Diy Chorus suggestions?

[Mark Hammer]

A.S.P.'s right.  There may well only be 14 pins of any interest but that doesn't mean the manufacturer can't stick some "spares" in there just to mess with our heads and layouts.  CD4049 is a 16-pin beast.

Can you use the MN3008/TDA2108?  Several answers to this.

1) Depends on the pinout.  There are "big" versions of the 3008 and small ones.  From what I gather, there is an 8-pin BL3208 which has the same everything else as a big (14-pin) BL3208 and MN3208, without the six NC pins.  I do not know of any such equivalent for the older MN3008.  I am not familiar with the TDA2108.

2) Just because the pins do not line up well enough to shove a different chip in the socket does not mean it can't be used.  There are a variety of retrofit techniques (dead bug, duaghterboard, etc.) that are a bit more work but allow substitution of chips with different pinouts.

3) Although, in some sense, a BBD is a BBD is a BBD, the same cannot be said for the relationship between time delay and desired effect.  Chorus and flanging each require use/production of a specific time delay range.  If you want to maintain the same time delay range, changing the number of stages requires changing the rate at which the clock steps through them.  If you double the number of stages (from 1024 in an MN3007 to 2048 in an MN3008), you will need to double the clock rate to make sure it takes the same amount of time to go from the input to the output of the BBD.  In this case (Small Clone), that means dropping the value of the 150pf cap to 75pf, or as close to it as you can get.

You can still get chorussing with the 150pf cap but it will not sound exactly the same.  You will also find that only a smal portion of the depth control will be usable.  The reason is that as delay time increases, the amount of pitch change in the delay signal gets VERY noticeable and you end up turning depth way down.

[birt]

so the only thing i have to do is make it fit (its a bit bigger), watch the pinout and every cap on the rotaryswitch should be half the value i would normally use with the mn3007?

(tda2108 should be identical to mn3008)

[Mark Hammer]

I'm losing track here.  WHAT rotary switch?  As far as I'm concerned, the only component you would need to change if replacing the MN3007 with an MN3008 would be that specific cap, and no more.

[birt]

if i'm not mistaking that's the cap wich is replaced by a rotary switch with some different caps in moosapotamus' wavy gravy. i want to do that mod too you see.

[Mark Hammer]

Okay.  Now I see.

The clock rate/range varies as a liear function of the cap being discussed.  So, in Charlie's version, he replaced 150pf with 33pf (border between flanging and chorus), 100pf (a little less thick than original, 180pf (a touch thicker than original), and 330pf (a little over double the original delay range).

In your case (using a BBD with twice the number of stages), a 150pf cap is roughly equal to using 300pf with a 1024-stage BBD.  So, to approximate Charlie's delay ranges, you would want 90pf, 50pf, and 16pf.

Charlie notes the expected popping from switching parallel caps in and out.  You could consider using series caps and use the rotary switch to "tap" a series of caps.  Note that the combined capacitance of series caps is given by the formula 1/C = 1/Ca + 1/Cb +..... 1/Cn.  So, if you had three 150pf caps in series, their combined capacitance would be 50pf.  If you bridged/shunted one of those caps so that there were only two in series, they would have a combined capacitance of 75 pf.  And if you shunted/bridged two of them, you would of course have 150pf.  You could easily do this with a 3-position (centre-off) toggle switch.  Common goes to the end of the chain.  One outside switch lug goes to the junction between the first two caps, and the other outside lug goes to the junction between the last two caps.  That'll give you 3 pop-free ranges.

[Fp-www.Tonepad.com]

That info is in page 2 of the Small Clone (Heladito) project PDF at tonepad:

http://www.tonepad.com/project.asp?id=8

Fp

[birt]

That info is in page 2 of the Small Clone (Heladito) project PDF at tonepad:

http://www.tonepad.com/project.asp?id=8

Fp

wich i already noticed, tnx

also the tonepad lay-out uses a 10k depth pot instead of a switch. but i also read the build reports and it also says a lot of people used a 100k pot a lttle further in the circuit. i suppose they don't use a 10k pot like the tonepad version nor a switch?

[birt]

and i DID find a substituete for the MN3007!

The TDA2107 is identical and is about half the price of the MN3007

[moosapotamus]

...you didn't use the extra pcb for the stereo mod as described in the tonepad pdf but just an spst switch right? with output 2 connected right before the circuit cut?

... yes, on the clean side. I made the second output a clean, unaffected output. The result is kind of pseudo-stereo. I think it sounds pretty good. But, you might be able to notice in the stereo clips on my site that one side (I forget if it's the left or the right) is not really modulating.

~ Charlie

[Mobisimo]

Little OT now, but is there a verified project for the Boss CE-1?  I've been pretty interested in that for a while.

[Mark Hammer]

No, but a buddy of mine makes a very nice clone of it in a 1590BB chassis.  You can see discussion of it here: http://thegearpage.net/board/showthread.php?s=98429649ff17400196bc5934a20d10bc&threadid=79026

and sales blurb about it here: http://www.musictoyz.com/guitar/pedals/retro.php

I was never a huge fan of the CE-1, but for what it does, this captures it nicely.  Tim is always working on improvements to it, but the core of it remains.

[Fp-www.Tonepad.com]

Nice pedals!

And, FYI, www.homebrewelectronics.com is coming up with a modified small clone chorus pedal. Worth checking out too. (Based on my layout, under license) 

Fp

[Mobisimo]

Ag! Another pedal I'm tempted to spend $200+ dollars on.  Oh dear...

[RickL]

First things first:

where do you guys find 4049 in a DIP14

I meant the 4047.

Second, it works! 

I didn't even have to adjust the trimmers. Mid point seems to work pretty well for both of them and the bias trim has a fairly big sweet spot.

The one thing that is a little weird is that if I turn the Depth pot up more than about half way I get a ticking sound in time with the clock. Also from this point up the Depth pot seems to act almost like a symetry control. The pitch shifting occurs over a smaller and smaller part of the sweep as the control is turned up. I tried increasing both c19 and c21 as high as 10uF with only a slight difference in sound. I suppose I could replace the Depth pot with a 50k pot and 47k resistor but it would be nice to get it working correctly.

With the Depth pot below half way it sounds great. Wonderful deep vibrato, thick chorus and phasey sounding vibraflange. Very wide range on the speed control - I love speed controls that go to almost ring mod speeds.

I'll have to try the new layout too, I admit it was a bit of a pain tracking down a 15 volt wall wart.

[RickL]

Update - problem solved, it was the FET.

I didn't have a 2N4302 or 2N5458 when I built it so I subbed a 2SK117 which is listed as a sub for 2N5458. I've since tried several other FETs and MPF102 seems to be the best of what I've got. I still get some asymetry in the sweep at maximum depth but less than with the 2SK117 and no clicking. Other FETs also solved the clicking problem but didn't give enough depth.

Next time I order from Small Bear I've get the proper transistor but until then I'm happy with what I've got, in fact I rather like the asymetry at the extreme setting.

Rick

[H.Manback]

I've built one myself, and sometime ago on this forum I think I posted something about the depth pot as well. Basically it boils down to this, the 100k pot was a typo or something and the correct value is a 10k pot. If you look at the original resistors you will see that that makes more sense.

That said, the depth pot works fine. One thing you may or may not consider is putting a 1k between the pot and ground so you limit the range to exclude a flat signal which comes down to no LFO. Without it you just get a very short delay if I understand correctly.

It's a nice effect by the way, and I still have to box it (I think I finished building it about a year ago or something in that area...)