Thermionic problem

[PKRPedals]

I need some help with my Thermionic OD. Just finished it and it has a crazy amount of noise and squealing. The D1 diode is getting really hot also. At first, the LED just below R34 would light up with 9 volt supply connected but now it doesn't. I've checked all caps and resistors, they are all good. Also checked for any solder bridges and there are none. Any ideas?

 

[Chuck D. Bones]

I used to work at a commercial outfit right out of school. They mass-produced circuit-boards on automatic assembly equipment. Resistors came on reels of 5,000. The Service and Engineering depts would snip a few dozen resistors off the end of a reel to stock our parts bins. One day, a reel of resistors marked 10K but actually 200 Ohms made it onto the factory floor. As luck would have it, some of those resistors ended up in Service, Engineering and onto a couple thousand production boards before the problem was discovered. There was no incoming inspection and the production guys had turned off the verifier on the assembly machines because "it slowed it down."

 

[Chuck D. Bones]

Hey, does anyone besides me find it strange that the Thermionic uses 1N5817s for clipping diodes when the Betty, Sanchez, Debbie and Deluxe all use 1N4148's? I'm wondering if a typo crept into the schematic & BOM. Besides having a much lower forward voltage, Schottky rectifiers are leaky and could adversely affect the gain on the 3rd stage.

 

[PKRPedals]

Didn’t even think about that. I think I will use 4148’s when I do the next one. Thanks for pointing that out.

 

[Barry]

Personally my favorite clippers are 1n4148's or LED's, especially in overdrive circuits

 

[Chuck D. Bones]

Same here. I recently picked up 500 FDH400 diodes from EG and I'm using those in place of 1N4148s. They're pretty similar. Right now they're on clearance for $3.95.

I'm waiting to see if Mr. PedalPCB weighs in on the Thermionic diodes.

 

[PKRPedals]

I was kind of hoping that too

 

[Robert]

Hey, does anyone besides me find it strange that the Thermionic uses 1N5817s for clipping diodes when the Betty, Sanchez, Debbie and Deluxe all use 1N4148's? I'm wondering if a typo crept into the schematic & BOM.

It's not a typo. There was a whole big "thing" behind this a couple years ago.... a bunch of debate on another forum about what was the most suitable diode.... (there were curves, simulations, speculations, accusations, and all that good stuff) I eventually bowed out of the debate and haven't really thought much about it since.

I've built a few of the variants with both 1N4148 and 1N5817. I can't recall haven't a preference of one over the other, but there's really no reason to not just use 1N4148 if that's what you'd rather use.

I should probably just bring the Thermionic in line with the others and spec them all with 1N4148 to avoid confusion.

 

[Barry]

Same here. I recently picked up 500 FDH400 diodes from EG and I'm using those in place of 1N4148s. They're pretty similar. Right now they're on clearance for $3.95.

I'm waiting to see if Mr. PedalPCB weighs in on the Thermionic diodes.

I used those on my Paragon mini, thanks for the heads up ordered some from EG

 

[Mourguitars]

Ive noticed on a few of my upcoming builds the 3PDT is wired like this pedal...can you use a breakout board instead ? I did buy the 3PDT switches with the hole in the soldering lugs just in case..

Mike

 

[PKRPedals]

I’m sure you can. I just wire the switches like the build doc shows, it’s just as easy for me that way

 

[Mourguitars]

I’m sure you can. I just wire the switches like the build doc shows, it’s just as easy for me that way

Cool thanks for the reply !

 

[PKRPedals]

Ok. I got the new Thermionic board today. Went ahead and built it up using the correct resistors this time, haha, and all I can say is this thing is a monster. I thought the Deluxe was great but this one beats it. I used 1N4148's instead of the 1N5817's and it has more gain on tap than I will ever use. I haven't even messed with the trim pot either. Anybody in to high gain needs to build this pedal for sure. I'll take a pic of it later and post it in the build reports section.

 

[Chuck D. Bones]

The trimpot makes a big difference in how the PRESENCE control responds.

 

[PKRPedals]

Hmm. I was under the impression that it was for adjusting the gain.

 

[Chuck D. Bones]

It does adjust the gain, but it adjusts it at a critical point in the circuit: between the last two Distortion stages. PRESENCE does two things when you turn it up. It lets thru more treble and it hits the last pair of LEDs harder for more crunch. The trimmer determines just how hard the LEDs get hit when PRESENCE is dimed. Back the trimmer all the way down and the last pair of LEDs barely get tickled. Play the pedal with the bottom plate off and you'll see what I mean. LED1 & LED2 never get enough current to make much light. LED3 & LED4 really light up when you crank GAIN & PRESENCE.

 

[PKRPedals]

I'll play with it some this weekend. I have the trimmers dimed out on the Thermionic Deluxe and it sounds really good. I haven't messed with the trimmer on the Thermionic and it sounds really good, so I'm not sure how much of a difference there will be. I'll report back when I do.