DD-3 'trails' mod

[Mondrian]

I'm trying to work out how on earth to mod a DD-3 to give trails - or more exactly, so I can set up a self-oscillation with a few drone notes and then shut off the input jack from the feedback stage, while leaving the effect otherwise 'on' to allow the trails or oscillating notes to continue.

I assume this should be doable by simply putting a killswitch between the input stage and feedback somewhere, does anyone have a schematic for the DD-3 that would help me out?

[Thomeeque]

 For this schemo http://www.8bitsindgenug.net/boss_dd2.png:

Pull out negative node of C18 and switch it between original point (Q6 emitter + R23 junction) [NORMAL MODE] and 1/2Vcc (R27 + R19 junction) [TRAILS ONLY MODE].

Good luck

T.

[Mondrian]

Cheers

looks like an ok mod, although I haven't inspected the circuit board yet.

If I were to put a cap on the level or feedback pot to add a high-cut, what sort of cap value should I be looking at for a subtle cut off? a few pf?

[Processaurus]

Be aware that there are several different versions of the DD3, that follow similar topology to the dd2, but may have different part numbers.  Should be able to follow the circuit through, and it should be easy to find that group of three transistor stages that form the lowpass filter.

I bet someone could make a version of the hold that could be turned off and on during regular delay, I think it just stops the writing of information to the buffer, but continues to playback what is in the buffer, that would be good if you wanted it to go forever without changing.

For your cap value, should be able to find it by searching for "DD3 mod" here...

[Thomeeque]

If I were to put a cap on the level or feedback pot to add a high-cut, what sort of cap value should I be looking at for a subtle cut off? a few pf?

Best place for high-cut capacitor for the delayed signal is IMO over (in parallel with) R42 (part of negative feedback network of IC2b output buffer). About it's value I'm not sure (as I have no idea what exact high-cut you desire), just experiment.. Try something from 100pF to lets say 10n..? You can even try to use resistor in series with this capacitor to soften the cut.. Or the pot (like 50k) to get "TONE" knob, if there was space for it.. lot of possibilities here..

T.