2nd EA trem build not as "Deep" as the first.

[Hiwatt25]

I finished a second EA trem for a buddy of mine last night and before I left for work this morning I plugged it in along with my 1st EA Trem build only to discover that the new one doesn't have the depth of the first. 

I left for work shortly thereafter so I didn't take any voltages but had to post anyway because I've been thinking about it all day.  I work alone so I have lots of time to obsess.

When the depth pot is all the way down, you can't hear tremolo but when it's all the way up it's not as strong as the other one. 

So, before I rip the thing apart, would anyone be willing to suggest a good place to start?

Thanks.

[B Tremblay]

Could be the variance among FETs...

[Processaurus]

Rip it apart and put in theconstant current source from Transmogrifox's REAgenerated tremolo.  It really solves that problem, rather than other mods around to try and squeeze a trifling bit more depth from the circuit.  He did some other things in that re-design to do with gain scheduling, but it works to just sub in the transistor and bias trim pot for the emitter resistor on the main transistor.  its 3 or four components, well worth it.  I couldn't be happier with mine.  If you're interested  in modding yours and would like help, I'll tell you how I inserted his mod into the existing EA circuit.

[Hiwatt25]

Well, I got home and headed straight down to the lab.  I measured voltages on the tranny's of the good EA Trem and compared them to the voltages of the bad one.  Everything was pretty much the same except for the gate of the depth tranny.  On the good pedal it was about -.68 volts with the depth all the way up.  On the bad one it was about -.03 volts. 

So I checked continuity and everything was good there.  I compared the resistor color codes of the good pedal with the bad and everything there was good too.  I even switched the good trannys with the bad and still no joy.   What I finally found was that I'd replaced the 250K linear taper "depth" pot with one of the 100K audio pots. 

So my question is, do you think this is the likely culprit?  I haven't time to resolder the proper pots this evening but I don't understand how adding more resistance would give me more depth.  Of course, I don't understand how people watch American Idol either so I might be slow. 

Thanks.

[mcasey1]

I experienced that problem with my first EA build.  Sounded great at first, but on faster speeds the tremolo becomes weak.  Also when high amounts of gain are introduced into the signal chain the tremolo nearly disappeared altogether.

[Processaurus]

Also when high amounts of gain are introduced into the signal chain the tremolo nearly disappeared altogether.

Do you put your trem after your distortions etc?  Anything that compresses/reduces dynamics will get rid of volume changes from before them in a signal chain.

[Processaurus]

hi, this was a response to Hiwatt's PM, thought other people might benefit,

Can you turn me onto the EA trem depth fix?  I searched the gallery but didn't find a layout for the mod.  I ended up ripping apart my second build and measuring all the values of the components.  Couldn't find anything wrong.  Weird.

no layout neccessary, its easy to figure out.  Did you see the Transmogrifox schematic?

heres the thread about it:

http://www.diystompboxes.com/smfforum/index.php?topic=43902.0

What I did was sub in the transistor, 1K on the emitter, and the bias arrangement on the base (the trimpot, 47K, 1uF cap), for the single 1.2K resistor to ground (off the BS170) in the stock EA trem.  Then bias it to 6v at point "A" like it says on the schematic.   Don't let it throw you, he uses a FET instead of the BS170, but they do the same thing.

Make sense?

[Transmogrifox]

Some ideas to try:

http://www.geocities.com/transmogrifox/EA_Revisited.JPG

http://www.geocities.com/transmogrifox/EA_Revisited.JPG



You had asked why making the pot a smaller value would decrease depth.  The EA Tremolo relies on the AC (real low frequency AC) signal passing through the capacitor.  A larger value (more resistive) pot increases the time constant on the high pass filter effect of that capacitor and the pot and series resistors.   The JFET has a high input impedance until driven more positive than the drain, so the LFO signal is not attenuated...although it is clipped on maximum depth by this effect (which is ok).

In short, the LFO signal is being reduced by high pass filtering.  A secondary effect is due to the nature of an open collector driver.  The input impedance of the stage following the LFO needs to be as large as possible.

The part that Processaurus keeps referring to is that 4 component group consisting of a 100k resistor, 10k pot, .1uF cap, and transistor are the love needed for maximum depth.

You could get away with a transistor and a 10k trimmer if you didn't mind the bias adjustment being a little sensitive.

[Transmogrifox]

Just realized I posted the wrong link.  The emitter resistor really helps:
http://www.geocities.com/transmogrifox/rEAgenerated_Trem.JPG