AD9 TROUBLE

[thejoe]

Hey guys,
I'm working on an AD9 (not a build. sorry if this is the wrong forum) and after figuring out everything else I needed to do I'm stuck on one part. The owner of this wishes to have the pedal on all the time but just roll down the effect level to get a dry signal. He uses it for keys and likes the idea of letting the noise build and then just bring it in with swells of the dry/wet knob.
I have looked at the schematic attached but can't figure out at all what it could be. There are no hidden resistors anywhere that prevent the pot from reaching 0. Any help would be greatly appreciated.

Joe

http://www.dirk-hendrik.com/Ibanez_ad9_analog_delay.pdf

[armdnrdy]

It's a bit unclear what you want to accomplish. You stated that the owner of this pedal want to "bring it in with swells of the dry/wet knob."

And then you stated, "There are no hidden resistors anywhere that prevent the pot from reaching 0"

So, does the owner not want to start from a completely dry signal? Or are you not able to get a completely dry signal when P3 is all the way CCW?

[thejoe]

The latter.
The problem is that when P3 is fully CCW there is still a bit of delay that bleeds through.

[armdnrdy]

Gotcha!

I built an AD-80 and an AD-900 and there is a difference in how the Mix/Delay level controls work. The AD-80 has more of a "mix" circuit, to where the pots wiper is grounded and the two outer lugs are dry and wet signals.

The AD-900 has a similar set up as the AD-9 to where the wet/dry signal is controlled by lowering the wet signal to ground.

In Dirks drawing I see R47 listed as two values, a 47K and in parenthesis, a 10K. Which value is in the delay you're working on?

If I'm reading this correctly, It looks like R44 is the dry mixing resistor and R47 is for the wet signal. You might try raising the value of R47 to lower the delay signal.

[scuzzphut]

The latter.
The problem is that when P3 is fully CCW there is still a bit of delay that bleeds through.

It seems that when P3 is fully CCW, the delay signal is a direct short to deck.

I know that when I do this accidentally in a pedal , it leads to complete silence.  

Maybe try temporarily hooking up a lead from the CCW lug of P3 direct to deck ?? Just in case it doesn't *actually* go straight to earth in real life.

[armdnrdy]

Maybe try temporarily hooking up a lead from the CCW lug of P3 direct to deck ?? Just in case it doesn't *actually* go straight to earth in real life.

I made that connection offboard to a star ground and it has the same effect, still a bit of delay. I think that a small amount of signal is making it's way through the 100K pot.

[thejoe]

The latter.
The problem is that when P3 is fully CCW there is still a bit of delay that bleeds through.

It seems that when P3 is fully CCW, the delay signal is a direct short to deck.

I know that when I do this accidentally in a pedal , it leads to complete silence. 

Maybe try temporarily hooking up a lead from the CCW lug of P3 direct to deck ?? Just in case it doesn't *actually* go straight to earth in real life.

I made that connection offboard to a star ground and it has the same effect, still a bit of delay. I think that a small amount of signal is making it's way through the 100K pot.

Thats pretty much what I'm hearing. Is there anyway to get rid of that little bit of bleed aside from installing a switch that would just shut off the signal?


The resistor there is a 10k. I am noticing also that the schematic says the capacitor that links them together should be "1/50" but there is actually a 4.7uf installed.

The CCW lug is already connected to the ground of the input jack and to the CCW lug of the repeats pot.

[scuzzphut]

http://www.tdpri.com/forum/tele-technical/127070-no-load-mod-cts-pot.html

This page shows how to physically mod a pot , so that at one extreme, it's an open circuit.

If disconnecting the wiper lead results in silence (i.e. it's not leaking through some other path or being induced elsewhere) then that might be an option.

[armdnrdy]

The cap will change the frequency not the level. Try changing R47 to 47K. See if that lowers the delay signal

[armdnrdy]

http://www.tdpri.com/forum/tele-technical/127070-no-load-mod-cts-pot.html

This page shows how to physically mod a pot , so that at one extreme, it's an open circuit.

If disconnecting the wiper lead results in silence (i.e. it's not leaking through some other path or being induced elsewhere) then that might be an option.

Interesting stuff here. I would try changing R47 first (that mod can be reversed) and if that doesn't do the trick, the no load pot thing. It depends on how far into this thing you want to get. (Can the pots in the AD-9 be taken apart?)

[thejoe]

Well I didn't have any 47k resistors lying around so I trimmed a 50k pot down to the right value. Didn't work. Looks like the pots might be able to be opened up. I'll have to take it out to really check.

But heres a question about that No Load mod; If this essentially takes the control out of the circuit does that mean it will be all dry or all wet?

[armdnrdy]

while you're in there, try a higher value (maybe 100K) before you rip that pot apart.

[thejoe]

100K helped in killing that bleed but also sucked out too much volume when the signal was desired.

[scuzzphut]

But heres a question about that No Load mod; If this essentially takes the control out of the circuit does that mean it will be all dry or all wet?

On reflection - what you really want is for the wiper to open circuit from the output lug at the end of the travel - so it should be all dry (i.e. wet signal is not connected at all)

[armdnrdy]

Try different values. See if you can find a happy medium.

I was looking at the schematic to see how much trouble it would be to convert this part of the cuircuit to a true "mix" circuit. It looks doable. It involves soldering resistors onto the outer pot lugs, attaching the grounded pot wire to the wiper lug, and changing the values of R44 and R47.

I think that Maxon changed the design of this control because unlike this pedal's owner's use, there isn't much reason to have the mix control go to zero delay. If you want zero delay you bypass the unit.

If you would like, I'll draw something up for you that will hopefully solve the problem.

[scuzzphut]

Joe - listen to Larry before you open up the pot !!

[thejoe]

Larry,
If you could draw up something I'd greatly appreciate it. I opened the pot and tried the no load trick but even that didn't work. I switched the pots, changed resistors... Not much luck. R47 is located in a really tight spot and the PCB trace is starting to lift so the less I need to mess around there the better. The only thing I found that actually worked was disconnecting the wire from the middle lug.

[armdnrdy]

Well, I wanted to try a quick and easy fix to start but....we know how that goes sometimes!

I have to make a quick trip to the bank and then I'll draw up a schematic and directions.

We're going to put the AD-80 blend circuit in it. The two circuits are almost identical. You will need (2) 7.5K and (2) 1.8K resistors.

[thejoe]

That would be awesome. Take your time, I won't have a chance to grab more resistors for a day or two. Thanks so much!

[armdnrdy]

I'm finished with the schematics and I'm working on the drawing but I've come up on a little problem. 

The input and the output stages come together at a point between R47 and R44 with T8 (JFET switching) in between.

We would have to disable the JFET switching, remove T12, T8 and pull a wire from the R44 side, (that would separate our dry signal to bring to the mixing circuit) and remove and jumper T7. (It looks like T7 shuts off the repeats/feedback loop to and from the compander (NE571) when the bypass switch is engaged. There are some other miscellaneous resistors associated with the JFET switching that should be removed as well.

In your first post you mentioned that the owner of this pedal wanted it to stay on the whole time right? You mentioned that you took care of that already. Did you disable the JFET switching?