tr-505 individual pitch help?

[rizla]

I am having a small problem with individual pitch mod on my tr-505. I am using an "hcf40106be" Hex Inverting Schmitt trigger IC, as suggested on Burnkit website (http://burnkit2600.com/gear/tr-505-pitch-bend-mod/), a CAP, and 1meg pots.

I have had some success when using it with a single 1meg pot, affecting only one drum group. It works well, and allows me to pitch up and down very well. My problem is that when I repeat the procedure on the next 4 pins of the chip, I cannot get a result.
I have referred back to the schematic, and to the pin arrangement on the data sheet and I cannot seem to figure out what I'm doing wrong?

Could you guys throw some light on the subject for me?

If it's any help, here is a link to the data sheet for the IC -

http://pdf1.alldatasheet.com/datasheet-pdf/view/22303/STMICROELECTRONICS/HCF40106BEY.html

I should also point out that I needed to use a 0.003uf NON polarised CAP (rather than the 0.03 POLARISED cap which was suggested), as MAPLIN apparantly don't sell 0.03 polarised caps. After some experimentation I found the only result I could get was with 0.003. :'

[rizla]

I've drawn up a little pic to show what I've done to the chip so far. Like I say, it's working fine with just 1 drum group, but I can't seem to get any result when I repeat the procedure on the next 4 pins of the chip. Hopefully a  more experienced bender may be able to see where I'm going wrong?

<a href="http://s454.photobucket.com/albums/qq264/badstatic/?action=view&current=505pitch.jpg" target="_blank"><img src="http://i454.photobucket.com/albums/qq264/badstatic/505pitch.jpg" border="0" alt="tr-505 pitch problem"></a>

          or here is the direct link if the other link isn't working -

http://i454.photobucket.com/albums/qq264/badstatic/505pitch.jpg

[computer at sea]

Your drawing doesn't include the transistor from the Burnkit schematic.  Is it in your machine but not your diagram?

[rizla]

No, I decided to leave out the pull-up resistor and the transistor as this mod will be a permanent fixture of my 505. I have no need to ever remove the mod or to keep the factory 'stock settings', and as my knowledge and experience is limited I thought I'd keep the parts to a minimum.

In my opinion most of the sounds will hugely benefit from a slight lowering in pitch anyway.

Another quick thing - I'd like to add variable decay to the hats and cymbals on my 505. I've found the cap which controls the decays, but I'm not too sure what to do next? I have attempted to wire a 1 meg pot across the connections for the cap, but it just kills the decay altogether even with maximum resistance. Can you give me some advice on what to try next?

Thank you ;-}

[Signal:Noise]

You'd need to rig something up with a rotary switch and various caps, so you have discreet decay settings rather than continuous.

[rizla]

You'd need to rig something up with a rotary switch and various caps, so you have discreet decay settings rather than continuous.

OK, I'm just looking at the service manual for the 505 and it doesn't seem to state the values of the decay caps.
I'm guessing that I'll need lower values for faster decay, right? Is there any way to measure CAPs with a multimeter?
Also do you know what kind of CAPs these green ones are, and will it make any difference to the sound if I use nice cheap ceramic CAPS?

thanks again

[Gordonjcp]

Trace out the circuit around the cap.  You'll find that it charges through a resistor.  If you vary this resistor you'll change the charging speed.

Find out what value the resistor is, and use a pot with a series resistor about a tenth the value of the original resistor - this will give you a nice short decay without risk of damaging the rest of the circuit.  The pot can be any value you like - if you use one about twice as high value as the original resistor, you'll go from ten times as fast to 2.1 times slower.

[sensor]

what cap controls the decay?

matthias

[Circuitbenders]

its that vertical row of green ones up where you source the individual outs isn't it? Theres one for each sound channel.

I was going to suggest that as the problem for your missing sounds on another thread as i've had a missing sounds problem with a couple of 505's both of which just played short blips for some sounds because these caps had died.