Iron Pumpkin(s) and other smaller vegetable animals, Tips 'n' Tricks thread

[Zen Mod]

leave them as is - not populated

that's for borderline case, if someone is so desperate to have more THD in system, so additionally loading buffers to their weeping point

 

[Eric]

Just confirming that I'm about to solder in the correct parts to the correct places:

My kit came with 4 pieces of LM336 Z25. The schematic shows U101, U102, U201, and U202 are all LM336 Z25.

However, the parts list txt file shows LM385 for U101, U201 and shows LM336 for U102, U202.

Am I good to go with soldering in 4 pieces of LM336 for U1-U4?

 

[Zen Mod]

Schematic is reference, Eagle generated BOM is here just for fun and producing dilemmas

LM336Z-2V5 is proper part, and I'm always sending right ones

 

[Eric]

That's what I thought, thanks for confirming. This was a good stopping point for the evening to avoid making mistakes

 

[Eric]

Here it is, all populated. Board is cleaned and solder joints have been inspected. Next steps are to apply power, set bias/offset for each channel, and then check the relay power supply. Have to order the chassis, too.

 

[Zen Mod]

first set pots in CCS portion of JFet buffers to max, confirm with ohmmeter across parallel 39R resistors

then power up, set rails to 12Vdc +/-

then buffer Iq to 20mV across 1R

then output DC offset with pots in signal part of JFet buffers

then you're good with trimpots

edit: NTCs you put there (NTC 101/201) - are they labeled as surge limiters. or you're having plain low current ones?

proper ones for position are of ~6mm Dia, really declared as surge limiting devices


besides - heatsinks orientation is your choice, nothing wrong with them tucked inside

 

[Eric]

Thanks for the trim pot protocol. For the sinks, I rotated them just to add some space between them and the adjacent caps. Without rotating, they were practically resting on the caps.

The NTC devices that I used are 22R 1/2w devices. I figured they were just to provide some isolation between grounds to prevent ground loops.
https://www.mouser.com/ProductDetai...VrDDudlaSiw==&countryCode=US&currencyCode=USD

Did you intend something more like a CL-60? If these are the wrong ones, I can replace them.

 

[Zen Mod]

in general, when speaking of current surge limiters (power NTCs), all you wanna know is said with their resistance and their Diameter - when you compare several, looking at current data and physical dimension ...... that's it


what you need there is- again - approx 6mm Dia, anything between 10 and 20R, and yeah - GND lifters, they are

but still, even if any catastrophe of leaking primary to secondary side is highly improbable, if you have it there, you must ensure that declared current capability of part itself is greater than mains fuse current capability

so, as you mounted small ones, which are having role of small sense or regulating variable resistors - you need to change them to proper, current surge limiting type

CL60 is too big - you can squeeze it somehow in space but no way to put them in pads - their holes are simply too small for fat CL60 pins

edit: "6mm Dia" is more like 8mm Dia

see here, few examples:

https://eu.mouser.com/c/circuit-pro...s/?diameter=8 mm&resistance=10 Ohms&instock=y

 

[Eric]

Thanks for the link. I'll look in my parts box and see if I have anything larger. If not, I'll order some new ones and replace those tiny ones.

I presume a 400mm deep chassis is better to put some distance between traffos and the board? Those little 10VA donuts are pretty cute, never used anything so small before. Each one measures about 2.25" wide by 1" tall. Don't know if it will be better to lay them side by size, or stack them with a brass screw through the middle.

 

[Eric]

Found two CL-60s in my box. I'll bend the legs to make little feet and solder them to the top of the PCB pads.

 

[Zen Mod]

do not

leave those you already have soldered, replace them later when you get proper ones

 

[Eric]

I'll order some more parts.

 

[Eric]

Voltage tests on each channel went well. Got rails dialed in easily - they are nice and stable with no "lag time" between adjusting and making readings. jFet bias was also nice and easy to set at 20mV and seems just as stable as rail voltage. Dial it in, hit the target, and it's done. Then I got offset adjusted down to +or- 0.05mV. Adjusting offset seems very sensitive and seems to want to move around just a little. Overall targets achieved. Haven't powered up the relay section yet.

 

[Zen Mod]

think mV, not necessarily decimals

if you get it to +/-0.5mV, just leave it and re-check in 10min, re-set if needed and you're done

 

[Eric]

Ha, that’s why I stopped fiddling, I was clearly below 0.2mV so I stopped. Relays for input selection work well, too, their power supply is 23.75v. Next up is connecting the transformers…

 

[Eric]

Got all of the assembly completed and everything seems to check out. I like the little red indicator LEDs in the Turtle board, I thought those little critters were resistors. All that I need now is a chassis.

 

[Zen Mod]

Fugly!

 

[Zen Mod]

is it going to sing before chassis arrives?

 

[Eric]

I'm honored to receive my first ever "Fugly" from you, Zen! Not sure if it will sing before the chassis arrives - I'll have to see if I have a board to screw things down to prevent mishaps while it's naked... I can't wait to hear it!

 

[Vunce]

Build is looking fantastic Eric!
🤩