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

[pinnocchio]

Looks like the BC546 and 556 are branded CDIL and are CBE pinout, so it does matches the silkscreen.

Now to rail noise...

Do

 

[Zen Mod]

its easy : positive rail , all N polarity bjts, P channel mosfet

negative rail opposite to above : all P polarity bjts, N channel mosfet

no surprises in parts pinout , everything by the book/silkscreen

 

[pinnocchio]

yep! That's all good

Rail noise seems to be ok...

Just tried
RCA input with RCA output = good
RCA input with XLR output = no good
XLR input with XLR output = good
XLR input with RCA output = good but last 3-4 volume notch I get low hum (I'll never reach that level in real life...)

This was tested on a single channel, left channel.

SE/BAL relay seems to be energized on both RCA inputs (1-2) as I see 22.5V on relay coil.

Do

 

[Zen Mod]

take care that is possible to get hum, if you're using input with nothing connected to it

now - I remember you confirmed all readings between channel GND and chassis

taking in account that practically everything is in board, all I can think now is - check all wiring once again ..... input by input, in between buffers and Turtle, from Turtle to MoBo, from MoBo to output connectors

 

[pinnocchio]

Hi ZM,

Just a quick question... When I received my second PCB, there was already two diodes under the PCB near the regulator heatsink, modification that was not present on the first PCB. I there any parts I should have omitted due to this modification or any value changes?

Thanks
Do

 

[Zen Mod]

these diodes are slight fix for Logic PSU (so fixed 7806 reg and two diodes to neg, giving 7V3, as proper voltage for Arduino board), in later batch of pcbs diodes are included properly on board

no other modifications on pcbs

 

[pinnocchio]

ok thanks!

I'm getting desperate... How much for a new bare PCB with SMD soldered? Just in case I crapped out some jfets... It's weird that both channels have the same issue but it seems to be just like that when using balanced input with SE output... Anyways, I might just try to rebuild everything again... If only customs didn't crapped out my first PCB...

Do

 

[Zen Mod]

make pause for few days, to let some air in the head

then prepare proper light and send me as much pictures you're in the mood to make

dunno is it possible that you did something with JFets, if you're able to set 20mA Iq and proper 0 output offset on buffers

same with small JFets beneath pcb (CCS for voltage references and feed for shunt CCS) ....... if you have steady rails without noise, everything there is OK

coincidentally - Behruz posted few days ago about his Bal IP finished ....... sole difference is that he got pcbs fully populated and set by me .......

even if there is, on first sight, plethora of parts, construction is basically simple and not at all complicated for assembly ........ I mean - it is deliberately made that way, seeking not just good performance but also durability and reliability for many years of joy

 

[pinnocchio]

Hi ZM,

Yes, construction is quite easy and setup is also a breeze. I just don't know what is wrong but I have decided to get rid of the three toroid and buy a single one from Toroidy with all required secondaries. I never had issues with R-Core in the past, so I decided to use the R-Core that were supposed to be assigned to this project, to another preamplifier I already had, only to realize I was getting a faint hum/buzz, which I didn't have before... I'm guessing those R-Core are not up to R-Core standards and probably super crappy made...

My project is now paused for a few weeks, or until I receive the new toroid from Toroidy. I somehow find it odd it could be as simple as that, but who knows... I'm testing all sorts of scenarios...

All the best!
Do

 

[Zen Mod]

 

[danny_66]

I'm testing all sorts of scenarios...

Hi Do,
Could it be that those R-core transformers are not really that good when configured as center tapped ?
Maybe try with adding a full bridge rectifier to each rail (like in pdf F5, F6) ?

 

[Zen Mod]

it came to my mind too, but I can't see a problem - circuit is quite symmetrically loading both rails

 

[pinnocchio]

Just saw this post... Missed it, sorry!

I did add a full bridge rectifier prior to ordering the new transformer, but it didn't change anything. I was hoping it could solve my issue but no difference.

Do

 

[MEPER]

Just curious......is it mechanical hum from toroid?
If not.....is it 50/60 or 100/120 Hz hum?

 

[pinnocchio]

I know it's not mechanical hum but I don't know if it 50/60Hz or 100/120Hz

I will need to check this and report back.

Thanks
Do

 

[MEPER]

If you have a scope it should be possible to see.

My experience is that 50/60 Hz noise is caused by magnetically induced noise from transformer. In an amp like M2X the Edcor can pick this up.

 

[pinnocchio]

Hello all!

It's been a while since I updated my project, but I was waiting on my transformer from Toroidy.

I did receive the transformers on Monday (only one for this project) but could only work on this tonight (or early in the morning...). Well... After installing the new transformer, the Iron Turtle is total silence, even at loudest volume!!! No more buzzing!!

So yeah... Just use a good transformer as per ZM!

So happy!!!

Here's a couple pictures of the temporary setup

 

[danny_66]

Great !
Thumbs up for the Toroidy

 

[vitalica]

I'm so glad you did it, great!

 

[sov]

The Turtle is awesome. This is probably my last pre-amp. It’s absolute quite despite the big trafo. Shielded Toroidy is like an inverted Tardis. It’s bigger on the outside.
I have listening a couple of days and my brain is thanking me. The sound is fantastic. I will do some measurements later but whatever the oscilloscope tells me I will never get rid of this pre amp.
A Pumpkin looks even better with some fruit.

ZM, thank You!