DOD - FX75C Stereo Flanger/FX747 Supersonic Stereo Flanger [schematic]
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astrobass
- Cap Cooler
I haven't gotten around to opening mine up to check, but in the meantime I've come into possession of an FX75B Stereo Flanger and there are in fact 3 trimmers inside that revision. So, probably some fairly substantial changes between the revisions there, which is very different from the FX69, which saw almost no changes from one rev to the next. Even the Digitech version of that pedal is very similar, despite being redone as mostly SMD and having a second output added.Fender3D wrote:"no trimmers" flanger ?
interesting enough...
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astrobass
- Cap Cooler
Okay, so I opened it up and yeah, all fixed resistors, no trimmers.
Anyhow. I don't know anything about clock based effects, so I need some help. How can I increase the maximum rate? Like if when I had the rate knob pinned it still wasn't enough, and I wanted it to go faster. What controls that and which values should be larger or smaller to dictate that?
Sorry if this is a bit of a dumb question!
Anyhow. I don't know anything about clock based effects, so I need some help. How can I increase the maximum rate? Like if when I had the rate knob pinned it still wasn't enough, and I wanted it to go faster. What controls that and which values should be larger or smaller to dictate that?
Sorry if this is a bit of a dumb question!
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astrobass
- Cap Cooler
Oh awesome, thanks! I swapped it for a 10K pot wired as a variable resistor, brought the speed pot up to max, and then dialed in the absolute max speed before the effect dissipated. 200 ohms on the one in front of me.
Since that speed control is a 500K pot, this really doesn't effect how slow you can set the flange (well, clearly it would but having the max resistance there being 500.2 vs. 507.5 is just over a 1% difference), but it opens up the max speed range. At really really high rates flangers can sound like a warbly synth layered on top of the guitar, something I discovered when replacing a busted trim pot on an FX75B (whose schematic is wildly different from this one).
So, before I start swapping more components with VRs and trying to tune other parts of the circuit, am I correct in assuming that:
R57 sets the base range for the Depth control
R38 sets the base range for the Regen control
Because if so, I believe I'll be tweaking R57 and R38 next.
Since that speed control is a 500K pot, this really doesn't effect how slow you can set the flange (well, clearly it would but having the max resistance there being 500.2 vs. 507.5 is just over a 1% difference), but it opens up the max speed range. At really really high rates flangers can sound like a warbly synth layered on top of the guitar, something I discovered when replacing a busted trim pot on an FX75B (whose schematic is wildly different from this one).
So, before I start swapping more components with VRs and trying to tune other parts of the circuit, am I correct in assuming that:
R57 sets the base range for the Depth control
R38 sets the base range for the Regen control
Because if so, I believe I'll be tweaking R57 and R38 next.
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Fender3D
- Cap Cooler
R38 sets the limit where auto-oscillation occours.
If you lower it too much, circuit will auto-oscillate (not harmful though..)
R57 is not connected with Depth control, their common contact node is U4's reference voltage.
What are you going to achieve by changing Depth control?
Playing with R62/R63 will lower or raise the center of the LFO waveform,
C28 will change the delay time involved.
If you lower it too much, circuit will auto-oscillate (not harmful though..)
R57 is not connected with Depth control, their common contact node is U4's reference voltage.
What are you going to achieve by changing Depth control?
Playing with R62/R63 will lower or raise the center of the LFO waveform,
C28 will change the delay time involved.
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astrobass
- Cap Cooler
I just want to swap in a trimmer for the fixed resistors that set the depth range to play with tweaking it up or down to see what I can get out of it. I can always revert back to the stock values, I've got plenty of resistors laying about, but who can resist the temptation to fiddle?
If there were any extra space in the chassis (there isn't) I'd swap the delay cap for a blend cap arrangement. I might still, to play with different values and see if there's a setting I prefer.
I mean, this is a really good flanger out of the box. They're usually inexpensive, they're not noisy, and they do all of the normal things you want a flanger to do. But I don't need a pedal that sounds like a normal flanger. I'm mostly interested in the effects you can get at the upper range of the speed control.
I'm going to do a demo of some of the stuff I've been able to do with flangers this weekend, I'll probably start a pimp my cheap pedal thread for it. Your help has been invaluable, as I've really only been working with fuzz and overdrive effects and these are a few steps outside my knowledge. I just stumbled onto it when fixing a busted one.
If there were any extra space in the chassis (there isn't) I'd swap the delay cap for a blend cap arrangement. I might still, to play with different values and see if there's a setting I prefer.
I mean, this is a really good flanger out of the box. They're usually inexpensive, they're not noisy, and they do all of the normal things you want a flanger to do. But I don't need a pedal that sounds like a normal flanger. I'm mostly interested in the effects you can get at the upper range of the speed control.
I'm going to do a demo of some of the stuff I've been able to do with flangers this weekend, I'll probably start a pimp my cheap pedal thread for it. Your help has been invaluable, as I've really only been working with fuzz and overdrive effects and these are a few steps outside my knowledge. I just stumbled onto it when fixing a busted one.
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astrobass
- Cap Cooler
That really doesn't explain anything, though. I'm looking for something on par with the electrosmash dissection of the Ruby, or R.G. Keen's analysis of the Fuzz Face. A detailed breakdown of the circuit blocks with an explanation of the purpose of each and ways to adjust them/different implementations, important variations on the overall design, that stuff's what I need. If no one is aware of such an analysis, then I'll start off by trying to learn about clock circuits in general and see if I can dissect what's happening in a flanger, but I thought I'd see if there was an easier way.square wave wrote:Might be an obvious source but the first section of wikipedia's flanging article explains it pretty well.
I already know the basic history of the flanger and what one sounds like.
I realize that this is an old thread, but it seems like the right place to post that I'm having trouble identifying the resistor in the FX75C that is the equivalent to the 2.2K trimpot in the FX75B (labeled as a 2K trimpot "P3" on the FX75B schematic, leading to "VCC" in one direction, a 7.5K resistor [R53] in the middle direction, and a 1N4148 [D3] to ground in the third direction). Any clues would be appreciated!