Cardinal Tremolo (Vactrol-base Harmonic Tremolo) - schematic & discussion

[mth5044]

I bet the stereo version is doooopeeee. Did you just invert the LFO? Can the TAPLFO supply enough current for 4 LEDs?

EDIT: wait nevermind I just remembered the TAPLFO drives a transistor.. you can have as many LED's as the heart desires (and can run on 9V)

[midwayfair]

I bet the stereo version is doooopeeee. Did you just invert the LFO? Can the TAPLFO supply enough current for 4 LEDs?

Some nice folks informed me that I just needed a PNP and set it up like the NPN. It actually has depth to spare -- the regular version worked fine with three LEDs after some work, and this one just has two LEDs per transistor, and they don't interfere with each other.

To be honest, I have no way to hear how it actually "sounds." It's slightly different from the Cardinal. All I did was confirm that both channels would work and then wrack my brain for days figuring out the switching and all the mods he wanted and making like three layouts.

I like a challenge, it's really the only reason I took the order. I probably wouldn't make another one and I was just shocked he was willing to pay the asking price.

[mth5044]

That's interesting! So another signal is tap'd off pin 5 of the chip along with a 10k to the base of a PNP with it's emitter grounded and a collector to the LED's?

[midwayfair]

That's interesting! So another signal is tap'd off pin 5 of the chip along with a 10k to the base of a PNP with it's emitter grounded and a collector to the LED's?

Yes, except I found that the PNP had to be in backwards (emitter to LEDs, collector grounded). I guess that makes sense -- it's an NPN circuit.

[mth5044]

Cool! Thanks Mr. P!

[mth5044]

Sorry, one more thing -

It's wired thusly:
DPDT on/on/on
1 4
2 5
3 6

-Jumper 1 and 5.

-Replace R6 on the PCB with a much larger value, e.g. 33nF.

2: This is the ground connection (pad 2).

3: This connects to the pad on the PCB that goes to C6 (pad 1)

4: This connects to the pad on the PCB that connects to the gate of Q3 (pad 3)

-Solder a smaller value cap across lugs 3 and 6. (See below for values and cutoff frequencies.) We will call this the "switched" cap.

Just to make sure, you say R6, but that was probably a little slip up and should be C6. But what I am a bit confused about is the wiring of lugs 3 and 4. For lug three, isn't pad 1 the pad that goes to C7, not C6? If not, then isn't pad 3, the pad that connects to the gate of Q3, the same pad that connects to C6?

And finally, in the taplfo schematic you have, you have the 3904 collector going to ground, but in the taplfo datasheet with the tap trem, the collector is grounded. Perhaps it doesn't matter, but in this case, as long as the NPN and PNP transistors have opposite connections per your last comment it may be ok? I end everything in a question mark because I don't actually know anything?

[duck_arse]

@ jon - what type # is your pnp that needs backwarding? just out of interest, mind.

[midwayfair]

@ jon - what type # is your pnp that needs backwarding? just out of interest, mind.

2n3906. Definitely 100% better when backwards.

@mth5044: I'm going by the 1776 build doc schematic, since that's the one most people use. That post was a x-post from the Madbean forum (which is also the 1776 home base). I just haven't redrawn my schematic to match Josh's numbering.

[pinkjimiphoton]

I know most folks on DIYSB are all about etching and vero and such, but I just thought I'd stick a note here that 1776 Effects released the PCB project for this today: http://1776effects.com/store/

It's red and has a bird. <3

mine just came in. psyched!! thanks jon!

[JohnForeman]

Jon,
has anyone done a PCB of the Blue Warbler?

[midwayfair]

Jon,
has anyone done a PCB of the Blue Warbler?

Not yet. Jacob at JMK has been working on it, but there turned out to be some PCB-specific issues (one of the PCBs had some sort of ground bleed distortion, and Jacob told me the second layout had some other issues like hiss). It's getting a small redesign (which will only have the vibe mode and a simplified envelope), and I hope the PCB will finally happen this year.

[9520575]

 
I'm having a bad time trying to get this to work. The Schematics on page one are correct? I have a lovely tremolo but no harmonic tremolo.
I tried just taking out the switch and having that 2.2 nF (C7) cap go to ground; No change. Just a normal tremolo, depth, rate, and volume all seem to be up and running correctly. I've built this three time on my breadboard today. I'm not saying I'm not making a mistake, I probably am , I just want to check. First post Schematics are good? Its a nice tremolo so far

[midwayfair]

I'm having a bad time trying to get this to work. The Schematics on page one are correct? I have a lovely tremolo but no harmonic tremolo.
I tried just taking out the switch and having that 2.2 nF (C7) cap go to ground; No change. Just a normal tremolo, depth, rate, and volume all seem to be up and running correctly. I've built this three time on my breadboard today. I'm not saying I'm not making a mistake, I probably am , I just want to check. First post Schematics are good? Its a nice tremolo so far

Check your voltages for Q3, if it's less than 2.5V it might not turn on. Since it's on a breadboard, just interrupt any connection to Q2 or remove that transistor so you can get the treble band working. Check to make sure your vactrol is working and oriented correctly. Make sure the LDR for Q3 is connected to both the gate and ground (remember, it's the gate bias).

[9520575]

  So, I built it again. Check voltages (replaced all the J201s for good measure.) Still the same. Then, I decide to replace the op-amp. Well man all of a sudden the treble is kicking in. There is all little bit of phasing happening. Its working, well. Its fairly mild, nothing close to yours in the demo. I did switch the order of my vactrols to see if maybe I had reversed the order. Whoa, definitely not what was wrong, the depth was basically on or no sound.  SO, I'M WAAAYYYY closer now. I'm going to play around with the resistance to the LEDs. I feel like I'm headed in the right direction. I replace the op-amp with a JRC5448, it was instantly different, treble side kicked in. Although it isn't very strong, like I said. So, bad OP AMP or... something...

[midwayfair]

  So, I built it again. Check voltages (replaced all the J201s for good measure.) Still the same. Then, I decide to replace the op-amp. Well man all of a sudden the treble is kicking in. There is all little bit of phasing happening. Its working, well. Its fairly mild, nothing close to yours in the demo. I did switch the order of my vactrols to see if maybe I had reversed the order. Whoa, definitely not what was wrong, the depth was basically on or no sound.  SO, I'M WAAAYYYY closer now. I'm going to play around with the resistance to the LEDs. I feel like I'm headed in the right direction. I replace the op-amp with a JRC5448, it was instantly different, treble side kicked in. Although it isn't very strong, like I said. So, bad OP AMP or... something...

What vactrols are you using? What's the on/off resistance you're seeing? What color LED are you using for the indicator? (It must be diffused, not superbright).

[9520575]

 

What color LED are you using for the indicator? (It must be diffused, not superbright).

Oh you mean i should use a diffused LED like it clearly states. NOT the clear bright, overhead planes can see me signalling LED, I'm currently using?
Oops...


I'm using the vac from small bear you link to in the first post.

[mwnovak]

Hi all.  I picked up the Cardinal PCB from 1776 and have it built and sitting on my bench right now.  It seems to work as intended, but I have a question about the following note from the build doc:

Q3 will sometimes overdrive slightly with high output pickups or a boosted
signal -- this is normal and simulates some of the breakup found in the
amp circuitry.

I'm getting quite a lot of "breakup" no matter where I put the Cardinal in my chain (front of amp, effects loop, first/last/alone, etc.).  It's not unpleasant, but I literally can't get clean tones unless I roll my guitar volume way back (below ~5).  This is with humbuckers wound to ~8k.  Is that expected?  And if so, is there a way to give the Cardinal more clean headroom?

If it helps diagnose or troubleshoot, I socketed R7 and R9 and ended up with 8.2k in both for the following bias voltages: Q1 8.21/0.33/0v, Q2 7.16/0.20/0v, Q3 3.27/0/0v.  These are about as close as I could get to the spec'd bias with what I had on hand.  I also tried the suggestion about pulling Q2 in order to isolate Q3 and bias by ear: with Q2 pulled and while trying R9 values from 4.7k through 10k, the volume increased but the distortion was pretty much constant.  Conversely, with Q3 pulled the output was quite clean.

If it matters: I'm using a TL072CP for IC1, a J201 for Q1-Q3, and a VTL5C1 for both vactrols (all sourced from smallbear).  
 
I'm new to these forums and relatively new to building pedals, so I may be overlooking something really obvious or fundamental.  Any feedback is appreciated,

--Matt

[midwayfair]

Hey, Matt, I posted this over on Madbean, but I forgot to add it here (sorry!):

---

The Vp of a J201 is ~0.5-1V peak to peak. This is the voltage swing it can accomplish before clipping. (Clever folks will also notice that it's typical of the source voltage when used as a buffer, and a big reason J201s make lousy input buffers for clean circuits.)

It's noted in the build doc that 2n5457 will sub in all three transistors without rebiasing (typically -- Q3's drain resistor might still need some adjustment, especially if you're going for cleaner). The Vp of a 2N5457 is closer to 1.5V, so you can get a much bigger input voltage swing before clipping is heard. The sacrifice is lower output (about less than half the available gain), but the circuit has gain to spare, including some wiggle room on Q1 (you can raise its drain resistor o get closer to 6V if you want).

---

Essentially, here's what happened:

First, I designed the effect around J201s from Tayda before I (and many others) realized they were pretty much all way below spec. I should probably ask Josh if he wants to just make the 2N5457s standard now.

Second, Q3 is odd, in that I was very stingy with its biasing. I did it that way in part because the added distortion adds content up where the harmonics are occurring, but many people building this wish I hadn't done that.

Here's what I'd do: Use a 2N5457 for Q3 at the very least, and raise its bias to around 4-6V (just decrease the 4.7K a hair, 3.3K usually does it in mine).

[mwnovak]

Hi Jon.  This is good news and great information, thank you!  I'll order some 2N5457s, re-bias Q3 as suggested, and see where that leaves me.  Thanks again, --Matt

[idy]

 Such a clever way to create a new sound from the old tremolo. My question is about the indicator LED and Vactrol LEDs. I recently built this on the 1776 pcb.

I found the main tremolo section worked perfectly but the high pass section hardly trembled at all. Multimeter could read the changing resistance of Vactrol 1, but Vactrol 2 seemed to not be changing at all. I disconnected the low pass side completely (lifted one leg of the LDR) so I could hear the high pass side by itself. Then I jumpered the current limiting resistor for the second vactrol and then I could hear the treble throb, subtly. The main channel provides complete silence on the wave troughs with depth set high, but even with the CLR jumpered the high pass side is just gentle.

I thought "with the three LEDs in series are those CLRs necessary?" I thought maybe the intention was to provide lower voltage to vactrol 2 for a more subtle effect. I breadboarded the three LEDs and CLRs as per the schematic (with normal LEDs replacing the vactrols), and they seem to be equal in brightness. So the designer had his reasons...

Don't you really only need one resistor on the end of the three series LEDs?  The 9 + volts already go through a diode and a 100ohm resistor first n the power section and each LED drops around 2v.

I am thinking of replacing vactrol 2. (I am using the recommended VTL5C1, and I bought extra.) Should have breadboarded first!

Also: Why diffused on the indicator? I am not aware of any reason why a diffused would behave differently than a clear. Or why a 3mm should have different fv than a 5mm. On the other hand, color would seem to be important. I first used a blue one and found a red seemed to work better, lower voltage drop, leaving a little more juice for Vactrol 2.