adding a tone control to a delay pedal?

[bolero]

had a question in another thread, that probably applies globally & would be useful to know, as a mod for all the old digital delays that don't have any EQ adjustment

is there a simple way to add a tone control potentiometer, to pretty much any delay?

a variable resistor and a capacitor i think would be fairly easy to tap onto the circuit, at the end of the wet/delay signal?

has anyone successfully been doing this, and if so, any recommended values?

thx!

[Kevin Mitchell]

There's usually tone controls everywhere (guitar, dirt pedals and amp). So why do you need another one? 
Since most delays are geared towards having a clean output, you could simply rely on the other devices in your chain.

You're on the right track for modding your pedals. Sorry I can't recommend anything! Feel free to tinker. Try out different capacitor values and see what you like most.

[bolero]

ah, thanks, I mean a tone control only for the WET delay signal, not overall

many delays signals are too clean/bright, and could benefit from a low pass filter/EQ so as not to interfere with the source signal

having this adjustable via a pot would be more versatile than just putting a cap somewhere

[Fancy Lime]

Many older digital delays like the Boss DD-2 (https://www.hobby-hour.com/electronics/s/dd2-delay.php) have an analog feedback path and effect level control. You can add an insert loop at the point that goes from the chip to the feedback and effect level pots (so that the LP is present on the first repeat and makes another pass at each repeat or just before the effect level (for a constant LP on the delay that does not degrade with multiple repeats).

Andy

[Sooner Boomer]

Many older digital delays like the Boss DD-2 (https://www.hobby-hour.com/electronics/s/dd2-delay.php) have an analog feedback path and effect level control. You can add an insert loop at the point that goes from the chip to the feedback and effect level pots (so that the LP is present on the first repeat and makes another pass at each repeat or just before the effect level (for a constant LP on the delay that does not degrade with multiple repeats).

Andy

Fancy Lime makes a good point. Adding a tone control in a feedback loop is a great way to do tone control. Just remember, if you're adding a circuit into the negative feedback loop, it works in reverse; low-pass to control highs and high-pass to control lows. A great way to play with different types of tone control circuits, and the values associated with each circuit is the Duncan Tone Stack Calculator; http://www.duncanamps.com/tsc/

[Vivek]

If you wish to try a variable LPF on the wet signal, without too much insertion loss

I can recommend the SIMPLY WONDERFUL TONE CONTROL (SWTC) that was studied by AMZ and Mark Hammer

[Mark Hammer]

I've probably beaten this one to death with a stick, but I like adding a shallow treble cut on the feedback path.  It has several pleasing consequences:
1) it counters the buildup of audio grime that tends to accumulate with more repeats, especially when aiming for "runaway" feedback,
2) it allows repeats to move to the perceptual background, making use of delay feel less cluttered when echoes and new notes are going on at the same time,
3) in the real world, later reflections get duller as their high-frequency content is eaten up by imperfectly reflective surfaces, such that progressive treble-trimming of repeats is more realistic.

The trick is to remove only a bit of the treble in each repeat, such that there is still more to trim off on subsequent repeats.  What I do is locate the resistor that mixes feedback signal with the incoming audio.  Whatever the value of that resistor is, I split it into two common values, connected in series.  So 22k might be split into 12k and 10k, or 10k might be split into 4k7 and 5k1.  Whatever the "first" resistor is in that pair, calculate a capacitor value that results in a rolloff somewhere in the 900hz-1khz range.  So, for example, if 5k1 were the "first" resistor in the series pair, run a 33nf cap to ground from the junction of the 5k1/4k7 pair.  That will provide a 6db/oct rolloff starting around 945hz. 

If it's a delay with wider bandwidth (e.g., 3khz on the wet path) then you can go with a lower cap value.  A cap of .027uf, with the 5k1 resistor provides a lowpass filter rolling off starting around 1.4khz.

Because the corner frequency depends on both resistor and capacitor values, one can always juggle resistor values.  So 10k could be replaced with 5k1+4k7, but could also be replaced by 6k8+3k3, or 5k6+4k3, and so on, in order to identify a suitable corner frequency using commonly available cap/resistor values.

The rolloff can be defeated by simply lifting the ground connection of the added cap.

[iainpunk]

mark makes a perfect explanation here, but i'd like to add a pot between the capacitor and ground, equal or twice as large as the resistor you split in two, so that you can regulate the treble cut.

cheers

[Fancy Lime]

The cool thing about adding an insert loop with send and return jacks at the delay chip output is that you can do all sorts of Interesting stuff with it. A low pass for analogish delay sounds, high pass for keeping busy delay settings from getting muddy, vibrato for tape echo simulation, another shorter delay for faux reverb, a reverb for Jules Vernesk giant cavern echos, a pitch shifter for shimmer, a chorus for mod delay, overdrive for lofi delay... Or any combination of the above. The possibilities are endless. It baffles me that more delays don't have that insert loop. Actually, I don't know a single one that does, but I don't know many delay pedals. I'm sure some of the modern boutique ones have it.

Andy

[bolero]

hey, thanks for the replies, everyone! much appreciated!

I have some old rackmount delays I would like to add a filter/EQ to, too. The insert loop would be a good idea as well

ps Fancy Lime: the old Moog MF104 has an insert loop, but it is not common

[Mark Hammer]

mark makes a perfect explanation here, but i'd like to add a pot between the capacitor and ground, equal or twice as large as the resistor you split in two, so that you can regulate the treble cut.

cheers

That can be a useful addition.  The principle reason why I opt for a simple toggle is because it is hard enough to find a suitable panel location and space for a toggle, let alone a pot!  Nothing wrong with a 3-position toggle, though, for a compromise between no cut, mild and stronger cut.

Clearly, full DIY builds will allow for planning out loops more variable controls, and such, than a commercial pedal will.  If you have the space for more control, go for it.

[iainpunk]

it can be just a tiny hole with the trim-pot's center underneath, so you can reach through the hole to adjust the resistance, and still have a toggle like this:


cheers, Iain