rEAgenerated Tremolo Redesigned: Have your cake and EAt it

[PRR]

> In particular the depth pot orientation - needs to work so that clockwise increases depth.

Look at the schematic.

When wiper is at the "+9V" end, trem is zero. When wiper is close to the transistor, wobble is maximum.

I dunno how you number your pots' legs, but hold a pot near your layout and it should be figurable.

(If we assume the Level pot is clockwise=louder, then the numbers on the Depth pot seem wrong.)

The Rate is absolutely a hard problem. The 1-2-3 leg issue is moot: if it runs backward just saw the jumper wiper-end and jump wiper to the other end. (Or note that in an R-C network big resistance is low frequency and work it out.)

But either way, smoothest action with normal "faster = clockwise" rotation will want a Reverse-Audio pot. Maybe not for a 100K pot with a 50K stopper, but here we have 100K and 1K and do need w-i-d-e range of resistance. A Regular Audio or Linear will have all the action in the last bit of rotation.

And no, you can't fix this with a "bend resistor". (Here our "pot" is working as a rheostat, not a potentiometer.)
_________________________________

> Doesn't D1 half-wave rectify the LFO signal, thereby changing the LFO wave shape?

The LFO AC is riding on the average DC flowing through the LFO transistor. The transistor current never *reverses*. It may get near zero but only for a blip. There's one-way current nearly all the time.

[Transmogrifox]

Bump. Anyone? Will your sim tell you T-x?

Ah...maybe PRR better understood the question you were asking. (Thanks PRR for chiming in) He has correctly identified what needs to happen from the point of view of circuit operation:
1) Clockwise rotation of the depth pot should move the wiper toward the LED.  Minimum depth is when the wiper is effectively shorted to +9V.
2)  Clockwise rotation on the rate pot should decrease resistance.  Maximum rate is when the series resistance is at its minimum.
3)  If you add the optional P2,P3 Pot, then maximum resistance across those two points is maximum depth.

duck_arse layout has these correct from this higher-level point of view.

My simulation won't tell me whether I got my pinout right because it all depends on whether CW rotation moves Pin 2 toward Pin 1 or toward Pin 3 and those assignments are whatever I arbitrarily decided in SPICE, while the real the pinout depends on a specific pot.  That's what I didn't know.

If you were asking for the more simple answer, then I will need to take out a pot and a DMM to verify what happens between pins 2&3 on CW rotation.

It looks like your initial question was right:
In my schematic the rate and depth pots are backward from the volume pot.  So whatever pinout works correctly for volume is the reverse of rate and depth. [EDIT] Upon closer examination Rate pot is correct if Volume pot is correct.  Depth pot is the only one to break convention [/EDIT]

[Kevin Mitchell]

I've been digging around for a while trying find the most enticing tremolo to build.

Mind sharing a sound demo?

[Transmogrifox]

Mind sharing a sound demo?

Maybe this weekend I'll have some time to plug it into the puker and record a clip or 2.  I can post audio samples from the simulation, but somehow it doesn't capture the more fluid effect of tweaking knobs and dialing it in more organically.

[duck_arse]

I never call pots 1-2-3, so I just lucked it if my connections correspond to transmogs designations.

I have tried the bend resistor on the rate pot before, trying to get a bit more resistance range, and was less than impressed. I used a 'C100k' for the trololo I built, nise and smooth.

[GGBB]

> In particular the depth pot orientation - needs to work so that clockwise increases depth.

Look at the schematic.

When wiper is at the "+9V" end, trem is zero. When wiper is close to the transistor, wobble is maximum.

I dunno how you number your pots' legs, but hold a pot near your layout and it should be figurable.

(If we assume the Level pot is clockwise=louder, then the numbers on the Depth pot seem wrong.)

The Rate is absolutely a hard problem. The 1-2-3 leg issue is moot: if it runs backward just saw the jumper wiper-end and jump wiper to the other end. (Or note that in an R-C network big resistance is low frequency and work it out.)

But either way, smoothest action with normal "faster = clockwise" rotation will want a Reverse-Audio pot. Maybe not for a 100K pot with a 50K stopper, but here we have 100K and 1K and do need w-i-d-e range of resistance. A Regular Audio or Linear will have all the action in the last bit of rotation.

And no, you can't fix this with a "bend resistor". (Here our "pot" is working as a rheostat, not a potentiometer.)
_________________________________

> Doesn't D1 half-wave rectify the LFO signal, thereby changing the LFO wave shape?

The LFO AC is riding on the average DC flowing through the LFO transistor. The transistor current never *reverses*. It may get near zero but only for a blip. There's one-way current nearly all the time.

Thanks Paul. That helps. And Thanks T-x as well for your explanations and most importantly all the work that went into this circuit. I love my ROG EA Tremolo, but I want more depth, and it needs rebuilding since there is some dodgy solder work that is acting up - it was my first pedal and was on perf. Eager to replace it with this one.

[GGBB]

Here is my contribution for the etchers in the crowd. Untested as of yet - proceed at your own risk. This thing is monstrous at 2.2"x1.8" compared to duck's but the pots and LEDs are all on-board (cause that's how I like em) and it should fit in a 1590B just fine. Note that the LFO caps need to be ceramics to fit on the board - unless you can find very small 1uF film caps or you go with a lower value.

[Transmogrifox]

Thanks for doing that.  It's really nice. 

Do I have permission to host it on my site with the original schematic?

Also, I didn't add a reverse protection diode because  I determined this circuit will not be damaged by reverse power supply connection...for whatever that is worth.

[PRR]

> I determined this circuit will not be damaged by reverse power supply connection...

I'd feel better if it was built and wrong-connected to 12V for test, but...

FWIW, as I see it, you are 99% correct. From "+9V" there are just two paths. Through the 10K Rate pot, and whatever is under that can only get 1mA, and worst-case 10mW in the pot, which is all safe. And through the "5.23K", which could flow 2mA, which still leads to all-safe.

The 1% concern: if C4 audio power filter is electrolytic (as it must be, though you don't note polarity), and power is backward, we have a backward-cap near-short, so nearly 9V across R7 470r. This will flow nearly 19mA and put 0.172 Watts in R7. If R7 is 1/8W, this is technically over-spec and it is allowed to die. (However 680r would supposedly live and hardly affect audio path bias.) A lesser chance is that C4 holds say 4V, flowing 10mA, dissipates 0.040 Watts... it probably won't burst, but may not recover (leading to unexplained excess power crap on the signal).

There may be some Akido way to cancel power crap without a large cap. Personally I'd use 1/4W parts (or 680r) and then not worry about it.

Higher voltage would lead to more failure modes, but the history of electricity (and Users) teaches that there is no 100% way to protect against overvoltage (or carelessness). However at a glance, the thing may be safe to over 30V (or to the limit of C4). It mightn't work right until re-biased for the high supply (or put back on 9V), but shouldn't die.

[PRR]

me> ....there are just two paths.

Idiot. I missed that Q3 is tied to 9V_SIG. However this third path can only return through C5 or R10, both large impedances, and no smoke-releasing current can flow.

The "+" side of C5 goes toward Q3, which was not obvious at a glance. I think Gord got this right.

[duck_arse]

a series schottky could be hairpinned into my layout, next to D2, by opening that orange trace. for the belts and braces types.

[knutolai]

nittypicky detail typo: GGBB you wrote 1N5718 when I'm guessing you meant 1N5817. Might cause some minor confusion.
This looks really exciting. Gotta build this at some point with a buffer -> fixed voltage-divider in front of it. Not a fan of extra volume controls.

[Transmogrifox]

This looks really exciting. Gotta build this at some point with a buffer -> fixed voltage-divider in front of it.

It doesn't need a buffer. R3 in parallel with the pot are the components determining input impedance -- your guitar looks right into the JFET gate otherwise.  Putting another in front is just duplication of what is already there.  R3 can be increased if you feel 1Meg is not enough.

To change to a fixed gain you can simply omit the volume pot.  To set the fixed gain, change the value of R8 to whatever suits you best.  For unity gain change R8 to something close to 4.5k.  This will avoid adding parts for a resistor divider, and especially an extra input buffer. 

I prefer gain at a bit over unity so it doesn't sound like a volume drop when active.  A gain of 2 usually sounds the most natural between on and off -- psychoacoustically averages to unity at max depth.  For this R8 = 2.2k to 3.3k probably would be the most natural sounding between active and bypass.

In either case you can most easily make this a fixed-volume unit using either of the layouts posted in this thread:  nothing more than a component value change is needed.

Typical use of the volume control on this circuit would be a set and forget until you change your rig.  At the same time by setting depth to min, this serves as a clean +10 dB booster, so the volume will be useful for anybody who likes to tweak knobs.

FWIW:  The gain is designed to yield approximately unity gain output when the pot is an audio taper pot turned to the 12 o'clock position.

For those concerned about the pot at the input vs input impedance -- there is nothing magical about the pot being used as a volume control to make this circuit need a buffer.  With the pot in place it presents a minimum of 500k impedance to the guitar when turned all the way up (my target input Z), and increases to about 950k at 25% (this is where the attenuation of the pot and the gain of the tremolo gain stage yield unity gain output and also corresponds approximately to 12 o'clock position on an audio taper pot). 

[midwayfair]

This looks really exciting. Gotta build this at some point with a buffer -> fixed voltage-divider in front of it.

It doesn't need a buffer. R3 in parallel with the pot are the components determining input impedance -- your guitar looks right into the JFET gate otherwise.  Putting another in front is just duplication of what is already there.  R3 can be increased if you feel 1Meg is not enough.

To change to a fixed gain you can simply omit the volume pot.  To set the fixed gain, change the value of R8 to whatever suits you best.  For unity gain change R8 to something close to 4.5k.  This will avoid adding parts for a resistor divider, and especially an extra input buffer. 

I prefer gain at a bit over unity so it doesn't sound like a volume drop when active.  A gain of 2 usually sounds the most natural between on and off -- psychoacoustically averages to unity at max depth.  For this R8 = 2.2k to 3.3k probably would be the most natural sounding between active and bypass.

In either case you can most easily make this a fixed-volume unit using either of the layouts posted in this thread:  nothing more than a component value change is needed.

Typical use of the volume control on this circuit would be a set and forget until you change your rig.  At the same time by setting depth to min, this serves as a clean +10 dB booster, so the volume will be useful for anybody who likes to tweak knobs.

FWIW:  The gain is designed to yield approximately unity gain output when the pot is an audio taper pot turned to the 12 o'clock position.

For those concerned about the pot at the input vs input impedance -- there is nothing magical about the pot being used as a volume control to make this circuit need a buffer.  With the pot in place it presents a minimum of 500k impedance to the guitar when turned all the way up (my target input Z), and increases to about 950k at 25% (this is where the attenuation of the pot and the gain of the tremolo gain stage yield unity gain output and also corresponds approximately to 12 o'clock position on an audio taper pot).

I have never encountered a situation where a large pot at the input of a circuit, when turned down, did not result in a noticeable loss of treble (even just the guitar's volume pot does that), not even other JFET circuits. That was the reason for suggesting a buffer and a smaller value for the volume control. It's only a few parts in a pedal that can EASILY fit in a 1590A. Though I like the idea of just trimming R8 as well (and in fact I'm surprised you didn't go with that.

[Transmogrifox]

I have never encountered a situation where a large pot at the input of a circuit, when turned down, did not result in a noticeable loss of treble (even just the guitar's volume pot does that), not even other JFET circuits.

As a general rule what you are saying has sound reasoning to support it.

What you're referring to is the Miller capacitance multiplier effect against parasitic capacitive impedances looking into a FET gate (or BJT base).

Here's my answer in this particular case:

Code Select Expand

[JFET_Miller_FX-0] $  crss=3p 2N5457 reverse transfer capacitance
crss = 3.0000p


[JFET_Miller_FX-1] $  ciss=7p 2N5457 input capacitance
ciss = 7.0000p


[JFET_Miller_FX-2] $  Av = 5 Volts/Volt max voltage gain
Av = 5.0000


[JFET_Miller_FX-3] $  cmiller = crss*(1+Av)
cmiller = 18.0000p


[JFET_Miller_FX-4] $  c=cmiller+ciss
c = 25.0000p


[JFET_Miller_FX-5] $  rpot = 1M
rpot = 1.0000M


[JFET_Miller_FX-6] $  rpotTheveninMax = [(rpot/2) | (rpot/2)]
rpotTheveninMax = 250.0000k


[JFET_Miller_FX-7] $  r=rpotTheveninMax
r = 250.0000k


[JFET_Miller_FX-8] $  f3dB=1/(2*pi*r*c)
f3dB = 25.4648k

[Commandline Calculator:  http://sourceforge.net/projects/crunchcalc/
]
3 dB cut-off will be something like 25 kHz, using maximum stated values in the datasheet.  Other JFETs will be similar.  Difference?  Low gain configuration. 

Now add guitar output volume pot to this:

Code Select Expand

[JFET_Miller_FX-9] $  r = r+r/2 Volume pot is 500k
r = 375.0000k


[JFET_Miller_FX-10] $  f3dB=1/(2*pi*r*c)
f3dB = 16.9765k

This is how I rationalize it to myself -- and also AC simulation in spice shows a -3dB cutoff of about 70 kHz with pot set to 50%, so this agrees my worst-case calcs are truly worst case.

In the case of removing the volume pot entirely and hard-wiring the gain into R8 -- you're now only looking back into the guitar output impedance, or at worst into the volume pot so the situation improves dramatically.

Because the drain-source capacitance is multiplied by the voltage gain of the gain stage you can see how this claim quickly falls apart as you increase the voltage gain.  I think you will find most places you have experienced tone-sucking from this has happened when the gain of the amplifier stage is more than 5.  A gain of 10 or more might bring this into a realm that may be considered audible, especially combined with filter formed by cable and guitar volume pot. 

It's only a few parts in a pedal that can EASILY fit in a 1590A.

I agree with this, so you definitely won't break the bank nor force yourself into the next size up on doing it with a resistor divider and additional buffer   

Though I like the idea of just trimming R8 as well (and in fact I'm surprised you didn't go with that).

I considered it but perhaps not closely enough.  It may be a good design change/update. 

As for what I was thinking, I tasked myself with the objective to be able to take output from a really hot input source and bring it down to a level where it won't clip yet still preserves the full headroom available in this configuration (~6Vpp output swing).  Is there such a hot source as this with which the guitarist has no control over the output level?  I don't know.  It was just an arbitrary design objective.

Zvex SHO may be an example of this -- If you crank it to where it's coloring your tone the way you like it's not like you have another volume control.  So if you switch from an SHO and drive into this trem, you would want to pull down the level at the trem input until the output is close to the pk-pk level of the SHO coming in.  Where this example falls apart is -- why wouldn't you put the trem in front of the SHO?  I don't have an answer. 

Food for thought 

[midwayfair]

Fair enough! You know I can't do the math on this stuff, and you're right, the best examples gain is ... let's say WAAAAAAAAYYYYYYYYYYY above 5. Charitably.

[Transmogrifox]

I appreciate your input. I think you have a lot more real hands-on experience with this stuff in terms of using it to make well-done music.  I just like to play with my guitar -- I'm a "bedroom rock star". 

I was fully prepared to say "you got me on that one" because you really did point out something I had failed to consider  .  In this instance it works out, but it's definitely noteworthy to point out that this kind of configuration can turn bad with a little more gain and demonstrates that the examples you have in mind are probably not subtle.

[GGBB]

nittypicky detail typo: GGBB you wrote 1N5718 when I'm guessing you meant 1N5817. Might cause some minor confusion.

Good eye! I've made the correction. If anyone builds it, please let me/us know here so others will know its been verified.

Thanks.

[Transmogrifox]

A demo with clean guitar is now added:
http://cackleberrypines.net/transmogrifox/rEAgeneratedTremolo/demo/cleantrem1.mp3

I have a bunch (probably 20 minutes worth) of clean and distorted stuff recorded now, so as I have time to edit down the raw recordings to things that demonstrate unique qualities of this circuit I'll keep posting them here:
http://cackleberrypines.net/transmogrifox/rEAgeneratedTremolo/demo

I'll probably be putting stuff bit-by-bit over the next couple of weeks until I have weeded out the redundant and/or uninteresting noodling about.

[Transmogrifox]

Also started a project web page, now with link to a zip file containing the KiCAD project file and gerbers for my SMT design (unverified at this point).
http://cackleberrypines.net/transmogrifox/rEAgeneratedTremolo/pages/index.html

You will notice on the page I also added a Rev B design which includes a capacitor in the FET gate linearizing resistor.  In Rev A the LFO DC biases the FET through this resistor limiting how deep the depth can get.  I didn't notice this as a deficiency until I put this on the front end of my amp's drive channel -- cranked.  It still is a very non-subtle trem effect, but it doesn't effectively mute on the off cycle, just trems between clean and dirty (which is a pretty cool effect in its own right).

With the capacitor in place, LTSpice tells me it goes from 30 dB depth to about 58 dB depth by adding this cap (same if in Rev A you just remove R9). 

Rev B is probably a good choice for anybody wanting to use this to drive a high gain distortion from the front end...downside is it comes after these good folks have created layouts for Rev A.  OTOH, Rev A is good, so it's a worthwhile build for anybody wanting an EA trem with more depth.