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Ross/MXR tweak or not to tweak

12/22/2004 5:56 PM
Ross/MXR tweak or not to tweak
Hi there, I just received a Ross red-box flanger. First this the same as MXR? Should I play with the internal trimpots? It sounds great now...but they are there and the temptation to tweak is strong. I read one review where the guy tweaked the trimpots and the thing died. I definitely do not want that to happen. What do the trimpots do exactly?.....I would like a bit more depth in the flange without getting the jet plane sound.  
12/23/2004 8:38 AM
Mark Hammer

First off, yes, many Ross products ARE virtual clones of their MXR equivalent. I wish I knew more about how that happened, historically.  
Second, though you can render any flanger nonfunctioning by mis-setting the trimpots, you won't destroy it.  
Third, the trimpots in flangers can serve any combination of the following functions:  
a) Biasing the delay chip. This feeds a DC voltage to the input of the delay chip, which is required for the delay chip to pass audio signal. If the bias voltage is wrong, the chip will either pass a very distiorted signal or none at all. Generally speaking, this can be set by ear. As you tweak it will go from no delay sound, to a dirty one, to clean, to dirty again and finally no delay sound.  
b) Clock trim. Achieving a characteristic flanging sound means producing the same range of minimum and maximum delay times. Some flangers will include a trimpot to adjust the delay time range for consistency across copies.  
c) Bbd balance. Some delay chips include a variable balance control to adjust the relative level of each of the two outputs found on the BBD. This helps to better cancel out clock noise that may come through. More flangers tend to use just a pair of matched resistors instead of a trimpot.  
d) Delay level. Maximum notching is achieved by a perfect 50/50 balance of dry and wet signal. What some flangers have is a slightly attenuated dry signal, and a trimpot on the output of the delay chip to trim back the delay signal for a 50/50 mix when it is combined with the dry signal downstream.  
e) Regen trim. Too much regeneration produces annoying oscillation. If the combination of components in the regeneration path does not keep regeneration under control, you can end up only being able to use maybe 80% of your regen/feedback pot's rotation before it becomes annoying. Consequently, many flangers (and phasers too) have a regen trimpot. During setup, the regen/feedback control is maxed and the trimpot is eased back just to the point where it stops howling, allowing the user to aim for as much regen as they can use.  
"Depth" in the flange can mean a lot of things. For example, it may be that the 50/50 balance to be aimed for is a little off and there is not as much notching as there might be. It may also be that the range of delay times is a little off, resulting in notches that never seem to sweep high enough or low enough.  
For a great many people, though, "depth" is really about how wide the flanger sweeps, and there you have a design issue rather than a trimpot or tweaking issue. Though it matters little for "bubbly" sounds, slow jet plane sweeps require a very wide sweep range and "sweep ratio". Conventional wisdom says that a sweep ratio of at least about 30-to-1 is needed for dramtic sweeps. So, if max delay time was 15msec, a minimum delay time of 0.5msec would be needed to get something that sounds really majestic. A sweep from, say 0.3msec to 14msec would be even better. Regrettably, the LFOs and clock circuits on many garden variety flangers don't permit much more than a 20:1 sweep. Unfortunately I forget what the swep ratio is on that one, though I suppose you could look it up somewhere on the net.  
All of this is the long way of saying that there may be some additional oomph you could wring out of your pedal with trimpot tweaking, but there may not be much else to squeeze out too.
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12/23/2004 9:42 AM

Hey Mark..thanks. Thats quite the detailed answer. I may try playing with them a bit. I will mark them first. This is a great sounding flanger. It is also the richest nicest chorus I have heard. I just got rid of my old Boss CE-2. This replaces it and more. I love the flanger sound. I'm just not crazy about the extreme wwwhhhaaaabbbb sound.  
Thanks again.  
Happy holidays.  
12/23/2004 1:27 PM
Mark Hammer

I had one of those grey MXR units some 20 years ago. Couldn't sell it fast enough. Didn't do what I wanted it to do. Wish I knew then what I know now about making these things behave properly.  
The MXR, and I assume Ross, used a Reticon SAD-1024 delay chip. While not inherently a better chip than the MN3007 and MN3207 used for most of the universe of commercial flangers and choruses, it is capable of producing very wide sweeps without needing a great deal of assistance the way the Matsushita chips do. As a result, many, though not all, of the flangers using an SAD-1024 tend to be better flangers. Again, not because the chip itself sounds any better, but because it allowed people to design great circuits easily without a lot of support circuitry.  
Happy holidays right back at ya.
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