Vintage Ross Flanger Noise Mod

[Glitch Magnet]

So, I've had this Red Ross Flanger since about 1986 or so. It was dead when I got it, and I just replaced the SAD1024 chip and it's been the only flanger for me ever since. Only thing was, I couldn't use it for anything too quiet due to how noisy it was. It wasn't the swishing noise that bothered me - frankly I LOVE that noise - like how I love to hear the rotors of a Leslie swirling underneath a barely audible B3.

It was the low-frequency hum that got to me. Not a problem for cranked up guitar - as long as the flanger follows the gain pedals - which is my preference anyway. But, try to take advantage of its chorus capabilities on clean guitar, and the hum is just too much. And I don't beleive in noise gates.

I've tried a couple other flangers, which didn't live up to the sound of the Ross. I figure a vintage MXR must have the same noise since it's practically identical, although I've never had the chance to hear one side-by-side. Anyway, the MXR is out for me as I think the knobs are just too close to the footswitch.

So, I had to find out if the hum noise is just due to the built-in AC transformer. I'm happy to say, it is. Here's what I've done to irradicate it.

And by the way, this should work for the vintage MXR Flanger as well, although I have no ability to try it myself.

The following image is of my proof-of-concept. First, I took measurements and found ~22VDC across the main power supply filer cap, and 15V following the voltage regulator. I also measured ~100mV ripple before the regulator, and none after it.



Next, I lifted the two 1N914 rectifier diodes to disconnect the internal transformer. I found a 15VDC wall wart (I think it was left over from a dead Tone Bone pedal I used to have). I found the wall wart put out ~24V unloaded. So I hooked that up across the flanger's main filter cap, and instantly it worked perfectly, and the hum was clearly reduced, but not gone. Any radiation off the tranny had been eliminated, but there was still some ripple in the DC.

So, I dug through some parts bins in my closet and found a 220uF 25V capacitor, and an old 34ohm wirewound resistor, which I added into the circuit to create a two-stage filter. Voila! No more hum!

The cavernous Ross enclosure provided plenty of room to install the new components beside the old transformer, which I left in place - no reason to remove it.



Above, the new filter components installed on the back of the PC board. The line from the new external wall wart power supply enters from the right.



Following reassembly, the old rectifier diodes are completely removed, and the DC power line now enters through the original AC power cable grommet at upper right corner. You may also notice the non-original true-bypass footswitch.

So, I now have a killer flanger that I can record with. No hum, just swooshy, swirly goodness! If anyone wants to try the same, well, first of all, don't hold me responsible for anything that goes wrong. Second of all, you can probably get by with a range of parts values - I just used what I happended to have on hand.

I should mention also, I had considered installing a DC jack instead of hardwiring through the grommet, but I didn't have clearance on my pedalboard for the connector, and the pedal is never removed from the board anyway. But, if you choose to put in a jack yourself, it is good policy to also put in a blocking diode to protect against reverse polarity. And here's my point - I tried this and it caused too much voltage drop, so if you do it yourself, you may need a power supply with a higher voltage. You'll have to figure that one out yourself though. I measured only ~25mA current draw, so any 100mA or larger supply should work.

Here's my pedalboard with the Ross Red Flanger installed:

[mahler]

Nice work, and nicer board !

[JacobW]

Wow! That looks great! Good work!

[Glitch Magnet]

Thanks mahler! The pedalboard is actually an old microscope case scavenged from a school surplus storage room. I'm still auditioning the microsynth. If it sticks, it looks like I may finally have to get a bigger board.

[Snaxster]

Thank you very much, Glitch Magnet! Based on your documentation here, I was able to implement your hum fix modification in my Ross Flanger. It works good... real good.

As I wrote in the documentation of my attempt,

"Success, at last. After many false starts, I correctly implemented the Ross Flanger hum fix modification without destroying anything. However, I could not replicate it exactly. Lacking the knowledge, skill, good sense and tools possessed by the designer of the modification, I made a bit of a mess, and I could not discover where on the rear of the circuit board the new components should be attached...

I am grateful to the designer of the Ross Flanger hum fix modification. Though my work didn't do justice to theirs, the sonic improvement I achieved is exactly as they described."

Here is my documentation:

8/12 hum fix mod to my ca. 1979 Ross Flanger

That's a photo gallery with captions. To publish it, I revived my old flickr account, since I don't buy web hosting these days. Have at it, everyone.

Thanks again, Glitch Magnet. You rock.

Best,

Snaxster

[drummer4gc]

Hey all,

I just fixed my ross flanger with some guidance from this page. Thanks! My transformer was bad, so I installed a DC jack and bought a 15v wall wart. It flanges and the effect sounds great! However, there is a really noticeable background hum/fuzz/noise that warbles up and down. It is affected by the flanger controls (ie, turning the rate knob makes it warble faster). I even hesitate to call it hum because I don't think it is from the power source. It is more like a lower, quieter version of the sound that comes from your amp when you short the tip of your instrument cable against your body.

Any ideas? I wonder if it is the vintage "swishing" sound the OP mentioned....but if it is, it is way too loud and present to make the pedal useful!