Some of the worst soldering you'll ever see = Roland TR77 / Bentley Rhythm Ace

[Circuitbenders]

This is some of the worst soldering i've ever seen, and as you can imagine thats up against some pretty stiff competition!

The pictures are from a Bentley Rhythm Ace drum machine made in about 1972. In fact its exactly the same unit that went on to become the Roland TR77, the very first thing to ever bear the Roland name.

Most of the soldering on this thing is atrociously bad with endless fractured dry joints along with abscesses and bubbles in the solder. God knows what flux they were using in this thing but it bubbles like boiling water when you heat it. Those black marks on the solder joints are in fact bubble holes. Against all the odds about 90% of the connections still work but i think i might reflow everything anyway.

And i though some of the soldering you get on modern chinese crap was bad.  

[selfpreservation]

its not his fault hes been buying solder form maplin again 

[electoyd]

Even Maplins solder does a better job than that  suddenly i feel quite good about my soldering skills, i've never seen solder 'grapes' as big as those though on a machine before, quite hard to believe it's professional.

What you got planned for it Paul, you doing that for someone else i take it?

[Circuitbenders]

I'm adding Midi triggering to this Bentley Rhythm Ace, but i also own a very battered TR77 that i hadn't realised was the same thing until this Rhythm Ace turned up. It appears to be virtually identical, apart from the Rhythm Ace doesn't have the Tamborine sound, which is odd as theres spaces and board marking for the tamborine circuitry on the synth board.

I'm hoping to put together some kind of guide to installing Midi triggering on these things when i've got it working as its a bit of a bitch. For a start they want -5v to -12v  negative trigger pulses, which aren't much fun to generate when theres no negative power rail in there. Theres also no regulation on the positive power rail so its absurdly wobbly.

Check out the size of the 1000uf dual power smoothing cap i pulled out of the power supply compared to the modern equivalent! 

In the end i went for something a bit better as the power line wobble was just ridiculous.

[Simon Vactrol]

it doesn'teven  look like solderind iron..is more like melted alluminium foil!!!  lol!!

[electoyd]

I've seen some stuff on the burnkit site about the tr77 and the negative triggering seems like quite a bit of hassle, but if you can figure it out then thats good.  They are big fuckers of machines yeah, what do they sound like, is there an analogue monster waiting to get out?

[Circuitbenders]

Well mostly they sound like a shitload of hum and background noise! Theres loads of big inductors used in LC circuits (http://en.wikipedia.org/wiki/LC_circuit) to create the drum tones and they pickup an amplify the slightest interference or hum. For some reason even my metal work bench was causing extra hum.

It doesn't look like theres that much in the way of mods possible, but i've been mostly working on getting the triggering sorted.

theres a load of information and demo videos of a TR77 here http://www.adambaby.com/studiotech_TR-77.html

[Circuitbenders]

The lengths you have to go to just to trigger some rhumba action! 

This is the +5v trigger to -12v spike convertor for every sound i've had to build for this this. Don't even mention the feckin Guiro, oh god how i have come to hate the Guiro...............

[selfpreservation]

awesome

[Circuitbenders]

Got a page up about how to do this http://www.circuitbenders.co.uk/newsarchive/BRA.html

[selfpreservation]

i love it , i have a korg 700 that needs a 0-12 v range for the filter cv control i know its a trigger but could any of this info be used to build a circuit that takes a standard kenton 5v range and map it to a 12v range
heres a pic cause shes awesome  , i did cykongs cvmods and its had oak panels and snakeskin facia these are seriously underratted synths

[Circuitbenders]

you can use a simple op-amp circuit to amplify 0-5v to 0-12v. I did the same thing on a Korg Micro-Preset a while back.

[selfpreservation]

you can use a simple op-amp circuit to amplify 0-5v to 0-12v. I did the same thing on a Korg Micro-Preset a while back.

any more details on how to execute this would be most helpful ie schema diagrams ect

[Circuitbenders]

Sorry, i didn't draw one, but take a look at the 'op-amps as amplifiers' section on this page http://www.bcae1.com/opamp.htm

[selfpreservation]

so if i build this circuit with these values it will amplify my 5v kenton to 12v ?


sorry for being dumb but i have a couple of questions
do i need to consider the 100ohm resistor on the input i? and what is its purpose , smoothing? and if so how does it affect the values of the resistors on the neg required ?
what happens at low values ie when my kenton is outputing .5v the op amp value will be 1.2v does this mean the filter wont close (well odviously it will close at zero value but i mean when its approaching  zero) im guessing cause its in ratio with the input it will be fine
can you recommend an opamp to use ? the 700 contains hp/lp filters so i can use a dual opamp and build 2 identical circuits the psu  is -15 +15v  this looks like it would work and its available from maplin http://www.national.com/mpf/LM/LM358.html