Pumpkin preamp - ordered by Steen , official making thread - Page 330 - diyAudio
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Old 7th January 2012, 02:37 PM   #3291
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Quote:
Originally Posted by KatieandDad View Post
tried to offer any suggestions as to where I went wrong.
A seasoned engineer with 30 years experience in building electronic circuits could have figured for himself a day ago that testing the sides of the Pumpkin for oscillation would have been easy peasy by taking either R9/R10 or R14/R15 gate resistors offline.
Part of the process is thinking for yourself.

The real engineering type would have measured each and every device himself before soldering, and tested every section of the circuit inbetween mounting on the board.
Old teach of mine said : trust is good, checking better.
Hard to communicate with someone who has total faith in the credentials, written by his own hand.

Worst case, you could have just asked someone to fix the boards for you.
Would have cost you P&P only, instead of the 10 Quid you charge for assembling DIY projects for others.
WTB: aleph pre-amp
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Last edited by jacco vermeulen; 7th January 2012 at 02:50 PM.
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Old 8th January 2012, 01:38 PM   #3292
10y is offline 10y  Italy
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Hi,

returned at home after vacations and before apply resistors mods as showed on cook book tested some voltage points on the two pumpie board.

So these are the results:

1) across r7 and r8 : board sx 4.85 V- 4,82 V; board dx 4,86 V-4,83 V.

2) across r24 : board sx 1,8; board dx 1,70 V.

3) across c6 : board sx 11,85 V; board dx 11,81 V.

4) across r22 : board sx 0,70 V; board dx 0,70 V.


Value at points 1-2-3 seems Ok , with slight differences compared to voltage reference schematic.
Value at point 4 is very different compared to 2,88 V showed on the schematic.
So where could be the faults? Q9, Q10 ?
R22 value is right, 47R on the two boards.

Ciao,

Anto
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Old 8th January 2012, 01:51 PM   #3293
Zen Mod is offline Zen Mod  Serbia
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Anto

there is some confusion - it seems that you are looking at schematic posted by Generg , where bias referent voltage for Q9 is taken across two LEDs ;
that schematic must be early one from thread ; final one is same as in CookBook - with just one LED voltage as referent - meaning 1V93 instead of 3V86 ....... and there is probably different value for R22 also ;

so - calculus is simple , emiter voltage is LED voltage minus Ube = 1V93-0V65 = 1V28

regarding LTP current ( direct voltage across R22 ) : in any case , 16mA through 47R will give you around 0V75 ; you are certainly in ballpark with 0V7

16mA is ballpark value ; final value will be somewhat different , after setting offsets
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Old 8th January 2012, 02:01 PM   #3294
leapcat is offline leapcat  United States
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I=E/R so I = .7/47= .01489= 14.9ma
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Old 8th January 2012, 02:06 PM   #3295
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Quote:
Originally Posted by jacco vermeulen View Post
A seasoned engineer with 30 years experience in building electronic circuits could have figured for himself a day ago that testing the sides of the Pumpkin for oscillation would have been easy peasy by taking either R9/R10 or R14/R15 gate resistors offline.
Part of the process is thinking for yourself.

The real engineering type would have measured each and every device himself before soldering, and tested every section of the circuit inbetween mounting on the board.
Old teach of mine said : trust is good, checking better.
Hard to communicate with someone who has total faith in the credentials, written by his own hand.

Worst case, you could have just asked someone to fix the boards for you.
Would have cost you P&P only, instead of the 10 Quid you charge for assembling DIY projects for others.
WTB: aleph pre-amp

Oh Shut Up.

I've sold them and given in.

If you had offered advice rather than caustic comments I might have accepted your offer.

My credentials are not in the audio field.

I am a systems engineer as my posts declare.

Last edited by KatieandDad; 8th January 2012 at 02:09 PM.
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Old 8th January 2012, 02:09 PM   #3296
10y is offline 10y  Italy
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Hi Alexandr,

yeah, a few minuts after posted noticed the different R22 value on the schematic. 180R compared to the right 47R.
So all voltages values seems Ok.
Will try your resistors mods and will post the result. Waiting for a decent double 10K pot bought on ebay some days ago and not yet consigned for a final-on hifi chain- sound.

Thank you ZM for your quick and esaustive reply, as always.

Have you fun with your WD toy ?

Ciao,

Anto.
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Old 8th January 2012, 02:11 PM   #3297
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by 10y View Post
......

Have you fun with your WD toy ?

......
yes indeed !

most clever acquisition in last 10 yrs
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Old 8th January 2012, 02:19 PM   #3298
10y is offline 10y  Italy
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Quote:
Originally Posted by leapcat View Post
I=E/R so I = .7/47= .01489= 14.9ma
Hi leapcat,

thank you!

I will learn how to apply law's ohm

Anto
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Old 8th January 2012, 02:23 PM   #3299
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Sorry - Picked up wrong quote.

Last edited by KatieandDad; 8th January 2012 at 02:29 PM.
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Old 8th January 2012, 02:26 PM   #3300
leapcat is offline leapcat  United States
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Hi 10y
Your welcome, its a useful tool, enjoy your pumpkin!
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