PT80 Modulation

[thedefog]

Hey guys,

I'm trying to add modulation to my PT-80 build. I know that a lot of other PT2399s have this built into them, so I thought it would be simple enough to build a small triangle LFO to do it with. Question is, what voltages does Pin 6 on the PT2399 want to see to modulate? Right now I have the tremulus lune's LFO feeding into it and it works, but it causes the rate to become pretty unusable. I'm guessing a need to throw a resistor after the output to tame it. Or should I just bypass that and just do the LDR deal on the rate pot off the LED of the LFO?

[Galego]

Search for "Echo Base".

[frequencycentral]

Probably easiest to do it the LDR way. Hook up a depth pot (same value as the delay time pot), connect lug 1 and lug 3 of the depth pot across the delay time pot. Hook the LDR from lug 2 of the depth pot to ground. Done. You may want to double the value of the delay time pot (and therefore the depth pot), as resistors in parallel reduce resistance. I'd go for 100kB for both.

[Marcvv]

Why not take it one step further and go for the taptation. Tap tempo and modulation. Works really well with the pt80.

Marc

[thedefog]

Probably easiest to do it the LDR way. Hook up a depth pot (same value as the delay time pot), connect lug 1 and lug 3 of the depth pot across the delay time pot. Hook the LDR from lug 2 of the depth pot to ground. Done. You may want to double the value of the delay time pot (and therefore the depth pot), as resistors in parallel reduce resistance. I'd go for 100kB for both.

Thanks! I'm going to do exactly that.

I'd like to do the tap tempo, but I already put a momentary switch on the left side of it that temporarily sets the feedback to 100%,  and I use that quite a bit. I guess I could always throw a 1/8" jack in the side and do an external tap tempo in a ABS box.

[chi_boy]

Search for "Echo Base".

+1

You should be able to copy and paste right from the Echo Base. I'm doing the same thing for a project and have an untested schematic, but no layout.

Looks great on paper. 

[tomas1808]

Search for "Echo Base".

I think he refers to this Mod Auke Haarsma (I think) posted on the Echo Base thread:



Here is the transfer:

http://i.imgur.com/RhUIv.png

I think it is tested and working if I remember correctly.

[Govmnt_Lacky]

I see that the layout calls for an IC. Anyone know what kind?

Seems to be missing from the parts list. 

[Thomeeque]

 Any common dual op-amp (TL072, LM358, 4558..). Btw. I'd say depth and speed pot labels are switched on the layout.. T.

[thedefog]

YES! I came across that a while back and forgot all about it. That's the one I wanted to build. Thanks a bunch for finding it Galego, and everyone else for helping out on this.

Question: What's the value of C1?

[tomas1808]

Have no idea about C1, sorry.

Here is the original post tho, maybe it helps:

http://www.diystompboxes.com/smfforum/index.php?topic=60662.msg572620#msg572620

[Thomeeque]

Question: What's the value of C1?

Something around 1µF, probably little more (when simulated is LFO range with C1=1µF 0.6Hz to 20Hz). You should use non-polarized (preferably ceramic or foil) capacitor here. T.

Edit: It is 1µF original post states that it's EchoBase LFO..

[slacker]

Tomas is spot on C1 should be 1uF ceramic or film. If you can't find any in that size easily use two 0.47uF in parallel.

[thedefog]

Awesome. I'm wondering what a really fast rate would sound like on it. It would be fun to get into synth range LFO speeds on it to make some FM type sounds. I'd love to be able to turn the repeats off completely and make some interesting sounds on it similar to the Clari(not). Got one of those built as well, just haven't housed it up yet.

[dule88]

I don't fully understand what are 9(or 12V) and 5V connections for... Would someone mind explaining it?
Thanx

[slacker]

Hi those conenctions are for power to the circuit, you connect them to the 9 or 12 volts and 5 volts on the PT80 circuit.

[dule88]

Oh...
Well, thanks man...
And, another question: are pots LIN or LOG?

[dule88]

I bought LIN, but it's not working...
I've checked my component values million times, and tried to switch pots, but there's no modulation at all...

...I'm using TL072, and BC560C

[thedefog]

I bought LIN, but it's not working...
I've checked my component values million times, and tried to switch pots, but there's no modulation at all...

...I'm using TL072, and BC560C

Check with a multimeter to see if you have 5v and 9v on the board first. Then check to see if the voltage is wiggling up and down when the modulation depth is up. Also don't forget about the jumper on the board.

[dule88]

thanks, for help, but i gave up that idea, i had voltage, an jumper on the board, but nothing happened when i turned the pots
thanks anyway