Pumpkin preamp - More Boring Making Thread

[Zen Mod]

Originally posted by dviswa

............

Let's say I want to double the Iq, what values should I be considering?

roughly speaking .........


halving all mosfet source resistors ;

so - R11 & R16 to 15~18E , R12/R26 & R17/R28 to 330//240E (all that in Pumpkin)


so - that also need changes in Shunty - besides xformer capable to give ~ 82Vct/800mA minimum for stereo , all heatsinks twice thermally capable ( that applicable for Pumpkin too ) and decreasing R7/R7a to 2E4 (Shunty)


in that case you'll double present current hunger of Pumpkin/Shunty combo , which is ~140mA/channel

so - you'll have preamp drawing 82V x 0,28A x 2 =46VA ......

more than some hifi DrekMKXX SE^2 amps

[lykkedk]

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

This is not a problem... no difference between soundsonics of 10xgain and 20xgain

Actually, i am not having trouble, with the gain anymore, it was just an idea i have, that maybee someone else was gainhungry like me too ! ... I allready adjusted the gain to my need's... I see ofcause that the phono-pre, can't be playing as loud as i would like it to, with a gain of 20x, but it's good enough for now.

I realise, that this is not the right place to ask, about howto calculate such thing's as X-feedback OLG, CLG... etc... seem's that anyone else but me, understand's this.

I am going to study these technicue's in future... regarding gain/loop etc... that i don't understand quite well... And maybee (can't promise) i will try the meassuring ZenMod suggested.

Anyway, in next few day's.... sneakpreview of my inputselector

Greeadylykkedk.... yes i am

Jesper.

[jormajj]

The Pumpkin and Shunty PCBs arrived today, Thanks Choky and OLy !

Great looking boards

Here are some examples of heatsink types fitting on the PCBs
( 50 mm high):

Fischer
SK81-50 SA
SK75-50

Austerlitz
KS100.3-50
KS32.1-50E

jormajj

[vitalstates]

I wonder...did steen ever get caught with his flies undone???

the real question, choky OLD chap....my F4 sings with my squeezebox and I can only get the volume up half way....this means that thinking about pumpkin is idling away the time for no good reason???

Ed

[vitalstates]

oh I do feel good playing OT with Mr OT himself.....apologies

1. yeah the buzz is with shorted and open inputs
2. buzz stops when switch is flicked off
3. can't measure any ac with dmm it only goes to 3 decimal places on 2v setting, i.e min reading is 1 mv.
4. spks are 96db average , which is why its probably annoying........

I'll get the scope out tomorrow and move stuff around.....seriously, I didnt mean to take your thread OT but thanks for sticking with me....

regards

Ed

[Zen Mod]

Originally posted by vitalstates
oh I do feel good playing OT with Mr OT himself.....apologies

1. yeah the buzz is with shorted and open inputs
2. buzz stops when switch is flicked off
3. can't measure any ac with dmm it only goes to 3 decimal places on 2v setting, i.e min reading is 1 mv.
4. spks are 96db average , which is why its probably annoying........

I'll get the scope out tomorrow and move stuff around.....seriously, I didnt mean to take your thread OT but thanks for sticking with me....

regards

Ed

how much caps you have in PSU filtering ?

are input RCAs isolated from chassis ?
have you PTC between safety and audio gnd?

is it 50 or 100 HZ buzzzzzzzz?

it's same in both channels?

is it same in one channel if you remove supply to other channel


etc

one by one ,please

[vitalstates]

Hi choky

sorted the F4 buzz, it was RF from the tranny, just the same problem I had with the F2. For info, the common factor is clairtronic transformers....

This cured it completely:

[Zen Mod]

Originally posted by vitalstates
Hi choky

sorted the F4 buzz, it was RF from the tranny, just the same problem I had with the F2. For info, the common factor is clairtronic transformers....

This cured it completely:

why on earth you place that drek ditto to input terminals and cables ?

turn it around - place it on blind front plate , place PSU pcb in middle of amp ;

find biggest tuna can , eat what's in it , and make lalalala shildie pot for crummy donut

[vitalstates]

patience mon brave, nothing is fitted in that pic, its all just resting in free space......I just took the pic to show the orientation that works.....

btw we don't have tuna tins that large(well maybe we do but I havn't seen one)...but I'm going to mount the tranny on a bracket in roughly the same place it is shown and turn the ps board round 90 degrees where is has more room.........its not artistic, but hey it works


this is what it looks like when lying flat on the floor in the middle

[Zen Mod]

Originally posted by vitalstates
patience mon brave, nothing is fitted in that pic, its all just resting in free space......I just took the pic to show the orientation that works.....

btw we don't have tuna tins that large(well maybe we do but I havn't seen one)...but I'm going to mount the tranny on a bracket in roughly the same place it is shown and turn the ps board round 90 degrees where is has more room.........its not artistic, but hey it works


this is what it looks like when lying flat on the floor in the middle

well - since all is sorta dismantled now - try it as I said ;

there is less harm in routing 220 line all the way to front plate , than keeping lousy xformer near sensitive lines

(I didn't invent that , so - don't thank me )