neutron - ?

[lowstar]

hi people,
put my neutron together today, and yes, it is behaving a little finnicky. i used r.g. keen´s layout, with charge pump/max 1044 (jumper 1-8), for the optos i used nsl32. no whining issues, except in sweep up/range high position with max setting of the peak knob, so i think that´s ok (if you move the peak knob a little bit, the whining disappears). i used a 150k revlog poti for the peak, wired backwards.
what´s bothering me: is it normal that the "up" mode needs much more gain than the "down" mode to work ?
and second: the rx...i use 6.8k at the moment, isn´t that a bit odd ? also, the sweep is very long, is that normal too ?
i wired it the "original" non-true-bypass way, and i wonder about the overall output volume, it seems a little low to me in the working settings. the successful builders (and users), did you opt for a different bypass scheme ? i know at pisotones they use true bypass with a volume pot, anybody else tried this (i dunno if i got it right with my spanish...) ?

cheers,
lowstar

[lowstar]

some updates -
i ended up with 20k for rx
from how it sounds like, i think the effect works alright. but the bypassing issue is bothering me...
i tried the pisotones idea of putting a trim- or normal pot behind the effect to be able to adjust the output
...BUT...
i start out with less than unity gain, so adjusting this way won´t work !
did i mess up somewhere ? i´ve read that the neutron always puts out more than unity...
if i crank up the gain knob, the effect doesn´t sound right.

btw, any neutron builders out there that used NSL32 ? what resistor value did you use

cheers,
lowstar

[lowstar]

update - at the moment, my rx is 51k
as i saw from nosamiam´s post, there actually are some people that will answer neutron posts
so i give it another try

cheers,
lowstar

[Manolo Dudes]

what´s bothering me: is it normal that the "up" mode needs much more gain than the "down" mode to work ?

Thanks for citing pisotones.com 

Read the original documentation in pisotones.com. In page one they talk about that phenomenon. It's inherent to the Mu-Tron III design.

[Mark Hammer]

The sense that sweeping downward does not provide the same feel as sweeping upwards is inherent to a lot of designs, not just the Mutron III (people who have implemented the up/down sweep in the A-Gua will notice this too).  Why?

Consider that the amount of high frequency content (the harmonics) in a plucked note changes over time.  This is very different than what a synthesizer oscillator (what ECFs were intended to mimic way back when) produces, which is constant harmonic content.  The most harmonics produced occur at the start of the plucked note (the diligent can go read about the Karplus-Strong algorithms), and very quickly afterwards, it is mostly lower-order harmonics which linger a while.  The sound you hear from any envelope-controlled filter is going to be a combination of what is taken away by electronic filtering, plus what is taken away by the naturally-occurring dropoff in middle and upper harmonics as the string,s stiffness overrides the energy the player has momentarily injected into the string.

When the filter sweeps upwards, whether bandpass or lowpass, what you will hear are the traces of that quick burst of harmonics you manage to catch before they fade out (and a few milliseconds can make a big difference), followed by the combination of "natural filtering" from the string, and whatever is left for the electronic filter to remove.  Those with a filter whose sweep decays quickly will sense a greater filtering action, and that's partly because there can be still some harmonic content left over for a wee bit, and if the filter starts to sweep back down to its starting point quickly, it can sometimes do so fast enough to "catch" some of this leftover high end and filter it out.  In a sense you hear the filter doing more work because there is still work left to do at that point. Wait long enough, it will feel like the filter is doing less because there is not as much filtering that CAN be done.  At the same time, our nervous systems notice how much is doen per unit of time - how much change there is - and detect more change per unit of time as somehow more "intense".

Okay, let's switch to the downward sweep scenario.  If we start the sweep a few milliseconds in, we are catching the last vestiges of the initial attack transients, but rather than sweeping higher to catch what little is still left, it's like the filter is simply shoving all the harmonics in a closet and locking the door immediately, as if mom was coming over to the apartment and all the dirty clothes, pizza boxes and porn had to be quickly hidden from view.  As the filter continues to sweep downward, it  cuts out most of the mids and highs, and as it starts to sweep back to the starting point, there will now be much less treble content to re-introduce.  As a result, the downward sweep will feel uncomfortably asymmetrical, like it was too fast on the initial downsweep and too slow on the upward return.  The pleasingly vocal quality of the upward sweep will be missing, and if not compensated in some manner, the downward sweep will feel clumsy and slightly unmusical.

The point here is that the timing and electronic properties of the filter are being applied against a signal whose properties change over time, and whose tonal quality will depend on how well matched the filter/sweep properties are to the signal at that point in time.  Personally, I find I want the downward sweep to start a little down from the highest possible point, have a slightly delayed attack, and sweep back up again faster than it might normally. 

The Mutron has a means of adjusting the starting point of the sweep in downward mode, but no real way to independently set time constants for up vs down sweeps.  Some of the envelope generators that Steve Giles has graciously contributed borrow heavily from the E-H Microsynth and provide a known start and end point of the sweep plus an adjustable stagger between them so that larger and shorter travels can be configured.  Sadly, these are fixed envelopes from what I understand, and not dynamically adjustable by one's playing.

[puretube]

you can choose the "start" frequency (fmax, in this "down"-case) with the E-H Tube Zipper.
The "stop" freq. (~depth...) will depend on how hard you slam, and the "sensitivity" setting.

[Mark Hammer]

You're a filter-lovin' kind of guy.  I'm curious about your view on whether the time constants needed for upward and downward sweep ought to be different.

[puretube]

the "original" TZ (the "Tube-Tron" (R) ),
had an extra "Depth" control, that would set the maximum deviation from the start frequency;
now depending on the picking strength and the sensitivity setting,
you had a variable (attack-)time constant at your right (picking) hand.