Reducing noise in vintage MXR 117 Flanger - SAD 1024 longevity tips?

[Rob Strand]

The thing is, there is a clearly audible clock whine in the samples that the OP posted.

Good point.

There could be noise on the supply.   There's not much in terms of supply bypassing in that circuit.  Maybe worth adding a 100uF to 220uF cap across the 15V rail.

Look at the Boss circuits and the take a lot of care with bypassing, and also keeping the clock + BBD stuff isolated from the audio.

You can also get that whine when the pot and audio wires get close to the clock and BBD circuits.

[Rob Strand]

There's a 12Khz filter and a 7KHz filter after the BBD and a decent pre/de network, for a flanger, that's quite a bit of noise control. From experience, they just lose most of their usefulness when the BBD is past the aliasing point, even the 9V mistress which has one 28kHz low pass on the input, a 1:10 pre/de network and a clock frequency of 35 kHz doesn't get much use out of one.

If your input filter is poor (like the MXR) the sampling process can compound noise from *all* bands and fold them back into the audio frequencies.

Another evil is high frequencies can self-modulate back down into the audio band.   That's what happens when you have crap on the power-rails of a BBD.

We often ignore secondary effects because they are small but audible noise is small!

[overtone85]

Thanks everybody for the suggestions.

I think my samples might be a bit misleading since the recorder was very close to the speaker, it wasn't clipping but I can do better. I will record new ones where I play the guitar both clean and distorted, so you can hear the difference when the pedal is off an on both examples. I hope I can do that tomorrow evening after work.

After the prior suggestions I made, there is also adjusting the bias (got a scope?) and the mix with the level trim in case they've drifted over the years.

I will also try to scope the BBD for the bias/distortion and report back. But without tweaking the trimmer for now.

Some serious corrosion in there, on the trimmers it can't be helping matters.  SAD socket could probably use a cleaning too.

The green oxidation seems to be only on the trimmers and the back of the regulator that was touching the foam that rotted away. Everything else seems clean. The top of the BBD has a little bit of black residue from the foam as well but the bottm of the legs inserting in the socket seem clean.

I feel a bit uncomfortable in unsoldering the bead of solder seal on the trimmers. If I have to do that I might as well replace them completely with new 20k trimmers and readjust... no?

Here's what I'll do for now:
Put a brand new Electrolytic at the input of the Regulator. 220uF 25V should be fine?
I have ordered some TL072s, when I receive them I will socket U1-2-4, replace them and re-record the audio with the same licks, and also try some NJM5532DD I have laying around (although too much current draw might stress resistors ect?).

Then I will replace the tantalums with new ones and redo the test again. And then we can go from there.

There could be noise on the supply.   There's not much in terms of supply bypassing in that circuit.  Maybe worth adding a 100uF to 220uF cap across the 15V rail.

Where do you think I should put this cap in the circuit and what point can I measure with a scope to check the noise level?

The pedal seems to sound really good on cleans. I just think it's not super clear when used before distortion and you can hear the rumble when using high gain, but again this is my first MXR flanger and I don't really know how it's really supposed to sound when new.
Hopefully it will perform better with the tweaks.

I don't want to change the filters just yet. I understand that it might affect the character of the pedal.

I'll keep you guys posted. Watch this space.

R

[Rob Strand]

Where do you think I should put this cap in the circuit and what point can I measure with a scope to check the noise level?

A start would be to put it in place of C20 (10uF).    There is probably a better location where you can add one but it depends on the layout.

You could also increase C9 (2uF) to 47uF.

You could also add a 100nF cap from the wiper of timmer R49 to ground.

The pedal seems to sound really good on cleans. I just think it's not super clear when used before distortion and you can hear the rumble when using high gain, but again this is my first MXR flanger and I don't really know how it's really supposed to sound when new.

Putting a Flanger before a distortion is asking for noise issues.  If your distortion pedal has a gain of 10 the base-line noise will go up by a factor of 10.   It could be 100's.    A flanger after a distortion is far less problematic.

Can you explain the rumble?    Rumble can be cause by many things:

- bad contacts on the connectors

- bad footswitch

- bad contacts on the pots, trimpots, sockets

- damaged opamps

- stuffed electrolytic caps.  not that many in that circuit but maybe C9 and C19.
  Haven't heard rumbles from tantalums.

[Scruffie]

The thing is, there is a clearly audible clock whine in the samples that the OP posted.  If it was just hiss, that would be one thing, but there IS clock whine...so that's two things.

That's cheating! I haven't listened to the samples and there shouldn't be any clock whine.

There's a 12Khz filter and a 7KHz filter after the BBD and a decent pre/de network, for a flanger, that's quite a bit of noise control. From experience, they just lose most of their usefulness when the BBD is past the aliasing point, even the 9V mistress which has one 28kHz low pass on the input, a 1:10 pre/de network and a clock frequency of 35 kHz doesn't get much use out of one.

If your input filter is poor (like the MXR) the sampling process can compound noise from *all* bands and fold them back into the audio frequencies.

Another evil is high frequencies can self-modulate back down into the audio band.   That's what happens when you have crap on the power-rails of a BBD.

We often ignore secondary effects because they are small but audible noise is small!

Two 1-P 16KHz filters? That ain't bad, more than the A/DA & Electric Mistress.

However it's not a lot of filtering no and zero power filtering, so as you say, could be an external factor.

[overtone85]

Here are more audio samples.

Pedal settings:
Manual, Width and Speed all between 10:00/10:30
Regen all the way up.

Chain: PartsCaster with Duncan 78 Custom + Wilde Noiseless Single Coils -> MXR Flanger -> Preamp -> Delays -> SS poweramp -> Greenback Reissue UK -> Unidyne III SM57 -> Zoom Recorder.

The volume is not very loud so you can hear my picking or the switching of the pedal.

First test is a Van Halen Riff both clean and distorted, without delays or reverb. I stop playing inbetween so you should be able to hear the difference with the pedal ON or OFF.
https://soundcloud.com/overtone85/mxr-flanger-pre-noise-mods-test-01-dry

Second test is some Unchained / ATBL distortion test without delays or reverb.
https://soundcloud.com/overtone85/mxr-flanger-pre-noise-mods-test-02-dry

Third test, same riff as test 01 but with delay and reverb added.
https://soundcloud.com/overtone85/mxr-flanger-pre-noise-mods-test-03-wet

Excuse the sloppy playing, I don't have the full riff down yet. Next up I'm going to scope the BBD to check for distortion.