can you add the tails mod to PT2399 + belton brick reverbs?

[tabbycat]

i know you can add the tails mod to the better known PT2399 delays such as the deep blue and the rebote, but can they be added to PT2399 + belton brick type reverbs?
or is there something about those circuits that makes that impossible or so complicated it's not worth considering?

i've got an eqd ghost echo and hope to have my dba reverberation machine finished this weekend, ghost is a PT2399 + belton 2 while the reverberation machine is TLC27M4 + belton 2 (so normal tails mod maybe not applicable).

i'm going to be taking the ghost apart soon anyway to add a wet-dry switch, and the dba isn't boxed yet, so i thought now would be a good time to ask the question and look into what would be involved.

this was the circuit i had in mind http://pedalparts.co.uk/docs/Tails.pdf though there are variations in the rebote and deep blue threads here somewhere.

has anyone here thought about trying this? i shall read around it as and where i can find useful info this weekend, but thought i'd throw it out to 'open chat' here anyway in case it's something someone here has done, considered or dismissed.

an idea.

[Beaker]

I believe you can - I'm sure I've read it somewhere, but can't remember where.

You could always ask Fuzzdog if you are using one of his boards. He's always been really helpful to me.

[induction]

Adding tails just requires the circuit to have a buffered clean path in parallel to delay/reverb path. The usual approach is to use an SPST to open the wet path just after the input buffer. Then the dry signal makes it to the mixer no matter what, and the wet signal loses input in bypass. Since the wet return signal is still present, you get tails.

The Ghost Echo has it's Dwell control after the wet/dry mixer, which means the dry signal will get sent to the delay and reverb circuit in bypass anyway, so you have to use a DPST (or DPDT, which is probably easier to find) so you can open the dwell path in bypass as well.

The Reverberation Machine does not have a buffered clean path. There is significant tone shaping after the mixing amp, so the bypass signal will not match the signal from the dry path, and traditional tails doesn't make sense. But you have options. You could have a second bypass switch using the usual approach. It will kill the reverb, but keep the tails and the effected dry signal. Alternately, you could add a bypass buffer, with only the inputs switched. Switching the inputs gives you clean, buffered bypass, and leaving the outputs always connected gives you tails. This option is a little more work because you have to design a new mixing stage, or just redesign the old one, but it shouldn't be too hard. Test it on a breadboard, obviously. You want to make sure that leaving the effected output connected in bypass doesn't add noise or hiss.

[tabbycat]

@beaker, thanks for the reply beaker. the ghost is actually fuzzdog's spectreverb, so i might go that route if i can't crack it myself. as it works as it is supposed to i think of mods as not being his responsibility, so don't bother him about that stuff, but he might be up for it. will see how it goes.

@induction. many thanks indeed, induction. you surpass yourself so often i wonder that you don't ever lose sight of yourself, or lap yourself. thanks for the seriously authoratitive reply. i feel a bit guilty for not posting schematics etc now. it was just a generalised question as i never anticipated anyone wanting to get into the practicalities of it. unlucky at lotto, lucky at gfx.

i will try to work out a basic tails daughterboard on vero for the schematic in the pdf above tomorrow, and try to patch it in to the ghost first as and where you suggest via the breadboard to see how it works sometime this week. might try to post a rough schematic of my plans here first (if you wouldn't mind giving an opinion) beforehand, just to check i'm making sense.

on considering the idea i also wondered, is there a way of making the main 3pdt and tails switch an all-in-one (using a 4pdt maybe?).
it occured to me that i actually always want tails with the ghost. it abruptly cutting from dreamy wet reverb to bypass is a bit brutal really, the ideal would be for it always to switch off via tails. or should i make the vero daughterboard to the above tails schematic and then just jumper it to 'always on' and not attach it to a switch at all?

http://pedalparts.co.uk/docs/SpectreVerb.pdf

as you describe it, the dba reverb machine mod sounds a bit beyond me at the moment so may come back to that one. i finished my build tonight so will test it this week and decide (depending on how much i like it) how much more involved i want to get with it. if it is legendary i might have to. a blessing and a curse.

[induction]

tabbycat wrote

i will try to work out a basic tails daughterboard on vero for the schematic in the pdf above tomorrow, and try to patch it in to the ghost first as and where you suggest via the breadboard to see how it works sometime this week. might try to post a rough schematic of my plans here first (if you wouldn't mind giving an opinion) beforehand, just to check i'm making sense.

A note about the 'tails circuit'. What this circuit does is uses a SPDT to emulate a DPDT. Similar to the Millenium Bypass, it uses one pole to both engage/bypass the reverb sidechain and turn on/off the led. If you want to explore the tails option on a simple reverb or delay, all you need is a SPDT for bypass. If you want an led, use a DPDT. For the Ghost Echo, you need two switches for bypassing the reverb, and one switch for an led. So you can modify the circuit in the pdf to control two jfets instead of one, or just use a 3PDT. No need to make a vero layout before you start playing on the breadboard.

There are pros and cons to this type of jfet switching vs. mechanical switching. You may decide to use the jfets in the build, but you can at least explore the functionality with simple mechanical switches.

on considering the idea i also wondered, is there a way of making the main 3pdt and tails switch an all-in-one (using a 4pdt maybe?).
it occured to me that i actually always want tails with the ghost. it abruptly cutting from dreamy wet reverb to bypass is a bit brutal really, the ideal would be for it always to switch off via tails. or should i make the vero daughterboard to the above tails schematic and then just jumper it to 'always on' and not attach it to a switch at all?

You have lots of options for bypass:
The simplest is to use the tails switch as the only bypass switch. This will mean you always have tails, but you can't turn off the buffering, or any other filtering that the dry signal chain receives. If you don't mind the coloration of the pedal in bypass and it's not noisy or hissy, then this is a reasonable option. One benefit is that the dry signal will be unity gain in bypass. The true bypass signal might not be.

What they suggest in the pdf is to have two bypass switches: One for true bypass, wired in the normal TB way, the other for tails and wired directly into the circuit board. This gives more options, but there is a gotcha: The switches aren't entirely independent. When the true bypass is disengaged, the tails switch will turn the delay chain input on and off. But when the effect is true bypassed, the tails switch does nothing. If pedals with multiple footswitches sometimes confuse you (which is which?), then you will eventually try to switch the reverb on with the tails switch while the true bypass is engaged, then you will start cursing.

Another option is to use one footswitch to turn the reverb on and off, and one toggle switch to select between true(-ish) bypass and tails. This is a little more intuitive to use, but limits your options a little. If you want true bypass in one section of a song, and tails in another section, you have to bend down and flip the toggle or go with two footswitches again.

But if you're certain you always want tails and never want true bypass, then the answer is simple. Just use the tails switch as the only bypass switch.

[tabbycat]

many thanks again for your wisdom, induction. have had a migraine-write-off week, so it has taken me up to now to be able to be able to think straight about what you are advising.

i will see how the buffer effects the signal re colouration with regard to the on-all-the-time stomp, and go from there. one stomp simplifies everything, but i'm very neurotic about leaving buffers on all the time. same kind of reason i stay away from compressors. just seems to make things not quite right. am disorientated enough most of the time, so sort of invisible forces like that ghosting around in the background i try to avoid. am more on-is-on and off-is-off (not looks-off-but-actually-a-bit-on).

if i can get away with the single stomp and tails all the time i will go for that. but the toggle switch wouldn't be much effort and i think that's probably where i will end up. that's idiot proof, which is my level. but i will try the stomp-buffer thing anyway, just to satisfy curiosity.

will report back with results as and when.