Pumpkin preamp - ordered by Steen , official making thread - Page 348 - diyAudio
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Old 24th January 2013, 03:30 PM   #3471
tonimxp is offline tonimxp  Italy
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Quote:
Originally Posted by Zen Mod View Post
Tony
I was working tonight (some mumbo jumbo which can be done just between day -shifts) and just arrived from trip , back home ;

I need to catch few hours of sleep

whatever - it seems you had difficulties reading Cook Book - (sorry - I'm ignorant peasant , knowing just few words of Italian , so I couldn't make Italian version ) , so you obviously messed up something , somewhere

most left schematic is last , valid one , while middle (and most right ) one are somewhere from thread , during testing and developing

whatever - it seems you solved those issues , except lack of highs , which I'm finding somewhat doubtful ; accoring to AR2's measurements - Pumpkin is some 0,5db down on 20KHz ( with highest gain setting - for F4) , but that's nothing comparing to our hearing capability , considering age

will take a look at e-mail I got this moment from you , and write what I have

now I need to nap , my eyes are already somewhere else

Ok! Alex i will wait!Please when you will open again your eyes ,please don't forget to me,and .....do not sleep long as a VAMPIRE!

You aren't ignorant peasant ,you are a big man but as all big man you are often busy!
Please is possible some others reference voltage point?

I'm excited as a teenager at his first time with the WOMAN!

I wish to close the Pumpkin Tomorrow ,and listen to it with my friends Saturday night .

Come on Alex!

Thanks!

Last edited by tonimxp; 24th January 2013 at 03:35 PM.
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Old 24th January 2013, 08:02 PM   #3472
tonimxp is offline tonimxp  Italy
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Default Pumpkin

Hi! I just finished testing the frequency response of the Pumpkin.

It is practically flat up to 30Khz, then starts a slight but gradual descent but I would say it is very good up to about 100 KHz.

Now I just want to be sure that everything is working fine in my Pumpkin ,so ..i can finally close the lid and start enjoying its sound!

Alex i have measured Vb of Q9 refered at gnd and it is 32V, is it ok?

What other measures should I do to sleep soundly?

Thanks
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Old 24th January 2013, 08:26 PM   #3473
Zen Mod is offline Zen Mod  Serbia
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Buongiorno !

it's base is practically at (-Ub + 2(Vled)) ,which is (-36+ 2x 1V93)=-32V14

it's emiter is for 0V65 lower , so -32V79

it's colector is at (-Ub+(6xUled)-Ugs) , which is (-36+(6x1V93)-4V)= -28V42

all voltages ref to gnd


I need coffee now ........
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Old 28th January 2013, 04:09 PM   #3474
tonimxp is offline tonimxp  Italy
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Default Pumpkin noise upgrade OK! Now the choice of output capacitors

Hi Alex! Yesterday I was finally able to listen the Pumpkin!
I must start by saying that I have not checked the voltage references that you sent me and which relate to Q9.
I can only tell you what the Pumpkin is GREAT!
In fact I think it deserve C4 and C5 ( currently Arcotronics 10uf )

10uF 10F 10000nF 10000000pF 250V POLIPROPILENE MKP ARCOTRONICS 5% - Elettronica Conveniente

I would to replace with MCAP Evo, please see its datasheet.

http://www.mundorf.com/downloads/MUN...talog_2012.pdf

I have a question.... What do you recommend for the Pumpkin, MCAP EVO
aluminum or MCAP EVO aluminum Oil?

I still have to tell you that I have already done to bypass C4 and C5 with
polycarbonate (please see ERO MKC 1860 datasheet)

MKC 1860 datasheet and application note, data sheet, circuit, pdf, cross reference | Datasheet Archive

Please Alex can you give me some advise for this delicate choise?


Thanks in advance
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Old 28th January 2013, 04:32 PM   #3475
Zen Mod is offline Zen Mod  Serbia
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I just started typing reply (to same questions) in private e-mail , but I can do it here

however - I'm not cap junkie ;

you don't need to be the one , too - especially when SUSY circuit is in question (there is sort of nulling possible distortions in cap , from side to side)

use decent caps which aren't costing you your left kidney , bypass them with proper MKC , and enjoy


let me propose something - use it as now ( bypassed Arcotronics with MKC) , and look at ebay for bargains of really exotic caps

or use wakoo Russian ones - teflon or PIO (they write МБГ on some of them ) ........ even if you need to mount biggie ones with some ingenuity

that way you'll enjoy both in finding them ..... and using them

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Old 26th May 2013, 06:21 PM   #3476
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If I experience oscillation in my Pumpkins - whats a good place and value for compensation?

Regards
Sven
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Old 26th May 2013, 06:28 PM   #3477
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tell me specific details - what gain you have set and few proper pics can't harm , along as many details you can show/write ;
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Old 26th May 2013, 06:49 PM   #3478
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High gain - R5/R1 and R6/R3 150k/10k, C1,C2 = 3,3pf.

What I hear sounds like this.

I've been trying a lot of different grounding schemes, didn't change anything. I replaced the Shuntys with Salas' shunt reguators. The chirping sound changes, gets shorter, there is more or less time between the sounds but it keeps coming back.

Pictures... currently there is just a pile of parts because I took it apart to install the offset fix. This was my test setup some time ago:

Click the image to open in full size.
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Old 26th May 2013, 07:40 PM   #3479
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after "offset fix" you still have oscillation , you need to take care of few things :

-all signal traces ( I mean wires ) need to be twisted or shielded , except those really short one
-same for all power carrying wires ; both Shunty and Salas reg (even if sort of made with different approach) are better when complemented with properly laid out wiring
-try higher value for C1 & C2 ( 4p7-5p1 for starters , but no more than 6p8 , considering 150K as feedback resistor
-if that not help , put RC cell , made of 1K resistor and 2n7 in series - between collectors of Q3 and Q4
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Old 25th September 2013, 12:40 PM   #3480
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Hi zm
About the bf245c, any problem if I use bf245a?

Thanks.
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