MOTM

I'm currently building my 820 kit, and I've been planning a few mods  
(basically the oakley 820 mods done on a perfboard since the PCBs are  
no longer available).

One thing I'm wondering about before I solder in the ICs - the bypass  
jack seems designed for a foot switch, but it also looks like it'll  
work with an external signal - if the signal is low, the lag is  
enabled, if the signal is high, the lag is bypassed. Does it work  
like that? There's 10K1 ohms of resistance between +V and the jack -  
if I did hook up another module's output to the bypass jack, could it  
hurt the other module?

Basically I hacked together a method to use one of the unused CMOS  
switches and a comparator to enable the bypass jack to work with no  
problem with either a foot switch or an external voltage. Before I  
solder the CMOS switch in though, I want to know if I should bend the  
pins my mod would need out, or if I shouldn't bother since, for the  
reasons stated in the paragraph above, this mod might be unnecessary.

Thanks for any help you can give!

-Chris

> 
> One thing I'm wondering about before I solder in the ICs - the bypass  
> jack seems designed for a foot switch, but it also looks like it'll  
> work with an external signal - if the signal is low, the lag is  
> enabled, if the signal is high, the lag is bypassed. Does it work  
> like that? There's 10K1 ohms of resistance between +V and the jack -  
> if I did hook up another module's output to the bypass jack, could it  
> hurt the other module?

Yes, you can use a voltage to bypass it as well as a footswitch.

Paul S.

>I'm currently building my 820 kit, and I've been planning a few mods 
>(basically the oakley 820 mods done on a perfboard since the PCBs are 
>no longer available).
>
>One thing I'm wondering about before I solder in the ICs - the bypass 
>jack seems designed for a foot switch, but it also looks like it'll 
>work with an external signal - if the signal is low, the lag is 
>enabled, if the signal is high, the lag is bypassed. Does it work 
>like that? There's 10K1 ohms of resistance between +V and the jack - 
>if I did hook up another module's output to the bypass jack, could it 
>hurt the other module?
>
>Basically I hacked together a method to use one of the unused CMOS 
>switches and a comparator to enable the bypass jack to work with no 
>problem with either a foot switch or an external voltage. Before I 
>solder the CMOS switch in though, I want to know if I should bend the 
>pins my mod would need out, or if I shouldn't bother since, for the
>reasons stated in the paragraph above, this mod might be unnecessary.
>

You don't need to change anything, it will work fine with an external 
voltage plugged into the BYPASS jack. It was designed that way, says 
so in the docs.

Thanks, guys. I got it completed and it does work with voltages,  
although it actually doesn't specify that in the docs as far as I  
could tell. The only time it ever mentions using a voltage with  
regards to the bypass jack is to say that there's a diode in the  
circuit to protect it in case one connects a negative voltage. The  
overly cautious among us might read that as an implication that  
you're not actually supposed to hook voltages up to it. Anyway - it  
works!

One small possible non-issue - when I hook the bypass jack up to a CV  
source that is only positive-going (800 EG, for example), the lag is  
bypassed when the voltage goes below a certain threshold, but the  
Bypass LED does not light up. The only time the Bypass LED lights up  
is when the voltage goes negative (or if I touch the tip of the patch  
cord to ground). The functionality is fine in this case, but the LED  
doesn't necessarily show the status of the bypass - is this normal?

-Chris

On Apr 27, 2006, at 10:04 PM, Scott Juskiw wrote:

>>
>
> You don't need to change anything, it will work fine with an external
> voltage plugged into the BYPASS jack. It was designed that way, says
> so in the docs.
>

On 4/29/06, xamboldt put forth:
>Thanks, guys. I got it completed and it does work with voltages,
>although it actually doesn't specify that in the docs as far as I
>could tell.

I don't think does either...

>One small possible non-issue - when I hook the bypass jack up to a CV
>source that is only positive-going (800 EG, for example), the lag is
>bypassed when the voltage goes below a certain threshold, but the
>Bypass LED does not light up. The only time the Bypass LED lights up
>is when the voltage goes negative (or if I touch the tip of the patch
>cord to ground). The functionality is fine in this case, but the LED
>doesn't necessarily show the status of the bypass - is this normal?

Yes, when controlling it with a jack, the LED does not necessarily
show the status of the bypass function -- the effect can be bypassed
and the LED can be off at the same time.  Notice the base of Q1 and
the control input to the MUX are on opposite sides of a resistor.
While it doesn't require a negative voltage to function properly, the
bypass input needs to "see" a low enough impedance in order to turn
off Q1.  When connected to an MOTM-800 it sees 2K.  Although, I don't
know why the bypass LED doesn't use one of the two unused switches on
the MUX.

Hi Mark,

Thanks for confirming this for me. I had the same idea about the  
unused CMOS switches. I put that IC in a socket so I might mod mine  
to use one of those to control the bypass LED more accurately.

For those keeping score at home, my rough plan was to disconnect Q1  
from the bypass circuitry (by removing R6); use the unused NC switch,  
leave one end attached to Ground, and hook the other end to the base  
of Q1 (in the Q1-side hole left by R6), also put a 10K resistor  
between +V and the base of Q1, then connect the NC switch's control  
pin to the other control pins of the CMOS switch. Then. This should  
probably do the trick.

Maybe just lowering the value of R6 would work as well, instead of  
all the rewiring I just mentioned? What is R6's purpose?

I can't say that I'll get around to trying this any time soon. I  
still have a few more modules to build, and for me it's more fun to  
get new ones working than to tweak ones that already work fine.

-Chris

On May 1, 2006, at 4:44 PM, Mark wrote:

> On 4/29/06, xamboldt put forth:
>> Thanks, guys. I got it completed and it does work with voltages,
>> although it actually doesn't specify that in the docs as far as I
>> could tell.
>
> I don't think does either...
>
>> One small possible non-issue - when I hook the bypass jack up to a CV
>> source that is only positive-going (800 EG, for example), the lag is
>> bypassed when the voltage goes below a certain threshold, but the
>> Bypass LED does not light up. The only time the Bypass LED lights up
>> is when the voltage goes negative (or if I touch the tip of the patch
>> cord to ground). The functionality is fine in this case, but the LED
>> doesn't necessarily show the status of the bypass - is this normal?
>
> Yes, when controlling it with a jack, the LED does not necessarily
> show the status of the bypass function -- the effect can be bypassed
> and the LED can be off at the same time.  Notice the base of Q1 and
> the control input to the MUX are on opposite sides of a resistor.
> While it doesn't require a negative voltage to function properly, the
> bypass input needs to "see" a low enough impedance in order to turn
> off Q1.  When connected to an MOTM-800 it sees 2K.  Although, I don't
> know why the bypass LED doesn't use one of the two unused switches on
> the MUX.
>
>
>
>
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