EA Trem ?

[I am the Walrus]

Hello all. New here. I just built a Ea Trem from ROG, and it is working, to some extent. The effect doesn't seem that pronounced though, probably because of this issue: I can't get the trim pot to 4.5 volts, that is recommended. I get to about 3.5v and it begins to howl and distort. I also have a  question about the Transistor voltages. Is Q3 voltage on C supposed to jump around?



Q1: D 4.8
      G 1.65
      S 1.26
Q2: D 0
      S 0
      G .55
Q3  C Fluctuates from 3 volts, and bounces all around
      B .56
      E  0


Do these numbers seem right? Is the hfe on Q3 critical?

Thanks for any and all responses.

[thermionix]

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

Is Q3 voltage on C supposed to jump around?

Yes, that's the LFO "doin' its thang."

Read up on the GGG version:

http://www.generalguitargadgets.com/effects-projects/tremolo/ea-tremolo/

Very quick glance, looks like basically the same thing with an added input buffer (Q4).

Er, my bad, the ROG version subtracted the separate input buffer.

[I am the Walrus]

Thanks for the reply, thermionix. Cool pic of EVH, by the way. I just noticed that if I turn the volume pot just slightly down, it lets me set the voltage up to 4.5-5v as prescribed and the effect doesn't go haywire. So, would I just use a different size pot to achieve this change for the better, smaller or larger value?

Thanks.

[thermionix]

Theoretically you could use a smaller value pot with a fixed resistor "on top" to limit your max volume, and thus prevent the noise.  But I don't think that's the best way to go about it.  I'm not sure what your issue is, but it might be instabilty (positive feedback).  I wouldn't really expect that from such a low gain circuit, but what do I know.  Maybe moving or shortening some wires will fix it.  Maybe the board layout needs to be changed.  Maybe it's something else entirely.

Can you post pics of your build?

[antonis]

I can't get the trim pot to 4.5 volts, that is recommended. I get to about 3.5v and it begins to howl and distort.

Just to make things clear..

4.5V should be measured on Q1 Drain...!!

[I am the Walrus]

Sorry for the slow reply, busy weekend. I pretty much followed the layout on the ROG site.

[I am the Walrus]

 I did measure it on the drain of Q1.

[I am the Walrus]

I was able to get the volume pot to full rotation without any problems by raising the value of the .47 capacitor that goes to the third lug of that pot. I really like the sound of this trem, but does anyone know a tweak to make it a bit more pronounced sounding. The depth pot doesn't seem to have a large impact on the strength of the effect.
     
Thanks for any info about this.

[I am the Walrus]

Has anyone tried these mods?  Did they work well?

  http://photobucket.com/gallery/user/GGBB1/media/bWVkaWFJZDo5MDYwMDcyOQ==/?ref=1

[Andrekp]

FWIW, the BYOC Trem layout, which is basically a modded EA, that you can find on the Tagboard Effects site, works perfectly.  I built a few of them.  If you can't find the problem here, it might be simpler to just start over and build that version.  Again, FWIW.

(There is also an EA Trem layout, as I recall) on that site.

Using already worked layouts generally means that if you have a major problem, it's almost always one of two things, you have a wrong component value, or a short in the wrong place.  The circuit works, YOUR version does not.