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TB3031 Question regarding CV+GATE
MUFF WIGGLER Forum Index -> Oakley Sound Systems  
Author TB3031 Question regarding CV+GATE
janvanvolt
Hi,

given the AC setup as described in the manual, how do i connect
CV+ GATE correctly from a sequencer?

From my understanding:

CV goes to KEYB
GATE goes to GATE
GND goes to G2

All is working and powered up, unless i connect G2, which seems to be
understandable as the original circuit is having one phase to ground.

How am i supposed to connect this so that i get out something "useful" on the 3031 ?

power LED is on when no GND, with GND to sequencer= no.
Synthbuilder
I'm a little lost with your explanation. You are using the TB3031 without tbDAC, is that correct? Are you using banana sockets? Normally there is no need for a separate ground connection. In a standalone rack the ground will be made via the connecting jack leads from the audio and CV/gate inputs. Or do you have a sequencer of some sort built into the TB3031's casing?

If the power LED is going out then you may have a problem with the ground wiring in your project. Perhaps there is a short somewhere. Check that the AC power line that is not connected to ground in the TB3031 is not being shorted to ground via the sequencer's ground connection.

Do you have a small photo of your test set up?

Tony
janvanvolt
I'll try to explain it easier:

15V wallwart into AC1+AC2
+12V to Transistor6 (another DIY project which is just the 303 sequencer)
-12V to Transistor6
from Transistor6 i use CV + GATE

Power lamp is on (and i read out correct values on all the testpoint + 12V)
but the gate is not triggered.

When i connect GND of Transistor6 and G2 of the Sequencer, i get an audible Humming (60Hz) and nothing works (obviously i am shorting the AC) somehow.
Synthbuilder
Ah I see you are also trying to run the sequencer from the TB3031. The first thing you need to check is how much current the sequencer takes from any connected supply. If it is over 40mA then you probably won't be able to use the TB3031's own power supply without modifications.

The +/-12V outputs are only really designed to run the tbDAC midi/CV converter.

If you are losing power when you connect ground its probably the current limit being reached on the TB3031's positive power rail.

How much current does the Transistor6 use?
janvanvolt
Good question. I would guess 200ma.

a)I will try to sequence it with my semtex ...
b)would this mod do the trick ? http://burnit.co.uk/sdiy/index.php?page=3031&subpage=mods or how do change the limit ? the PSU itself has 500ma.
Synthbuilder
janvanvolt wrote:
I would guess 200ma.


Yes, that would overload the power supply on the TB3031.

janvanvolt wrote:
would this mod do the trick ?
http://burnit.co.uk/sdiy/index.php?page=3031&subpage=mods


No, Seb increases the current limit up to 180mA or so. You'd need to go well above that. The TB itself takes around 80mA, so you'd need add your bit to that. However, the heatsinks are going to be pushed to their maximum if you try and take too much. And the smoothing caps are probably going to need to be bumped to 2200uF.

janvanvolt wrote:
or how do change the limit ? the PSU itself has 500ma.


Careful, a 500mA AC wallwart can only supply 250mA per rail. In practice you're pushing it at that so better keep to a maximum of 200mA per rail.

I think you'll need to think about either upgrading the power adapter or giving the sequencer its own supply. I think the latter is probably best.
janvanvolt
Sounds like it. I will test the board with my semtex in a minute, so we'll see if that works. if not, i'll provide more details of the outcome...
janvanvolt
Okay, i think something is borked, but i should wait until the MIDI Interface is fully assembled.

With CV/GATE from Semtex fed to Semtex -> all working
With CV/GATE from Semtex fed to TB3031 -> nothing.
With LFO's used from Semtex fed to TB3031 CV/GATE -> works to some extend, at least GATE LED is blinking.

however, i am not sure if the voice circuitry is outputting something.
Are they other test points to look at for checking the Voice ?
Synthbuilder
janvanvolt wrote:
With CV/GATE from Semtex fed to TB3031 -> nothing.
With LFO's used from Semtex fed to TB3031 CV/GATE -> works to some extend, at least GATE LED is blinking.


If the LFO causes the gate LED to light then I am surprised that the gate output of the Semtex does not.

However, if you are getting no gate LED then you must first check all the circuitry from the gate input. Check pin 3 of U13 follows the gate signal. It should rise to +12V every time the gate is active. If not check circuitry around Q33. Page 3 of schematic top right.

Do you have a scope?
janvanvolt
I do got a scope, two channel one.
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