Pumpkin preamp - ordered by Steen , official making thread

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hershann

Member
Joined 2007
Thinking of putting together the Opus balanced DAC (as described in the Digital section of the forum) to feed the pumpkin.

Can the Pumpkin accept a common mode DC of 2.5V? I am wondering if I can omit the DC coupling caps at the DAC output to improve its sound.

The pumpkin has output caps - thus will block any DC from going to the power amp - but will the DC itself damage the preamp?

her shann
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
hershann said:
Thinking of putting together the Opus balanced DAC (as described in the Digital section of the forum) to feed the pumpkin.

Can the Pumpkin accept a common mode DC of 2.5V? I am wondering if I can omit the DC coupling caps at the DAC output to improve its sound.

The pumpkin has output caps - thus will block any DC from going to the power amp - but will the DC itself damage the preamp?

her shann
Click to expand...


nope ; you can't do that - from two reasons - you have attenuator ( pot ) on input which is based on ground ; even in case that you use shunt attenuator (between two inputs , without connection to gnd) , gates are still leaned/based on gnd

after universal Headphone preamp , you now need voltage convertor ....... :clown:

you can't have anything .

put xformer on output of your DAC
 
H

hershann

Member
Joined 2007
Zen Mod said:



nope ; you can't do that - from two reasons - you have attenuator ( pot ) on input which is based on ground ; even in case that you use shunt attenuator (between two inputs , without connection to gnd) , gates are still leaned/based on gnd

after universal Headphone preamp , you now need voltage convertor ....... :clown:

you can't have anything .

put xformer on output of your DAC
Click to expand...


We are GREEDY boys - 1 Pumpkin to rule (do) them all! :clown:
I'll just use the coupling caps on the output of the DAC then before feeding the Pumpkin.

her shann
 
H

hershann

Member
Joined 2007
Cookbook says EI transformer is preferred - I supposed due to better noise characteristics and ability to withstand DC etc.

For my Pumpkin the transformer is going to be mounted near the front panel and the audio circuit right at the back (the pot probably actuated via an extension rod).

So should I go for the old EI transformer 250VA, 42VCT x2 (pic 1) or the toroidal transformer 600VA 90VCT (pic 2). They are similar in price - with the EI at $20 and toroidal at $29.5.

BTW how easy is it to shield the EI's stray magnetic field?

her shann
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
hershann said:
Cookbook says EI transformer is preferred - I supposed due to better noise characteristics and ability to withstand DC etc.

For my Pumpkin the transformer is going to be mounted near the front panel and the audio circuit right at the back (the pot probably actuated via an extension rod).

So should I go for the old EI transformer 250VA, 42VCT x2 (pic 1) or the toroidal transformer 600VA 90VCT (pic 2). They are similar in price - with the EI at $20 and toroidal at $29.5.

BTW how easy is it to shield the EI's stray magnetic field?

her shann
Click to expand...


use that EI and place it in separate box ; 600VA donut is really overkill ....... even for Pumpkin :clown:

both transformers you show are probably too large ( physically and inducing hum wise) to be in same box with active electronic
 
Zen Mod

Zen Mod

Official Court Jester
Joined 2003
zenmod.in.rs/
Paid Member
Re: last last F4

cviller said:
Interesting drawing, but I think you'll still need something for balanced to single ended conversion, because the input you have shown on your last F4 must have identical phased inputs, only with 8V dc difference...

I bet pumpkin will kill those tl431 very fast! :D
Click to expand...


dunno ......... I'm still fuzzy - flue ....... dumb ( that last like always ;) )

I'll think more maybe tomorrow ......... :clown:
 
mpmarino

mpmarino

Member
Joined 2004
Ya know,

I had a hard time deciding whether or not to put the trafo in the pre case. In the end I decided to chicken out and keep it outside. I've been having cr@p luck with noise lately - I think it's the 106dB horns' fault.

That is, when I can get back to work on this stuff - I had to put the pumpy on a high shelf :bawling:

edit: Aleph J? is that anything like the Babelfish?:clown:
 
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