Current Lover w/MN3009

[lars]

Well, I've been putting off building the Current Lover, but always wanted to try the circuit out with an MN3009. With the right mods to the circuit, it works incredible! This is as close to "tape flanging" as I've heard in any flanger pedal I've tried. The sweep is very analog, very washed-sounding, exactly what I was looking for. If you manually adjust the rate knob while sound is going through, it almost makes a through zero type effect. Next up is to use a second 3009 in the SND/RTN loop to try to achieve true through zero. Overall this is a very recommended mod.

Here's a list of things I've changed:
First, it's running at a very well regulated 12v.
Omitted R1, R2, R37, R38, R39, R40, C3, C5, D4, D5, Q3, and the volume pot
Changed R4 to 100K, R8 to 6K8, C1 to .1uf, dropped the C12&C13 combo for just one 4.7n, and C18 to 47p
D1 has been changed to a 4148, and D2 to a 1N4001
IC1 has been changed to a 1458
The clock pot has been changed to 20k
Jumpers:
R1 needs to be jumped, as well as C5 (as per the build doc), and put a jumper from the first leg of C22 to the wiper #2 connection of the volume pot pads.
The "clock" trim has been changed to 25k

[chordball]

I'm definitely intrigued here. Can you explain why you made these changes? If it's readily apparent by looking at the schematic just let me know. I admit, I'm being lazy and not looking right now

Do you have a reliable source for the 3009's?

[Scruffie]

I can explain them, the delay time is shortened to about half the originals (shorter delays sound closer to zero which is why the A/DA is so liked as the delay gets very short, that and it's large sweep ratio) if the Current lover VCO can cope with it you could just drop the clock cap to a smaller value with an MN3007. Noise is increased with the LM1458 (I actually don't think this is a bad thing, I think noise is partly what makes the SAD1024 'sound') but the S/N is improved with the 6k8 resistor and MN3009 having slightly better S/N anyway but headroom is a bit reduced, then the boost on the output has been dropped seeing as there's more volume at the input now I assume.

That's about the strength of it.

I don't think you're going to have much luck just popping another BBD in the send/return...

Oh and as always, there is no reliable sources of BBDs apart from suppliers such as smallbear.

[chordball]

Thanks Scruffie! I fully understand the risk in buying BBD's having bought a number of them already. I thought maybe if he had found a decent source for now I would get some while I had a chance.

[lars]

Yeah, I just happened to get some good MN3009s from the bay, but it's very hit and miss so not recommended.

My plan for the SND/RTN option is to make a daughter board with an MN3101 as the clock driver, so I can independently adjust the delay on the second MN3009 to what works best with the circuit. All the mods I've made were simply based off looking at the original schematic for the 2nd edition Electric Mistress (dual 9v version). I wanted to try to achieve that "sound" as close as possible, since those tend to be the most sought after models. Sure enough, the build I have right now can nail those Andy Summers type flange/chorus sounds.

I have noticed that the Bias control may need some reworking. The 100k pot along with that 82k resistor just seems to be too high for an MN3xxx series chip. The BF-2 used an MN3207, and had only a 22k adjustment pot for bias. I've already dropped the 82k resistor and can still adjust the bias correctly, but still with a lot of wasted sweep on the 100k pot (the bias point is very narrow, usually an indication of too high a potentiometer value). I'm going to try a 22k in there just for kicks and get back with my findings.

[Scruffie]

You need a shorter delay than the MN3009 is getting in the main path for proper through zero so a MN3101 isn't going to cut it probably (depending on what frequency range you're sweeping at the moment) you'll need a clock buffer, also, through zero flanging tends to work better with the send/return delay path inverted so you get subtractive rather than additive at the through zero point.

Yeah the bias has been commented on a few times, some people can't get it biased at all with the 82k resistor, i'd actually just jumper the resistor my self...

[lars]

Thanks for the info. I wish I had the proper equipment to know what frequencies I'm operating at right now. It would take a lot of guesswork out of the equation, which is basically all I'm doing right now.

If the 22k bias works, I might even try deleting the bias control altogether . Somehow the original mistress worked without one, and I've seen other projects that didn't have a bias on the BBD as well, like the original schematic for the Zombie Chorus. How did they do that?
Could dropping C4 and adjusting R8 bias the signal correctly on the Current Lover? Just what is the magic voltage on pin 3 that "activates" an MN3xxx series chip? I noticed that when I changed my BF-2 from an MN3207 to an MN3209, I didn't have to adjust anything. So the correct values must be consistent from chip to chip in the MN series. Hmmmmm.....

[Scruffie]

Thanks for the info. I wish I had the proper equipment to know what frequencies I'm operating at right now. It would take a lot of guesswork out of the equation, which is basically all I'm doing right now.

If the 22k bias works, I might even try deleting the bias control altogether . Somehow the original mistress worked without one, and I've seen other projects that didn't have a bias on the BBD as well, like the original schematic for the Zombie Chorus. How did they do that?
Could dropping C4 and adjusting R8 bias the signal correctly on the Current Lover? Just what is the magic voltage on pin 3 that "activates" an MN3xxx series chip? I noticed that when I changed my BF-2 from an MN3207 to an MN3209, I didn't have to adjust anything. So the correct values must be consistent from chip to chip in the MN series. Hmmmmm.....

A frequency counter is all you need, don't need to buy a scope or anything and they can be had for under $25.

In the original mistress BBD bias is set through the opamp bias, as it is in the zombie chorus, although the mistress bias was adjustable where as the zombie has a fixed bias.

Dropping C4 would let the opamp bias the chip but adjusting R8 only affects the gain, you'd have to change the bias on the non-inverting input which isn't ideal as the opamp and BBD probably have different bias points, sure you can get away with it, but it's not optimal.

Biasing isn't just about getting the chip in the working range (which is in the ball park of half supply, there's charts in the datasheets) what you're missing is that while yes, a BBD in a 9V circuit probably does work over a, say, 20% range of the bias trimmer, it's the optimal bias that we aim for. If you looked on a scope while performing the factory set up procedure while those 2 chips swapped happily and worked, the output may not have had (and probably didn't have) the least possible clipping which proper biasing would achieve.

For those without scopes though, it does give the option to tweak the trimmer by ear for what they find is best, the effect is more noticeable with higher output pickups when the BBD clips.

[lars]

Very interesting stuff. I have many things to try out. I'll either end up with something really good, or  a couple of dead BBDs

*Well, i went ahead and dropped the bias control entirely along with C4, and sure enough, it works! It turns out that I'm getting 5.85v off pin 7 on my 1458, which is almost exactly half my supply voltage of 11.88v, right around where an MN3xxx series chip is supposed to be. Turns out the bias voltage for the op-amp is already set to the right 1/2 supply voltage range off of pin 1 of the LM324.

*1/8/15 - Something I didn't really take into account was clock pin capacitance. On an MN3007, it's around 700pf, much higher than an SAD1024, which is why a buffer is necessary in the original Current Lover design. I didn't consider that on an MN3009, the clock pin capacitance is much lower than an MN3007, basically 1/3 of it. The circuit works great without the CD4049 buffer! Yet another reason the MN3009 is very well-suited for the original Electric Mistress circuit. It requires much less modification to the original design, and can achieve those short, unbuffered delay times.

[JC103]

I know this is an old post but I am curious if you used the 2015 current lover or the older 4 knob version of the pcb?