Plexitone squeal

[still4given]

Hi Guys,

I have built a few stompboxes lately. All have been successful up until now. I just finished building a Plexiton using boards I bought from Tayda. It works except there is a slight squeal pitch that plays the whole time the pedal is on. With the tone control turned all the way down the squeal is almost gone but still there. Have any of you had an issue like this? If so, did you find a solution? Here is a link to the info for the build.

http://www.taydakits.com/instructions/plexitone

Thanks, Terry

[aron]

Usually this is because of wiring. High gain and crossed wires creates this feedback and whine. Keep the leads short and input and output away from each other.

[still4given]

Thanks for the quick reply. It is late now but I will try your suggestion first thing in the morning and get back to you. I can also try using shielded cable for the signal runs. I do have the leads running around the outside of the 1590BB case so they are a little long. I was trying to keep the center of the case clear so all the wires run around the outer limits. I think I can just run the signal wire straight across and still have room for the battery.

Thanks again, Terry

[still4given]

Hi Aon,

I replaced all of the signal lines with shielded cable and there is no change, the squeal is still there. If I turn all of the knobs down except for the level the squeal is pretty much gone but obviously something is still amiss. While trouble shooting I must have shorted something because now the 4 LED bank is dark. Unfortunately, Tayda did not provide a schematic so I have sent a request to them for one so I can try to locate the problem. Thanks again for your help.

Blessings, Terry

[still4given]

Well it seems that Tayda doesn't have access to the matching schematic. They offered to refund the cost of the board. 

So, I'm hping that one of you may know where I can find the schematic for this Plexitone with the boost channel. If I can see how it's compensated maybe I can try some things to get rid of the oscillation.

Thanks, Terry

[Kipper4]

http://www.diystompboxes.com/smfforum/index.php?topic=90158.0

Maybe something here too


http://www.newtone-online.nl/forum/index.php?topic=6802.30

[still4given]

Hi Kipper,

Thanks for the links. In the mean time I found also the Boneyard.

http://www.madbeanpedals.com/projects/Boneyard/docs/Boneyard.pdf

All of the values in the Boneyard seem to agree with the Plexitone I just built. The only difference is that it uses one LF347 and mine uses two TL072 ICs. I don't know if these require different compensation than the LF347. Do any of you happen to know? If so, do you have some suggestions about where to start?

Thanks, Terry

[still4given]

Hi guys. I am making some headway. I swapped out the 7660 and the squeal is reduced. One issue I am noticing is that case is very sensitive to touch. Almost microphonic. Any tapping on the case or plug jacks and the sound is transfered to the amp. Any suggestions where to begin checking is appreciated.

Thanks, Terry

[bluebunny]

I swapped out the 7660 and the squeal is reduced.

I notice that the 7660 part listed in the page you linked doesn't have an "S" in it.  This is important.  The "S" part has the capability to run its internal clock at a frequency above human hearing.  Perhaps this was your squeal?  What was the exact part number you had installed originally?

[still4given]

http://www.taydaelectronics.com/icl7660cpaz-icl7660-cmos-voltage-converter-ic.html

Can you recommend a better device? A link would be nice.

[Groovenut]

http://www.mouser.com/ProductDetail/Microchip-Technology/TC7660SCPA/?qs=sGAEpiMZZMsUzhEcHltCuR0J1U1hEvIK

Here you go

[still4given]

Thanks, I'll order some.

[LightSoundGeometry]

i recommend a maxx 1044 over the 7660

[still4given]

I was looking at those at Tayda.
http://www.taydaelectronics.com/max1044-max1044cpa-switched-capacitor-voltage-converter-ic.html

A bit more pricey but the specs address the oscillation directly. I'll order one and try it out.

Thanks, Terry

[debrad]

I had the exact same squeal/whistle issue with my recent Tayda Plexitone build.  After several searches, I read that many people experienced the same issue but resolved it with the addition of a buffer.  I tested this out by first running a Boss pedal in front of the Plexitone and then my DIY Klon/Cornish buffer pedal and both eliminated the problem.

[still4given]

That is interesting. I don't own any Boss pedals or any other "manufactured? pedals at this time. All of my pedals are DIY. Tayda is working with me to resolve this. I have ordered some MAX1044 chips from them and will install one when they get here. Yesterday I noticed that a few of my other pedals were displaying a squeal. I discovered that I had them on a daisy chain power cable along with the Plexitone. As soon as I removed the Plexitone the squeal was gone from the board. Seems that 7660 was affecting the whole bunch. I will let you guys know if the 1044 fixes the problem in a few days.

Blessings, Terry

[debrad]

I am eager to hear how the IC replacement goes!  I used the default "ICL7660CPAZ ICL7660 CMOS VOLTAGE CONVERTER IC" and didn't realize that it had a reputation for whining.

Is the MAX1044 a direct replacement?  I assume it is supposed to take care of the whine?

How about the "ICL7660S" option that bluebunny suggested...although I don't see that one in Tayda's catalog (guess we'd have to shop elsewhere...).

[bluebunny]

It's not a reputation, it's a design.    The "S" variant gives it the supersonic clock capability of the 1044.  The 7660S and 1044 (and others) are more or less equivalent and may be substituted for each other.  But beware that the MAX1044 has a lower maximum input voltage and is reputed to die horribly if you give it a hair above 10V.  The 7660S (and others) isn't so suicidal.

[debrad]

It's not a reputation, it's a design. 

Yes...poor word choice on my behalf (although still probably better than me saying, "...didn't realize that is was designed for whining" (ha ha ha).

I just noticed the 10V rating on the MAX1044 after posting so I can see why the 7660S might be a wiser choice in the Tayda Plexitone application.  I am going to see if I can source on locally and then test drive it in my own build to see if it takes care of the whine currently being taken care of by a couple of buffered pedals already in my chain.

As an aside, my original tests showed that the whine/squeal/whistle in my Plexitone build was SIGNIFICANTLY worse when using single coils.  It was quite subtle when using my Epi Dot and Les Paul and only became really noticeable when I cranked the gain and/or volume beyond any setting I would even THINK of using; however, it was "loud and proud" at just about every setting when I plugged in my Strat or Tele.

If you take that into account along with the fact that buffers seem to tame it, would it make sense that there is some kind of impedance factor playing into things (just looking for explanations since I've come across several discussions on "remedies" but virtually none on "reasons" and...as you can undoubtedly tell from this and all my other posts...I'm definitely at the beginning of the learning curve when it comes to really understanding electronics!).

[debrad]

Just wanted to provide the OP with an update on my own Plexitone adventures:

I ordered some "s" variants of the ICL7660 and they finally arrived this week.  I immediately tried one in my Tayda Plexitone build and it actually ADDED noise...and not only noise to the affected signal, but to the bypass signal as well.  Perhaps it was just in my mind but I swear the output level with the "s" variant was significantly louder so maybe it didn't "add" noise, but just amplified noise that was already there (hey, I'm just guessing here).  Anyway, I was surprised to hear an audible hum/buzz when the effect was bypassed that wasn't there with the "c" model.  Needless to say, I swapped out the "s",  put the "c" back in place and the new noise was gone.

By some strange coincidence, the very next day I came across a post on the "DIY Stompboxes (unofficial)" Facebook page that claims Tayda's ICL7660 are "fakes".  According to the poster (Assaf Abramovich), test show a genuine Maxim ICL7660 draws about 0.2mA without any load using a 9.5V input but the Tayda is drawing 40.6mA.

I have to admit that I don't fully appreciate the implications of that (other than knowing it's drawing 200x more current than it should)...especially in terms of how that might impact the sound and function of the pedal.  I also don't know if that kind of detail might just be a symptom of one bad ICL7660...but I figured I would share it in case it helps in some way (I know I'd certainly like to hear more about what this might mean for my own Plexitone build!).