Mosfet Boost into EA Trem= distortion. Simple fix?

[squidsquad]

Yeah,  I know, I can turn the booster down...but luv the sound of it up.
The boost goes into the Rocket...then into the trem...and I don't wanna fiddle with knobs onstage.  Was wondering if there'd be a simple mod to stop the distortion I get from slamming the front end of the Trem?(Rocket bypassed).
Of course I tried putting the trem first...but adding fuzz to that loses everything....although it sounds cool as the fuzz dies...and the trem creeps in...hehe!

[bigjonny]

Not to hijack this thread, but from the title, I thought someone was going to suggest that you could turn the MOSFET boost into a trem with ease.  Seems possible...

[Michael Allen]

The issue is adjusting the bias of the first stage transistor in the EAN. Sometimes it distorts on its' own, so driving it with boost will completely smash it. I think runoffgroove has some fixes for this with their version.

[gez]

Squid, is your circuit on perf?  If so and there's a little room for tinkering you can change the buffer arrangement slightly for the EA to prevent clipping.

I posted a little design earlier on in the year and it's been verified.  I'll link to it when I get the opportunity.

[gez]

It's an alternative to the buffer of the runoff version of the EA trem.

[Gripp]

Hi!
Gez,
I build this alternative buffer in my ROG EA and can also verify that it works. Them EMG's being a tad to hot for the original.
However, I just cut one trace, drilled a new hole and inserted the trimmer instead of the 1M resistor into the pcb (the Gringo ROG layout) and didn't change any cap values. Worked perfectly fine.
I just wonder about the changed cap values in the alternative buffer, ie 22u elyte instead of 47u and 2u2 elyte instead of 0.47u np. Error or purpose and if so why?
Best!
/Pelle Garpebring

[gez]

I just wonder about the changed cap values in the alternative buffer, ie 22u elyte instead of 47u and 2u2 elyte instead of 0.47u np. Error or purpose and if so why?

When I suggested using a MOSFET for the amp, I just posted values in written form (no schematic).  Brian picked up on the idea and did the work of trying the circuit out (I've never built the EA trem).  I probably said something along the lines of 'use a large cap from wiper to ground' and Brian ended up using a 47u.

My preperence for a 22u is as follows:

1.  I have lots of 22u caps (I could end the list here)
2.  They're slightly smaller than the 47u caps I use
3.  Circuit will bias up slightly quicker (not that this is a problem, or so I gather).

It's not critical, use whatever you've got.

For output caps I use 2u2 - 10u, whatever I've got in my parts bin.  You never know (most of the time) what's going to follow so making this cap as large as possible (within reason) is always a good idea...

[Gripp]

Thanks Gez!
That's what I suspected, just wanted it confirmed from the source :wink:
Anyhow that pedal sounds and feels really good. It has a warm, classic feel to it and I guess it is largely due to that buffer. Must try to build some mosfet buffers for my pedal chain next.
Lots of credit to those who put the ROG EA together!
My friend Maria got an EA for her 30th birthday and she was really happy too. Wonder if she has tried it out on the rhodes yet...

Best!
/Pelle Garpebring

[squidsquad]

Hey guys...thanks for the tips...luv this board!  Was also wondering if trying 12 volts would help?  Squid

[gez]

Was also wondering if trying 12 volts would help?

It wouldn't matter so much for the amplifier part (and yes, it would help), but the LFO would probably need some attention.  The amplitude of the sine would almost certainly be larger so you'd have to increase the value of the resistor in series with the depth pot to drop some more voltage.  You might have to add a resistor in series with the 2M2 to get the LFOs trannie to bias up right.  Sort of thing you'd have to check with a meter and (ideally) a scope.

You could use a low-drop 9V regulator to power the LFO.  Perhaps get away with sticking a zener in between V+ and the LFO's collector resistor to drop some voltage (crude, but would probably work)?