Pumpkin preamp - More Boring Making Thread

[lykkedk]

clear enough ?

Yep... allmost

in any case - it's better to use as low attenuator value as you can, considering output impedances of your sources ; if sources are happy with 10K pot - then use 10K pot ; anyway Pumpkin is made with input impedance in that range ( remember value of resistors in both J310's gates )

Are you telling me, that 5k is better suit's than a 10k one, if i got the choice ?

when rely is not in use , both signal rails are grounded .

Just soo, that any unused 'source' are grounded, when not in use ?

NICE answers ZenMod...

Jesper.

[Zen Mod]

Originally posted by lykkedk


Yep... allmost



Are you telling me, that 5k is better suit's than a 10k one, if i got the choice ?

naah ........ 5K is too low . just use 10 K and be happy

Originally posted by lykkedk


Just soo, that any unused 'source' are grounded, when not in use ?

NICE answers ZenMod...

Jesper.

it's better that they are gndd when not in use

[mpmarino]

Originally posted by Zen Mod



crazy yank....

what "chicken scratches better" means ?

ya know that I'm dumb serb

Chicken Scratch = messy writing

[dviswa]

Originally posted by AR2
I did adjustment per Choky's instructions. I do not have F4 and wanted to drive my Aleph 30 so I needed to lower value for two resistors and voila!
AR2 [/B]

AR2,
I am not sure in understand, please explain.

Originally posted by AR2
I did had a brief listen at BAF but I wouldn't take that seriously. Now I had it set up and I had my X BOSOSZ to compare to. It is unbelievable difference. Do not take me wrong - I still like my X BOSOZ, but I was just speechless once I heard amount of top detail from Pumpkin. I was amazed how come that I didn't miss all that detail before? I do not know but it is like Pumpkin has opened whole another dimension on the top of the spectrum. It is very detailed and bright amp. When I say bright not in the negative way, and amazingly there is still very strong and deep bass.

My pumpkin is still based on make shift XBOSOZ power supply while I am waiting for Shanty boards. This pumpkin has special value! It was constructed by Choky, Anatech, Magura and myself. I am afraid to change it since it might loose its international flair.

There is a special shielded wire that Magura and Anatech called Wire from Hell, but they still succeeded in completing it for the BAF.
I will be trying different caps in output to see how it will affect sound. I would strongly advise to try this preamp for F4 or any other amp. It is just unrealistically good.
[/B]

That is one glowing rave

Dinesh

[Zen Mod]

Originally posted by dviswa

AR2,
I am not sure in understand, please explain.


....

matter of gain ;

see cookbook for assembly

[lykkedk]

ZenMod, I know that you can't remember the open loop gain / close loop gain, of the circuit, but is it possible that it can be explained howto calculate it.

The thing ís, that maybe somebody want to increase the gain, which is 100k / 10k = 10x of 'standard' circuit (R1, R3, R5, R6) give's this gain. I increased the 100k(R5, R6) to 147,5k, and decreased the R1, R3 to 6,8k giving me approx. 20x of gain... eg. the swings around 40v with an input of 2v in my case.

I can't remember the excact, 'max' voltage which the F4 can handle... But if one look forward to attach, an not so gain-strong phonostage perhaps, giving out.. say 1v, the F4 will only be feeded with 10v on standard , and around 20v in my setup... If the F4 need's... let's say around 25-30v for full throttle, the thing is still missing something to drive it to the max.

I know, that all such adjustment's has a backside, but i hope you got my idea, to conclude the stuff in the revissed cooking-book, BUT this is just an idea i have.

My DAC, gives around 1,6v out, so i think my setting's on is perfect for that, giving around a voltageswing of 34v (16v on standard )...

Jesper.

[dviswa]

ZM, anybody,

C4/C5 & C11/C12 are the output caps, I know you have said use your fav. But, I do not have a "fav". I am thinking of using
Black Gate N 47mfd 50V available in partsconnexion for $10, bypassed with 1mfd Vishay MKP 416-420 available on Digikey for a buck.

Why 47mfd? Well, my pumpkin will also be doing double duty of a headphone amp. I thought a larger cap will help with lower impedance cans. Or is this not a good idea?

What do you guys think of this choice? Any other suggestions?

Thanks,
Dinesh

[Zen Mod]

Originally posted by lykkedk
ZenMod, I know that you can't remember the open loop gain / close loop gain, of the circuit, but is it possible that it can be explained howto calculate it.

lykkkkkgreedydanske

it's hard to please everyone ;

with phono section as that - you can't have all ;

I told you before - you can't go near OLG without sacrifices , just beacuse everything is matter of compromises ;

near OLG , you loose both freq extremes ( not that both are necessary)

what you also loose is amount of X feedback ;

anyway - it's up to you to choose what's best for your ears

in your boots - I'll toss both and F4 ( as a gift to Magura , just because he doesn't have them ) and make one nice toob system ...........



anyway - for test - desolder feedback resistors and measure OLG at 1KHz ; you can measure also OLG at 20Hz and 20KHz , while you are at it . I'm sorta short in time , because it will take few mnths that I make my own ; all I have in this moment is just one populated Shunty pcb.

let us know what results are

regarding calcs - I remember that my calcs aren't very near measured ; I'm primary toob guy - used to graphs and rulers ,along with calculator ; there must be something I missed for OLG calculus .... those dreky mnfctrrs of 3-7 legged fuses make so small and useless graphs

[Zen Mod]

Originally posted by dviswa
ZM, anybody,

C4/C5 & C11/C12 are the output caps, I know you have said use your fav. But, I do not have a "fav". I am thinking of using
Black Gate N 47mfd 50V available in partsconnexion for $10, bypassed with 1mfd Vishay MKP 416-420 available on Digikey for a buck.

Why 47mfd? Well, my pumpkin will also be doing double duty of a headphone amp. I thought a larger cap will help with lower impedance cans. Or is this not a good idea?

What do you guys think of this choice? Any other suggestions?

Thanks,
Dinesh

Dinesh ;

you package ( + ) , along with others is packed and ready to sending ;

I just kissed closed doors of post office today ;

seems to me that you found your fave caps

just go for it .

somewhere - in one of my useless OT threads - I mention that I tried with cans - with stock (4uF) output caps , cans's impedance was ...... both channels in parallel - so must be no more than 50 ohms........

to cut a ... sound was pretty decent , no flabbyness ....... blabla

think about decreasing output resistors to ~ 22E , from 47 as they are now ;

if needed - we can later try something simple - increasing Iq in output stage(s)

don't forget to take cans off the head , if BG's need little burning in

[dviswa]

Originally posted by Zen Mod

you package ( + ) , along with others is packed and ready to sending ;

Thanks a lot.

Originally posted by Zen Mod
seems to me that you found your fave caps just go for it .

Thanks, I will.

Originally posted by Zen Mod
somewhere - in one of my useless OT threads - I mention that I tried with cans - with stock (4uF) output caps , cans's impedance was ...... both channels in parallel - so must be no more than 50 ohms........

to cut a ... sound was pretty decent , no flabbyness ....... blabla

think about decreasing output resistors to ~ 22E , from 47 as they are now ;

OK, anything else I should be changing?

Originally posted by Zen Mod
if needed - we can later try something simple - increasing Iq in output stage(s)

don't forget to take cans off the head , if BG's need little burning in

I was wondering about it too. Let's say I want to double the Iq, what values should I be considering?