Help building an old(?) FX it seems it's called minisynth

[arma61]

Hi all

I've found an old schematic

[img=http://img204.imageshack.us/img204/3551/minisynthlq5.th.png]

(is it clear enough?)

I hope I'm not breaking copyright as I don't know where it cames from

The Fx will produces 3 sounds :
1st sound - the base one played by the guitar
2nd sound - 1 octave lower
3rd sound - 2 octave lower

the 3 pots will mix these  sounds

I've already build 2 prototipes of it with different layouts (on PCB), and it works almost fine but there's a problem with decay/sustain. It seems that the SAJ110 is working fine as I have the 3 sounds (playing high E string (E cantino?) and with clean sound to 0 and -1 octave also to 0 it sound like a bass!!).
But I'm getting this decay/sustain problem, so after a while (as soon as string vibration start to decrease) the FX sounds disapear and I can only hear a distorted/dirty sound of the guitar string. So it seems the problem I have is to be found in the first section of the schematic, before the signal enters in the IC.
FoxFire thinks about a bias issue, but I don't know very much what's he's talking about. I've used 2n914 in one PCB and (I'm not sure) 2n5457 in another one instead of BC239 (cannot find them in Italy, I know Banzaieffect have them but too expensive for an "experiment"!).

Just to point out the problem is absolutely the same on the 2 PCB.

May be someone of you can, looking at the schematic, understand what the problem could be, I thought also I may need to amplify the guitar signal before the FX.

thx for help, and forgive my english,
Armando

[theehman]

The schematic is kind of small and hard to read.  Can you post a bigger pic?

[oskar]

The original transistors are supposed to be bc239, right?
These have much bigger amplification than the ones you've got in there.
Just swap Q 1-3 to something stronger.

[GREEN FUZ]

It seems that when the signal falls below a certain level it`s no longer triggering the effect. It might just be in the nature of the circuit or perhaps changing some resistor values might help. The schematic isn`t too clear so I can`t really help anymore than that.

[oskar]

The original transistors are supposed to be bc239, right?
These have much bigger amplification than the ones you've got in there.
Just swap Q 1-3 to something stronger.

PS... This will extend the sustain alot but you're going to have the same decayproblem when the guitar signal fades away.
The thing you've got is something like
http://topopiccione.atspace.com/pjimages/ShinEiOctave.sch.jpg
But with an integrated divider instead of a discrete solution.
You should redo it with a 4013 chip instead of an obsolete chip, especially if you plan on
putting the thing on the net.

Check out Craig Andertons
http://www.amazon.com/Do-Yourself-Projects-Guitarists-Inexpensive/dp/087930359X/ref=sip_rec_dp_6/104-0408657-1931908
which presents...
http://hammer.ampage.org/files/rocktave.pdf
which solves the problem with decay.

[arma61]

thx to all for advertise/suggestions

here is a link to a different picture of the schematic, hope it's good enough (may be now it's too big!)



by the way I heard it working years ago (late '70s early '80) so it would be nice to reproduce a kind of FX.

thx oskar for those links, very useful, specially when talks about how hard/soft you play a string. May be to let this FX working I should also find a different way to play the guitar. any suggestion for new Q1 and Q3.

[GREEN FUZ]

As the chip you are using was originally intended for frequency dividing in old organs, is it possible that they are not designed to work below a certain frequency/level. As organs have a fixed level of velocity this wouldn`t have been an issue.

Just a thought.

[Paul Perry (Frostwave)]

I don't believe it will ever work as well as you would hope.
Because, it works by using the amplifying stages to square up the input signal, so it can trigger the divider chip.. so the signal needs to be high enough to do that, but if it is TOO high, then harmonics and noise will trigger the divider as well.
I'd try putting a compressor before it, and mixing some of the original guitar with the output.
I don't think there is anything wrong with the divider, just suprised you could find any!

[slacker]

I think the SAJ110 is similar to a CD4024, if so it needs a good loud signal to drive it, a squarewave works best. Once the signal drops below a certain voltage the chip stops triggering.
If you haven't already seen it my Slacktave design is a similar effect, but using a CD4024. You could try using the first 3 opamp stages off my design as they give a good strong squarewave with decent sustain. 

[alex frias]

I CAN'T BELIEVE!!!

Are you guys talking about this little beast?





I love this thing, It sports a bell clip design.
I use it in the loop of my McMeat (MeatBalls autofilter clone) and it mimics a very strong analog synth. Big and fat!
I built a MXR BlueBox, but the "tracking" is not that good.

Nothing beats this DIYstompboxes forum.
Any questions regarding it, pics, sounds, please, feel free for asking!
If I may be of any help I would be happy to do it.

[GREEN FUZ]

Looks interesting. It`s the same chip alright. I`d love to hear a clip of it. Does it exhibit the cutoff problem that arma61 was talking about?

[Jaicen_solo]

I can't see the pics or anything, this is frustrating! If it's the one with the article that talks about whistling into it or something, i'd be very interested to hear a sound sample of it. In fact, can we hear some anyway? Anything synth'y is good by me!

[oskar]

1.by the way I heard it working years ago (late '70s early '80) so it would be nice to reproduce a kind of FX...

2.May be to let this FX working I should also find a different way to play the guitar.

3. any suggestion for new Q1 and Q3.

1. Well a squarewave is a squarewave is a square...     Basically it's a digital effect actually,
and so is the bluebox. All that matters in these type of effects is.
Filter away them overtones, amplify like a madman, amplify some more, go schmitttrigger, drive a digital chip (not just a
frequency divider try the complete 4000- cmos series. You can make a simple ringmodulator by an XOR gate or divide it with
a 4017 to give it a non-octave subwave. go wild man!!!)
The actual chip you use to achieve the result is completely unimportant. You shouldn't bye expensive ones...

2. Yes, that's what I found out to. Heavy string action, legato style and don't wait for the decay to happen.

3. Whatever is stronger. BC549...

Oh, it's fashionably uggly to, just keeps getting better!!!!     

[oskar]

This is an alternative divider for your project. It isn't pin to pin compatible but the chip is available from
just about everywhere and you can use it for a lot of things. I don't know if the subwaves will come out
the correct phase though. If they dont you just swap the outputs to pin 2 and 12. These are inverted
outputs. I've done octave dividers with this one alot. This is the same chip MXR's Bluebox uses.

[Paul Perry (Frostwave)]

I can't see the pics or anything, this is frustrating! If it's the one with the article that talks about whistling into it or something, i'd be very interested to hear a sound sample of it. In fact, can we hear some anyway? Anything synth'y is good by me!

I suspect that you are thinking about the MiniSynth (there was a kit for it that went with the Dick Smith "Funway Into Electronics").

[Jaicen_solo]

Possibly, it's the one on GGG. I've never heard of anyone building it, so I was curious. Doesn't look like tihs is the same beast at all.

[oskar]

Ok. I give myself a high score for optimism and what I recalled as something easy to build just gave me a sleepness night. 
You rather easily end up triggering the divider ( not the Minisynth specifically... I haven't tried that one ) with the overtones which
actually isn't bad at all if you can controll it. Eventually it worked and I'll try the Slacktave too soon I hope.
I think optimally the machine for the job would contain a compressor and a good tracking filter but it actually is rather easy
to have serious fun with even a simple circuit.

ps. I had a live recording with Bootsy Collins with some rather heavy strange noise from the bass on one or two tracks. I actually
ended up with some rather similar noise when I drove the circuit with too strong signal. If the signal hits the roof you'll get a
S***load of overtones and it's more noise/gameboy style that actually someone could enjoy. I didn't... 

[arma61]

nice to see all you guys so interested and helping me to get it working, I would like to post a sound sample but my soundcard stops working yesterday night (brang new Pc bought last saturday!! #@%$@%#$!!!!!!!!!!!)

yes, alex frias, that's the beast I'm talking about, if you look at the first picture posted you can see M3 at the top. just a couple of questions :

can you see which kind of transistors are used in your FX
can you compare the components value in the schematic I've posted with the FX
my SAJ110s are black not red like yours, do you think this could be a problem (different rating, max voltage..)

I'll be on vacation (finally!) for 2 weeks, when back I'll put in place some of your suggestions and post the results,

Keep DIYing

[alex frias]

Well... No IC racism here.
I don't think they are different in anyway... Aside the "Mojo Factor".
"Look, my red one is the real Holy Grail IC of MiniSynthes"

[Dan N]

'Scuse the brief hijack.

Possibly, it's the one on GGG. I've never heard of anyone building it, so I was curious.

I've built a couple. A fun device! This clip used to be on the internet of one trying to keep up with a singer:

http://users.rio.com/senorris/junk/MINIASIA.mp3