So, story so far :
Circuit boards built as per Pauls layout, but on vero.
Thank you very much Aron/Paul BTW :D
Subs:
The 50k resistor (?) is a 47k
The input cap is a 0.047
Tone pot is a 50k
The AC PSU was giving me 18.5 volts ( no load )
I used an "in-line" 680 Ohm 1 watt resistor, giving me exactly 12 volts !
For around 10 seconds ( while I got my meter on it ) I had 15.7 volts
going to the board/valve !!
So:
With the "gain" at 100% I have a nice "medium crunch" overdrive :-)
Tone/gain/vol pots are working, the power board trimmer is set at half
resistance and doesnt seem to make a difference.
With the gain set to anything lower than 3/4, I get a "square wave" very
nasty distortion with signal "cutting in/out" all the time, like a very
"splatty" badly biased transistor circuit would sound, but worse !!
Ideas ?
Did I "screw" the 12AX7 ??
Thanks, as I said "almost there" !!
Marty.
I doubt you've damaged the tube, if it is lighting, and relatively 'new' it's almost certainly 'good'.
The easiest way I know of to test a tube in a known working circuit is to compare it with a known good tube...
You didn't mix up Pins 6 & 8 on the tube, did you? They're kind of obscured on my layout. Maybe that is the problem?
Quote from: Paul MarossyYou didn't mix up Pins 6 & 8 on the tube, did you? They're kind of obscured on my layout. Maybe that is the problem?
AHA !!
...... NO, i spotted that one, my connections are right unless I have the
whole thing reversed..... but that would not work at all !!
Just popped in a brand new 12AX7 and its the same .... there's an awful
"cut out" going on along with this very "square wave" sound.... almost
a "digital" sounding thing .. wierd unless its the PSU cutting out, or
not supplying correctly via that 680 Ohm resistor .. ??
It happens even at max pot rotation, but is worse lower down, seems
like I can't get a "cleaner" gain setting at all ..
Damm, so close ! :x
Marty.
Well, I guess this is not going to be a simple fix. :?
OK, well, what power supply are you using? I am using a 13VAC 800mA wall wart with mine.
From what you've described, you have the same problem I do. If so, it's not the tube, but the opamp.
http://www.diystompboxes.com/sboxforum/viewtopic.php?t=35100
I have an unconfirmed suspicion that this circuit is sensitive to the opamp. The original schematic is using 1/2 of a TL072, and my layout uses a TL071. All I can think of is that this somehow affects the operation of the opamp, I don't know how, but it seems to be the case....
EDIT: Can one of you guys try to wire it up using 1/2 of a TL072 instead and see what happens?
EDIT #2: I etched my PCB per the layout I have on my Shaka Tube page, but when I built mine, I modified it for use with 1/2 of a TL072. Mine works, and you guys seem to have problems getting yours to work. There might be something here.
Mark04, thats interesting, it DOES sound like we have the exact same problem......
OK, my vero layout is a little "tight" for re-arranging with a TL072.. so
how about some other "single" op-amps.. NE5534/LM741/TL070 I have.??
One "extra" component I used a 1M pull down resistor right at the input
before my 0.047 cap
Marty.
MartyMart-
Try all of those single opamps and see what happens. Maybe this is a case where the actual opamp used will make a noticeable difference. That 1M resistor to ground at the input shouldn't mess things up at all.
OK:
NE5534ap - just farts a lot
LM741 - farts very quietly !
TL070 - farts very quietly
Another TL071 - Same as original - occasional "Eureka" followed by lots
of "farts" :cry:
Do we need a resistor "into" pin 3 here ... like a 1k5 or something ??
EDIT : It's such a shame, when I get the minute of "working" sound it's
really wonderful, in particular with the new Marshall ECC83 valve :-)
EDIT2 : I dont understand how 1/2 a TL072 would be any different ??
Marty.
its pretty hard to damage a 12ax7... hmm... maybe try building the 'diode comp. opamp' for this one?
thats what i was planning on doing for my shaka tube. with everybody talking about it, i just had to start building one... :lol:
too many things on the go for me... heheh
QuoteDo we need a resistor "into" pin 3 here ... like a 1k5 or something ??
Worth a try, I guess.
QuoteI dont understand how 1/2 a TL072 would be any different ??
This is my quandry as well. There must be some kind of difference between the two of them, otherwise we wouldn't be having this discussion. :wink:
Hmm, just thinking through some "similar" circuits .. the "Rat" for instance, has a 1k resitor before pin 3 and also some voltage coming
down from a 1M resistor from 4.5 volts to the input ....
I may try this and see if we can "kick" the input a little
BTW what's the purpose of the 470k to ground right before pin 3 ?
Marty.
http://diystompboxes.com/sboxforum/viewtopic.php?t=35100&postdays=0&postorder=asc&start=0
there has been another PS problem with this circuit here, lately...
QuoteBTW what's the purpose of the 470k to ground right before pin 3 ?
I'm guessing that it's to set the input impedance. Maybe adjusting this resistor value might have some effect on the gating problem as well.
that`s the bias resistor to centre on 0V, while the opamp worx on +/- something...
Quote from: puretubethat`s the bias resistor to centre on 0V, while the opamp worx on +/- something...
OK, that makes sense. I am a little ignorant about opamps running on a dual power supply. :oops:
Quote from: puretubethat`s the bias resistor to centre on 0V, while the opamp worx on +/- something...
OK, could we have found the problem ?
How about a 500k trimmer here..... perhaps its not 0 volts ?
Marty.
Marty, take a look at the opamp thread. I played with values here and got no further.
But maybe it needs to be specific as only a trimpot can be?
It must be some sort of weird problem with the layout or power supply layout.
There's nothing special about the front end of this circuit.
http://diystompboxes.com/sboxforum/viewtopic.php?t=35100&start=15
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.
imho ,it`s the offboard wiring between the 2 PCBs (no ground reference).
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
Quote from: puretubeimho ,it`s the offboard wiring between the 2 PCBs (no ground reference).
Sounds like a strong possibility.
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.
Quote from: aronYes, 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:
:D
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...
show off :lol:
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.
SCHEMO (http://www.diystompboxes.com/pedals/schems/shakatube.gif)
PCBs (http://www.diyguitarist.com/PDF_Files/ShTube1590BB-PCB.pdf)
just to see what`s the fuss all about :wink:
QuoteCircuit boards built as per Pauls layout, but on vero.
mmmhh...
btw, what voltage rating do (did?) your PSU caps have?
QuoteFor 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?
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.
"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-
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;
:P
Quote from: puretube"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.
Quote from: puretubeBTW: 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;
:P
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.
BINGO:
Quote"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!
Quote from: puretubeBINGO:
Quote"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.
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!
Quote from: Paul MarossyJust 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.
Any progress MartyMart? I'm a hotel called Ayres in Los Angeles today, they have a computer, so I thought I'd check in... 8)
MartyMart,
Just a hunch... try a 10K resistor between the audio board ground and the AC "ground". It cleared up this problem for me.
(http://img.photobucket.com/albums/v442/lectronix/SH.jpg)
does this look like your build?
additionally to the components in my PSU schem:
GND (0V) is connected to inputjack-sleeve, outputjack-sleeve, chassis.
GND (0V) also goes to:
2µ2 cap;
470k res;
0.01µ cap;
10k vol-pot.
in Aron`s schemo - nowhere else.
and also:
the IC`s powersupply pins go:
pin4 to V- ;
pin7 to V+ if using a TL071 only (single opamp);
OR:
(pin8 to V+ if using a TL072 only (dual opamp));
pin2 is neg. input;
pin3 is pos. input;
pin6 is output for TL071 only;
OR:
(pin1 is output for TL072 only);
all other pins: not connected anywhere.
(if in doubt, compare pinout from this 900kB pdf file:
TL071/72/74 (http://focus.ti.com/lit/ds/symlink/tl072.pdf))
when this all applies point for point to your build,
please explain, where your 680 Ohm inline-resistor is situated,
when you would draw it into my schem...
[EDIT] R3 in my schem (above) should read 1k instead of 470R!
(for the rest, it corresponds exactly Aron`s schem, viewed "european style".
Ton.
That's EXACTLY what I have here !!
All other pin connections are also correct for TL071
The 680 Ohm resistor is in line with the PSU BEFORE it hits the board
top far left :
PSU centre pin --> 680 Ohm 1 watt --> power board/tube pin 4
PSU barrel ---> power board Ground/tube pin 5
AC value hitting the power board 10 Ohm 1 watt connection 12v
Op amp pin 7 +12v DC
Op amp pin 4 -12v DC
Connecting power ground to opamp board/jacks ground produces NO output
at all ..... SILENCE !!
Thanks,
Marty.
so that would be inserted xactly where I marked "x" ?
while the transformer is 16V instead of 12V.
in that case you only have ~ 1.7V AC across the filaments (tubepins4/5)...
[16V:(680+80)Ohm]x80 Ohm = 1.7V;
>those 80 Ohm is the filament (heater) resistance<
and I wonder how those 1.7V rectified come out as +/- 12V ???
Be sure of measuring V+ and V- against GND in DC-mode!
and measuring ONLY tubepins 4 and 5 against each other in AC mode!
the tube won`t lite up clearly visible with 1.7V...
you probably had measured the V+/- against the AC GND at the xfmr,
before you had the connection of all grounds completed.
The right value for the input-inline-series resistor ought to be between 22 Ohm and 68 Ohm, to reduce 16V to 12V when loaded by the 150mA of the heaters, and the few mA of the plates and IC.
This R should be rated at least 1W (better: 2x1W parallell with appr. values; e.g. 2x 100 Ohm).
Quote from: puretubeso that would be inserted xactly where I marked "x" ?
while the transformer is 16V instead of 12V.
in that case you only have ~ 1.7V AC across the filaments (tubepins4/5)...
[16V:(680+80)Ohm]x80 Ohm = 1.7V;
>those 80 Ohm is the filament (heater) resistance<
and I wonder how those 1.7V rectified come out as +/- 12V ???
Be sure of measuring V+ and V- against GND in DC-mode!
and measuring ONLY tubepins 4 and 5 against each other in AC mode!
the tube won`t lite up clearly visible with 1.7V...
OK, interesting stuff :
The AC transformer ( Peavey ) is rated at 16.5 v AC, but supplies between 16 and 20 v AC. ( 1.2 amps max so it's quite muscle bound )
**** Unloaded it reads 18.4 v AC ****
It connects via the 2.1mm power socket to a tiny piece of perf, with the
680 ohm resistor on, then out via small lead to point "X"
At the "board" side of the 680 Ohm resistor, I read 12 v AC ..... unless by
your calculation, I have 1.2 volts ?? !!!
So ... to drop 18.4 volts to 12 volts, you are saying that a resistor between 50 and 80 Ohms is required ? ?
Cheers,
Marty.
Hmm ... this is making no sense now :?
I just tried 100 Ohm 1 watt between PSU and power board :
AC readings : 16.8 volts at the board/tube ref power board ground
DC readings : + 16.8 volts at op amp pin 7 ref ic board ground
- 16.8 volts at op amp pin 4 ref ic board ground
I guess the op/amp and tube could be dead now !!
Marty.
Calculation :
18.4 (volts) divided by 270 ( 100 ohm + 150 tube +20 ic board) = 0.0681481
0.0681481 X 170 = 11.58 volts
Correct ?
if xfmr stays at 18,4V when delivering 150mA for the heaters (which have a resistance of 80 Ohm),
a series-resistor of 43 Ohms is needed,
to bring down the voltage across the heaters to 12V.
(forget about the low consumption of the DC circuit for a moment...)
OK. 680 ohm resistor back in :
AC reading from tube pins 4 /5 ONLY ....... is at 12.4 volts !!
Circuit works again, when the "ground" between the boards is disconnected :? :? :shock:
It will intermittantly "cut out" but a "touch" on the floating board ground
cable ( still connected at power board end ) ... kicks it back to life !
My god this is so close to working now ?? grrrr
Marty.
either the tube`s filaments are broken, or connected by cold solder joints/broken wire,
or the meter needs a new battery.
What resistance do you measure between the naked tube`s pins4 & 5?
(tube taken out of socket)
What resistance do you measure (wallwart un-plugged / out of the circuit;
caps discharged) between the points in your build, from where the wires to the tube-heaters origin (tube in socket, now).
Disconnected tube, across pins 4&5 I have about 11.2 Ohms resistance
Disconnected psu and caps discharged :
Between the power boards 11.7 Ohm resistor and tube pin 4 I have 11.7
ohms reistance.
This is as close too the power board 10ohm/1 watt as i could get
between power board AC entrance point and tube pin 4 "0" resistance
Meter measuring a new 9 volt battery, gives me 9.26 volts DC, so seems
to be working !!
M.
how about disconnecting the wallwart again,
and measure the resistance across the leads of theof the 680 Ohm series-resistor?
68 Ohm?
[EDIT]: those ~12 Ohm for the tube is an OK value, when it`s cold...
will go up (to ~ 80 Ohm, when hot)
the only other cause for the strange behaviour is a mis-wiring,
i.e.: it doesn`t really look like Aron`s/my schemo... (IMHO).
:?: :shock:
Man, you are so close to getting this thing to work! :?
(http://img.photobucket.com/albums/v442/lectronix/SHakatuII.jpg)
RS is the inline series resistor (your 680 Ohm);
RH is the tube`s heaters nominal resistance;
On the left side you plug in the transformer,
the right side (dotted) UF goes to the diodes via a 10 Ohm resistor on the top-,
and is GND on the bottom-side...
my proposal comes from equations 1 & 2
(depending how much the xfmr voltage goes down, when loaded).
(I`m ignoring the current draw from the rest of the circuit, which I
calculate to be ~ 5mA)
Ton,
Thank you SO MUCH for going to all this trouble on my behalf, it is VERY
much appreciated :D
I promise you that I am making the correct and relevent AC/DC readings
I did check that 680 Ohm resistor and a few more from that batch and
can confirm that they DO read 680 ... not 68 !!
The meter is working correctly.
I've gone through both boards/schems/layouts with a finr tooth comb and
can find nothing "wrong" in the values/connections ....
As I said yesterday, I have the circuit almost "working" now, the gain/tone/volume controls behave normally and the circuit is producing a
healthy amount of level ...
It's just that the "cut off" and seemingly "rail to rail" stuttering continues
but can be "fixed" by a connection from the "power board" ground, to
MY SKIN ..... and whatever explination for resistance/ground that gives
seems to be the answer .
I realize that in comparison to your calculations for the voltage I should
have, it makes NO SENSE whatsoever ...! and I just dont have a reason
for that .
If I only had 1.9 volts at the tube, I'm presuming that I would not have
any "gain" nor a working "overdrive" circuit .. correct ?
I do now have approximately +12 and -12 volts where it needs to be and
I have 12.3 volts at pin 4 of the tube ref to pin 5/power board ground
I will try to connect the "grounds" again with some resistance, as this
seemed to solve Mark's problem, but so far, whenever I reconnect the
two boards ground rail, I loose all signal .. not even a "hum" remains !!
I know, its wierd and the more I think about it, the more it hurts my very tiny brain :D
Marty.
doesn`t the sound appear when you slowly turn the bias-trim in that last case?
is that "SKIN-connexion" ( :) ) while you`re holding/playing the guitar?
and: do you use a bypass-switching or directly guit>shaka>amp?
Quote from: puretubeis that "SKIN-connexion" ( :) ) while you`re holding/playing the guitar?
and: do you use a bypass-switching or directly guit>shaka>amp?
Yes,
Strumming guitar with fingers/toes holding the end of the power board
ground lead ( floating )
No switch as yet, just gtr --> circuit --> amp
The only other "grounded" components are :
1M pulldown resistor at input, 470k from pin 3, in/out jacks and lug 1 from the volume pot.
M
and the 2µ2 (schemo, top left), the 0.01µ tone-cap,
and the 4 big electrolytics in the PSU...
Quote from: puretubeand the 2µ2 (schemo, top left), the 0.01µ tone-cap,
and the 4 big electrolytics in the PSU...
... yes, yes and yes :D
Though the third "yes" would seem to still be "floating" apart from hitting
pin 5 on the tube ....
Give me a few minutes, while I warm up the "Iron" ... !!
M
**********EUREKA********** !!
.... almost !!
Well Marks 10k resistor to ground from the power board "does" make the
major problem of "cut outs" and "stutters" go away !! :D .... BUT ...
At the "clean" end of the gain pot, I have a good overall "level"
At the "dirty" end of the gain pot, I have a nice crunchy OD tone, but
around half the level .... ! ( there just had to be a down side eh !! )
Ton,
being the "tube meister" that you are .... what could cause this "drop" as
the gain is pushed ?
Your going to tell me about the voltage at the tube arn't you ??
"I swear by almighty god" that I have 11.7v AC at pin 4 ...: D
I'm almost smiling now ....
EDIT:
Just compared it to my SD-9 clone and there is around "double" the
overall volume from this circuit !
Marty.
I don`t care about the filament-voltage of your tube at all - as long as it is between 9V & 14V...
I`ll gladly send you a NOS original SIEMENS ECC83+ a brandnew Sovtek 12AX7WX
if my measures provingly ruin your tube!
I recommend 12.6V +/- 5%, though.
But your volume drop has nothing to do with that.
I suspect markr04`s 10k resistor is the same as your "skin-connexion",
just smaller, and that it behaves as the ground-return to the xfmr
(I have repeatedly recommended this resistance to be 0.0 Ohm...),
and therefore causing a powersupplyvoltage "sag", when the IC draws more current by being pushed harder, than when at idle.
It`d be nice to see what happens at the IC`s pins 4 & 7, when gain is turned up, and plucking the guitar... (compared to gain turned down with no signal).
be sure to "play" with the bias trimpot!
at some point, the sound will break off...
it should be turned back then, until the sound stays on
even with the loudest signal (highest gain).
turning further, it will get distorted and fart out again.
I would gladly except your kind offer !!
I do have a sovtek 12AX7 and three new Marshall ECC83's
I prefer the "sound" of the marshall's but all of them seem to be working
fine in the circuit .
Here's my findings taking readings whilst "playing" - which involved one
very small "croc clip" !
"Clean gain" setting : Pin 7 11.11 volts no change when played
Pin 4 -10.38 volts no change when played
"100% gain" setting : Pin 7 11.12 volts increases to 11.33 when played
Pin 4 -10.38 volts increases to -10.67 when played
Should I decrease that 10k resistor to ground, maybe try a 4k7 then 2k2
etc to get the "minimum" before the gating/fart comes back ?
Marty.
yes, and keep adjusting bias-trimpot
Quote from: puretubeyes, and keep adjusting bias-trimpot
I'll do that, but to this point, the "bias" pot has made zero difference
either way... its "centered" at the moment.
M
I`m going swimming... see ya :)
When the 10k resistor to ground between boards is reduced, the overall
level ( which is a problem already ) is also reduced .
I tried several resistors from 10M down to 47k - the higher the value, the
louder the circuit is but the worse the "jumping from rail to rail" becomes.
Even at 47k, there is a slight improvement is overall level, but I get a few
"jumps/cut outs" still.
Looks like 10k - 20k is it !!
I may have to re-make this one some other time, and try a better layout
all i can think of is that somehow my layout is causing this, but it has
"zero" errors, so I'm not sure how to improve on it, other than bigger
vero with more space etc to keep tracks/ + - further apart .....
M.
Sorry to keep bringing this up, but I just wanted to say that the bias pot should have some effect on the voltages. It sounds like your bias may not be connected properly or something...
Quote from: Paul MarossySorry to keep bringing this up, but I just wanted to say that the bias pot should have some effect on the voltages. It sounds like your bias may not be connected properly or something...
It is changing voltages, just doesn't seem to change the "sound" any.
I did a "noise set" for it, with the gain flat out and no input lead connected
I adjusted it to give me as much "hiss" as poss = max gain :D
I have a problem with the layout ... MUST be so !!
I'll remake another when I get a chance .... ?
Marty.
Oh, OK. Yeah, it doesn't seem to have a huge effect on the tone in mine, either. 8)
I think I just figured out my last problem with this layout: input signal is too strong. But I don't know how to fix it, or why the problem exists.
Here's a recording. The part I'm concerned about is the unpleasant clipping that occurs at and just after the attack. Signal chain: passive humbuckers (neck, full volume and tone)>Shaka>mixer>A/D converter>computer.
I believe the clipping is at the IC. I'll be happy to provide voltages if they will help. Please tell me if you want the voltages with no input or with a hard strum as in the recording... or both.
http://www.siteofmark.com/shaka_trouble01.mp3
Classic mis-biased sound. Post voltages of every pin and the plate, grid and cathode pin voltages too.
Thanks for your reply, Aron.
I adjusted the trimpot to the point where my sound was full and loud, just before the screaming sound.
From the power supply board:
V-: -10.9v
Bias: -8.6v
V+: 13.3v
IC (TL071)
1: -10.8
2: 0
3: 0
4: -11.1
5: -10.8
6: 0
7: 13.6
8: 0
12ax7
1: .3
2: -10.3
3: -10.4
4: 14.2VAC
5: ground
6: -4.2
7: -10.1
8: -10.5
Yep, something isn't biased properly.
EDIT: Oops, I didn't see your reply to Aron's post. Those voltages on the 12AX7 don't look right to me...
are you still having that 10k between the "grounds"?
[EDIT]: ooops I wanted to stay out of this project, until I built one up... :oops:
Paul: I don't know how to fix the odd voltages at the tube, or what to compare them to. Will you elaborate?
Puretube: I desoldered the ground wire a week ago for some reason, so when I came to record the first sample, I used some clips to connect the grounds. When doing that, I forgot about the 10K and connected the grounds before the 10K. It has a fuller sound and whatever I thought I had fixed by using it isn't an issue any longer. So... no, I'm no longer using it :).
For kicks, I connected the grounds to the 10K and recorded this (same chain, vol, tone, etc. as previous):
http://www.siteofmark.com/shaka_10k-between-grounds.mp3
Here's the first sample again for quick comparison - grounds are directly connected:
http://www.siteofmark.com/shaka_trouble01.mp3
mark04 - that sounds quite "nasty/bad" !!
Is the "Fart gate" just from the pedal or from the audio sample overloaded ??
I actually have a fully working "OD" which just doesn't get very
"distorted" nor very loud ... but it sounds quite good !!
I dont have that kind of "hard farty" sound going on .....
There's a "boutique" pedal builder that I know quite well and he took a look at the schem/layout.
He recommended a few things, like .1uf caps to ground directly off pins
4&7 of the op amp ( v+ and v- ) and possible another trim pot on the
PSU & some 10uf caps between v+/v- and ground on the PSU.
I'm going to give that a go.
He builds fantastic "Tube" pedals, so should know his stuff !!
Marty.
Marty,
Yeah, it's a nasty sound. I hope to fix it with you guys' help though. It's not the recording itself - I made sure of that. I get that sound out my amp also.
QuotePaul: I don't know how to fix the odd voltages at the tube, or what to compare them to. Will you elaborate?
Well, I can't remember exactly what I had voltage-wise in my Shaka Tube, but you should have something like 12 to 14V on Pins 1 & 6 (V+) and around -12 to -14V on Pins 3 & 8 (V-). Bias should measure somewhere around -12 to -14V or so. These numbers are all dependent on how you set the bias, of course.
Something is definitely awry... :wink:
EDIT: You are absolutely sure that you have the 470uF caps connected up properly, right? If you look at the schematic, two of them have the positive lead connected to ground. Just a thought.
Paul, I just compared to your pdf and I'm absolutely sure I have them oriented correctly.
Quote from: markr04Paul, I just compared to your pdf and I'm absolutely sure I have them oriented correctly.
Hmm... that's perplexing.
Pin 1 and pin 6 should have DC voltages on them - higher than tenths of a volt. Not only that, they should be positive voltages, not negative(as in in 6). There is a miswiring somewhere in the pin 1 and 6 connections.
Build an audio probe and verify that the signal is good and clean after the op amp. (pin 6)
Debug pin 1 and 6 on the tube.
Paul,
I messed with the trimpot, so my voltages are about -.8v different from my voltage posting earlier. +V is now 12.5v.
On the audio board:
I have 12.5v at V+, IC pin 7, and all the way up to the two 50K resistors. On the other side of those resistors, the voltage goes negative as shown in my voltage post before. About -9.4 now.
This kills me. I don't understand. Why does it go negative there? :roll: :x
That sounds better, but if the voltages on the tube are still the same, you have more work to do.
I can't measure at the socket pins because I used heatshrink. I'm measuring at the wires coming off the board toward the tube. I'm under the impression that the measurements would be the same (at our level).
So... it goes negative at the 50K resistors (pin 1 and pin 6), but it should be positive (if I understand you correctly). Why is that? How do those resistors turn +12.5V into -9.4V? And it seems I should remove and jumper them if I want +12.5V, right?
No, the resistors don't turn positive into negative. The problem is before the resistors. At one end of the each 50K resistor should be the full V+ (positive DC voltage).
Aron,
There is +12.5v (V+) at one end of each of the resistors (and at pin 7 of the opamp). It's on the other side of those resistors that there is -9.4v.
Pull out the tube and measure again and tell me the voltages.
12ax7
1: 14.9
2: -9.4
3: -12.8
6: 14.9
7: -9.4
8: -12.8
When I put the tube back in, I get -3.7V at pin 6 and .3 at pin 1.
Well, your voltages on Pins 1,3,6 & 8 look about right with the tube pulled out... :?
I futzed with the trimpot some more and found more gain. Again, turning it CCW to just before oscillation.
bias: -9.5
V+: 12.6
V-: -10.4
With the tube:
1: 3.7
2: -10.1
3: -10.1
6: -0.3
7: -9.9
8: -10
without tube:
1: 14.9
2: -11.6
3: -12.8
6: 14.9
7: -11.6
8: -12.8
Any ideas?
Do you have another tube to try out?
I guess you can try one more thing. Try changing the 10K bias pot to 50K and see if it helps.
I don't know why it would be oscillating.
I just noticed and guess I should mention I raised :oops:
the .01uF input cap to .022uF
the .01uF cap between tube pin 6 and tone to .1uF
the .01uF between tone and ground to 1uF(NP)
(these last two are on the bottom right of Paul's layout)
I was looking for some low end. Would those caps cause this problem?
To tell the truth, I don't understand biasing. I modded my Peavey 5150 to have an external bias pot because I was temporarily caught up in the "run power tubes to just before meltdown" thinking. While I could perform the "surgery", I still don't understand the "hows and whys" of it all. I turned that pot back to give the factory -50V setting and can't tell a difference myself. But I digress:
I turned the trimpot even further. Now this thing has gain and strong output! I hear some hum, which was silenced when I had it biased the other way, but maybe a bit of noise is expected? The oscillation I spoke of might've been feedback. I can turn my guitar down, twist the trimpot all the way CCW and it doesn't squeal.
now:
Bias: -10.7
V+: 13.6
V-: -11.4
12ax7:
1: 5.2
2: -11.2
3: -11.1
6: 2.6
7: -10.9
8: -11.1
How are those numbers?
A new recording:
http://www.siteofmark.com/shaka_maybe_fixed.mp3
[SOT]anybody ever heard/read about the "circlotron" with the 2 individual floating power supplies?
:wink:
Cecil Hall. ;)
No DC in da OT.
Bridge circuits can be wonderful things. (http://img.photobucket.com/albums/v280/Snowberg/diy/bootsy.gif)
It sounds better but I still think that the tubes are still not biased correctly yet.
You might try changing out the bias trim pot....
Anyone else have any ideas???
Peter: you`re the 1st,
that doesn`t instantly reply: Futterman!
:D
Probably not the case, but are you sure that you have the bias trimpot connected up properly? The wiper is what would be connected to the bias network. Are you absolutely sure that your bias network is connected to the wiper of that trimpot?
In this circuit, how the bias is adjusted will influence how it sounds by making the signal on the grids (Pins 2&7) of the 12AX7 more or less negatively biased. It almost sounds like you have a wire crossed somewhere, and the plates (Pins 1&6) are becoming a negative DC voltage instead of a positive DC voltage as a result. The voltages that you measure on the cathodes (Pins 3&8 ) will be dependent on what is going on at the plates (Pins 1&6).
Basically, what is happening in your tube is that it is in a "cutoff" mode, and it can't conduct much current. As a result, you get that blatty, gated sound.
The fact that those negative voltages on the plates don't really change much with the tube pulled out seems to point to a wiring error...
Thank you all for your help! I put a 25K trimpot in there and cranked it CCW. I have:
V+: 14.7
V-: -13.2
bias: -13.3
1: 9.0
2: -13
3: -13
6: 9.0
7: -13
8: -13
How are those? I don't hear any more gating at this point.
I made new recordings. These are 4mb .wav (for quality) files of different tubes in it.
Chinese 12AX7 (I think it's Chinese. Pulled from a 1995 Peavey 5150):
http://www.siteofmark.com/Chinese_12AX7_(from_5150).wav
Electro-Harmonix 12AX7EH:
http://www.siteofmark.com/Electro-Harmonix_12AX7EH.wav
Sovtek 12AX7WA:
http://www.siteofmark.com/Sovtek_12AX7WA.wav
Well, now those voltages are looking better! And it sounds a whole heck of a lot better, too. You look a little low on the V+ voltage at the tube, though. You'll have a little more headroom if you can get that to around 14V. What transformer did you use (V, mA)?
Paul,
I used a 12vac 800mA. I have a 1w 10ohm in series before it ever hits the PS board. Maybe I ought to remove it?
Quote from: markr04Paul,
I used a 12vac 800mA. I have a 1w 10ohm in series before it ever hits the PS board. Maybe I ought to remove it?
You know, I was just thinking this morning... I forgot about those 50K resistors on the plates of the 12AX7. A measurement of around 9VDC on those sounds about right. I never actually measured mine. :oops:
What is your voltage on Pin 4? If it's within 10% + or - of 12.6VAC, you're fine. If not, you may want to adjust things a little bit. It's not really that critical if you're a little higher than 10%, your tube just won't last quite as long - not really too much too worry about since preamp tubes last a very long time compared to power tubes. 8)
Quote from: Paul Marossy
You know, I was just thinking this morning... I forgot about those 50K resistors on the plates of the 12AX7. A measurement of around 9VDC on those sounds about right. I never actually measured mine. :oops:
Mine are all 47k's - I've never even seen any 50k resistors !!
I just tried some decoupling caps to ground from the op amp pins 4 & 7
( TL071 remember ) and also from the trimpot + & - to ground, plus a
10uf from "bias" to - on trim pot.
I got a slightly "smoother" sounding OD, but still have a serious "level"
drop on full gain.
At clean gain pot setting, I have a volume lift above unity and no more
"farty" stuff going on.
If I used an output boost on this, it would be sounding fine, though at
full gain, its still only a "mild overdrive" tone .... ??
BTW - it's not re-built yet and is starting to look like "Frankensteins baby"
.. !!!!
Marty.
I can get a pretty high gain sound out of mine. But, I do have a FET preamp in my guitar, too. It gives some boost, but it's not a huge amount...
Mine was high-gain too, i had to do some modding to lower the gain. But i do have that FET pre in my guitar as well.
...
emre
Can somebody tell me why the distortion will loss after some seconds( low sustain) ? I am really stressed
Quote from: wui223Can somebody tell me why the distortion will loss after some seconds( low sustain) ? I am really stressed
The Shaka Tube isn't a real high gain circuit, and it's working in a "starved plate" mode, but you should be able to push your amp into a fairly heavy overdrive with it. Mine doesn't have tons of sustain, either.
What kind of tube are you using? Are you sure that it's in good condition?
Mine is a RSD 12AX7, it is a brand new one. the tube light up as usual. But just i could not get overdriven sound from it. maybe the opamp is not working right. I dont see any changes when i turn the biasing pot. WHY?
What opamp did you use?
i try both TL072 and 4558. i use 1000uF caps in the power board, does it matter? and i use jumper instead of 10 ohm/1W resistor, coz the transformer output is 12+ only. i change the cap parallel to gain pot to 220pF and 47k resistors to replace the 50k used in series with tube. basically thats is what i did
What voltage are you seeing at V+?
around 13~14+ and V- is -10~v, i use analog coz my DMM blow fuse already. Is the voltage too low?
Maybe just a little low, but I'm not sure it's enough to cause your problem. In my last Shaka Tube build, this is what I measured at the settings I liked best:
Incoming AC voltage: 12.8VAC
V+: 11.8V
V-: -14.6V
Bias: -13.6V
It sounds like you are in the ball park, but something still seems off. What power supply are you using? (voltage/current)
12-0-12 centre taped transformer, current i think is 1000mA coz i dunno how to measure it. the shopkeeper just tell me it is 1000mA rating. Did i screw anything up? i can hear very low sound volume but is clean also
Those specs on the transformer sound OK. You must have something killing your signal somewhere - it should be quite loud and you should have some distortion, too. Time to build an audio probe! :wink:
Quote from: wui223Can somebody tell me why the distortion will loss after some seconds( low sustain) ?
So, are you saying that it works *normally* for a few seconds 'till it suddenly becomes quiet and "clean"?
.
e
Yeah, as i strum chord it produce sound then the sustain will went off after about 3 seconds, it is a suddenly drop, just like 'pop' the sound gone.
Can i use another transformer which is 12-0-12 center taped and rated 6VA which i believe is 500mA ?
I use audio probe last time but cant solve my problem, maybe i should try
i am thinking of integrate a signal generator and amplifier to audio probe, so that i dont have to plug to guitar amp. What do u think?
It sounds like you're describing a mis-biased opamp...
Yes, sounds like something is misbiased.
Misbiased? How to solve it? My electronic knowledge is far behind urs, i need to work hard.
Post your pin voltages first.
Here there are:
V+: 12V
V- : -10V
BIAS: -5V
OPAMP
4: -10V
8: -12V
OTHER PINS ARE AROUND ZERO
12AX7
1: -2.8V
2: -9V
3: -8V
4: 12VAC
5: 0
6: -10V
7: -8V
8: -8V
Something must be wrong coz all tube pin measure negative voltage
Finally got it sound after a recheck, one spot is miswiring :oops:
But the hiss is extremely loud why? and i couldnt turn the gain pot past half rotation, else the hiss is more and more and the volume will drop significantly. Anyone know solution?
Quote from: wui223Finally got it sound after a recheck, one spot is miswiring :oops:
But the hiss is extremely loud why? and i couldnt turn the gain pot past half rotation, else the hiss is more and more and the volume will drop significantly. Anyone know solution?
Look for questionable solder joints and connections to ground. Also, verify that the pins of the preamp tube are making good contact with the socket.
Paul could u take a look at ur PCB layout? I was confused bout the connection of gain pot, in schematic centre lug is connected to pin1 (output) while in PCB centre lug is connected to pin2. Which one is correct?
It doesn't matter, it's wired as a variable resistor. If your gain pot works backwards from what you expect, just switch the outside lug connections.
Yeah i got it. Why in my built, the pin 1,2,3 of TL072/RC4558 didnt show any voltage? Do u think it is normal? I use strip board for this project. I am sure i have all the ground tied up. But the hiss/hum is extremely loud when i turn the gain pot up. the only usable range is just 1/4 of the full rotation. Do u think i can swap the transformer with a 500mA 12V output transformer?
Quote from: MartyMart on December 08, 2005, 07:08:18 PM
Hmm, this thread is becoming a little "annoying"
.... EVERY week !
grrrrr ....
MM. :icon_eek:
http://www.diystompboxes.com/smfforum/index.php?topic=39797.msg284871#msg284871 (http://www.diystompboxes.com/smfforum/index.php?topic=39797.msg284871#msg284871)
Sorry Ton, as John Cleese said in a fish called wanda " I apologise unreservedly" !!
Yup, I DID reverse the tube pinout .... :icon_redface:
Now I'm going to go away and "hide" for a week !!
MM.