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

[duck_arse]

~arph,

I breadboarded as per your mosfet cardinal, but it "didn't work". there was no sign of any output below 200 Hz, and not much at 200Hz either. is there a 10M missing from pin 6 to ground?

[~arph]

Yes, there is one missing there. Nice to hear someone tried it. I'm not too surprised it doesn't work, as I just drew it out of my head and I have no experience with the CD4007 at all.
You can use an audio probe to see if the problem is with the mosfets as resistors. or earlier in the chain.
Btw, you need a 1M to pin 3 as well and then tailor the output of the LFO for optimal response.

[duck_arse]

hmmmm, I seem to recall I had 470k there anyway. I'm not sure where the signal goes, but it certainly does go. not really knowing what I'm doing doesn't help, and I had the switch on the 2n2/470pF wired wrong.

I'll have to try it again, I s'pose.

[pinkjimiphoton]

jon, the vactrol came in today, thanks so much bro!!

look forward to getting started on it soon.

[duck_arse]

I have a question about the 2n2 cap. at 22nF, the filter f was 723Hz, but with the corrected 2n2, it now goes to 7230Hz, yes? I mean, I know the answer is yes, but I'm just checking the values.

I had another read and redraw, so I understand the circuit somewhat better. ~arph, the mosfets just didn't seem to like doing things w/ resistors between them and supplies. I re-breaded the circuit with jfets, and there was lots of bass missing due to the source cap being too low. but the fets would chew just about all the signal thereafter, anyway.

[midwayfair]

I have a question about the 2n2 cap. at 22nF, the filter f was 723Hz, but with the corrected 2n2, it now goes to 7230Hz, yes? I mean, I know the answer is yes, but I'm just checking the values.

I had another read and redraw, so I understand the circuit somewhat better. ~arph, the mosfets just didn't seem to like doing things w/ resistors between them and supplies. I re-breaded the circuit with jfets, and there was lots of bass missing due to the source cap being too low. but the fets would chew just about all the signal thereafter, anyway.

Yes, I'll fix the numbers in the write-up. Pretty dumb that I knew it was a 2.2nF on the breadboard but still punched in 22nF on the calculator when doing the write-up ... I think 723 just looked in writing like a more reasonable number. I know a single-order filter isn't exactly the steepest rolloff, but 7K is some really high notes to still accurately produce the effect. :/

Incidentally, I tried it with discrete MOSFETs over the weekend -- I DID get it to trem in both positions by feeding foltage into the gate (you need a decoupling cap between the LFO output and the MOSFET gate if you didn't already use one -- though I couldn't tell you the electronic reason it needs to be there), but they sounded distorted and just terrible. I think I got FETs to work this way, too; same thing with the distortion.

[duck_arse]

I tried a pot from V+ to ground on the mosfets, just to see, and on the cro, they made huge distortion on the neg half-cycles before they cut off.

[duck_arse]

jon,

I've got a modified-to-jfet cardinal working on my breadboard, but I'm not telling anyone until I've heard what it's supposed to sound like. I can see nothing but a white space in place of your sneak preview video; is this really here and I'm gone blind?

I thought 59 redraws of yr circuit would have coverd all possible ways to connect 4 resistors and a cap to a fet. after 135 rebuilds, I decided I'd give it one more day on sunday, and it seemed the idea was to leave out the cap and 1 r. it was working, sans distortion! hurray.

it's now monday, more redraws and rebuilds, the parts are back in, and now working, w/added sound! what sound, and the balancing of the fets to follow .....

[midwayfair]

I've got a modified-to-jfet cardinal working on my breadboard, but I'm not telling anyone until I've heard what it's supposed to sound like. I can see nothing but a white space in place of your sneak preview video; is this really here and I'm gone blind?

Woops. I can't go back and edit the first post, but this is the "full version" demo:

Can't believe I forgot to post it in this thread!

I hid the sneak peak video because it wasn't the final version of the circuit.

glad to hear you got it working with FETs! I'm excited to hear it.

[pinkjimiphoton]

i haven't even had a chance to consider laying this out yet... sucks. too much stuff i gotta do...i hate when life interferes with my addiction!!

[duck_arse]

hmmm, so it's supposed to sound like an auto-wah connected to a double speed osc, with bass tremolo. well, that is good news, cause that's sort of what I'm getting. and super bright and hard on the bridge pickup.

with the pso, I can get sine all the way to that yang-yang-yang type square wave sound, but I'm going to need to try and balance the waveforms for overlap with seperate fet biases.

we'll see.

[midwayfair]

hmmm, so it's supposed to sound like an auto-wah connected to a double speed osc, with bass tremolo. well, that is good news, cause that's sort of what I'm getting. and super bright and hard on the bridge pickup.

with the pso, I can get sine all the way to that yang-yang-yang type square wave sound, but I'm going to need to try and balance the waveforms for overlap with seperate fet biases.

we'll see.

There are a couple ways to adjust the overall treble content:

1) A simple gate > drain treble bypass cap (100-220pF) on the input stage to soften things a little.
2) A 1nF or so cap across the volume pot.
3) You could shift the treble cutoff downward some by adjusting the input cap to the treble stage and the treble cut cap at the input of the full-range stage. This will start to move toward phaser sounds, though. The harmonic tremolo on the amps was actually quite bright sounding every other cycle.

However, I caution against doing this. The pedal sounds different in isolation than in a band mix. Here's what someone told me after testing out the pedal in the video, after we had some discussion regarding the overall brightness of the effect:

The bypass vs activated was also much less noticeable in a band setting.  Especially with a little dirt in front of it.  The increased treble actually made the effect a little more noticeable and it "cut" nicely through the mix.  I guess the question is whether others would find it to much.  I use more treble than most to begin with.  It may lose some of it's "sparkle" if it's changed.  Sorry, lacking a better term than "sparkle".

[SpencerPedals]

That sounds killer.  The last thing I need is one more thing to build, but I'm sure happy it's this one.  Well done.

[duck_arse]

jon,

I watched most yr vid before the connection got hung-up. I even thought I recognised part of what you were playing. don't ask me what it was, though.

I've currently got 1nF to the treble instead of 470pF, I just haven't reached up for it yet. I don't have a vol, just mix resistors. I'm hoping to rework the fets for a bit of headroom, and near unity overall. I've got 2 cases waiting for the "world's best tremolo" I was designing to death 10 years ago. they are ready for 3 pots and 2 rocker switches, which looks a good fit.

except for the third pot hole, cause now I've got a bias pot for the treble side: the different (treble trem) waveform/threshold? verses depth setting has some quite interesting. and then I put a perkolator in front of it, and it became *VERY* interesting indeed.

but what do I know?

[duck_arse]

jon, I just read yr troubles w/ counterfeit j201's on that thread. did any value changes come out of your findings? I ended up selecting mine, w/ 3 diferent part #'s for the amplifying fets.

[midwayfair]

jon, I just read yr troubles w/ counterfeit j201's on that thread. did any value changes come out of your findings? I ended up selecting mine, w/ 3 diferent part #'s for the amplifying fets.

It wasn't so bad. I didn't change any parts, but we're going to suggest socketting the drain resistors to get to the following voltages:
Target bias voltages (acceptable range): Q1: ~8v (6v-8.5v); Q2: ~7v (5v-7.5v); Q3: 3.5v (2v-4.5v).

We did have a handful of Tayda J201s that were biasing all the way down below 2v in Q3, which was just nuts (they're very loud at 2v, but quickly drop off and get distorted below that, obviously). I did find that Tayda's 2n5457s can be plugged in no problem, though. They're a little gained up in Q1 and Q2, but I didn't have any distortion issues with single coils or minibuckers. I got other fets to work with different drain resistors, including 2SK30 (twisted the leads), and almost anything will work in Q1 and Q2*. The weird thing is this is the opposite of what happened on the breadboard, so I wonder if maybe I was using a different drain resistor at the time. Usually if 2N5457 is an option, that's what I'll use. I love the sound of them.

I don't have any known-to-be-genuine Fairchild 2N5457s to test.

*I may have been too greedy on Q3. I could have gone with a tiny source resistor and a 47uF or 100uF cap and that would have made pretty much every FET useable, but grounding the source maxed out the gain/output and saved two parts.

[duck_arse]

how odd, my first drawing of yr circuit has only 3 voltages marked on it, all j201's right in the ranges you gave. after much fartarsing about, I ended up with mpf106 as q1, j210 as q2 and j201 as q3. I reduced the q2 and q3 drains to 3k3 and split the q2 source to 470R +470R//10uF. I still need to listen again and stuff about w/ mixing resistors at the output.

my j201's are all natsemi, bought around 2001. the 2n5457's I've had for 25 or more years, also natsemi, so not much counterfeit worries there. about time I used them for something.

[mth5044]

Awesome project! I think I'll work up a PCB with the TAPLFO and see how it goes! Is the schematic on the first page/first post still correct? You had also mentioned that there was a compromise for C8 - 2.2n for one mode and 470p for the other. Would it be beneficial to make the mode switch a 3PDT switch and switch that cap? I guess it would be hard to find a three position 3PDT though.

EDIT: Actually not that hard http://www.amazon.com/3PDT-Mini-Toggle-Switch-Center/dp/B001TJ6MDK

[midwayfair]

Yes, if you want to spend extra for the 3pdt switch, knock yourself out. I have an eagle layout for the TAPLFO version if you want it. It's mostly confirmed; I've made a correction since my build, bout it should be fine. I was planning on uploading it to pedal geeks united, but I haven't gotten around to it.

[mth5044]

I had never heard of Pedal Geeks United until now! Thanks for mentioning it, I'm going to have to check it out. As far as the taplfo version, I've worked with electric druid's lfo a few times before, so I've got that part down, I just wanted to make sure the schematic on the first page was still the most up to date. I noticed you mentioned some updates throughout the thread, but I'm not sure if that first schematic reflects them or not. Thanks!