EA tremolo Depth pot not working.

[nguitar12]

So I built the modified EA tremolo from the following site.

http://www.home-wrecker.com/eatremolo.html

Everything it working except I don't get the Depth pot function properly. The depth is still very intense even I turned the pot all the way down. In fact there is no change in the depth when I turn the pot. The only substituted part is 180ohm resistor ( I am using two 91R in series. )

Can someone please suggest a possible solution on this? Many thanks.

[antonis]

Maybe you should disconect the pot and create a resistive voltage divider between lugs 1,2 &3...
(actually 2 settings, say 180k/68k and 68k/180k and listen if there is some difference in Depth..)

[Elijah-Baley]

Did you built it on that perfboard?
Are you included the led?

When I built my tremolo I had omitted the led, it sounded but that was necessary for the tremolo effect.

[antonis]

When I built my tremolo I had omitted the led, it sounded but that was necessary for the tremolo effect.

Quite right..

If you want to omitt the LED you have to replace it with a 4k7 resistor or make the 10k one up to 15k...

[nguitar12]

When I built my tremolo I had omitted the led, it sounded but that was necessary for the tremolo effect.

Quite right..

If you want to omitt the LED you have to replace it with a 4k7 resistor or make the 10k one up to 15k...

I didn't omitt the LED. I think the problem should be on the LFO part.

[antonis]

I didn't omitt the LED.

I didn't say that you did it...

If the Rate works properly (changes LED's blinking frequency) you have to focus around 470nF, Depth pot, Q2 and - the most suspect - 22μF electro....

[nguitar12]

I didn't omitt the LED.

I didn't say that you did it...

If the Rate works properly (changes LED's blinking frequency) you have to focus around 470nF, Depth pot, Q2 and - the most suspect - 22μF electro....

Yes the Rate works properly, the volume working properly. The pedal sound very nice. The only problem is the depth pot. Now I changed the depth pot into 1M and I can hear the depth decreased.  The is weird the first 25% of the 1M Depth pot rotation should big enough to result in no audible tremolo effect to allow use as a pre-amp. (according to the web site.) but now the 1M only decreased half of the effect on my build? Will the J201 be the problem? They are my very very old stock and I am not sure whether they are still working........

[antonis]

The 250k pot along with 120k and 68k is used to bias Q2...
(I'm not sure if the 1M (1.2M actually) resistance allows enough current flow for gate biasing - propably it does..)

<Will the J201 be the problem?>
The 2nd suspect...
(after 22μF cap)


P.S.
Wait for a down under guy with tremolo vice...

[duck_arse]

me? (I might get one built, one day. anyone got spare smd fets?)

if you're using a j201 to modulate, it's probably getting too much gate volts, going way past "all it can use". so you need to reduce it some, before it gets to the depth pot. you can improve the response by reducing the bottom 68k to ?22k?, and increasing the top 120k to ?330k?, you can even change the pot to a 100k. you will have to fiddle the string values to suit yr fet, basically.

you might even fit a 100k in series with the pot wiper and the fet gate, as in the rEAgenerated_trem of transmogrifox (use search, there is some current discussion).

[nguitar12]

me? (I might get one built, one day. anyone got spare smd fets?)

if you're using a j201 to modulate, it's probably getting too much gate volts, going way past "all it can use". so you need to reduce it some, before it gets to the depth pot. you can improve the response by reducing the bottom 68k to ?22k?, and increasing the top 120k to ?330k?, you can even change the pot to a 100k. you will have to fiddle the string values to suit yr fet, basically.

you might even fit a 100k in series with the pot wiper and the fet gate, as in the rEAgenerated_trem of transmogrifox (use search, there is some current discussion).

Thanks for your suggestion. I will try it soon. But why only I have this problem? I don't see any other people have this problem. Now I am using a 1M pot and it help a little bit on the depth control. Isn't that using a 100k will make the depth stronger?

[duck_arse]

a 1M looks like nearly all the resistance in that string, so has more volts end to end. a 100k is a much smaller proportion of the total string, so has a lesser voltage gradient (wh?).

try doing ohms law pencil and paper on the two strings, see what voltages you get if you start with 10V at the top, for instance, and a 1M or a 100k pot.

and other people don't say because they are too embaressed to admit, not like all the brave and strong folks here.

[nguitar12]

a 1M looks like nearly all the resistance in that string, so has more volts end to end. a 100k is a much smaller proportion of the total string, so has a lesser voltage gradient (wh?).

try doing ohms law pencil and paper on the two strings, see what voltages you get if you start with 10V at the top, for instance, and a 1M or a 100k pot.

and other people don't say because they are too embaressed to admit, not like all the brave and strong folks here.

Thanks for your suggestion. However I never study electronic. I even don't know what do you mean by 10V at the top. And what voltage at what pin in order to make the depth pot work and why it works. Basically I don't know the principle behind the circuit. That's why it is almost impossible for me to debug it myself.

I don't think other people don't say because they are too embaressed. At least the guy who wrote the website get the depth pot working.

[PRR]

> no change in the depth when I turn the pot.

Re-re-re-check that the "bottom" leg of the Depth pot goes to the 68K resistor and then to Ground.

If you have an OhmMeter: with power off, measure Ohms from Depth pot wiper (center terminal) to ground (such as a jack shell). As you turn the pot, the resistance should change smoothly from 250K (or 1Meg) down to 68K Ohms. If the Ohms never gets "small" (or is always "OL", infinite Ohms, open-circuit, no-connection), then the pot to 68K to Ground has a missing or bad connection, or the pot end-lug is busted inside.

[nguitar12]

> no change in the depth when I turn the pot.

Re-re-re-check that the "bottom" leg of the Depth pot goes to the 68K resistor and then to Ground.

If you have an OhmMeter: with power off, measure Ohms from Depth pot wiper (center terminal) to ground (such as a jack shell). As you turn the pot, the resistance should change smoothly from 250K (or 1Meg) down to 68K Ohms. If the Ohms never gets "small" (or is always "OL", infinite Ohms, open-circuit, no-connection), then the pot to 68K to Ground has a missing or bad connection, or the pot end-lug is busted inside.

I am sure the pot is well connected. As I mentioned before. The pot will work but it is far less effective than expected. A 1M ohm pot should make the depth flat but it only make it half in my built. Can you suggest some possible reason?

[deadastronaut]

what led are you using?..

standard diffused red/green/yellow?  ,  or a superbright?...

just curious..

[nguitar12]

what led are you using?..

standard diffused red/green/yellow?  ,  or a superbright?...

just curious..

I am not sure whether it is a super bright led but it is pretty bright to me....

[PRR]

> I am sure the pot is well connected. As I mentioned before.

If it were wired exactly as shown, there would be a LARGE change as the pot is turned.

Is the lower resistor 68K ?? (If it is 680K then there would be very-little effect with a 250K pot, some effect with a 1Meg pot.)

Did you do ohm-meter checks?

[nguitar12]

> I am sure the pot is well connected. As I mentioned before.

If it were wired exactly as shown, there would be a LARGE change as the pot is turned.

Is the lower resistor 68K ?? (If it is 680K then there would be very-little effect with a 250K pot, some effect with a 1Meg pot.)

Did you do ohm-meter checks?

I finally reducing the bottom 68k to 10k and increasing the top 120k to 470k,
now I can get the depth completely flat with the original 250k pot.
Does this value make sense and will it contribute a possible bad side effect to the tone?
Also I find that the depth respond is not linear. Is it due to the changes of the resistor value I made?

[PRR]

Your FET has a lower Vto than the one used in the documentation. (Did you use the specified parts? Even so, there is wide variation across FETs of the same number.)

Yes, make the bottom resistor quite small. Keep the 250K pot. Increase the top ("120K") until "full up" is max and "almost full up" is "almost max"; that gets your big trem about right. Now turn down, trem MUST go to zero. Typically it goes to "almost zero" before you get to the end of the pot. Find that "barely zero" point, measure resistance wiper to ground, and put in a fixed resistor about that size.

If you get the two ends about right, you should have a full range between. The trem will not be exact proportion to knob setting because an FET is a bent little beast, but it won't be a problem. If it seems way out, check pot taper (linear is probably best).

[nguitar12]

Your FET has a lower Vto than the one used in the documentation. (Did you use the specified parts? Even so, there is wide variation across FETs of the same number.)

Yes, make the bottom resistor quite small. Keep the 250K pot. Increase the top ("120K") until "full up" is max and "almost full up" is "almost max"; that gets your big trem about right. Now turn down, trem MUST go to zero. Typically it goes to "almost zero" before you get to the end of the pot. Find that "barely zero" point, measure resistance wiper to ground, and put in a fixed resistor about that size.

If you get the two ends about right, you should have a full range between. The trem will not be exact proportion to knob setting because an FET is a bent little beast, but it won't be a problem. If it seems way out, check pot taper (linear is probably best).

Thanks, you are always being so helpful.