My own Pumpkin preamp - Construction

Algar_emi

Member
Paid Member
2002-10-30 11:57 pm
Canada, Qc
sites.google.com
I'n my spare time from the Maxon GB 2007 (and night and weekend :cannotbe:), I started to work on some enclosure to mount the Pumpkin preamp. I bought a set of PCB a few weeks ago. I'm collecting the parts for now.

The preamp will have a separate supply module that will contains a custom Plitron surplus transformer that I got directly from Plitron. It is hugely overkill. It has also some extra secondaries, one of which I will use to supply the preamp digital section and input selection boards, more on that later.

This is the transfo enclosure. It is made of laminated dried maple on the outside. The inside is a complete aluminium enclosure. The top has some spare space reserved to receive a plate of black tinted glass or black plexiglass for a nice finish all around.
 

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Algar_emi

Member
Paid Member
2002-10-30 11:57 pm
Canada, Qc
sites.google.com
I'm still working on the preamp enclosure. It is built the same way but has 1/4 inch alu inside side panel and a center 1/4 inch alu spine for extra case rigidity. The central spine will also insulate each channel from each other.

I'm planning to use my Placette attenuator kit as volume control. A set of external connectors will allow the Placette to be used by itself if I choose to. The Placette I have is fully balanced, as needed by the Pumpkin. The kit will also allow volume remote control. The processor and LCD Placette control PCB will be mounted on the front, inside the wood. The back will be closed by an alu plate for shielding. The processor and relay will use a separate digital supply. This supply has a built-in EMI filter.

The source selection will be done using a selector switch and back mounted relays PCB, close to the inputs conenctors.

The preamp back is made of brushed, anodized panel that I recycled from an other enclosure. The round notch on the back will receive the input power connector.
 

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As some said on this forum, what is the point in building something simple and cheap. We may as well buy some noise box from Circuit City and be done with it. Maybe half of the price of the very high end stuff is casing and cosmetic anyway.

Part of the fun is to try to build things differently and reach for the top.

I guest the Pumpkin with its sophisticated supply is worth nothing less :cool:
 
I agree, I have limited metal machining tools, however wood is relative easy to machine. I like to refer to mine as the Pass woodies. I was reviewing your 2.2 BOM as mentioned R20,23,24,25 on Pumpkin need updating. On shunty D6,6a,7,7a leads are to big for holes, C19a),C4(a) C12(a) need to have 15mm spacing. C17,C17a,C18,C18a, Is Wima ok to use in place of ceramic (plead ignorance on my part)? I appreciate your work on the BOM Have you had any luck with heatsinks? I looked in all my catalogs and am unable to locate the ones used on Q1,Q1a. I will make a trip to Apex JR soon to see if I can find something suitable for the larger heat sinks, if something looks usable I can pick some up for you.

Thanks
Bill
 

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located heat sinks:
Futurlec has the little ones part # TO218S049B $.90 - http://www.futurlec.com/Heatsinks/TO218S049B.shtml and the Larger ones Surplus sales of Nebraska (HSK) HS-DMC501 $4.50 - http://www.surplussales.com/Heatsinks/HeatSink1.html . Will have to file the fins a little bit mabe 1/16, and they may overhang the sides a tad but close enough for me. Oh yea and Apex Jr has a Transformer 15-0042 92 VCT 250 VA (a little over kill ) $25.00 http://www.apexjr.com/miscellaneous.html#Transformers .

Bill
 
Not center tapped, but 4 times $3.95 is less than $25.
-Plus they ensure perfect channel separation.
-Plus an EI/M core transformer is a preferable choice to use.
-Plus Mercury Magnetics is a pretty OK transformer manufacturer.
-Plus they likely have fully separated windings. By the looks of it, the pictured block type is the TA110-W, with the sizes given >50VA each.
-Plus you are free to use either the 48Vac or the 40Vac tap.
 

dviswa

Member
2004-10-10 12:50 am
wirewiggler said:
located heat sinks:
Futurlec has the little ones part # TO218S049B $.90 - http://www.futurlec.com/Heatsinks/TO218S049B.shtml and the Larger ones Surplus sales of Nebraska (HSK) HS-DMC501 $4.50 - http://www.surplussales.com/Heatsinks/HeatSink1.html . Will have to file the fins a little bit mabe 1/16, and they may overhang the sides a tad but close enough for me. Oh yea and Apex Jr has a Transformer 15-0042 92 VCT 250 VA (a little over kill ) $25.00 http://www.apexjr.com/miscellaneous.html#Transformers .

Bill


Darn,
Little heatsinks are to large will have look for some more.

Yup, I did the dumb mistake too.
:eek: I should have measured the size on the pcb before ordering. The larger heatsink needs filling of 3-4 mm or so. Not my favorite activity.

ZM,
Sorry to say, finding heatsinks are the bane of this project. There are components all around the heatsinks with no space available, making it very difficult to use other heatsinks. I still do not have any of the heatsinks needed. :bawling:
 
dviswa said:


Yup, I did the dumb mistake too.
:eek: I should have measured the size on the pcb before ordering. The larger heatsink needs filling of 3-4 mm or so. Not my favorite activity.

ZM,
Sorry to say, finding heatsinks are the bane of this project. There are components all around the heatsinks with no space available, making it very difficult to use other heatsinks. I still do not have any of the heatsinks needed. :bawling:


I wrote more than once - just use plain sheet of 3mm Alu plate .

approximately 50% bigger than heatsinks in case , and it will be more than enough .

ya need fabric heatsinks to be in fashion ........ and real man use plain Al or Cu

:clown:


I wrote that more than clear in Cook Book .