EA Tremolo problems

[good mourning]

i finally measured voltages in my
inproved EA Tremolo (by GGG)
Speed and Depth don't work, Volume works
here are: :shock:
power supply:12,30 (it's high... it causes by adaptor!) :?
Q1 - 2N3904
E:1.30
B:1.99
C:7.80
Q2 - BF224
D:0.00
S:0.00
G:7.69
Q3 - BC549
E:0.00
B:0.60
C:7.70
Q4 - BF224
D:12.30
S:8.23
G:5.93
i think Q2 drain cannot be 0.00
is Q2 burned? :oops:

[Ge_Whiz]

There's certainly a problem around Q2. Either it's shorted (dead), or perhaps the drain just isn't connected properly...

Have you checked the capacitor connected to Q2 drain?

[gez]

ipower supply:12,30 (it's high... it causes by adaptor!)

How can you expect it to work as intended if you don't use the required power supply, ie 9V?!

How much difference will a 12V supply make?  I couldn't say off hand, but if you could link to the schematic it would help.

Just looking at the figures you've posted suggests a few problems...

[good mourning]

the link is:

http://www.generalguitargadgets.com/diagrams/eatrem2_sc.gif

and the circuit is ok.
the capacitor connected to Q2 (C3) is right
i tried replacing R8 with a 10k - green LED to see if it pulses...
the LED remains switched on, 'moving' speed and depth too!

i'll try to replace Q2 with a new one...

i use 9V power supply!  :x but when i tested i used an adaptor,
that one gave 12V instead of 9V... :evil:
but voltage never mind! :wink:
the terrifying thing is that i must do 200km to buy a FET! :cry:

[gez]

Thanks for posting the link.

You've shorted C4 (solder bridge?) by the look of things.  There should be 0V on Q2's gate.

Q4 looks OK

Q1 (accounting for tolerances etc) is roughly in the right area.  Its collector should be around the 6V mark with a 12V supply, so your reading is a little high.  Probably an idea to check your resistor values, though it's not too crucial.

Correct the problem with C4.  If it still doesn't work get back to us and we'll see if Q3 needs some tweaking.

At 12V you'll probably need to mess around with the value of R7 to set the depth right.

[gez]

Is R13 connected to ground?  Either that or is R7 shorted too?  The 560k forms a divider with the 1M pot so the voltage on Q2's gate should be lower than you've quoted if just the cap (C4) were shorted...

[good mourning]

thanks gez.
take a look at this:

http://www.generalguitargadgets.com/index.php?option=com_wrapper&wrap=eatrem_inst

it says:
Q2 gate:varies / source: 0.0 / drain: 0.1
so drain mustn't be at 0.0!
watching the other voltages, it seems that everything is ok but
ca. 3V up!

C4 is 0.47uF and connections are right.
R13 is grounded and R7 is 560k.
the only change is C8, replaced by 0.047uF
but i tried to raise it up and there were no changes!maybe in tone...  :?

but when you say 'shorted' do you mean burnt (that is '@#$%ed up')
or do you mean that is a bridge/jumper (a 'missing')? :oops:
sorry but i'm italian :wink:

i better buy a new FET and then i'll tell you.

[RDV]

Pinout?

RDV

[gez]

it says:
Q2 gate:varies / source: 0.0 / drain: 0.1
so drain mustn't be at 0.0!
watching the other voltages, it seems that everything is ok but
ca. 3V up!.

What does 'ca. 3V up!' mean  :?:

I haven't read the link, there's no need to, you can see from the schematic that Q2 has no DC connections!  The drain and gate are AC coupled, therefore 7V (or whatever it was, I can't see your post as I type) on the gate is wrong.  The 0.1V on the drain you mention would be caused by a leaky C3.  I'd change the cap if I were measuring that (ideally the drain should be at 0V).

C4 is 0.47uF and connections are right.

If they were right you wouldn't be measuring 7V on the gate of Q2.  When I say that C4 is probably shorted I mean you've probably bridged the pads/leads of the capacitor with a bit of solder, or wired it up so that it's bridged.  If you've used an electrolytic cap then you might have got the polarity wrong, in which case replace it.  Even if the cap is shorted the gate should still be lower that it is so this suggests you've got other connections wrong/shorted.

You don't need another FET, there's enough resistance to prevent the gate-source junction from being fried by being forward biased.