rEAgenerated Tremolo Redesigned: Have your cake and EAt it

[GGBB]

You will notice on the page I also added a Rev B design which includes a capacitor in the FET gate linearizing resistor.

I've added that change to my layout - stroke of luck that it was a simple change.

[Transmogrifox]

Nice work.  Do I have permission to copy and serve that image on my site?  At the very least I could link to it, but I like to have as much as possible hosted on the site so that if the site is up, all it's goodies are there too.
Thanks

[GGBB]

Nice work.  Do I have permission to copy and serve that image on my site?  At the very least I could link to it, but I like to have as much as possible hosted on the site so that if the site is up, all it's goodies are there too.
Thanks

Hosting it is fine (thanks!), but please also provide the link to the original: http://www.aronnelson.com/gallery/main.php/v/diyuser/GGBB/Tremolo/rEAgeneratedTremolo.png.html.

[duck_arse]

RevB - done - needs checking. wangle your own P2 and P3.

[Cozybuilder]

Very tidy layout DA, I note 3 differences to the schematic:
  1) S and D are reversed for both Q1 and Q3 (OK)
  2) Cap C9 has been inserted between R9 and junction Q3G and R10
  3) C5 and R8 order reversed (OK)

[Transmogrifox]

  2) Cap C9 has been inserted between R9 and junction Q3G and R10

C9 looks correct in the layout to me.  This is the Rev B update so maybe you are comparing to Rev A?

[Cozybuilder]

I was 

[pacealot]

Long-time lurker, first-time poster. Giving this a 5-year necrobump to say that I just breadboarded this circuit, and it’s fantastic. I had to make some tweaks to get the depth control to play more nicely — as the pot approached maximum, the tremolo would die out, and then reappear at max, but very distorted. I also found it took a while for the travel of the pot to kick in the tremolo at the minimum. My solution to both issues was to swap the 10K pot for a 5K, and put resistors on either side (currently I have 2.2K going to +9V and 3.9K going to the junction of Q4C/C6/R11). That has improved the control and usability of the depth pot significantly — and plenty of chop still.

I’m also still tweaking the rate values. The stock 1µF configuration was too slow for me, so I doubled them up in series (I have a lot of 1µF lytics around) to drop each of them to .5µF, which has been great so far, but I have yet to alter the 1K resistor R13 to see what that accomplishes (I’m shooting for maximum rate range on the one pot). Going to play with that next. (Edit: tried messing around there, but couldn't improve on the configuration above.)

I’m splitting the difference on the gain/input issue — I initially bypassed the 1M volume pot entirely and put a 5K trimpot on R8, but my hottest guitar did clip it a bit at its loudest. So now I’m planning on padding the input with fixed resistors and using the trimpot to fine-tune it. It does indeed have plenty of extra gain. I prefer the “set-and-forget” approach to the volume control.

I had planned/hoped to omit the blinking LED as I’m not really a fan of them on pedals in general, but I put one in the circuit for testing purposes (and because it was helpful to see when it was actually oscillating). When I bypassed it and connected the depth pot/resistor combo directly to Q4C, the maximum rate increased ever so slightly, and since I want as much range as I can possibly get, that helps me feel just fine about ditching the LED.

This is by far the most functional and versatile transistor trem I’ve heard yet! Thanks to Transmogrifox for coming up with this one, and to everyone else for their input as well…

[duck_arse]

welcome to posting, pacealot.

changes to the collector current will change the osc range. there are different ways to add the flashing led, and I can't remember, and you haven't shown, how it is implemented in this inst. there are ways to get a much wider range from this type oscillator, and steady consistent output at both extremes - some involve staggered cap values, some w/ caps on range switches, some using dual-gang rate pots. and some people use a mosfet instead of a bjt.

[pacealot]

Thanks, d_a — I'm already beginning to notice the interactive effects on both depth and rate in changes to Q4 collector current. Right at the moment I'm trying to settle on the most likely "usable" range of rates from a series of new experiments on the values of caps 6, 7, & 8. Interestingly, I'm getting better results with a slightly higher value for C7 than the other two — could be a quirk of the specific 5089 I have in there, not sure. This is actually the fun part for me — auditioning values until the "best" ones present themselves, and then trying to replicate it upon boxing up!

Regarding the LED, I'm honestly much happier omitting the LED, so I haven't really come to grips with how it's designed into this specific circuit. I know people seem to like having a blinking light on pedals with LFOs these days, but I'm not one of them!

I do have a dual anti-log 100K pot on order actually, so maybe when it arrives I can play with that as a means to really get absurd in the rate department!

[duck_arse]

if you stagger the values of the three phase-shift caps, you can extend the range of willing-to-oscillate. shoot me a pm with an email addy, and I can send you some lfo diagrams on the q.t.

[pacealot]

Done — PM sent. Thanks so much d_a!!

[pacealot]

A brief follow-up on my experiments in getting more range on the rate sweep:

I explored the dual-ganged pot situation by adding an extra cap/resistor stage between C6 and C8, and taking that resistor to the other side of the rate pot. I also followed duck's suggestion to play with staggering the cap values, and I also changed a number of resistor values as well. What I came up with was touchy to get working, but once I settled on some values, it became the largest and most versatile sweep of any tremolo I've experienced yet.

I was going to try subbing in a MOSFET as per duck's source materials, but this arrangement has worked out so well that I decided to leave well enough alone for the time being! (I do still have some extra 5458s and 5089s and a 2N7000 I've not used yet, so I could continue exploring further later....)

Here's where my version of the circuit ended up (I renumbered the components to try to make more sense with the new arrangement):

[pacealot]

I realised that I made a mistake in the previous schematic and connected Q3 source to the wrong voltage source. Here's the correct one:

[cab42]

After some, not very successful, experiments with the EA Tremolo, I came to think of rEAgenerated Tremolo instead. After having it on breadboard for some days and trying some modifications, I decided to make a permanent build and made a vero layout as I couldn't find one. Click image to go to the gallery for full size.



It was a pretty easy build other than it is a bit tight around C6, C7 and C8 if you have large capacitors. I used J201's instead of 5458's. Does that make much of a difference?

A  couple things was a bit odd, though. On breadboard, much of the rotation of the depth pot had no effect both in start and end. I used the suggestion by Pacealot above and tagged some resistors in series with the pot and another across the pot to lower the value. However, on the final build I had no such issue. I also had issues with distortion on breadboard, that went away in the final build.

I tried different values for C6, C7 and C8 for rate. I liked 680n, but the ones I had were huge, so I built it with 1u's, but socketed them, for when I get something smaller.

I might also see if I can get away with ditching the volume pot.

Thanks to Transmogrifox and every one else that has contributed.

[pacealot]

Nice work! I really love this circuit. So much so that I've built three versions of it so far (including a stereo one for my bass rig which I still need to populate onto a PCB). The only area that requires re-tweaking each time has been the resistor network at the depth pot which you mention. I think that's due to the variation between JFETs (I've used 5458s, 5457s, and most recently BF244Bs, all with equally good results), so if your J201s are working, then I'd assume they're just fine. But I have had to dink with the resistor values there with each iteration to get the optimal depth range. It does seem to prefer a total of 10K at that point, just portioned out slightly differently each time.

Also Duck's suggestion of staggering the LFO caps to increase overall range is a very good one, and tantalums would fit nicely size- and value-wise (and in my experience tend to make for a "cleaner" oscillation shape than regular aluminium 'lytics). Since you socketed those, it could be beneficial to play around with some there...

[Transmogrifox]

...but very distorted.

It's fun to see people improving upon the idea and tweaking further to their taste   I'm happy to see it's getting some mileage.

Some notes to help others understand why the Rev B rEA ended up the way it did.  I hope these notes will help other builders to decide whether to start with some of the modifications/improvements suggested in this thread or try the original first.

In addition to the design rationale doc, which summarizes the overall purpose of each piece (https://cackleberrypines.net/transmogrifox/rEAgeneratedTremolo/pages/projfiles/rEAgenerated_Tremolo_Design_Rationale_RevB.pdf), these thoughts may be useful:
With input volume maxed, that was a "feature" that it would become distorted, and also has significant gain boost.  I used the volume knob to drive my amp into a pulsating distorted sound, and also by adding a switch disabling the oscillator it could be used as a booster for getting a good crunch out of my amp.  For a clean tremolo, the volume knob was always dialed down to a level where the peak output was somewhere between unity to 6dB.  With those input volume settings I did not notice the distortion as being prominent  -- it was a purposeful decision the volume control was placed at the input.

For a transistor amplifier like this also using  a JFET as a variable resistor the best way to reduce distortion is to decrease the amplitude of the signal subject to the devices (smaller gate-source voltage, or for the variable resistor, smaller drain-source voltage).  Best to attenuate at the input and amplify by larger drain resistor (R5). 

If going for a fixed configuration ( no volume pot) the best setting if you want the loudest part at about unity would be somewhere around 1/5 resistor divider ratio at the input (e.g replace 1M pot upper leg with 750k, lower leg with 250k). 

As for the LFO depth control range, I agree it can become fairly extreme.  The purpose in the rEA implementation is after a certain point it begins to change the duty cycle rather than the depth of the effect.  This is a feature for those who like to exploit the chopper type of effect, but definitely limits the usable range for those who want to dial in more of the smooth pulsating tremolo effects.