Florist hiss

[LJangel]

I just built the florist.  Everything works correctly, but I have hiss at volumes above the half way point.  Louder volume, louder hiss.  Also, unity volume doesn't happen until around 4 o'clock on the pot.  I can deal with the volume, but the hiss is too much.  Maybe the PT2399 or 2n5457?  Going to try swapping them out and reflowing all the solder joints.  Anybody have any ideas before I dive into it?  thanks

[madbean]

Do you have hiss when the Blend pot is full CCW? IOW, when it's just dry signal.

[gordo]

Usual suspects of reflow and check parts values.  I believe mine was a tad hissy but no more than a standard PT build.  I'd be suspect of the chip as well.  But especially if you're getting hiss at the dry side I'd supect a part value.

[LJangel]

I reflowed everything and changed all the chips.  Values are definitely correct for everything.  I suspect the 2n5457 may be fake or really out of spec.  Ordered new genuine ones from GuitarPCB that are hand tested.  I only get hiss when blend is above 2:00 and volume is also above 2:00 (very little at this point and louder as these controls are increased).  It isn't affected by any other controls.  The volume and blend both share the part of the circuit with the TL072 (which I swapped and no change) and the 2n5457.  I'm thinking this might also be the reason why I don't reach unity volume until about 4:00 on the pot. (low gain/out of spec 2n5457?)  thanks

[madbean]

It sounds more like the hiss is coming from the PT2399. You could just have a noisy one, so if you have it socketed maybe try a couple different ones if you have them on hand. The 2n5457 is just a unity gain buffer. But, you could audio probe the gate and source pins to see if you have about the same volume level on each.

The effect itself isn't meant to offer a large signal boost so achieving unity higher on the control doesn't necessarily mean there's an issue there. You can swap out the Vol pot for a linear tape to move unity further back though.

So, my recommendation is use an audio probe if you have one. Check the input and output of Q2. Also, check pins 16 (input) and 14 (output) of IC2 to see if either of those are the hiss source. If so, swap the PT2399. If that doesn't help you can increase C9 to 3n3 and C12 to 22n to dampen the noise a bit. The design is light on the filtering but since the delay time is so short in this effect (to achieve chorus) it shouldn't need nearly as much as a full featured delay.

[LJangel]

I did swap the PT2399 (everything is socketed) and that didn't help but I have one more to try.  I'm going to try one of the J201s I have temporarily just for the heck of it in Q2 while waiting for more 2n5457s.  I don't have an audio probe (just a dmm and o-scope).  Then I think I'll double check all the values again for sanity before swapping c9 and c12.  thanks for the help 

[LJangel]

I was wrong.  I do have a small amount of hiss when blend is fully CCW.  I just didn't have the volume high enough to hear it.

[LJangel]

I just tried 5 different PT2399s, including 3 out of pedals that are working fine (admittedly, these are probably from the same vendor, Tayda, but from multiple years).  Also swapped in a J201 to try.  nothing changed.  I have a lot of hiss, actually now that I put the knobs on the pedal, I can see that I have hiss at all positions of the blend (more as it increases, or volume increases).  I guess I'll go through the whole board again and recheck component values.  I haven't made a mistake with them in all my years of building pedals but there's always a first time.

[madbean]

Okay, let's try this: pull the PT2399 out completely. Now listen again with the Blend pot full CCW. Is the hiss still there? What about when you start turning the Blend pot up?

[LJangel]

With no PT2399, I have some hiss, seems to be less but definitely still there.  It is there with blend fully CCW and does not change at any position of the pot.

[LJangel]

I have C25 backward.  I'm looking at it while on a work meeting.  Will change at lunch today and try again.

[LJangel]

I installed a new cap in C25.  it took care of the low volume problem, but I still have hiss.  without the PT2399, it's very low.  As soon as I put in the PT2399, it's amplified exponentially.  I tried 4 of them.  All the same result.  I'll go through all the components again against the schematic.  Almost ready to scrap this one, order a new board, and put a new one together.  This one's giving me fits.  I just did 4 builds and this is the only one causing me issues.  I swapped the other chips and put a J201 in place of the 2n5457.  None of them made a difference. (I didn't expect them to)

[madbean]

Where did you get your PT2399 from?

[LJangel]

I've gotten them all from Tayda over the years.  I took ones out of other pedals that are working.  I've got low level hiss without the chip in there.  But I do have a low level hiss in one of the other delay pedals that uses two (but it's very low with both of them).  I made that pedal years ago.  I tried those in this pedal and same hiss.  The hiss in the other pedal is low when they are installed.  The florist is low when it's not installed and then loud with it in there.

[LJangel]

I just went through and verified all my component values against the schematic and they are correct; however, I do have different values for the led resistors (10k for R35 and 1k for R32).  I can't imagine this would cause hiss.