Plexitone squeal

[still4given]

I tried the MAX1044 and the squeal was just as bad if not worse. It is definitely coming from the voltage converter though. If I place my finger across the pins of the converter the squeal will go away. I have thought of trying to add some caps to the converter to see if I can find it. For now the pedal just sits and it is unusable as it is. I suppose someone who is playing is a loud band could get away with it.

[PRR]

> squeal pitch that plays the whole time

I'm looking at the picture. Did they really put the voltage converter right ON a small audio board, behind an audio pot?

That's a bit like putting your drinking well IN your out-house. Maybe convenient, but begs for leak trouble. Laws here want me to put the poop 50 feet away from my well, and further box it up (septic tank) to mellow it out.

I'd be thinking about a totally separate power conversion board, maybe in a small tin box, as far as possible from precious audio signals.

Does anybody know a stand-alone voltage converter?

[Fender3D]

... If I place my finger across the pins of the converter the squeal will go away. I have thought of trying to add some caps...

Why don't you try with sausage?
I guess Rob has a nice cache of it...

BTW a proper designed PCB would be better...

[still4given]

Well, I looked at the Boneyard and they have the voltage converter on the board as well. The original Plexitone just has its own power supply built in so it doesn't need the converter.

BTW, Tayda refunded the cost of all the parts I bought for this pedal so I am still very happy with them.

Next thing to try is pulling the MAX1044 and feeding it with an 18V supply. It will mean adding an 18V circuit to my power supply.

[J0K3RX]

If you don't mind etching a board or getting somebody to do one up for you then you might want to try this one! It is probably one of the best layouts I have seen and it sounds as good as it looks! Eagle files are there for download.
https://soundwavedesign.wordpress.com/ember/

[Markw5]

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.

Probably because the low output Z of the buffer is lowering the impedance around the input circuitry of the Plexitone. A similar thing can happen with tubescreamer type circuits. The proper fix is usually to reroute the input circuitry away from later more amplified stages. A little stray capacitance coupling back into the input can have a big effect if impedances are high there, and that's what you have with FET input opamps and 1M bias resistors.

Also, it would be helpful for understanding the problem better if someone could sketch a schematic from the PCB traces, if someone has one handy for that purpose. Unless of course, we are convinced the boneyard schematic is exactly the same.

[Markw5]

Something else I just noticed from looking at the PCB picture at Plexitone. The gain switch and crunch controls circuits are sitting right next to the high-z input circuitry. Mostly likely that's where the problem is. If it were me, I would probably move the input R's and C's off the PCB and mount them somewhere else. On a tubescreamer clone I have, they ended up soldered to the foot switch and the input jack, with a node or two floating in air. It worked though, and was reasonably mechanically sturdy. I ran one little coax to the input pin on the opamp soldered right on the bottom of the socket, and cut away the trace that was there before.

[J0K3RX]

Don't use the on-board voltage converter.. build one up on perf or etch a small board and keep it well away from the main pcb. Even the madbean boneyard has a Noise/Oscillation write up in the Notes section of the pdf and in bold red letters at the end of the doc "DO NOT, and I repeat, DO NOT box this up until you first test it out on your prototyping/testing rig."

[debrad]

Also, it would be helpful for understanding the problem better if someone could sketch a schematic from the PCB traces, if someone has one handy for that purpose. Unless of course, we are convinced the boneyard schematic is exactly the same.

Thanks for the "feedback" Markw.  I have ordered a second Tayda Plexitone PCB to build for a friend so I could give the trace a shot whenever it arrives (I'll warn you ahead of time, I have ZERO experience doing that sort of thing...but everyone has to start somewhere, right?!?!?).

Interesting points about the relative location of various components of the circuit and how they may interact.  I will also take JOK3RX's advice into consideration on the next build (and anything similar).

[still4given]

From what I can see, the Boneyard is the same aside from the Boneyard using a quad IC and the Plexitone uses two dual ICs.

[still4given]

Hi Guys,

I have good news. I bought a TC1044SCPA from Tayda.
http://www.taydaelectronics.com/tc1044scpa-tc1044-voltage-regulator-ic.html
They didn't carry them when I bought the pedal PCB. It came in today and I switched it out. The squeal is gone. Finally! It is kind of a cool pedal. For some reason the MAX1044CPA didn't work but this one does. Perhaps it is the S version that makes the difference as stated above. Anyway, I just wanted to report with the good news.

Blessings, Terry

[debrad]

I have good news. I bought a TC1044SCPA from Tayda....It came in today and I switched it out. The squeal is gone. Finally!

I glad to hear Tayda is now selling the "S" version and that this did the trick for you.  As I mentioned, the "S" version I bought and tried in my build seemed to make MORE noise.  Having said that, I only tried 1 of the 10 that came in the package so it MIGHT have been faulty...or maybe the whole set is bad (they were a cheap eBay purchase...).  If worse comes to worse, at least I know the Tayda "S" version has the potential to eliminate some squeal.

[still4given]

The part is 99 cents. Well worth the investment.

[debrad]

Ya, I think I'll put a couple on my next order!

In the meantime, here are a couple of hi-rez photos of my newly arrived Tayda PCB.  I was all set to create a schematic but thought the internet would be better served to have that done by someone who knows what they are doing rather than suffer through my erroneous interpretation!  It should be obvious but, for the record, I've flipped the photo of the backside so that the orientation of the holes matches the front...





and here are the component values (my assumption is that resistor "13" should really be labelled "R12"):

[debrad]

I have good news. I bought a TC1044SCPA from Tayda....It came in today and I switched it out. The squeal is gone. Finally!

I ordered the TC1044SCPA from Tayda but, in my mind, I was thinking it was the ICL7660S (DOH!!)...

still4given appears to have used it in his build and it removed the whine/oscillation but I want to make sure it won't fry (or fry anything else) if I put it into my Plexitone build.

Can anyone confirm that the TC1044SCPA is an acceptable alternative for the ICL7660S (the spec's appear to be similar but I am quite new to reading those things!)?

Any help would be MUCH appreciated!


- brad -

[still4given]

I think someone's concern was the max voltage is +13v. However the power supply circuit has a 9.1V zener included so it won't see more than that. I have been using it daily with zero issues.

Here is the data sheet in case you want to check for yourself.

http://www.taydaelectronics.com/datasheets/A-1377.pdf

[bluebunny]

I would say you're good to go with the TC1044 in place of the 7660. The MAX version is somewhat picky with input voltage. These two are fine. And the S will do the supersonic trick.

Sent from my GT-N8010 using Tapatalk

[debrad]

Thanks...the TC1044SPC seems to have cleaned things up nicely!