Fuzzy EA Trem

[smashinator]

Hi Everybody,

I've breadboarded the R.O.G. EA tremolo, and after making some tweaks to the depth control (more depth!) I really like it.

Anyway, when I hit the strings hard, it starts to clip the guitar sound (the trem effect is still smooth).  Which resistor(s) should I change to clean it up?

[B Tremblay]

Are you certain that the MOSFET is biased correctly?

What transistors did you use?

[smashinator]

It was a BS170 for Q1, a J201 for Q2, and a 2N5088 for Q3.  I adjusted the trim pot for 5 volts originally, then 4.5 (just on the off chance).  It behaves the same in either case.

[RDV]

Are you completely sure you're not just overdriving your amp?

RDV

[smashinator]

RDV - Pretty darn sure.  Actually, that was the first thing I checked.  I turned the volume on the effect down to unity and it was still doing it.  Didn't go any lower than that, I'll try it again tonight just in case my volume perception was off (darn tricky tremolos, screwing with my sense of LOUD).

[smashinator]

Ok, I turned the volume WAY down on the tremolo last night, and it was still fuzzy when I play hard (incidentally it's not a "BAD" fuzz, I just want it to be CLEAN).

I measured the voltages on the BS170 and, of course, forgot to bring them with today.  They were something like D=4.55 G=2.6 S=0.6.  What kind of voltages should I have?  

Would hot pickups cause the trem to cut off?  I don't THINK mine are especially hot, they're just the stock PAF-lookin' deals that come with an epiphone explorer.

[gez]

I measured the voltages on the BS170 and, of course, forgot to bring them with today.  They were something like D=4.55 G=2.6 S=0.6.  What kind of voltages should I have?  

Please double check the colour codes of your resistors.  If you do have 0.6V on your source then you have the wrong resistor (too low) in there, which would account for the higher gain and clipping problems (as well as your need to tweak depth).  If my calculations are correct, you should measure about 1.3V at source (with correct resistors) if you've biased the drain at 4.5V.

[smashinator]

Thanks! I'll double-check that tonight.

[smashinator]

Ok!  So, I've ripped the sucker completely apart, double and triple checked all of the resistors with my DMM, carefully reassembled using the original components (restored to pre-depth-tweak values), fiddled with the trimpot and it's STILL distorting.  Also, the trem is extremely, uh, lame, especially after checking the sound sample on the R.O.G. site.  

I'm assuming that it's mis-biased.  The voltages on my bs170 are D= 4.82; G started at appx 2.6, and then just kept dropping, is that normal?  S is 0.63 which is even further off the mark than it was before.  

I've noticed that the lower voltage I have at the drain, the higher it gets at the Source.  Is that how it's supposed to go?

Ok so, sorry for the dumb newb question, but which resistor(s) do I need to monkey with to get my voltages into the right ball park?  

Can y'all think of anything else I can check for errors on my part?  

Thanks for the suggestions so far, by the way.

[gez]

S is 0.63 which is even further off the mark than it was before

Replace the 22u cap between drain of Q2 and the 1k2 resistor, it's leaky.  Either that or you got the polarity wrong and it's gone leaky...

Measure the source once replaced.  If it measures about 1.3V then everything is ok, but you'll probably need to re-tweak (is that a word?) the resistors which set depth, seeing as you've messed about with them already.

[smashinator]

A ha!  I'll check that out tonight.   I actually un-tweaked everything last night, just in case I got it right when I re-assembled it.  

Thanks for the help!

[smashinator]

Ok, so changing the 22u cap did take care of the dropping voltage on the gate, but the source voltage is still off (can't remember exact measurement, still way too low).

So, having looked at the new "things that matter" list, I wonder if perhaps the mosfet is bad.  Like I said, I measured all my resistors, and pulled it apart and rewired it.

Should I yank the mosfet and replace it with another?

[gez]

Sorry, I didn't see that bit about 'falling gate voltage' in your previous post.  It does sound as though the MOSFET is dodgy.

Are you sure you got the pinout right?  RG just posted something the other day saying that BS170s have more that one pinout (gulp!).  Best check with your supplier's catalogue to see what they have for the pinout.

Either way, best to pull it.

[RDV]

Best to socket it.

RDV

[smashinator]

Thanks for the tips guys.  I'll double-check the brand of the MOSFET.  I did swap it out last night, and the voltages were only a TINY bit different.  Hmm.

Incidentally, it's on a breadboard right now, the ultimate socket.  :wink:

Well, I'll make sure I have a datasheet for the right brand.  If that's all it is, I'll be a happy guy (though embarassed).

[smashinator]

...Yep, right datasheet.

Well, I'll make sure I've got it in there right tonight.

[theaxeman]

Hi

I found a mod on GGG that may help!

Heres the link: http://www.geocities.com/basspreamp/effects/EA_Tremolo_mods.html

Hope this helps!  

[theaxeman]

OOPS!! Acidental Double post!!

[smashinator]

Thanks!  I'm using the R.O.G. schem, but I'll try slapping an extra resistor / bigger resistor to ground on the gate of the mosfet, just to see what happens!   :twisted:

Perhaps this weekend I'll try just throwing the sucker together (after measuring everything and using sockets) on Perf using the R.O.G. layout and see if I didn't just goof on the wiring somewhere (Twice, no less!).

[smashinator]

Well crap, I put in an "extra" resistor on the gate (just for giggles), and it didn't really help.  Checked the pinout, and even tried flipping the sucker around just in case, that didn't help either.

I'm debating whether or not to build it on perf using the R.O.G. layout this weekend, or if I should just shelve it and get started on the amp emulators.  

Maybe I'll build a pulsar instead.   :wink: