Ampeg - Sub Blaster

lolbou · Post by **lolbou** » 21 Jan 2009, 19:50

Hi,

The bass player in my band has lost (at least he wishes no one has stolen it from him) his Ampeg Sub Blaster bass octave pedal...

He asked to think about buikding a new one, but nothing can really be found, exceptc those gutshots: http://www.theburlingames.com/2008/06/0 ... -addition/...

But the pics are rather hard to use successfully...

Does anyone has data about it?

Cheers!

lohstah · Post by **lohstah** » 22 Jan 2009, 14:49

i was in the process of tracing this some time ago but stopped.
if i can get my act together, i´ll post gutshots.
basically it is just the boss oc-2 type circuit, minus the second octave.
but the filtering must be different, because it is really tracking better than the oc-2. on the other hand, the oc-2 sounds better, the sub blaster´s octave is too muddy for my taste.

cheers,
lohstah

lolbou · Post by **lolbou** » 22 Jan 2009, 15:04

I'd be happy to cooperate on this!!

...

And will let "my" bass player about the oc-2 sounding better for your taste... He plays a Victor Bailey Jazz Bass through an Ampeg SVT4-Pro with a 6x10 Ampeg cab...

Your delays in posting will be mine

Cheers!

lohstah · Post by **lohstah** » 30 Jan 2009, 12:31

hey guys,

it´s been some time but i´ve been a good boy and tried to trace that gizmo from what info i´ve got.
first, two gutshots. one front, one trace side, already mirrored.

cheers,
lohstah

lohstah · Post by **lohstah** » 30 Jan 2009, 12:39

and now here´s what i got so far.
i´ll start with the easiest parts and get to where i think there might still be some mistakes.
so firtst, the power section (yawn!):

: Power Section.jpg (11.77 KiB) Viewed 5220 times

next, the output mixer:

: Output Mixer.jpg (10.78 KiB) Viewed 6406 times

now, the 4013 section:

and, finally, the input and suirrounding (also outputs 2 and 5 from the 4013). some strange things here, i also probably drew some stuff weird. but hey, i´m no expert !

so, let the discussions begin !

cheers,
lohstah

lohstah · Post by **lohstah** » 30 Jan 2009, 12:47

to make it easier to locate certain parts of the trace, here´s the location of the opamps according to the trace side mirrored shot i provided:
starting from the top, you have:
topmost, right of th 4013: U4
below, slightly to the right: U3
on the bottom the left tl062 is U2, the right one U1

oh, btw, opamps are marked "062"
npn is 2n5088
fet is marked "176<triangle>P642CT"
pots are prolly 100K log
cheers,
lohstah

lohstah · Post by **lohstah** » 01 Feb 2009, 13:58

where are the bass players now ?!?!

lolbou · Post by **lolbou** » 01 Feb 2009, 14:54

Thank you lohstah!!

lohstah · Post by **lohstah** » 02 Feb 2009, 05:30

we still need some help of the experts with this one, there are some things that don´t seem right, like the diode pair kinda "hanging in the air" in the input&surroundings part.
lolbou, if you can borrow the real thing (i only got the pics), you could further check some connections.

cheers,
lohstah

lolbou · Post by **lolbou** » 02 Feb 2009, 06:58

lohstah wrote:we still need some help of the experts with this one, there are some things that don´t seem right, like the diode pair kinda "hanging in the air" in the input&surroundings part.
lolbou, if you can borrow the real thing (i only got the pics), you could further check some connections.
lohstah

I'll get it then...

george giblet · Post by **george giblet** » 02 Feb 2009, 14:21

I started a trace but I haven't got the time ATM to finish it.

On lohstah's last schem, the circuit just before the filter looks wrong to me and and I traced it I got something more like the Boss OC-2 circuit.

Here's my corrections in words. lohstah's last schem:

- the (shown) 1uF NP cap goes between U1b and the 4k7.
- there is another resistor between U2a and the cap marked ?,
ie. it's a 3rd order filter like the OC2
- the two 10k's near the 1uF NP cap and U2a should be removed
- the output of U1b feeds two 47k resistors, one of these resistors
connects to U2a +input the other connects to U2a -input.
- The JFET connects to U2a +input and Vr
- The JFET gate connects to pin 5 of the 4013 via a 10k resistor.
(4013 pin 8 doesn't connect to pin 5 as shown)
- Another 10 goes from the JFET gate to +V (pin 14 of 4013)

If you draw those up you will see some similarity to the Boss OC-2.
Another example is the DOD FX35 but I suspect the on-line schematic has an error around the JFET.

Hope that edges you guys on a bit further.

[Edit] To add a few more things:

The circuit around U1b is wired as a conventional gain of two amplifier stage.
- The feedback and gain resistors are 10k (not 1k).
- There is a hidden bias resistor from Vr to U1b +input
- The diodes point towards each other, one end connects to U1b +input, the other connects to Vr. Diode presumably for protection here and both are zeners.

markjazzbassist · Post by **markjazzbassist** » 03 Feb 2009, 05:14

hopping in here. thanks roland for putting this up. i can't wait till the schem is finished and i can build one.

george giblet · Post by **george giblet** » 03 Feb 2009, 15:33

Here's the new trace using lohstar's initial trace as a guide and the posted pics:

- cleaned up a few bugs
- used the same designators as on the PCB
you should be able to extract the missing stuff from the PCB fairly easily now.
- There's a few part values and part designators unassigned.
It would be good to nail the cap values of the filter and the tracking ckt (C10, C16)

Feel free to scrawl fixes over my drawing and repost.

It's very much like the Boss OC-2. The pre-filtering is much simpler on the sub-blaster. The phase-switching circuit doesn't use the diodes like the boss unit. I seemed to remember with the diodes the boss unit produced a cleaner waveform and seemed to compensate for the pre-filter phase shift to some degree. It also made the octave stronger. The simpler pre-filter on the sub-blaster (probably) keeps the phase shift low. The variations in this area do change the tone, and the "best" is pretty much a preference thing.

lohstah · Post by **lohstah** » 03 Feb 2009, 22:08

hey, thanks for chiming in.
i´m in a real hurry, but here´s the pcb with the component overlay.
click on it to really get the big pic.
more later.
cheers,
lohstah

: Sub Blasta Traces w Component Overlay

george giblet · Post by **george giblet** » 04 Feb 2009, 11:46

Thanks lohstah.

I've fixed the 470k at the input, cleaned-up the schem a bit and fixed the spelling of your name!

That's about as far as I can take it. I'm not so convinced about the filter cap values.

I was thinking the JFET could possibly be a J176, a P-channel JFET.

One thing I forgot to mention before was the 470k on U1a makes the tone quite different to the Boss.

lohstah · Post by **lohstah** » 04 Feb 2009, 19:31

cool, thanks !
for the missing cap values, maybe lolbou can help and measure them with a dmm when he gets hold of the real thing.
cheers,
lohstah

p.s. will be in teresting to compare this to the foxrox octron when the trace gets going

lolbou · Post by **lolbou** » 04 Feb 2009, 21:15

Looking forward to have the unit here on my desk...

lohstah · Post by **lohstah** » 05 Feb 2009, 13:27

here´s george giblets schem with some missing designators drawn in.
cheers,
lohstah

george giblet · Post by **george giblet** » 06 Feb 2009, 12:57

Thanks lohstah

Post by **audioguy** » 28 Apr 2009, 00:22

Has anyone come up with a layout for this baby???

Thanks!

Ampeg - Sub Blaster [schematic]