Another EA Tremolo Debugging: No effect

[Germanium_Boy]

I got a great headache trying to make an EA Tremolo works, and even being a full-patience guy, I'm starting to think about throw it out the window! 

This is the issue: The stompbox sounds, but without any tremolo effect. I followed  the Tonepad schematic (http://www.tonepad.com/getFile.asp?id=130). But there is a couple of strange things...

a) The Volume pot works perfectly, and without Q1 there is no sound, so I suspect the trouble to fix is around Q2 or Q3.
b) Sometimes, when I engage the pedal on, the effect is there. But only if I use medium-speed settings. If I set the highest speed, the effect disappear.
c) I checked this a thousand times, even I resoldered it completly a pair of times: the Speed pot works in anticlock way. Maybe is a issue of the Tonepad schematic, because in GGG, for example, I saw that a antilog pot is used.
d) If I get Q2 out of the PCB, the effect still sounds, but you can hear the lack of volume. If I do the same with Q3, I can hear the cracks and pops when I get it out of the sockets, but there isn't any other consequences. Anyway, the subtle tremolo effect only happens if Q3 is socketed, so the thing is in the circuit path, I think.
e) I revised of the solders, and the PCB itself. There's no issue with them.
f) Well, I think that I lied a bit when I said 'a couple of strange things' about the pedal... 
g) And here are the voltages of the transistors. I have a bunch of replacements, and I tried them in the circuit, but the effect is the same, so I suppose the transistors are fine.

Q1 (2N5088)
C = 0.58
B =1.09
E = 3.39

Q2 (2N5457)
G= From 0.01 to 0.48, depends of Depth pot
S= 0.00
D= 0.00

Q3 (2N3904)
C= 0.00
B= 0.63
E= 5.20

So... what do you suspect is failing? For me, the most important is to learn. To know why, with this info and symtons, I can know if the failing component could be one or the other...

I wait for your help! Thanks!

[psychedelicfish]

With the voltages listed, both Q1 and Q2 have emitter voltages higher than their collector voltages, perhaps you've got collector and emitter mixed up?
To answer some questions:
a) Without Q1, how does your signal get from the input to the output? I'm not surprised that you get no sound without it.
b)Sounds like you have a loose connection, a dry solder joint, or an accidental short circuit somewhere.
c)Try swapping the outer lugs of the pot around.
d)When you say the effect still sounds, do you mean you can hear your signal, or you get tremolo? Q3 is the oscillator, without that you can't modulate the output level, so I'm not surprised with that.
e) If you have a Multi Meter, check the continuity of your PCB traces, there might be a break in one of them that's too small to see. Then check continuity between traces, there might be a tiny solder bridge you haven't seen.

At this point, I think the most likely reason it doesn't work is that you've put the wrong part in somewhere. If you have a multi meter, check that all your resistor values are correct, it's very easy if you use the colour bands to identify resistors to put one in your circuit that's ten times or 1/10th the value, for instance.

[MaxPower]

If my calculations are correct, the collector to Q1 should be around 4.6V (dc). I could be wrong though, jeez how quickly I forget these things....

You can try LT Spice or Tina-ti to analyze the circuit and see what kind of voltages and currents you should be getting. They're not too hard to figure out. For basic analysis anyway.

[Germanium_Boy]

Thanks for your replies! Yes, without 2n5088 I have no sound. I don't know how, but now I get the tremolo sounding, not perfectly, but with the depth pot set to max, I cand hear the effect. If I set the max speed, it dissappears in a pair of seconds...

About Q1, sorry for my mistake. I changed the C/E values, but something curious happens... With the transistor socketed as the layout says, the sounds is a bit distorted, even setting volume pot for unity gain. If I flip switch the transistor, the sound is clean, with a very few volume, but the tremolo effect is very very subtle...

I'm trying to do a pair of thing with Tina-Ti, because... yes, I want to learn of this mistake! I hope I can find it...

On the other hand... the depth control is near unusable in more than a half... and the most usable setting is at 10 Is that what it happens really? By the way, I checked all the resistors and the values are OK. Now I have to know the way to know how the capacitors should be checked too... I think that I'm going to learn a pair of things with this project...

[GGBB]

Thanks for your replies! Yes, without 2n5088 I have no sound. I don't know how, but now I get the tremolo sounding, not perfectly, but with the depth pot set to max, I cand hear the effect. If I set the max speed, it dissappears in a pair of seconds...

About Q1, sorry for my mistake. I changed the C/E values, but something curious happens... With the transistor socketed as the layout says, the sounds is a bit distorted, even setting volume pot for unity gain. If I flip switch the transistor, the sound is clean, with a very few volume, but the tremolo effect is very very subtle...

I'm trying to do a pair of thing with Tina-Ti, because... yes, I want to learn of this mistake! I hope I can find it...

On the other hand... the depth control is near unusable in more than a half... and the most usable setting is at 10 Is that what it happens really? By the way, I checked all the resistors and the values are OK. Now I have to know the way to know how the capacitors should be checked too... I think that I'm going to learn a pair of things with this project...

The tonepad layout has the speed pot backwards so you can use a log pot since they are more common.  With this circuit, it is not uncommon to lose the tremolo effect at the max speed setting - if you want that to stop happening (you could just live with it), you can either increase the 1K resistor to 1.2K or whatever you need to get it to work (or use a 2K-5K trimpot), or you could replace the three 1µF caps with smaller ones (e.g. 680nF).  But the drawback there is that you will not be able to set it as slow - so it is a trade-off.  I find the slow settings not that useful so if it were me I'd lower the caps.

The depth control is designed so that the first quarter turn or so doesn't do much so that you can use it as a clean boost.  If you don't care about that, add a 22K-47K resistor between the depth pot pin 1 and ground.  To increase the max depth available, reduce the 120K resistor to 47K (experiment - you can even jumper it if you want to be able to get a choppy kind of sound - this is especially useful at higher speeds).

[MrStab]

the two transistor tremolos i've built (EA and Heartthrob) have shown the inconsistent performance issue as you guys have mentioned, depending on where the pots are set to - fixed by using resistors as Gord suggests.

just a thought: are you using an LED to indicate speed? if so, what kind of LED? i'd read reports and experienced first-hand the intensity of the effect getting weaker upon installing one. a better solution might be to put the signal into the base of another NPN in order to light the LED, instead of just piggybacking off the circuit itself. if you're not using an LED, ignore the above!

[duck_arse]

well, yr oscillator is working, at least sometimes. all versions of this type oscillator have drop in output either side of "a" particular frequency, determined by the matching of the components. you might be able to improve its performance by changing R10//15k for 10k, or 22k. as for the depth, try shorting the R7//120k and see what happens.

I really like the variation on the single transistor pso that rick holt uses in the vibracaster (schematic: http://www.aronnelson.com/gallery/main.php/v/frequencycentral/Vibracaster+Stock+12AU7+V2.JPG.html). I don't know that it is more reliable or not, because I don't seem to have trubble with this osc usually.

[Germanium_Boy]

Wow! What a lot of useful info! Thanks a lot, guys! I'm gonna take a look, again, to the circuit, because I'm not very pleased with some voltage values. I think that Q1 collector, now around 3.50v, should be a little higher...

Anyway, I'll give a try to some of the mods you told me. I need a bit more of speed, and a depth control more usable. And the same time, I think that I'll try too the J201 buffer of the GGG schematic...

[Germanium_Boy]

Mr. Stab, I did't put the speed-led. It's something that I don't really like, in fact, I think that I'd get very nervous seeing that flipping light! 

[Germanium_Boy]

This can be useful, if someone has the same troubles as me: I swapped Q1 and Q3 (2N5088 and 2N5093, according to Tonepad schematic, but the opposite in GGG). The little distorted sound has dissappear; and the speed pot can be set to 10. Maybe, before another test, and comparing the transistors in the other position, I perceive less speed at max setting, but anyway, the rest of the troubles are gone. Time to relax, it's a beautiful and warm effect. I think I'll go for a reverse pot for speed, and a pair of the changes you suggested me, surely. And maybe, a test with a buffer, as GGG schematic.

[Germanium_Boy]

Well, and the most important thing... Thanks for your incredible help, and useful tips. I learnt a lot, and... that is the most important thing, isn't it? 

[MaxPower]

Well, I simulated it in Tina-ti and the collector on Q1 should be about 3.9V dc apparently, so your 3.5V reading may be correct depending on the actual values (due to tolerance variations) of the resistors used, etc.

I just redid my calculation and came up with the collector being about 4.1 V which is close enough considering I didn't take the base resistance into account. Wonder how I got 4.6V previously though...

[Germanium_Boy]

What a good new what you're tellin me! With the flip of the transistor, now I take measurements between 3.9 and 4.1V, so it's in the perfect range! Thanks for your help and time! By the way, I downloaded Tina-ti, and I'm trying to learn a pair of things... there's a lot of work to do with it! And I have a very simple doubt... is there electrolytic capacitors? Because I don't find the way to get them!

[Germanium_Boy]

In fact... would it be too much to ask you for the file with the schematic? As a sim lesson, would be very helpful! Thanks, and sorry for the inquiry 

[MaxPower]

I hadn't even noticed about the lack of polarized electrolytic capacitors in Tina-ti. Using a regular capacitor shouldn't matter as far as analysis goes.

Send me a private message with your email and I'll email you the file. It's about 12.6 kb in size.

[duck_arse]

@maxpower - do me a sim favour, max, and sim the circuit with one end or other of the middle cap in the oscillator shorted to ground. the osc won't run, but I'm interested in the expected voltages around the transistor. thanks.

I named a fuzz after max headroom. he should have ducked. just thought I should tell you that.

and good work ge boy.

[MaxPower]

Germanium boy, I emailed you the file. Let me know if you receive it. I just realized it has an error. I forgot to make the connection from the 2.2Meg resistor to the collector of Q3, so you'll need to fix that.

duck_arse, you'll need to draw me a picture. I don't understand which capacitor I should ground. I assumed one of the 1uf caps by Q3 (the vertical one)? But for dc analysis aren't all caps opened? I shorted the vertical 1uf cap (tried both sides separately) and it didn't change anything. Unless you want me to run an ac analysis (I'm still trying to figure it out since what passes for manuals don't explain how to do analysis and use the oscilloscope, etc.).

As it is, assuming I made no mistakes in the schematic, the readings are:
Q1
Collector: 3.92 V
Base: 1.08 V
Emitter: 468.74 mV

Q3
Collector: 6.15 V
Base: 610.01 mV
Emitter: 0.0 V

FET has nonsense readings since there are caps on both sides.

max headroom? I have vague recollections.... but to quote Homer Simpson: "I got it off a hair dryer".

[MrStab]

Mr. Stab, I did't put the speed-led. It's something that I don't really like, in fact, I think that I'd get very nervous seeing that flipping light! 

i originally pursued rate LEDs in my builds for aesthetic reasons, but i actually find em useful! although iirc the EA Trem - at least with an LED hooked up directly - seemed a little inaccurate. congrats on getting it working anyway!

I named a fuzz after max headroom

i'm fascinated by the Max Headroom TV signal hijacking event, was re-reading about it just a coupla days ago actually. he definitely needs more audio-electronics tributes.

[duck_arse]

max, with referende to the following circuit:

http://www.generalguitargadgets.com/pdf/ggg_eat_sc_improved.pdf?phpMyAdmin=4a28f86a515b7883e7bc35a68d4e7b6d&phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

if you short either R10 or R11//R14 to ground, it will stop the oscillator. I was intested in the dc voltages around Q3, to see if there was a way to spot the reason an osc wasn't working. I might end up sticking a range of transistors on the breadboard and measure their voltages, see if I can make it "not work".

and since first saking, I realised with a grounded emitter, the E=0V no matter what and therefore B~0V6, so it will only really be the C voltage that will be interesting.

I know of some blokes, used to fight on tour over who had the best haidryer.

[MaxPower]

I see. So it was shorting either end of C7 to ground. Well, with Tina-ti (and LT Spice I believe), all caps are opened (disconnected) when running dc analysis. So when you run the dc analysis all you're left with is  Q3 (with emitter grounded), R9, and R8. So grounding the middle cap or R10, or R11 doesn't make any difference to the analysis.

I modified the schematic I had to match the one in the link you posted. These are the dc voltages (again assuming I made no mistakes in the schematic):

Q1
Collector: 6.62 V
Base: 1.34 V
Emitter: 705.69 mV

Q3
Collector: 2.95 V
Base: 619.61 mV
Emitter: 0.0 V