Showing posts with label DIY. Show all posts
Showing posts with label DIY. Show all posts

Sunday, 25 January 2015

Korg SR-120 (Mini Pops 120) Drum Machine.

The Korg SR-120 came out in 1976.
In that same year Korg also produced the Mini Pops MP120, the Mini Pops MP35  & the Mini Pops MP 45 Rhythm Machine.
The SR-120 is identical to the MP-120. This was the final drum which Korg produced under the mini pops label.... and was supposed to be their best. It has all the bells and whistles.


She boasted 6 sounds (BD, SD, Cy/HH, low conga, high conga, claves) and 16 presets (slow rock, swing, bossa nova, beguine, rumba, mambo, samba, waltz, tango, polka, foxtrot, march, rock 1 to 4).
making 32 patterns.
The sounds esp the Kick are awesome.

The Korg 120W

This version has a wood case, but they also came covered with tolex.
The cube shape also seems to be catching on both with Roland & Korg. Roland's CR78 is just two years away.

Korg, in addition to the tolex version, re-branded these as Univox SR-120s which came in a road case with lid & handle (the 120-P).
 https://www.youtube.com/watch?v=bb9n2PhmfCo
Another important point to make about the 120 is its use of a ROM (read only memory) chip to store the patterns. Looks like the identity of the ROM is a AmericanMicro Semiconductor uPD471D

UPD471D

The Roland CR-68 & 78 also followed this trend with ROM chips too.
Earlier machines of both companies used what's called a diode matrix to store the patterns.

The mini pops 120 schematics indicate the use of both a diode matrix and a ROM chip.
The diodes are easy to fix. However replacing a integrated circuit made in 1976 is much trickier, if you can't find a replacement chip.



There are lots of mods for this machine if you can find one that works.
A good place to start is here:
http://www.estecho.com/gear/Korg_Mini-Pops_120.php
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For more info on the history of Korg Drum Machines Click Here

Friday, 23 January 2015

Roland TR 330

Roland TR-330  (late 1972 / early 1973 ??)

This is a bit of an odd one with respect to the name. It's pretty rare too. The TR label belies its roots - it's from the Roland family of Transistor Rhythm Machines.


Did Roland base it on the TR-33 and add a zero - thus TR-330 ??
She probably lies between the TR-77 which came out in 1972 & the TR -66 which was first manufactured in 1973. (It's definitely not as advanced technically as the TR-66 which is why I think it comes before the 66 & after the 77).
And I think it sounds a lot like my TR-77 too.

Take special note of the wooden cube shape. The 330 was the first of Roland's drum machines to take this appearance which would finally evolve into the ground breaking CR-78 in 1978.

There is heaps of bass and great analog percussion - claves etc. There are 8 drum sounds.The Kick is very very good. Reminds me of my TR-808. Lots of bottom end.

The voice board has trimmers (variable resistors) for tuning the oscillator's pitch & resonance....and/or for some very nice distortion. Nice warm & round analog sounds.

The circuit boards & speaker slide out of the wooden sleeve very easily They are held in with just 4 screws on the bottom.
And it has it's own built in speaker which you won't find on any other Roland drum of this vintage.
The speaker isn't of the highest quality but if you like rather cheezy distortion you will love it.

I don't have any service manual or schematic so if anyone out there has one I'd be forever grateful.

The tempo slider is unusual. It displays the tempo both in modern BPMs (40 to 280) and in the traditional classical way ..... in Italian, as was the custom before the invention of the metronome.
The old way is def more romantic. Largo (rather slow; stately), andante (walking speed) & presto (Very fast) are words you rarely see on a drum machine.

There is one "Balancing" knob which sets the volume of the Kick  & Hi hat. It can completely mute the hi-hat or totally remove the kick which I think is very useful.

There are 10 Preset patterns. Waltz, Slow Rock, Rock Beat, Bossa Nova, Mambo, Cha-Cha, Beguine, Rumba, March, Swing.
Size: 9-1/2" wide, 7" high, 12" deep. Weight 10-1/2 lb.



On the rear panel we have a jack for an external amplifier. There is also a jack for a foot-pedal control.

The speaker is on the top. Tempo switch to the left. To the right is the transformer. Careful with this if you open your 330 up. There are high voltages here which can be lethal.

At the bottom is the clock & tempo board. I haven't modded this one yet, but I reckon here is a good place to start looking for that external sync input. Above the tempo PCB is the power regulation board.

This is the underside of the machine. On the right we have the voice board. The left is the pattern board. I haven't opened it up but I understand that its completely made from diodes..... the famous diode matrix where we have a network of intersecting horizontal and vertical buses. All discrete logic. Nice !!!

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For more info on the history of Roland Drum Machines click here

Tuesday, 20 January 2015

TKB build (The Human comparator kit) - Build Part 2

TKB build (The Human comparator kit) - Build Part 2 

***Click here for the Index of the TKB Build ***

I though that before I start building the Human Comparator's TKB kit it would be fun to see what a vintage TKB looks like. I just happen to have one.
This was built by my friend Warren Burt in the late 70's / Early 80's.
And it still works.


The first TKBs also appeared in kit form.
Here are the build instructions care of Ken Stone:
http://www.serge.synth.net/documents/kit/tkb.html

The particular TKB was restored in 2013 by Andrew F of Non-Linear Circuits.



 





OK, now it's time to begin my own build of this Serge classic 
J
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***TKB - Build Index ***
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Monday, 19 January 2015

TKB - Touch Keyboard Sequencer - Build Part 1

TKB Build - Part 1 - Pics of the kit 
The Human Comparator Clone.


*** Click here for the TKB Build Index ***

I've been looking forward to building this so much.
I remember back in the day, the TKB was the Holy Grail of Serge.
I understand these first came out in 1977.
The TKB is a combined touch sensitive keyboard and 16 step analogue sequencer.
What's not to like.

Zthee's website where you can purchase this kit is here:
http://thehumancomparator.net/tkb/ 
And the official build notes of the Human Comparator
http://build.thehumancomparator.net/ 
and Muffs has a thread here:
http://www.muffwiggler.com/forum/viewtopic.php?t=104513

Also, of interest are the original Serge build documents.
More useful links:
http://www.serge-fans.com/wiz_seq.htm
https://www.youtube.com/watch?v=c2jpZuY1lj4
http://www.vintagesynth.com/misc/serge.php
http://en.wikipedia.org/wiki/Serge_synthesizer
And some pics of the inside of a vintage TKB:
http://djjondent.blogspot.com.au/2015/01/tkb-build-human-comparator-kit-build.html


 Thanks to Zthee (THC) for making this kit available.... all the way from Sweden.
.... a land famous for synths.

I love the Japanese theme.



The Unpopulated Faceplate.

Of course you can use it as a normal 4-bank sequencer, but it can do so much more... You can program your own scales for example. There is also a  four-stage vertical sequencer which can step through each of the four layers.... this allows for sequences up to 64 steps.

The MM74C150N - A 16 line to 1 line multiplexer.

This is the main component PCB.(front side)


5 simultaneous outputs


We have 16 capacitive touch-sensitive keys

Let the building begin.

Part 2. Some pics and info of a vintage TKB.
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*** TKB - Build Index ***
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Saturday, 17 January 2015

Bently Rhythm Ace test video

This is a test video of the Bentley Rhythm Ace sync Mod.
Here is my previous post with the mod details:
djjondent.blogspot.com.au/2015/01/bentley-rhythm-ace-fr-8l-roland-tr77.html


The Bentley is almost identical to the Roland TR 77 however its sync input
appears in a different place.



We are testing the drum using a combination of modules: lots of Buchla
for the background sounds but the actual drum is triggered from a Eurorack format Flame Arpeggiator sending +5V clock pulses


Seems to work perfectly. More mods coming soon.



Friday, 16 January 2015

Bentley Rhythm Ace - FR-8L - Roland TR77 - Mods - Adding clock sync

We (Cobramatic & I) purchased some Bentley Rhythm Ace  & TR-77 drums the other day.
Some we got to mod and some to just preserve in their vintage glory.

The TR77 and the Bentley Rhythm Ace are Roland's very first drums so we feel that they have
a special place in the history of electronic music.
They are both beautiful & warm sounding analog (1972) machines with discrete components.
Thus they are perfect candidates for modding.
One of their drawbacks however, is the lack of a way to sync them to our modular gear.
I guess Roland never envisioned that someone 50 years into the future would want to sync them with a modular synthesizer.

BurnKit 2600 has a mod for the Roland version of the Bentley
http://www.burnkit2600.com/tr-77/
that shows where to add external clock sync.
However, after opening the Bentleys we discovered that their PCBs are slightly different to that of the Roland TR 77.

After a bit of probing we located the revised sync input for the Bentley.


 Here is a closer pic:

A +5V clock pulse will do the trick.


If you are game to open your Bentley PLEASE BE CAREFUL.

The Power Supply section to the right is exposed and will KILL YOU if you aren't careful.
If you are not sure leave the mods to a qualified technician.

 The power supply - be very careful !!


The brown PCB on the left is the voice board.... ripe for individual triggers. (a future mod)
The TR -77 uses a very basic circuit to produce the sounds. The circuit consists of just 3 main components : A resistor, a capacitor & a inductor. Called a RLC circuit or "tuned resonant circuit"
The circuit forms a harmonic oscillator for current and will resonate.

Further reading that you may find useful re resonant circuits:  
Inductor-capacitor "tank" circuit
and
Simple parallel (tank circuit) resonance
and
https://www.youtube.com/watch?v=8vu9WDjBAho


The Voice board apparently needs -5 to -12v spikes to trigger the sounds.
CircuitBenders UK has very informative site re this:
http://www.circuitbenders.co.uk/newsarchive/BRA.html

Another great site with TR 77 mods is here:
http://www.adambaby.com/studiotech_TR-77.html

Bently Rhythm Ace test video
The Roland Drum Machine History

Tuesday, 4 November 2014

Roland mixer - power supply replacement (Part2)

This is part two of the search for a replacement power supply for my old  Roland M-240 mixer.
It's morphed into a discussion about the nature of power supplies with one of my good friends who is also a excellent synthesizer technician.

By chance  I have another Roland mixer (Boss BX-16) that also uses a DC +/- 21.5V psu. It's however 300ma .... not the 500ma that the M240 needs.



I opened it up yesterday:

So simple. The PSU is made up of a stepdown transformer, 4 diodes & two capacitors.


The caps are 2200uf, 35V

How simple !!!!!

The incoming AC power is first stepped down by the transformer (120 - 21.5V). 
Then it's converted from AC to DC by the 4 bridge rectifying diodes & finally filtered with the capacitors. (There don't appear to be any voltage regulators in this PSU).


This circuit uses a centre-tapped transformer.
Most of the circuits like this seem to use 4004 diodes. (I only have 4001s handy).
It's highly likely that the PSU for the 240 mixer uses a similar circuit.
I'll breadboard this when the correct diodes arrive.

If you wish to be really safe add some regulators.