Sunn Beta Bass preamp schematic

guile31 · Post by **guile31** » 28 Aug 2015, 19:02

Ok so, i checked the board with audio probe,the issue start on IC1 so I re-checked the converter with voltmeter and different 9v sources; the problem definitly come from it
it delivers +15/-15 but have a cyclic some kind of "leakage".
my voltmeter is just a cheap "hobby" tool, i don't know if it is enough reactive to show the real voltage drop but i can already see a leakage at each "cycle"
and the result is clearly and sadly hearable
i don't know what causes the issue so i think i'm good to test each cap of this converter

morain51 · Post by **morain51** » 14 Sep 2015, 07:46

Finally, here is my recording of different settings on this pedal.
Quality is really bad, like my bass playing, but it's all I can share right now

kyuss · Post by **kyuss** » 27 Feb 2016, 16:34

Hey there ! If I were to use polarized instead of non polarized caps, how should I orientate them ?

Thanks !

Xavier

grrrunge · Post by **grrrunge** » 27 Feb 2016, 18:42

kyuss wrote:Hey there ! If I were to use polarized instead of non polarized caps, how should I orientate them ?

Thanks !

Xavier

The positive leg should connect to the side with the highest DC potential

kyuss · Post by **kyuss** » 27 Feb 2016, 19:05

Sorry but that doesn't help me at all...

johnk · Post by **johnk** » 10 Mar 2016, 23:39

I just finished building mine and I absolutely LOVE it!

tra · Post by **tra** » 16 Mar 2016, 16:58

If any of you have Eagle or Diptrace files for this I'll happily fabricate a board for you. I'm lazy and don't feel like doing the layout myself.

arcaarca · Post by **arcaarca** » 17 Mar 2016, 17:17

Hi everyone,
here are my Eagle version of the schematic, should be correct to last version... hope so

http://www.mediafire.com/download/s666l ... _Eagle.rar

cheers and good luck!

andregarcia57 · Post by **andregarcia57** » 18 Mar 2016, 10:55

arcaarca wrote:Hi everyone,
here are my Eagle version of the schematic, should be correct to last version... hope so

http://www.mediafire.com/download/s666l ... _Eagle.rar

cheers and good luck!

thanks!

HENK · Post by **HENK** » 23 Mar 2016, 13:06

Morning;
The 1N.... Diodes at the End of the last IC:
Can someone please explain,what is going on there?
I have trouble to buy them.

(Sorry for my crap English)

grrrunge · Post by **grrrunge** » 23 Mar 2016, 19:19

Any small signal diode should work fine there. Try 1N4148, 1N914 or similar. Those are widely available

HENK · Post by **HENK** » 23 Mar 2016, 21:03

Skol to Danmark,specially to Kobnhavn

(and Greets from Haithabu...OOOOODIIIN!

)

But what is the purpose of this part???

grrrunge · Post by **grrrunge** » 23 Mar 2016, 22:37

They're probably there to protect the op-amp output from odd DC voltages that might eventually be present in the superseding stage.

Zozobra · Post by **Zozobra** » 22 Apr 2016, 12:41

johnk wrote:I just finished building mine and I absolutely LOVE it!

[ Image ]

[ Image ]

Very nice! I'm thinking of putting together a beta bass/lead pre to feed into a small class D power amp for use as a small pedal friendly practice amp and this looks just the ticket.

jwhtn · Post by **jwhtn** » 06 May 2016, 16:07

[quote="johnk"]I just finished building mine and I absolutely LOVE it!

John, this looks fantastic. I know there's no lack of box finishing info on fsb, but how did you get such clean engravings? It looks CNC'd.

bigbonedstacks · Post by **bigbonedstacks** » 13 May 2016, 22:18

Anyone want to hook a brother up with a labeled pcb?

rune-hammer · Post by **rune-hammer** » 22 Nov 2016, 09:50

andregarcia57 wrote:
arcaarca wrote:Hi everyone,
here are my Eagle version of the schematic, should be correct to last version... hope so

http://www.mediafire.com/download/s666l ... _Eagle.rar

cheers and good luck!
thanks!

Was there a verified layout made available by someone here also? As far as I can see this file does not have the layout completely done.

Thanks in advance!

I started doing a beta lead thing a few years ago, but never finished it, this thread got me going again!

arcaarca · Post by **arcaarca** » 01 Feb 2018, 09:45

Finally here's mine,
use tagboard layout, and a 7660 for bipolar converter (I've got +/- 17V, it works but I will put a 15V zener diode to get +/- 15V), layout is a tribute to P. Druillet.
Really good! Thanks to all FSB community!
Long live bass diyers!
Distort the world!

Arca

HENK · Post by **HENK** » 01 Feb 2018, 13:16

DiscoVlad · Post by **DiscoVlad** » 10 Sep 2018, 05:48

I've redrawn the service manual schematic for the power amp board (using the Alpha 4 PA for reference as it looks like the power sections are identical?) if anyone is interested...

This is very much unverified w.r.t. component values etc. but should be correct, and... since it's mains powered, use at your own risk. I'm not responsible if you burn your house down, or kill/injure yourself or others.

I've taken the mains part out of the schematic anyway, it's just the part from the low voltage AC input forwards.