Pumpkin preamp - ordered by Steen , official making thread

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#3,061
Hi,

so it's time for me to build pumpkin and shunty.

I have a problem regarding x-former / 2200 uF workin Voltage condos.

I've soldered twelve 63 V condos and I after doing that I have realized that trasfos wounded customly for me are double 50 V- 50VA: so after rectifier I will have around 70 volt.🙁

My three solution:

1) Buy another batch of 100v condos ( and, yes, desolder the older and drill new holes)

2) Buy another couple of x-former with a double 40 V secondary.

3) Put a 50 ohm 20 W series-resistor before graetz bridge for a 10 V voltage drop.

What is best solution?

Please, let me know your opinions.


Ciao,

Anto
 
#3,065
My Dual-Mono Pumpkin Shuntky has developed a strange anomally.

Now, when I first turn it ON it sounds like waves at the beach. Not a high pitched scream of oscillation, but just a quiet WHOOSHING sort of sound. After less than a minute it settles down and is silent then for the rest of the day.

Has anyone got any ideas what could cause this ?

The original Shuntky boards were poorly manufactured and had problems. This manifested itself with some very ODD LED indications. However, with Zen's help this was resolved.
 
#3,066
to exclude unneeded variations , try this :

ground all active inputs to Pumpkin , connect it directly to power amp and power up ;

then write do you have same situation ;

just observation - Pumpkin doesn't have any mute relays or something similar - that part was leaved as builder's choice .
usual practice is to power up source , then pre , then power amp ; that way one will not have any funny noises
for powering off - exactly opposite procedure - amp first , then pre , then source .

in any case - Ocean like sound is atypical for :Pumpkin: intended behavior
 
#3,073
DMM on continuity/buzzer test
lay pcb on table , bottom side of pcb up
one probe on pad which is through-holed with upper groundplane

other probe - just move zig-zag across pcb , across all pads

there must not be continuity between any of traces/pads and upper gndplane

that is sole problem , which happened with Shunty pcbs
 
#3,077
Mine was obvious. Only the top four LEDs were illuminating. Simple ohms law stated that there must be a short somewhere. I couldn't detect it with an ohmmeter nor a magnifying glass. I simply ran a craft knfife along all the gaps in the PCB tracks.

The short must have been at almost atomic level. Anyway, the craft knife did the trick.
 
#3,079
KatieandDad said:
If you look at Zen Mods posts about KK-PCB circuit boards, apparently he is not the only one with PCB supplier problems.

I'm now searching for my own CNC PCB cutting machine. Shame I haven't got $10K
.
Click to expand...

Why not a light box (home brew) few kemicals and free PCB design software.

I have been brewing my own for a while and maybe £200 is enough to get started.

Altrough in pumpkin case I (but this is me and my own choice You do as you like) I rather wait for new batch and the chance to be able to pay for them if and when Pay pall let me and by doing this support a felow member.

If you rather put up with the noise and tool changes You can get cheaper one at about £4000 from RS and Elektor or build your own for £350 as RS and Rapid electronics use to sell a kit with software.

Sorry can not find links to those at present but will post eventualy
 
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