Which EA tremolo version is worth buliding?

[nguitar12]

I saw different version of  EA tremolo out there. Including original ggg version and modified version:

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

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

I see only three fet is used in modified one. Can someone please tell me which version is better?

[antonis]

I'll sugest you the homewrecker modified one..
(I've builded it and it's realy "cool"...)

Q1 is a MosFet which combines the input buffer and gain stages...
(and it's easy to properly bias it even with a less that 1 turn trimmer..)

Suggestions: Don't use J201 for Q2 (MPF102 is OK..)
                    Don't substitute the Rev Log Rate pot with a linear one..

[nguitar12]

I'll sugest you the homewrecker modified one..
(I've builded it and it's realy "cool"...)

Q1 is a MosFet which combines the input buffer and gain stages...
(and it's easy to properly bias it even with a less that 1 turn trimmer..)

Suggestions: Don't use J201 for Q2 (MPF102 is OK..)
                    Don't substitute the Rev Log Rate pot with a linear one..

Thanks for your reply. Can you suggest more substitution for MPF102? I don't have MPF102 in hand. Just the J201. What fet else can be used?

[antonis]

2N5487 is tested with  good behavior...
2N5952 also (reversed at 180 deg..)
BF245 (B or C) (also reversed)

Maybe J113 but I haven't try it...


Wait for duck_arse's more experienced opinion..

[duck_arse]

well, J210, maybe 2sk30aY (I have bf245C, and am yet to find a 9V circuit they will work in. a or b would be ok.) 2n5457, 5458. the original article specced mpf105 (does anyone besides me have any?). there are plenty of others.

try the j201, I know of someone else that used it, said it was "cool". if it works good, problem solved, search over.

[Transmogrifox]

A while ago (years ago) I built the EA tremolo and liked it, but sometimes when I wanted that really hard-chopper tremolo depth, it just wasn't there on the EA.

I came up with a way to get EA tremolo gain/depth down to nil, so it can be adjusted to a really deep setting. 

In the schematic below, notice the FJN598J are obsolete parts.  See above comments about JFETs, just about anything can be substituted with minimal tweaking, minimal consequence  (by minimal consequence, I mean I can't think of many common JFETs that would make this circuit fail to work as a tremolo).

Anyway, if you find you want more depth from the original circuit, it wouldn't be hard to add the BJT follower to the circuit in the form of flying-leads components, or a little corner of the perf board to provide that hard cut-off gain.

[GGBB]

One of the problems with the FJN598J as a substitute for MPF102/2N5457/J201 is that the pinout is not compatible. So on a PCB meant for an MPF102, adapting it is possibly but messy.

[duck_arse]

interesting bias setup on the input fet, transmog, how and why, please? what benefits over a vol control?

[also, nice work w/ the 15k in the osc!]

[nguitar12]

none of the fets you guys mentioned I have......

[duck_arse]

if the j201 is all you have (while you wait for some real fets), throw it in and try it. what other fets do you have?

[davent]

I built my EA seven years ago as per the Homewrecker schematic, BS170, J201 & 2n5089. Has always worked fine, why the avoidance of the J201, reflection of the current state of J201's available or has there always been a J201 issue?

Used a regular log pot wired backwards for the speed control, that's worked out well as well.
dave

[duck_arse]

also @ transmog, I was looking at that 1uF on the base of the extra-chop bjt, and was wondering if it might be a usable mayhem injection point. maybe a second, limited pso lfo switchable at that point, would it be usable mayhem or try it yourself on the breadboard and find out mayhem?

[Elijah-Baley]

I built the sabrotone veroboard layout, schematic by RunOffGrove.
It is nice, but not much depth.
It is a bit deeper with the power supply compared with the battery. Further, I've used a 2N5089 (260 hfe circa) higher than my 2N5088, and I used a pulsing led. Again, more depth with a 5mm yellow than other some colours.

[Transmogrifox]

interesting bias setup on the input fet, transmog, how and why, please? what benefits over a vol control?

The bias setup in the FET is configured as a constant-current source.  This allows getting bias currents high enough for reasonable amounts of gain, but the AC impedance looking into the drain of the biasing transistor (BJT in this case) is very very high.   When the control fet is turned off, there is virtually zero signal transfer to the load resistor (6.8k) since voltage changes on the input don't result in any change of current.


Another benefit is it makes the EA circuit much more agnostic to the FET.  If you do this bias job, you can pretty much just use whatever JFET you have readily available.  You could also use a BJT or MOSFET without much consequence to the circuit's operation. 

That BJT in the FET source is the heart 'n' soul of my EA tremolo version.  The rest is just stuff I came up with messing around with the circuit on the breadboard with whatever parts I had available at the time

I was looking at that 1uF on the base of the extra-chop bjt, and was wondering if it might be a usable mayhem injection point.

Probably not so much.  Anything you inject there will be amplified directly, so it wouldn't be much different than injecting mayhem at the input FET.

The best place to inject mayhem (think chopper modulator) would be at the gate of the control FET, like at the pot wiper.  That will actually modulate the signal with minimal carrier bleed-through.
 

[GGBB]

why the avoidance of the J201, reflection of the current state of J201's available or has there always been a J201 issue?

I'm not sure, but having read a lot of EA Tremolo threads and build reports, I have gotten the sense that the J201 can be a bit harder to get right, probably because they vary a lot in terms of specs so some are bordering on unsuitable for this circuit, whereas the other JFETs don't vary out of the suitable range. Just a guess though.

[Jay]

I've built two or three different versions of the EA, including the improved one, which is good.  Main thing for me was the depth and the Transmogrifix bias/ccs really cracks that.  It has more depth than you'll need!  I think I tweaked the input stage a little and used some different values in the LFO but otherwise the same.

I built an LFO output into mine, and another with an LFO in so I can run two in sync.  I opto-coupled them to avoid any hum problems. With this arrangement I've had myself and the other guitar player in our band both playing the heavy tremelo part in the Smiths How Soon is Now, sounded %^&*-on!  I called it the "Synchronous Double Tremulator". 

[GGBB]

@Transmogrifox:

You have me really interested in your BJT mod - I've seen this before but thought the FJN598J was an integral part. (I actually ordered a handful but then realized the pinout was different so put them aside.) I intend to rebuild by Modified EA Tremolo sometime soon (was my first pedal - on perf - and my soldering is starting to fail - this time I'll etch my own PCB). I would definitely like to get more depth out of this pedal.

What is the function of the 100k resistor between the depth pot wiper and the JFET? Is there anything to it other than another way to set the minimum depth, which is also set by the 47k resistor from depth pin 3 to ground? Why not just a single 150k resistor in either place instead of two resistors?

Also - why did you want to move the volume from the output to the input? Any advantage there? Does adjusting it have any effect on the input JFET?

[duck_arse]

well now. @ transmog again. yes, the mayhem turned out to be in my pc instead of the bias bjt, which did nowt but thump. I was actually referring to the input section, the level pot stuff, but ne'r mind.

something, though. when you switch to "booster" mode, you are setting the osc output to ac ground, which loads and kills the osc. my rate led stayed on, which means the 22uF cap now has +V on the (-), and something less than +V on the (+). this can't be good for the cap. a non-polar would be alright, tho.

and I spent some time with the sig gen and cro looking at the output envelope. there is some tuning can be done in the depth pot string. on the bb w/ 2n5457's, I've got 120k-B100k-68k to ground. this gives a decent minimum and a usable range on the depth down to dead flat.

and everyone here knows to switch a cap ~~120nF across the mod fet and it's tant cap, for a non-tremmed sparkle, no?

[Transmogrifox]

@Transmogrifox:

You have me really interested in your BJT mod - I've seen this before but thought the FJN598J was an integral part.

Yeah, I just happened to have a few FNJ598J laying around so I used them.  It really is agnostic to the fet with this BJT mod.

What is the function of the 100k resistor between the depth pot wiper and the JFET?

IIRC this was to soften the thump gained by the increased depth.  Less feed-through from the oscillator as the JFET transitions to fully on and the gate essentially becomes a forward-biased diode.  The resistor creates a voltage divider that prevents much of a voltage from developing across drain-source.

Also - why did you want to move the volume from the output to the input? Any advantage there? Does adjusting it have any effect on the input JFET?

The original method gives you distortion if you have hot pickups or are driving it from a distortion pedal (and sometimes \more\ distortion doesn't sound better). 

By moving the volume pot to the input you get 2 things:
1) Control over the amount of distortion
2) Lower output impedance

[davent]

The rEAgenerated Tremolo schematic has a "B" identifier but i can't find a reference, significance?
Thanks,
dave