general chorus mods

[keith71]

I own a Deep Blue chorus from Rocktron, it's an analog chorus not bad at all, but I find it to be a little thin sounding, I mean that it enhance upper frequencies more than low and mids. That said, I replace the input cap for larger value, and it give me back some off the bass, but I want to go further.

My feeling, correct me if I'm wrong, is that every analog chorus are "variation on the same theme", in mine there are some caps, resistors and jrc4558 and MN3202 (or something like that)...Consequently, my idea is that I can make my chorus thicker by changing a few caps or resistors, but I don't know wich ones. Could someone here help me to find them ?

[keith71]

up

[Mark Hammer]

The delay-time range of any delay-based pedal that uses a Matsushita chipset (MN3007/MN3101, MN3207/MN3102, etc.) is partly set by a small value (<1nf) capacitor that will be sitting right next to the MN3101 or 3102.  If  you make it larger in value, this will increase the delay time proportionately.  So, if hypothetically the current delay range is 5-12msec and the cap value is  150pf, changing it to 220pf will increase delay time by 47%, shifting the delay to 7.3msec to 17.6msec.  Once you move out towards 15msec and up, it starts to sound a little more like Pat Metheny.  Is that the kind of "thickness" you want?

[keith71]

Thanks dear helper,
I don't really know what you mean by "pat metheny chorus", but I can describe what I'm looking for :
The rocktron chorus seems to apply its modulation to the upper frequencies, and then lets the bass "unchorused", a least that's what I'm hearing...it's a very subtle chorus. But from what I'm hearing on records (think andy summer) a boss chorus sounds fuller, applying modulation to the hole spectrum, and that's the sound I'm after.
I could get rid of my rocktron pedal, buit I think it is a good place to start with some mods, since there is thi matsushita chipstet inside.
Right now I will try your suggestion and give you some feedback.
Thanks again for sharing great knowledge !

[H.Manback]

The delay-time range of any delay-based pedal that uses a Matsushita chipset (MN3007/MN3101, MN3207/MN3102, etc.) is partly set by a small value (<1nf) capacitor that will be sitting right next to the MN3101 or 3102.  If  you make it larger in value, this will increase the delay time proportionately.  So, if hypothetically the current delay range is 5-12msec and the cap value is  150pf, changing it to 220pf will increase delay time by 47%, shifting the delay to 7.3msec to 17.6msec.  Once you move out towards 15msec and up, it starts to sound a little more like Pat Metheny.  Is that the kind of "thickness" you want?

Yeah I agree completely, very useful mod. One thing you have to keep in mind though is that the noise does get worse with a bigger cap (at least that was my experience).

Also be careful to implement it in such a way that it does not pop. I did it the wrong way, using a 6 way rotary switch and just switching capacitors with it, which of course produces pops.

What you could do is just place 6 caps in series and switch the point where you bypass caps (so bypass for example 4, 5 or 2). I don't know if that has any other drawbacks though.

[Mark Hammer]

Unless they have some special reason to do it differently, when it comes to BBD-based effects most companies will aim for the most bandwidth they can afford with the clock range they have selected.  So, hypothetically, if the clock never gets slower than 15khz, many companies will consider it "safe" to try and get something like 5khz bandwidth from the delay chip (remember that a 5khz corner frequency on the lowpass filters still lets a tiny little bit of higher frequency content through).

I mention this because if one increases the delay time a bit by changing the clock cap beside the MN3101/3102, it is possible that the slower clock rate will still be acceptably filtered by the onboard filters, but it is also possible that the existing lowpass filtering will be set too high and the clock becomes annoyingly audible.  If the chorus has built in companding, then I imagine it would be more tolerant of bigger changes in the delay range, but in any event one should not aim for too drastic a shift in delay range unles the filtering can be guaranteed to keep out the clock noise.

By "Pat Metheny" I was just trying to find a point of reference.  What I mean is a chorus sound that starts to approach a double-tracking sound.  Some describe this as "thicker" sounding.

I find it ironic that you comploain of the lack of bass.  Some players, myself included, often find that there is TOO much bass in the delay signal.  This has a few consequences.  One is that the higher amplitude bass signal can distort the delay chip if no companding is used.  Another is that the chorus sounds more "wobbly".  And another is that the chorus  sounds too "box-ey".  Of course the extent of these problems, or rather the extent of the improvements provided by shaving off bass end would depend on where and how it is done.  For instance, if I insert highpass filtering AFTER the BBD, that does nothing to reduce unpleasant distortion by bass frequencies in the BBD itself.  The "wobbly" quality I described comes from the pitch changes produced by the time delay speeding up and slowing down.  The longer the delay time, the more obvious (and annoying) such changes become.  If one reduces the bass content in the delay signal so that the fundamental is not quite as loud, the pitch changes become much less annoying.  But again, that is only an improvement if the delay range made the pitch changes annoying to start with, and if the highpass filtering goes up high enough to reduce the amplitude of the fundamental significantly.  Even a 4-pole highpass filter would do little to alleviate the problem if set to 100hz.