Pumpkin preamp - ordered by Steen , official making thread

[Zen Mod]

yup , Almighty



you can use any type of attenuator on ( as I prefer) input - which your signal sources can handle ;

to itself - is irrelevant , what type of attenuator is mounted on his input.

 

[generg]

Hi Zen Mod,

when I combine Pumpkin with F1 I have two times 10 uF in the signal path.
My idea is to keep the pumpkin output caps and to bridge the 10 uF of F1.


O.k. .....?

Is it important to keep the two 22 Ohm gatestoppers in F1 or can I choose one of 40 Ohm when I shorted the cap?. Why is one before and one after the cap in the original?


ThX

 

[400]

yes , you can .

Thanks!

Any downside to using a switched attenuator between them for volume control?

I build up a remote controlled volume controller and source selector with the possibility to mute via shortening.

Marcel

 

[Zen Mod]

Generg

just leave out R1 , C1 ,R13,R2,R,14,C2

just R3 and R4 are actual gate stoppers ; rest are protective resistors for cap charging/discharging

 

[generg]

Yes I understood Zen Mod, thanks for the help!

 

[generg]

Dear ZenMod,

I have on the negative side of one shunty driving pumpkin only 7V instead of 36V. I opened Jumper 1a, 50V coming from zeners, O.K. But after R7a, 4,7 Ohm only 7V. I changed Q2a, Q3a, nothing better. I proofed the resistors around Q3a, all o.k..

Maybe you have a hint, before I change all the other semiconductors.....


Have a nice evening.....!

 

[generg]

shunty

forgot the picture for you...

 

[Zen Mod]

what's happening when you remove bridge , labeled as R20 ?

in any case - while repairing Shunty - disconnect from it

 

[generg]

yeah, 42V! means problem is Q11a?

 

[Zen Mod]

now - do you have 5V on base of Q5 ?

and also 0V65 across R17 ?

 

[generg]

should I close the gap at R20 I made to remove bridge? or let it open?

 

[generg]

I left bridge open, 0.k?

0,6v over R17 and nothing at base of Q5!

sorry for the delay my wife came home and told stories from her work, she tries to sell houses on Sunday.....

 

[Zen Mod]

yes - bridge open

connect mA meter across U1 - you must have around 1mA through Q10 CCS ;

if you have - U1 is toasted

if you don't have that 1mA , then Q10 is toasted

....... I'm here

 

[generg]

don't have that 1mA .............. Q10 is toasted.


Tomorrow shops are open I ll buy ten BF245C!


HAPPY GENERG THANKS ZENMOD MILLE FOIS!!!!!!!!

 

[Zen Mod]

 

[generg]

Dear Zen Mod,

when I changed the LM336 and the BF245C I did something to the board by the too often resoldering. The problem got even worse, the current was so high on the negative side that the fuse (315mA) blow many times.

Over hours I checked the paths, cleaned the pcb, proved all parts again, no success, only blowing the fuse.
I constructed the branch with LM336 and BF245C apart, on the fly, now it delivered the 5 V for the base of Q5a and I got 36V at the output.

Unfortunately BDX33c gets very hot. I compared the current at R20 and R20a and the negative side has 300mA current instead of 140mA! (right side and correct value I suppose)

May I ask you again for a hint?

I thought the current is determined by R7a, the value is correct.

I had never before such an obstinate problem.

 

[Zen Mod]

you obviously have oscilation

use cheapest elko ( C14(a)) on Shunty output , and as small as you dare

remove C13(a)

put 1n cap between B-E of Q11(a)

 

[generg]

Tanks Zen Mod,

That is a good hint! May be my air wiring did it. I' ll try it tomorrow. Today nada, too exhausted. I did a little bit tai chi to stretch my poor body.
On the other side I like this being absorbed in electronics, it is a good drug, and a good training for creativity to solve a problem.....
When I get the new shunty boards I will build up one completely new. I damaged to much of the traces and my sight is no more the best.

 

[Zen Mod]

seems we both need this :

 

[generg]

seems we both need this :

Dear Zen Mod the picture is small, I cannot recognize what we need.....