Bontempi Memoplay

[untune]

Hi all,

I should be getting a Bontempi Memoplay in the next few days, and I've seen a few on Youtube and the like - other than that, there's not a lot documented online about bends or mods.  Since I've read that it's analogue, I'm interested in adding a few modifications to make the sound a little bit more interesting (not looking for noise, but musically useful modifications.)

So I've been thinking about the possibility of adding little additional 'modules' - LFO, vibrato, tremolo, filters etc - to the circuit, as well as line out and the usual.

Does anyone have any experience with this unit, or any advice on exactly how to implement such features?  It's been a while since I've messed inside anything electronic, apart from building a little buffer circuit a few months back.  I'm ok at piecing a circuit together from instruction/diagrams, but designing them is something i can't do

Are there any sources where I could buy semi assembled modules that would fit in *relatively* painlessly?

Cheers

[electoyd]

you could try a 555 lfo from get lo fi they are simple circuits, easy to put together and cheap, pretty easy to knock together a basic filter as well.

[untune]

Hi,

Cheers for the reply.  I've had a look into a few of those circuits, they seem good.  Where do you have to put them in order to modulate the volume/pitch etc?  Also, can these be powered from the battery of the keyboard itself rather than having an additional power source?  I've not had much luck finding simple filters or kits

Cheers

[Gordonjcp]

You'll need to track down somewhere to connect them up to control pitch and volume.  As for filters, it depends how simple you want.  If you want a very simple "tone control" then it's just a resistor and a capacitor.  If you want a proper resonant filter then it is necessarily a bit more complicated.

[untune]

Hi,

Cheers for the info

I'll have to wait until I get the uni itself so I can open it up and poke about on the board.  The innards are supposed to be fairly simple, with a huge amount of space inside the case.  To me, it looks almost as if it was made to be expanded

How difficult would it be to add an additional oscillator circuit to be triggered by the keyboard/mixed with the original tone?

I know that I want to put an LFO or two in, and I was thinking of maybe a highpass, lowpass and a tuneable bandpass (got a schematic from the Forrest Mims/Radio Shack notebooks).  Some kind of ADSR would be ace, but that might be out of the question.  I've also pondered modding one of the Maplin/Velleman running LED kits as a simple sequencer.  A delay circuit based off a PT2399 could add some depth too.  Any other ideas?

[untune]

Well I got it...  half the keyboard doesn't work and some of the traces are corroded.  Looks like a spillage, inside was filthy.  I'm still going to keep it, gonna try and get a bit of money back though!

I went over the board and took a load of pics anyway.  This thing is so easy to open up!  I saw a little mark on the board that says 'CS' with an arrow pointing to a single point, anybody any idea what that is?  I've put a pic up so you can see.  I've marked it on the component side as it's not visible on the pic I took of the other side.

http://yfrog.com/5dcomponentsidecomposite3j

[Gordonjcp]

I've no idea what that is.  Looks interesting, though.  The corrosion can probably be cleaned up and linked across if you're really careful.

What's the number on the big Nat Semi chip beside the 4011?

[untune]

Hi

Yeah I was thinking that, I tried to clean a lot of it up last night but to no avail.  The wires make contact with a crossbar when pressed, the ones towards the right of the picture seem to work ok (with the exception of one or two - even on some of the wires that share a bar, one might work and yet the other doesn't.)  Any ideas on how to restore it?

All I did was go over the traces with a rubber.  Might of messed one or two up though.

The NS chip is socketed, and reads S/B8404, and 27430500.  I couldn't find any info on that one.

[Gordonjcp]

Scrape or sand off the varnish - fine wet'n'dry is good for this.  Take photographs before you start, though, because you can lose sight of where the traces are supposed to go.  Now solder wire across the broken ends of each track - if you find you've got a blob of corrosion at each end then you can link out the bit in the middle, if it's convenient to do so and the track doesn't go anywhere else in between.

8404 sounds like a date code, does mid-80s sound about right?   It's quite possibly some custom part.

[untune]

It could well be a date.  I seem to remember 1981 being associated with this particular model, so it very well could be from '84.

I'm curious as to where exactly the sound is generated.  The memoplay has a pretty useless record/playback function and some pre-stored songs (that I can't trigger because they're all assigned to the lower keys!) so I assume the big mystery IC is responsible!

[untune]

I was just outbid on one of these at the last minute by 50p, so now I'm just stuck with a dead one

Serves me right for playing my bass when I should be watching an auction...

[Gordonjcp]

I wonder if the big mystery IC is some flavour of TMS1000 microcontroller?  I seem to recall they had a version which implemented a simple monophonic "organ" with a few tunes and a way to record notes in.

[Circuitbenders]

dammit! i was looking up the datasheet for the TMS1000 the a few weeks back but have no recollection of what it was in.

Thats really going to bug me now..............

[Gordonjcp]

I've got a copy of Hobby Electronics with a toy organ based on the chip somewhere.  If I'm snowed in tomorrow I'll get round to scanning them.

[General-Calisti]

First post, hello!

Considered starting a new thread but there was this thread about the Memoplay already so yeah, y'know, not adding to the clutter or whatever

Just finished some experiments on a Memoplay, i got it with the express idea of trying to bend it into a weird bass-synth, get my dub on and stuff.
I'm very new to this bending business so i just did some pretty easy stuff:
added a line out, put a (clumsy) volume control to it since this thing is LOUD!!! Switched out the 10k tuning trim-pot for a 100k and a 500k in series (fine and coarse pitch adjustment kinda), it goes low and sounds really thick.

I also whipped together a LFO (proto-board version of the one from Casper that is for a S&S) that piggybacks on the batteries and connects to the circuit after the pitch control. I put a 2-pole switch so i can turn it on and off (kills both the + and -).

Anyway, fun to mess with and all but a problem/quirk also developed:
When i turn the pitch down to really crunchy levels it starts to wobble and fluctuate in pitch, is this because the cap takes longer to charge now that it's getting fed a lot less juice? I was hoping to find a way to make it more stable, maybe replace the cap for another value? Higher? Lower? Any thoughts?

Turning on the LFO circuit raises the pitch an octave or so, i'm guessing that's because it adds voltage to the circuit after the pitch controls, i tried hooking it up before the pitch controls but it was barely audible, i'll try some variations on the theme...

EDIT-

Runs on a variable wall wart now, thinking i should chop the battery compartment away, make room for cupcakes and tuna.