EA trem problem

[m-theory]

I built from this layout in the gallery
http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/album19/album145/EA_TREMOLO_VERO.gif.html

The LED doesn't light, and the unit acts only as a boost.  It passes signal just fine, and the volume control works, but no "tremming" going on, UNLESS I short out the LED leads, in which case, it works perfectly. 

Somebody on another thread suggested that this could be an indication that the LED is drawing too much current.  I've tried a smaller LED, and got the same results, and I'm working with a fresh battery. 

Here are my numbers:

Battery - 9.21
Q1 D - 3.97
     G - 1.79
     S - 1.33
Q2 D - 0.00
     G - 0.00
     S - 0.00
Q3 C - 0.02
     B - 0.02
     E - 0.00
LED +  0.03
       -  8.46

C1 + 3.43
     -  0.00
C4 + 1.17
     -  0.00

I've done the usual checking for obvious errors, and have also reflowed all connections, but nothing changed.  Any ideas? 

[adf]

looking at that layout shouldnt the Led + and - be reversed? so that +9v goes through R9 and into the + of LED.

[gez]

Q3 isn't oscillating.  Collector voltage is too low.  Check the joint at the collector.  If still no joy: check you've used the right collector resistor value; reflow resistor & LED joints; check the orientation of the LED.

[1878]

I removed the LED and (thanks to a peeps on this board) it worked fine. A pulsing LED looks cool, but I'll leave that to my Rotovibe. Remove the LED and see if everything works after that. If it does, you know where the problem lies and you can solve it later.

Don't forget to check the 10k resistor after you remove the LED !!

[gez]

Layouts are meaningless to me - just don't understand them - but assuming you built the pulsating LED version of the EA, then reverse the polarity of the LED.  Judging by the readings you gave, you had it in the wrong way round.

Edit:  Al is right, there's a mistake on the layout.  All you have to do is switch the connections to your LED.

[m-theory]

Oh jeez, I hadn't even noticed that...the LED does appear to be oriented incorrectly in the layout.  I'll swap that around tonight, and report back.  I suspect that'll cure the problem. 

[Mark Hammer]

I recommend splitting up R7 (120k) into two series resistors of roughly equivalent total resistance (e.g., 56k+68k, 82k+39k), and running a cap to ground from their junction.  This smooths out the peaks of the LFO a bit and, to my mind, yields a suppler gentler kind of modulation.  On mine I have a little toggle that either makes or breaks the ground connection of that cap.  I find myself regularly leaner towards leaving the cap connected.

If one had the suggested 82k+39k pair (82k first), and placed a .22uf cap to ground from their junction, this would provide a lowpass filter whose action would be maximal for content above 9hz.  That is, it would have minimal effect for very long/slow sweeps, but as you start to get something that even remotely resembles a slow throb, it impacts on the "turnaround time" of the negative and positive peaks.  It,s a small change, but gives two different feels to chooe from.

[m-theory]

Changing the orientation of the LED fixed it, and it also had the added bonus of lowering the depth, which, without that LED in place, was still rather large, even with the pot at zero.  I was going to look at making some changes to get the depth down more at minimal pot level, but now that won't be necessary. 

I'm really not that into tremolo, but a couple of friends have built recently, and I thought "sure, what the heck."  I really just intended to throw it together for giggles, but now that I've played around with it a bit, I might just find a place on my board for it after all.  I don't know that I'll find heavy use for it, but there may be a song or two that I can use it on. 

I'm not sure I have a need for a gentler, milder kind of trem, Mark, but that's an interesting mod option.  I'll try that and see if it fits into anything for me.  Thanks!