Pumpkin preamp - More Boring Making Thread

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steenoe

steenoe

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Joined 2004
Zen Mod said:



naah - just go for it ;
in Cook Book you'll find everything you need to know about setting gain for your needs ;

just one note - and you'll probably note my words not as ones from seller , but .........

without shunt reg ( not just Shunty , any other decent shunt reg) Pumpkin is very decent preamp ;

with shunt reg - it's great preamp .

few volts up or down aren't so important .
Click to expand...

Couldnt the Shunty be set up for the lower rail-voltage? And what modifications would be needed for that?


Mrs.Magura said:



Well, I'm immune to flattery, but I do love to be bribed :angel:


Mrs. Magura.

Ohh, and hello all :)
Click to expand...

Hello Sweetheart, nice to see some postings with a fresh attitude
:) Maybe you can get the OT bunch to behave in a civilized manner? :D :D

:)
 
Zen Mod

Zen Mod

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Manu said:
ZMod : What is the purpose of R20/20A in Shunty. BOM says : 0R or 0R1.
Why can't it be simply a trace on pcb?
Manu
Click to expand...


Oly want 0R1 nad mosfet as shunt element

I want shortie and darlington ; lower output impedance

edit : I forgot to say - I use small dia shortie - dummie shortie , eek thing looking as resistor , with just one stripe in middle ..... once I measured them - they burn at 500mA
 
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hershann

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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
 
steenoe

steenoe

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Joined 2004
hershann said:
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
Click to expand...

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

jacco vermeulen

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Joined 2004
hershann said:
replacing it with a 1N4740A which is 1w and lesser current
Click to expand...

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

Zen Mod

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hershann said:
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
Click to expand...


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

Zen Mod

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Cook Book notes

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 .
Click to expand...

where else than :

DOWNLOAD Cook Book

ya all nutz

:rofl:
 
jacco vermeulen

jacco vermeulen

Member
Joined 2004
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.
 
jacco vermeulen

jacco vermeulen

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Joined 2004
HBarske said:
Reichelt obviously does the job
Click to expand...

Nix gut, die ones at Reichelt sind probably polyester typen.
Google for (philips) 2222-808-11109

PTFE trimcaps have long gone out of production iirc, but are the only true good ones. (the dielectric of the ptfe trimcaps is pure white)
No touchy other types.

Vishay Beyschlag-Components numbers and datasheet : here
German made, what else ! :clown:

2nd hand ones example : here
 

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H

hershann

Member
Joined 2007
jacco vermeulen said:
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.
Click to expand...


The pumpkin has C8 C10 C13 C14 - rated for 220-470uF and the Shunty has C2 2a 15 15a 16 16a rated for 1000 - 2200uF.

So assuming the same grade and series of electrolytic caps - what is the advantage or disadvantage of using a bigger vs smaller cap? Bigger cap = less ripple?

Still a noob

her shann
 
jacco vermeulen

jacco vermeulen

Member
Joined 2004
Rough formula:

Vripple = [ 1700 x Current(max) ] / uF number.

A smaller same brand/type cap is cheaper and has a higher ESR number.
By increasing the resistor value the number R*C remains constant, same corner frequency, same noise reduction before entering the 1st. reg. stage.
Does mean the voltage drop across the series resistors is higher, picking a transformer with 1 Vac higher secondaries straightens it out.

(btw: USA guys looking for fancy food spindle ptfe caps should type in : Voltronics A1 series, the big vendors likely have them for at least $25 the pop)
 
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hershann

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Zen Mod

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hershann said:
Looking for heatsink alternatives - I suppose the silkscreen PCB on the Cookbook is to scale?

And therefore the following below, which is 40mm wide would not fit?
http://www.futurlec.com/Heatsinks/TO218S049B.shtml

So I'm considering the below:
http://www.aavidthermalloy.com/cgi-bin/stdisp.pl?Pnum=513202b02500
http://www.aavidthermalloy.com/cgi-bin/stdisp.pl?Pnum=6032b-tt
http://www.aavidthermalloy.com/cgi-bin/stdisp.pl?Pnum=sw50-2g

Comments?

her shann
Click to expand...


silkscreen is in scale - if you look it in 100% scale on screen ;)

anyway - on last page you can find Fischer numbers

download this :
http://www.fischerelektronik.de/fischer/uploadfischerfcool/Fischer/A.1.E.pdf

and look

~ 4MB , but worthy
 
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