Boss DD-7 relay bypass?

[headcrash]

Hi all, first post here, although I have found lots of useful info and answers here since many years. So: big thanks to everyone contributing here!

I really like my Boss DD-7, but when used in front of a high(er) gain amp, the buffering and other stuff in the signal path is amplified to a decent hiss/noise. Which I don't like And I don't want to use a true bypass looper, because...well, I don't want to
So, since this is a rather modern pedal, there is no typical flip-flop based switching circuit (where I could attach a FET with relay), but a processor.
Using my oscilloscope and the schematic, I traced the respective outputs of the processor, where I was hoping to get some logic high for a FET+relay (bypassing of signals still is done the typical way, using JFETs, so I thought...).
But none of the five or so switching outputs of the processor does actually any switching.
I traced the signal output of the wet audio leg of the circuit, and it seems muting of the wet signal is done in digital domain (I think this is also why more active components than necessary contribute to the hiss ...).

I had some tiny uC-controlled bypass module lying around, but connecting its switching input to the momentary switch of the DD-7 does not work reliably or properly.

Does anyone have any idea what else I could do to get some switching signal?
I was wondering if there is a DPST version of the Boss momentary switch, so I could use the second contact to switch the aforementioned bypass module. But so for I've had no luck finding the manufacturer of those switches.
Schematic can be found here: http://www.synfo.nl/servicemanuals/B...VICE_NOTES.pdf, schem starts on page 18.

Would really appreciate any hint or idea !

[x-pro]

Am I correct that there are no control signals at the processor output on the buses? :
BYPASS_A_MUTE
DA_A_MUTE
BYPS_A_TO_B_MUTE
BYPASS_B_MUTE
DA_B_MUTE

[headcrash]

Thanks for the reply, x-pro!
Yes you are right, I cannot measure any change of level at these outputs. I think one of them was on a permanent high level (+5V-ish), can't remember which one. The others are on 0V. None of them changes its status, when pressing the footswitch.

[x-pro]

Basically, from the control of these output field-effect transistors you need to take a signal to control a relay. The latter will switch the bypass you need.
You can put a standard trigger on the native button and also control it via a relay. The relay needs a small size and gold-plated contacts. Just organize the input to the device in a standard way.

[headcrash]

Thanks x-pro. I know all that. Problem is: there is no switching signal happening, when I press the footswitch. It looks like Boss decided to omit the switching in analog domain, and rather let the signal-switching FETs be on permanently. Muting of wet signal is done inside the DSP.
Also putting an electronic switch parallel to the native switch resulted in an unreliable switching behavior. Sometimes it would switch on, sometimes not, sometimes it switched on for a fraction of a second.

[x-pro]

It looks like Boss decided to omit the switching in analog domain, and rather let the signal-switching FETs be on permanently. Muting of wet signal is done inside the DSP.
.

If they are all on all the time, then how is the bypass not summed with the processed signal?

[headcrash]

If they are all on all the time, then how is the bypass not summed with the processed signal?

Thank you x-pro!
Bypassing of processed signal is done in digital domain. This is what I wrote above in my first post: when I trace the effected signal, for example for output jack A, coming from the _DA_A leg, it is muted before that. I use TP32 for tracing the signal there (see page 19). I would have assumed, Q9 would mute the effected signal, but it's always on.

[g1]

BYPASS_A_MUTE line should toggle Q6. Check at TP40. From there the gate of Q12 is turned on or off to mute the dry signal.
(edit: TP40, not TP4. TP40 and TP41 should be both toggling when switch pressed)

[headcrash]

BYPASS_A_MUTE line should toggle Q6. Check at TP40. From there the gate of Q12 is turned on or off to mute the dry signal.
(edit: TP40, not TP4. TP40 and TP41 should be both toggling when switch pressed)

Thanks g1 for chiming in!
I did also check all the TP's on the collector legs or "outputs" of the switching transistors (Q4 - Q8). There is absolutely no "analog" switching going on in that pedal.

[g1]

My post #8 above got a bit mixed up with the edit, due to the schematic being broken up right at the area of discussion. So TP4 and TP41 should be the ones to check.
I don't want to argue about what is happening, but the schematic definitely shows some analog switching going on.
That leaves 2 possibilities: either the schematic does not match your version of pedal, or something is wrong with the pedal.

[headcrash]

Hey g1, thanks for not giving up on that subject

The fact, that there are switching transistors present (both on paper AND the real PCB, btw.), in the case of the DD7 doesn't necessarily mean, that there's some switching happening. Because these are driven by one of the processors. Hence my assumption, Boss for some reason left out the changing of lo and hi levels there in the programming.

Maybe on an earlier or later revision of the pedal things are different, who knows.

[R.G.]

I would cheat.

I would open the series resistor from the SPST footswitch and use it to trigger a circuit that BOTH controls a true bypass relay AND feeds a momentary pulse to the Boss footswitch input. Suitable circuits include an 8-pin PIC or ATTiny or similar, or even a CMOS inverter chip. In the circuit below:

the momentary switch triggers a latch made of two CMOS inverters. This output is buffered by another gate, largely because there were six inverters in the chip I used, and I could use them up. The buffered flipflop is then used to drive an LED indicator for on/off and a half-monostable to generate a momentary pulse to the "reset" side of a latching relay. It's inverted to generate a momentary pulse to the "set" side of a latching relay.

The circuit as is can do what you're interested in with a two-coil latching relay for bypass if you tap off one of the momentary pulses to go to the Boss processor input. Or, you could use only one of the two momentary pulses for the Boss processor and drive a non-latching relay.

You might be interested in the number of switching articles at geofex.com.

[headcrash]

I would cheat.

I would open the series resistor from the SPST footswitch and use it to trigger a circuit that BOTH controls a true bypass relay AND feeds a momentary pulse to the Boss footswitch input. Suitable circuits include an 8-pin PIC or ATTiny or similar, or even a CMOS inverter chip. In the circuit below:

the momentary switch triggers a latch made of two CMOS inverters. This output is buffered by another gate, largely because there were six inverters in the chip I used, and I could use them up. The buffered flipflop is then used to drive an LED indicator for on/off and a half-monostable to generate a momentary pulse to the "reset" side of a latching relay. It's inverted to generate a momentary pulse to the "set" side of a latching relay.

The circuit as is can do what you're interested in with a two-coil latching relay for bypass if you tap off one of the momentary pulses to go to the Boss processor input. Or, you could use only one of the two momentary pulses for the Boss processor and drive a non-latching relay.

You might be interested in the number of switching articles at geofex.com.

Hey R.G., thanks for chiming in and the useful info. Sometimes cheating is easiest to do, but sometimes you need someone to tell you to do so

I'm not sure what you mean by half-monostable. Also this solution would make parts count higher, wich I was - of course - hoping to avoid.
Also while thinking about this matter over and over again, I may end up with a little true bypass loop box, because it might help avoiding tap dance, because I could put all my pedals (buffered or not, analog or digital) in that single loop box. Which in turn I could switch together with my amp channel footswitch at a time.

Thanks again nevertheless, very interesting read and good help to learn more about switching!

[R.G.]

The half-monostable is the series capacitor/pullup resistor driving an inverter. At rest, the cap has one side at the voltage of the previous stage and one side pulled up by the resistor. If the previous stage is high and goes low, the cap couples in a drop to ground to the next inverter input, then is RC-timeconstant pulled back up by the resistor. The next inverter input sees a short low that goes away as the cap charges, so its output is normally low, but rises briefly to high, then drops back down. One high-going pulse results. If the previous stage was low and goes high, the cap shoves the next stage input high-er, and this is bled away by the input protection diodes; no pulse results.

It's called a "half-" monostable because although it makes a pulse of kinda-defined length, it does not have a lot of the other characteristics of a good mono. But it's handy if you can live with its limitations. Works best with Schmitt trigger input inverters. You can use a pull down resistor to get a single low going output pulse.

Mouser sells DIP14 and DIP16 CMOS hex inverters for about $0.30 to $0.40. They sell six- and eight-pin PICs in SO-6 and SO-8 packages for about the same price; in DIP, the controllers cost up to $0.80. The processor variant will have the same number of parts on the switch input, and generates clean, reliable output pulses debounced and all, with half the IC pins and half the space. It's kind of a tossup for something as simple as debouncing. I often went with the CMOS just to have a spare gate already on the PCB.

Also while thinking about this matter over and over again, I may end up with a little true bypass loop box, because it might help avoiding tap dance, because I could put all my pedals (buffered or not, analog or digital) in that single loop box. Which in turn I could switch together with my amp channel footswitch at a time.

That works too.

Good luck with whichever you use.