Pumpkin preamp - ordered by Steen , official making thread

[hershann]

Assuming I use 1 transformer to power 2 shuntys (?shunties) - is the correct way to wire 1 board to the transformer and using appropriately sized hook-up wire to connect this shunty to the AC in of the next shunty?

Looking at the schematic - I assume that a transformer with 2 separate secondaries can be used - as long as the centre 2 wires are connected?

her shann

[hershann]

Another question:

Shunty D1-5a, BOM says ZY10 - which is a 2w zener.

I guess it is no issue replacing it with a 1N4740A which is 1w and lesser current?

her shann

[steenoe]

Originally posted by hershann
Assuming I use 1 transformer to power 2 shuntys (?shunties) - is the correct way to wire 1 board to the transformer and using appropriately sized hook-up wire to connect this shunty to the AC in of the next shunty?

Looking at the schematic - I assume that a transformer with 2 separate secondaries can be used - as long as the centre 2 wires are connected?

her shann

The trafo's secondaries must be connected to both Shunties AC input. You can do that by taking the secondaries to the first Shunty's AC input, and from there to the next Shunty's AC input.
Or you can connect the trafo's secondaries to a screwterminal and fan them out from there, which I think would be a bit more practical. Especially if you have to take it apart, for some reason. Yes you must connect the 2 centerwires on a trafo with dual secondaries, allright.

[jacco vermeulen]

Originally posted by hershann
replacing it with a 1N4740A which is 1w and lesser current

A 1N4740 will still be good for some 0.9W if the surrounding temperature of the Zener-D is 40C.
900 mW divided 10 volts Zener-D drop is 90mA.

In steady state condition (C3/C3a loaded), there's some 10-20 volts difference between the rectified rail voltage and the stack of Zeners. (42-50Vac sec. transformer)
=> 3.5 to 7 mA Zener-D current.
3.5-7mA times 10 volts translates to some 5-10C temperature rise.

How much current/power handling you think the Zener-D will require ?

(ps : Zener diodes have a rotten accuracy, with at least 20 at hand it's easy peasy to match them in 5-string sets with an equal voltage droppie, personally i don't fancy a heatsink running 20% hotter than his opponent. In the worst case you don't have enough voltage slack for the 2nd regulation stage)

[Zen Mod]

Originally posted by hershann
Another question:

Shunty D1-5a, BOM says ZY10 - which is a 2w zener.

I guess it is no issue replacing it with a 1N4740A which is 1w and lesser current?

her shann

it's easy:

say that you have ~ 60Vdc on input ;
so - you have just 10 V across 2x1k5 resistors (R1 , R2)

10V / (1k5 +1k5) = 3mA

dissipation in each zenner is 10V x 3mA = 0,03W , so - you can use whatever you find ............

[Zen Mod]

so - again - few new lines of additional notes JUST ON LAST PAGE ;

this is what's new :

Also important note :

- For Shunty : Resistors R21 ,R22 , R23, R24 , R23a , R24a need to be either plain carbon 0,5W ones , or decrease them to 1E8 or 2E2 , if you insist to use metal films of 0,25W variety . Few clever Shunty builders pointed that these resistors are prone to burning , if you use low ESR biggie electrolytics in input side of Shunty .

where else than :

DOWNLOAD Cook Book

ya all nutz

[jacco vermeulen]

Junk Fuwed Book:

With 1000uf caps instead of 2200=> charge ripple without CRC still less than 100mV.
Use 1000uf and double the R21/R23/R24(a) value, 0.6W typies (Cheesecakes even go doublesided)

MUR1xx, just as fast.

[Zen Mod]

Originally posted by jacco vermeulen
Junk Fuwed Book:

With 1000uf caps instead of 2200=> charge ripple without CRC still less than 100mV.
Use 1000uf and double the R21/R23/R24(a) value, 0.6W typies (Cheesecakes even go doublesided)

MUR1xx, just as fast.

[jacco vermeulen]

Another Junk Lunch :

Instead of a 5pF Mica, find a PTFE trimcap.
Look for Phili types in Europia.

In the North-Amerrygoround it's Sprague Goodman Filmtrim@ GXA/GXE series.
Last time i looked i saw a single one of the non-SMT listed for $4/pc.
So for the Yanksters it's either Flea-Bee, go Filmtrim SMT wacko or hit someone over the head.

[Zen Mod]

Originally posted by jacco vermeulen
Another Junk Lunch :

Instead of a 5pF Mica, find a PTFE trimcap.
Look for Phili types in Europia.

In the North-Amerrygoround it's Sprague Goodman Filmtrim@ GXA/GXE series.
Last time i looked i saw a single one of the non-SMT listed for $4/pc.
So for the Yanksters it's either Flea-Bee, go Filmtrim SMT wacko or hit someone over the head.