freestompboxes.org

I just finished to build and debug a veroboard version.
I will correct my design and post it here very soon

It still some points to clarify.
I was chatting with guile31 by private messages about the resistor and capacitor at the end of the schematic.
Both arcaarca and grrrunge schematics are ending after points 2 & 3 of the volume knob, but on the original Sunn schematic, it leads to the effect loop "to accessory channel A". And just after the return of effect loop "from accessory", there is a resistor R201 27K and a capacitor C146 2,2µF NP 25V.
Does anybody knows if these resistor and capacitor are important before leading to the output ?

No. They make up the summing network before the final master volume, so the two channels can be played through at the same time. They introduce additional LF roll-off at 2.7Hz, and the summing amp does some HF attennuation above the audible spectrum. All in all, it's nothing to worry about, if you just want to build a single channel unit

thanks grrrunge but i don't clearly understand the definition of "summing network".
i wanna build a two channels version
i have the idea to put two "single channel boards" in parallel (common input,+/-15v,ground,and individual fx loops/outputs)
mixing them with a simple toggle 3pos selector (A,Y,B with leds) and after the selector to a 100k master volume and last to the preamp out.
in my head, i need to put the res/cap combo between each channels loop returns and common selector switch (almost like the original schematic) and so,
is it worth it?

and question to all, for selector i need a toggle like this (for separate audio and 9v paths and together switching)
but don't have the reference,




i've found a lot of slightly different ones like this but ,this is not what i need



anyone can help me?

Hi guile31 !
I think you should use a rotary switch, with 4 poles and 3 positions like this one : http://www.banzaimusic.com/Rotary-Switch-1x4x3.html



Link A and B poles together and to "Master Vol",
and C and D poles together and to "+9V"
then link 1 and 2 together and to "From A"
nothing on 3
nothing on 4
link 5 and 6 together and to "From B"
link 7 and 8 together and to "Red LED"
nothing on 9
nothing on 10
link 11 and 12 together and to "Green LED"

I hope you understand what I'm trying to explain

thanks morain but i really want a simple 3pos toggle switch
i know i can achieve that,even i will have to build it
(and the joke is that it's not the ultimate goal; i also need a footswitch input jack wich will bypassing the toggle switch but already mixing channels and leds...lol)

Ok, so I think you could use a 4P3T toggle switch (I don't know if it's the right designation), that are like two DP3T in a case.
For example APEM 5664. You will have to check how are the connections in middle position, but the wiring could be like this :

Here is my veroboard version of Sunn Beta Bass preamp, based on Sunn Service Manual.
I kept the components numbering from original diagram.
For the +15V/-15V section, I used a daughterboard from Guitar FX Layout called Bipolar Voltage Converter with 1N4001 diodes : http://tagboardeffects.blogspot.fr/2014 ... erter.html

I know the disposition of components could be a bit unconventional, there is a lot of cuts and jumpers, and legs of an IC socket must be cut... But it could be some kind of basis for a better work.

I will edit a Beta Lead version later (just a few component values to change)

Good job morain
I'll check this later and thanks for the switch, it's exactly what i need

And here are pictures of my build.
It makes sort of oscillation at low values on the level pot. But it disappears beyond about 9 o'clock.
I wish I could record sound clips, but I don't have recording system for the moment.

morain51 wrote:And here are pictures of my build.
It makes sort of oscillation at low values on the level pot. But it disappears beyond about 9 o'clock.
I wish I could record sound clips, but I don't have recording system for the moment.

Looks cool, I might build one and see if I can find out what's causing the oscillation and maybe figure out a fix for it...

morain51 wrote:And here are pictures of my build.
It makes sort of oscillation at low values on the level pot. But it disappears beyond about 9 o'clock

Electric supply?
I can't plug my fuzz's in the wall without oscillation issues.with batteries, no problem
I think i will have to build a filtered power supply for this preamp.

Ps:cool design romain ,the sunn logo is badass

my converter breaking me bad
it send ~+15v/-7v

my layout seems good but without this ******** ***** ********* , i can't verify it

diode,cap,IC?

To be honest, I don't have the required equipment to measure the voltage of my converter.
I simply used the Bipolar Voltage Converter of Tagboardeffects, but maybe I have the same issue.
I will try to find a Voltmeter to check it

guile31 wrote:my converter breaking me bad
it send ~+15v/-7v

my layout seems good but without this ******** ***** ********* , i can't verify it

diode,cap,IC?

I borrowed a voltmeter from a friend and I have measured voltage values from my converter with 3 different transformers.
with 9,08V input, I have -14,32V / +15,55V
with 9,52V input, I have -15,18V / +16,40V
with 9,64V input, I have -15,39V / +16,60V

Have you find a way to fix your converter ?

After opening and closing my build to make measurement, the oscillation have nearly disappeared.
Maybe the problem is because my wiring is way too long

Nope, i think the IC is damaged or something like that
I'm waiting for a new one with new pots (banzai order problems...like always)

i had wiring old stock pots and the converter like it is and it works ...
my freakin layout is alive lol
next step a dual pedal, the amp size will waiting

Here is a Beta Lead version, without reverb section.
The only modifications are C138, C140, C141 and C143 values.
If a moderator or administrator have a look on this thread, maybe it could be renamed to "Sunn Beta Bass and Beta Lead preamp schematic" as they are very similar.

i recieved the IC and the pots, i have now the correct +15/-15v powering

but i have a new big issue
frequently i heard a "pick" in the signal and after that, the volume briefly jumps loud and preamp suddenly "reboot"
i checked with multimeter the converter and no prob before and after it,
checked the connections and seems ok
maybe an electrolytic or preamp IC
is someone ever had similar issue on a build?

morain, how works your mid pot? mine is so subtle i can't hear it doing anything

I definitely have to record sound clips, even if the quality will be bad, just to make realize how it sounds.
But I can already tell you that the mid pot is anything but subtle. It makes a great difference between when it's cut and when it's turned !