EA Tremolo questions

[nobodysweasel]

Hi everyone.  So I just finished my first build and it actually worked!  It's an EA tremolo with the flashing LED and boost only mods.  I really, really love this pedal.  Thanks to all the regular posters here that helped me figure out some of the basics.

I have just a few questions, and hopefully someone can help.  The one thing that I'm not completely happy with about this pedal is the speed knob.  It gets much slower than I would ever need, and not as fast as I might like.  I doubt I'll ever have it at less than 12 o'clock.  Is there something I can do to just shift the overall speed up?  I've seen a few posts about adding another speed knob and switch, but that seems a little overboard for my needs.

More importantly, what resources are out there that would help me answer this question myself?  I learned some of the basics of electronics in a physics class a few years ago, so I can run the basic equations and I can follow a schematic.  But when I look at a schematic for a pedal, I don't know what it's doing.  Are there any good books or online resources that will help me really understand these circuits, as opposed to just knowing how to put them together?

Thanks in advance for any help you guys might have, and thanks again for all the info I've found searching these forums!

[boogietone]

To understand the workings of this tremolo read up on phase shift oscillators.

[Seljer]

There is a resistor in series with the rate potentiometer that limits the maximum speed. Lowering the value of that resistor will make it go faster when its set at 100%
To make the slowest setting faster as well you need to use a lower value of potentiometer or wire a resistor in parallel with the potentiometer for the same effect (some changes to the sweep may occur)

[nobodysweasel]

Thanks for the advice.  I've read up a little on phase shifting oscillators, and I think I can identify where that's happening in this circuit.

I used the schematic from generalguitargadgets.com, which apparently already has a lower value resistor going into the speed pot to allow for a higher maximum speed.  It's now a 1k ohm.  How much am I going to have to change it to get a noticeable difference?  750 ohms?  500 ohms?  I'm now starting to realize the benefits of breadboxing a circuit before putting it all together  .

Sorry if this is a noob question, but to make the slowest rate faster, would that mean putting a resistor between lug 3 of the speed pot and ground?  I just want to make sure I understood you correctly, and using a resistor would be cheaper and easier than changing out the pot altogether.

[PRR]

> I learned some of the basics of electronics in a physics class a few years ago, so I can run the basic equations and I can follow a schematic.
> Is there something I can do to just shift the overall speed up?

Basic electronics should have covered R-C networks. There is a frequency. You find it with some math around R and C.

The EA oscillator has a variable R, and a C next to it. Actually three R and three C. Nominally of similar value, except here the relationship is confounded by the way R9 is tied. R11 is variable with 10K-20K at mid-turn, R10 is 15K, and R9 is a 2Meg part but fed-back from a point with high gain and "acts" much smaller.

As the frequency equation shows, you may vary either R or C or both to change frequency.

However the R parts _also_ set DC bias conditions. So you don't want to change them.

Also: How much am I going to have to change it to get a noticeable difference?  750 ohms?  500 ohms? somewhere down there, it will just stop working. the benefits of breadboxing a circuit before -- while your iron is hot, bring long leads out where you can clip any resistor desired.... but already you are fighting a losing slope on frequency and will soon load it so far it quits wiggling.

Changing the C values will change frequency without changing DC conditions or loading.

I hope you can work-out if you want to take C5 C6 C7 bigger or smaller.

[nobodysweasel]

Sorry to bring back a dead thread, but I finally followed through on this and wanted to report back in case anyone ends up searching for it later.  I opened up the first pedal I made almost a year later to the day, and boy was it a mess.  I've come a long, long way in a year.  I also understand what PRR was getting at now, so I made the changes to C5 C6 and C7 in order to increase the speed.  In the GGG schematic they are 1 uF caps.  The smaller you make them, the higher the speed will be.  Cut them in half and you get twice the speed (i.e. you slowest speed is twice as fast as well as your fastest speed).  I had 0.47 caps on hand and made the change.  I'm really pleased with the result, but I think that change was just a little too much.  I'll probably swap them out with 0.68 uF caps the next time I buy parts (which will probably be soon, 15% off at tayda with code 933666 for the next couple days).  Anyways, this is a really easy change and I'd recommend it to anyone building an EA tremolo.  It's just too slow stock.  Hope this helps someone.

Also, thanks to PRR for the help.  Gave me just enough info to understand why changing the resistors is a bad idea and work out what I needed to do with the caps.

[Hallmar]

Sorry to bring back a dead thread, but I finally followed through on this and wanted to report back in case anyone ends up searching for it later.  I opened up the first pedal I made almost a year later to the day, and boy was it a mess.  I've come a long, long way in a year.  I also understand what PRR was getting at now, so I made the changes to C5 C6 and C7 in order to increase the speed.  In the GGG schematic they are 1 uF caps.  The smaller you make them, the higher the speed will be.  Cut them in half and you get twice the speed (i.e. you slowest speed is twice as fast as well as your fastest speed).  I had 0.47 caps on hand and made the change.  I'm really pleased with the result, but I think that change was just a little too much.  I'll probably swap them out with 0.68 uF caps the next time I buy parts (which will probably be soon, 15% off at tayda with code 933666 for the next couple days).  Anyways, this is a really easy change and I'd recommend it to anyone building an EA tremolo.  It's just too slow stock.  Hope this helps someone.

Also, thanks to PRR for the help.  Gave me just enough info to understand why changing the resistors is a bad idea and work out what I needed to do with the caps.

So if you make the caps bigger the speed slows down?

Also, changing C2 and C8 for a higher value might get more bass if you want too.

Worked for me.

[nobodysweasel]

So if you make the caps bigger the speed slows down?

Correct.  The frequency of oscillation is inversely proportional to the capacitance.  Look up "phase shift oscillators" if you want to find the whole equation (wikipedia is good here).

[Hallmar]

So if you make the caps bigger the speed slows down?

Correct.  The frequency of oscillation is inversely proportional to the capacitance.  Look up "phase shift oscillators" if you want to find the whole equation (wikipedia is good here).

What about the depth?

it's a bit little to my taste, should i maybe change R7 to a lower value?

[GGBB]

What about the depth?
it's a bit little to my taste, should i maybe change R7 to a lower value?

Yes.  But doing so will also raise the minimum depth a bit so you might need to adjust that a bit as well.  The 68K, 250K pot, and 120K control depth.  The 68K sets the minimum depth, and the 120K sets the maximum depth - since they are functioning as one large divider it's the ratios that matter so lowering one end effectively raises the other end and increases the pot's range of depth adjustment.  You can adjust them to taste.  You could even have just a pot which will give you a broader range of depths, but the shallower settings will probably be mostly unusable.  I lowered the 68K to 18K and replaced the 120K with a 100K pot that is on a second footswitch which works as an adjustable depth boost.  With both the depth and boost on full, it's the same as having 0 instead of 120K and is nice and deep.