dont know what to do, the only "working" fix is to ground the power
board to me !!
Gain pot still has zero effect -  other than making the circuit more
splatty than before .  :cry:

M.