First off, I'm by no stretch of the imagination a regular here. I would like to thank forum member JehuJava for his trust, generosity, and recommendation that I post here, in this case. Recently, by way of diystompboxes.com, he was kind enough to entrust his Resonator to me for an LED mod, and tracing. While it was on my bench, I found that information on tuning the filters was nonexistent. After some research and judicious adjustment, I was not only able to develop a procedure, but also to get the unit to sound a bit better. I don't know if someone had gone in there and fiddled with the trimmer before he got it, but it did allow me to confection the tuning procedure. No oscilloscope, or fancy equipment required, just a DMM with frequency counting capability, your ears, and personal judgement.
Here is the schematic. I would recommend that you download it, print it, and enclose a copy inside the unit. If ever it malfunctions, it would help the person troubleshooting to know what is going where, and doing what (click on image to get bigger version).
Before I continue on to the tuning section, I must mention the following information. The unit JehJava sent me had some... particularities about it. These were either omissions, or mistakes, that the unit left the factory with. Namely;
- +15VDC power filter cap to one LM13700 IC installed backwards.
- -15VDC power filter cap to one LM13700 IC not installed.
- 1N4148 diode on CV input side of LP Resonance installed backwards.
Amazingly enough, the +15VDC power cap was still OK, even though it was working with reverse voltage. Why the -15VDC power cap was not installed is unknown. However, the diode reversal was a critical issue. This error forced the resonance trimmer to the extremity of it's oscillation adjustment. Although the unit was still tunable to operational form, it made oscillation point matching between the LP and HP Resonance pots impossible beyond a certain point. Funnily enough, diode orientation for installation at the time of assembly is silkscreened on the PCB. As I hypothesized to JehuJava, his unit may have been a "Friday afternoon" product, with the "call of a cold one" affecting the assembler's vision. These errors/omissions have been corrected on my schematic.
Here is my tuning guide for getting the most out of the Resonator. AS WITH ANY TRIMMER TUNING, REMEMBER TO WRITE DOWN WHAT YOU'VE DONE. OTHERWISE, RETURNING THE UNIT TO IT'S ORIGINAL SOUND WILL BE TOTALLY DEPENDANT ON YOUR MEMORY. YOU HAVE BEEN WARNED.
- Small screwdriver for adjusting the trimmers.
- DMM with frequency counter function.
- Your ears.
1) Set all four trimmers in the unit to center.
2) Power up the unit, and connect only the output to an amplifier. Don't turn on your amp just yet.
3) Set the Frostwave controls as follows; LP Freq. max, Input Level max, and Wet/Dry to 100% wet. Set the other controls to minimum.
4) Turn on your amplifier, but keep the volume low. The unit can generate very high frequencies that can hurt the ears.
5) Turn the HP Reso pot to maximum. At this point the circuit should self oscillate. If it doesn't, adjust the 20K trimmer on the HP side until it JUST does. Keep in mind that the frequency of the oscillation may be quite low, so judiciously raise the volume on your amplifier if you're not sure.
6) Once oscillation is achieved, connect the DMM/frequency counter to pin 6 of the TL072 on the HP side (between the 4K7 resistor to ground, and the red LED's). Observe the frequency.
7) Ensuring that the HP Freq pot is at minimum, dial the 1K trimmer on the HP side until the frequency counter shows 30Hz. If you dial up your amp a bit, you should hear a low pulsating oscillation.
8 ) Return the HP Reso, HP Freq, and LP Freq pots to minimum. Lower the volume on your amp as well.
9) Turn the LP Reso pot to maximum. At this point the circuit should self oscillate. If it doesn't, adjust the 20K trimmer on the LP side until it JUST does. Keep in mind that the frequency of the oscillation may be quite low, so judiciously raise the volume on your amplifier if you're not sure.
10) Once oscillation is achieved, connect the DMM/frequency counter to pin 6 of the TL072 on the LP side (between the 4K7 resistor to ground, and the red LED's). Observe the frequency.
11) Ensuring that the LP Freq pot is at minimum, dial the 1K trimmer on the LP side until the frequency counter shows 30Hz. If you dial up your amp a bit, you should hear a low pulsating oscillation.
12) Once the base frequencies have been set, you may tweak the 20K trimmers a bit more to decide at which point the HP or LP Reso pots fall into oscillation. Personally, I prefer it around the 70 - 75% of the pot rotation. If you're going to tweak the resonance at this point, then...
Just remember; - When working on the HP side, you'll need to max the LP Freq, if you want to hear anything, and zero the LP Reso, so as it does not to interfere with the HP side.
- When working with the LP side, zero the HP Freq and Reso pots, AS WELL AS THE LP FREQ POT. Then raise the LP Reso, and make your adjustment.
- If your ears find that the frequencies are too low when finalizing the resonance oscillation start points, then you may raise the frequency of the side you're adjusting to a comfortable level.
A good test to tell if you're tuning is in the zone, is the didgeridoo test. A didgeridoo is an Australian mouth pipe, which produces quite a harmonically resonant sound. If you've never heard one, Google it.
- Set the HP Freq pot to minimum.
- Set the LP Freq, and Reso pots to max, as well as the LP Reso pot. The unit should be in low oscillation now.
- Raise the HP Freq pot to a point between zero, and the 9 o'clock position.
- Quickly swing the LP Freq pot back and forth between zero and noon.
Nudging the HP Freq pot a bit, as you swing the LP Freq pot, should give you not only a decent didgeridoo sound, but a very good raspy "WOW!!" sound depending on the speed you sweep. (See my Youtube video demonstrating the JehuJava's unit. My channel name is "mrdigi2t")
As for CV control, I noticed in my internet travels that there quite a few people that were not getting the result they expected using CV control. The lack of info (none actually) in the user guide may be to blame for this. For the most part, we seem to have been domesticated into the 0 - 5 VDC world of CV control. This, for the most part, is fine for CV control of a majority of equipment out there, but not for the Resonator. As I've pointed out on the schematic, it requires either -10 / 0 / +10 VDC, or 0 - 15 VDC (0 - 10 works too) to function properly. It's also VERY important to observe that each CV scheme comes with it's own behavior.
- -10 / 0 / +10 VDC: This scheme will always be dependant on the position of the controlled parameter pot on the unit. If, for instance, the pot on the unit is set at the middle position, then the CV voltage will be able to sweep the parameter through the entire range. Negative voltage will sweep to the lower end, positive voltage to the higher end, with zero voltage anchored to the pot position. This also means that if your pot is set at say, the 9 o'clock position, the range of the negative CV voltage is effectively compressed, and the positive voltage, now much further from the max end of the pot, will not be able to reach the maximum range of the parameter.
- 0 - 15 (or 0 - 10) VDC: Firstly, 0 - 10 VDC will work fine, and it should be noted that since the circuit operates on +/-15 VDC, using the higher voltage won't damage anything. My tests with both voltage ranges showed good results, either way. If there are any short comings using the 0 - 10 VDC scheme, my ears could not detect it.
This scheme operates independently of where the unit's parameter pot may be set. 0 VDC becomes minimum of the pot, and 15 (or 10) VDC becomes maximum.
Neither scheme is better, or worse, than the other. Depending on the user, and his/her operational requirements, either scheme may provide advantages, so feel free to pick the one that works for you.
Hope this information is of use to you. Background info;
My name is Dino, I'm a guitar player, and pedal cloner in my spare time. For those who don't know me, I'm quite active over at diystompboxes.com (digi2t), and I have a Youtube channel, under the moniker "mrdigi2t". My specialty is, as I introduce all my videos with, the "Hen's Tooth". At the Hen's Tooth Café, rare effects, with limited availability, and even less available information, are the stars here, as well as the occasional mod or tuning tidbit. Free sharing of information concerning these pedals is the basis of my endeavours, so please continue the circle, and pass it forward. Thank you.