Should the EA Tremolo distort?

[xnery]

I have built a few pedals, but my latest is the EA Tremolo. It definitely has a tremolo effect, but mine is distorting. Is it supposed to be a clean pedal? I've heard one or two soundclips of it clean, but do I have to mod it in order for it to be a clean effect? I built mine according to the information at general guitar gadgets: http://www.generalguitargadgets.com/index.php?option=content&task=view&id=108&Itemid=138

Thanks. 

[rockgardenlove]

In short, no.

[MarcoMike]

I made the MOSFET one, and it had the same problem, then I "fine-tuned" Q1 (the one with the trimmer...) and it works great. which version is yours?

[xnery]

I built the one from General Guitar Gadgets. There is no trimmer. According to their list of materials, these are the transistors that I used:

Transistors
Q1 - 2N3904
Q3 - 2N5088
Q2, Q4 - 2N5457 or J201 or possibly other JFET

I used J201's for both Q2 and Q4.

[dachshund]

There's also this schematic, which is even simpler to build, and has better pot & resistor values. I breadboarded the GGG version, then found this, which is what I ended up building. Very nice, and you can use the LED in the circuit as the "on/off" LED. It blinks in sync with the tremolo, which is a nice feature. Clean, "transparent"; no distortion.
http://www.runoffgroove.com/eatremolo.html

[xnery]

It says that Q3 is a BS170. Would I be able to substitute some other transistor for that? I think that I have all of the other components.

[Processaurus]

It distorts by design because there is a lot of gain happening in that circuit (thats why it can get super loud), that you later attenuate with the volume control.  Mine would clip badly with hot pickups.

There isn't a way I'm familiar with to lessen the gain without affecting the depth, because the circuit works in a way were there is a minimum volume of the signal (it may be a gain of 1, not sure), and then it amplifies on top of that to make it trem.  Then you turn the volume down so that the amplified peaks are at the level of your signal coming in, and that makes the minimum volume signal much lower.

Best way to avoid that is to move the volume control to the input, or attenuate the input somewhat (maybe cut the signal in half with a two resistor voltage divider) and leave the volume control on the end.  If it were my thing I would buffer it with the JFET buffer at GGG (like the GGG version of the EA has on its input for high impedance), and then put the volume control, to avoid potential tone sucking from the volume control connected directly to a guitar.

[xnery]

But would I be able to build the Runoffgroove ea trem with a different transistor in place of the BS170? I've got j201 jfets & several types of NPN transistors.

[rockgardenlove]

I don't think you could directly sub anything in there.

[Threefish]

I got distortion in my EA when I built the ROG version with a 2N70000 (BS170 equivalent), so I modded it with the help of Brian at ROG, using a mod originally done by Gez (salutations and thanks again gentlemen!)
Here's my build report on it: http://www.diystompboxes.com/smfforum/index.php?topic=45546.0

The single BS170/2N7000 is there to give enough gain as the two JFETs in the GGG version. I doubt that you would get it to work well using a single JFET stage, if at all.
Where are you? Can't get hold of MOSFET's?
I don't know why you'd bother with the GGG version - ROG's is much simpler. I did the pulsating LED mod too. It looks really cool, pulsating in a darkened room....
I love this trem. Get hold of some 2N7000/BS170's and build the ROG version. You'll need an extra 2N7000 for your Millennium II bypass.....

[dachshund]

You can add the pulsating LED to the GGG version, by replacing the 15K resistor with the 12K, for what it's worth.

[xnery]

I'll be ordering another load of parts tomorrow, including some BS170's. Has anyone used the pcb layout at this link? http://www.runoffgroove.com/eatrem-pcb.pdf

I'll etch the board and try it for my next tremolo pedal if anyone has anything positive to say about it. I'm really just looking for a clean, non-distorted tremolo. I liked the sound clips of this tremolo at ROG.

[Transmogrifox]

I haven't made a layout or board for this, but you may be interested in looking at it:
http://www.geocities.com/transmogrifox/rEAgenerated_Tremolo

If after you build one and find the depth lacking, then here's the solution.  The JFET can be a 2N5457, J201, or any other that seems to be available (really). 

It's pretty clean sounding, really.  I was having the same distorting problem with the EA, so I moved the volume knob to the input.  This allows you to trim the input back before it starts banging on the rails.  The input pot could be 500k, really.  I used 250k just because that's what I had on hand, and the schematic is a record of what I actually built and not particularly a completed plan for how it should be done.  It does work great by the schematic I have shown.

[Paul Perry (Frostwave)]

I'd just like to add, that of ALL effects, I consider tremolos the most difficult to design & build successfully.
That is because, unlike every other effect, you aren't actually adding or modifying the signal, just changing the level cyclically. So any distortion at all, or noise injection, is horribly obvious.
And another thing: I personally have always stayed away from fets as much as possible, because of the wide variation in characteristics (even for the same part number). This is why a circuit that works well for one person, often is a bummer for another.

If I were making a tremolo, I'd be looking at vactrol (led/ldr) based designs. And I'd be careful about interference from the LFO circuit - but if you base the LFO around a wein oscillator, at least that would be taken care of.

Best commercial trem I ever heard - not that I spend a lot of time listenting to trems! - was a Dunlop that was based on a voltage controlled amplifier used in ghetto blasters.

[Transmogrifox]

Best commercial trem I ever heard - not that I spend a lot of time listenting to trems! - was a Dunlop that was based on a voltage controlled amplifier used in ghetto blasters.

The obvious question is, do you have a link to that circuit or a snippet of the ghetto blaster VCA?  It would be interesting to see that.

[Paul Perry (Frostwave)]

Unfortunately I never had the circuit. I'm sure the box was purple. I remember a toshiba SIL chip.

[mac]

I found that whit some low Vgsoff fets like 2sk117 it is ok to add a resistor from source to gnd to make it work better. I used a bf245A and no distortion at all.
Maybe a lower gain transistor?

mac