[BUILD] K13117 (ClassA MicPre by Darius Kubarth / Kubi)

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Hi every one,

still working from time to time on this build.

I just mailed with Volker about wiring the Gain switch.
On the PCB are 2 connections labeled RG1 and RG2, these are
Ra and Rb in the Gain PDF "Widerstandstabelle für die Wahl der Verstärkung".

In a nutshell:
RG1 = Ra
RG2 = Rb


Wiring the 2 pol Gain switch, e.g.:

20db Gain -> Ra = 31623Ohm, Rb = 47000Ohm (Calculated Values, page 1)
Ra = 31623Ohm ~  33kOhm parallel with 820kOhm
=> 1/(1/33kOhm + 1/820kOhm) = 31723Ohm (Resistor Error ~0.3%) (Page 2)

So, Ra has to be made out of 2 Resistors in parallel at the first row of the switch!?
(20db@ Row #1: 33k || 820k, Row#2: 47k)

A'm I right Volker?


ROCK-ON!
 
Aaaaaaaaaaaaaaaaa...............    :mad: :mad:

It was too late at night...
Thanks for the hint!

Now I have a pile of unused resistors laying around...  :D
...and have to order some resistors...


ROCK-ON!
 
... fired it up right now the first time... no smoke  :D
.. voltages are fine... and we've a nice "Tonfrequenz Verstaerkung" on both channels...  ;D  GREAT!!
... and dead quiet!

Where's my beer.... and my DIY booze...  ;D

ROCK-ON!


P.S.: Pix coming soon...
 
Cool, another one joined the small club!
The K13117 became instantly my favorite pre for bassguitars! Thinking about building some Harrison Ford Filters: i need some low-cut-filters now  :D

 
Hi Chris,

funny, when i play a bit around with the unit i although plugged a bass in my new BoHansen DI and into it... :)

Well how small is the club?!  ;) 

ROCK-ON!
 
Hi,

when switch through (up and down) the gain steps from time to time the unit is dead for a minute or so. Sometimes switching phase helps...
Any ideas?

I'll have to do some more testing...

ROCK-ON!
 
Here we go...  ;D

Front panel, as nearly always, from Frank (NRG).

ROCK-ON!
 

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... and the guts...

I've used only white leds, they're very bright shining... maybe I'll play around with some higher resistors to lower current.
We'll see...  ;)

I had to lay down all capacitors to fit it all in 1HE case.
And of course i found out nearly after finishing soldering... grrrr...  :)

I although had to cut the heat-sinks to fit, temperature seems to be still ok. 

ROCK-ON!

 

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I'm very interested in building a stereo pair of these pre-amps. Has anyone utilized a potentiometer instead of a 2x24 switch? I'm curious what value and type (log or linear) I should use. I really am insecure about doing my own switches, so any advice on what values i should use helps to. I've spent two hours looking for advice on stepped switch wiring with little luck, the only source I found was for stereo attenuators for volume control.. Is it the same idea for gain control in a mic pre?
 
Hi all,
I would like to choose an input transformer for this build, and i would like some adaptations. I would like to use it exclusively as line preamp. Could you please help me ?
 
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