Next Project: 1980 Ibanez FL-301 Flanger

[Audiotrove]

Everything works fine on this pedal except that it's quite noisy, a lot of hiss/white noise despite everything else working well.  I tested it using 2 brand new 9V batteries at full capacity.  The LED lights up, the pedal does what it's supposed to do, it just has an unreasonable amount of hiss in the background no matter what the input volume and no matter what the controls are dialed to.  When the switch is clicked and it's in bypass mode it is dead silent.  I counted about 14 electrolytic caps.  40 years old.  Do I just need to do a whole new set of caps? 

[DIY Bass]

I would trace through with an audio probe first and see if you can find a more definite location where the noise is starting.

[11-90-an]

Yep. What he ^^^ said 

[Mark Hammer]

Swapping all the electros will not only be tedious, but risk damaging some of the traces.  It generally takes more heat to desolder and remove a component than it takes to install one on a fresh board.

Having said that, the pic you posted shows three different dual op-amps.  The schematic shows TL022 chips all around.  One of them is certainly appropriate for a tick-free LFO, but I don't know how much the circuit itself compensates for use of a TL022 in the audio path, where you currently show a TL072 and MC1458.  The TL072 is touted as a lower-noise chip, but requires certain conditions to be that way.  I don't know if the circuit design meets those conditions.  The MC1458 is not generally used for white noise sources, but it is NOT known to be low-noise.

[duck_arse]

audio probe base and emitter of Q101.

[ElectricDruid]

Looking at that schematic, I wouldn't be surprised if it was just that noisy straight from the factory.

There's very little filtering either before or after the BBD. Ok, there's some, but it's *light*. That means aliasing going in, and clock noise will leak out of it, and my experience is that although you can't hear ultrasonics, they often show up as broadband noise sooner or later. Especially in this age of A-to-D conversion, where they cause aliasing effects that fold back down into the audio spectrum you *can* hear.

About the only noise reduction measure in the whole circuit is pre-emphasis/de-emphasis. That's pretty basic. Plus I suppose using a higher voltage supply for improved signal/noise ratio - the 3007 instead of the 3207. So my advice is put a clean booster in front of it, feed it a walloping great signal (as big as you can without distortion) and then turn the output down! (along with the noise).

Remember that back when this thing was built flangers had a reputation for being noisy. There weren't any really quiet ones (not that anyone I knew could afford, anyway!), so it was just accepted as part of the package. Hey, rock'n'roll, right?!

[Scruffie]

Looking at that schematic, I wouldn't be surprised if it was just that noisy straight from the factory.

There's very little filtering either before or after the BBD. Ok, there's some, but it's *light*. That means aliasing going in, and clock noise will leak out of it, and my experience is that although you can't hear ultrasonics, they often show up as broadband noise sooner or later. Especially in this age of A-to-D conversion, where they cause aliasing effects that fold back down into the audio spectrum you *can* hear.

About the only noise reduction measure in the whole circuit is pre-emphasis/de-emphasis. That's pretty basic. Plus I suppose using a higher voltage supply for improved signal/noise ratio - the 3007 instead of the 3207. So my advice is put a clean booster in front of it, feed it a walloping great signal (as big as you can without distortion) and then turn the output down! (along with the noise).

Remember that back when this thing was built flangers had a reputation for being noisy. There weren't any really quiet ones (not that anyone I knew could afford, anyway!), so it was just accepted as part of the package. Hey, rock'n'roll, right?!

Pre & De-Emphasis, 2 pole 10kHz input and a 2 pole 7.5kHz output filter, how much do you want for a Flanger? We're not talking pulling 100mS out of it and while I don't know what the clock is for this, even at 35kHz that shouldn't be too offensive. People are still using electric mistresses and they only dream of that kind of filtering

I'm going to say replacing 40 year old caps especially tantalum and in the power section is going to help, plus Mark's comment about the TL022 in the audio path.

[ElectricDruid]

I agree Scruffie - sort out the crucial caps, put some decent op-amps in it, and maybe additionally make sure it is well adjusted if it has any bias or balance trims. Beyond that, there's not a lot we can do and I wouldn't expect it to be silent even working perfectly. New caps and changing a couple of op-amps won't make a noisy pedal quiet, but it should help a bit.

The EM is highly regarded, but there are plenty of threads here about people struggling with clock noise problems with them, so the light-touch filtering causes problems as well as having benefits in terms of potential bandwidth. It's always a trade-off.