Emulator II Repair part 2

Two days of on/off poking around with a multimeter and pulling each and every socketed IC, de-soldering any capacitor across -15v and AGND and removing a whole group of capacitors that had at some point been (badly) re-soldered yielded absolutely nothing.

The interesting thing is that the earlier repair work had been the filter capacitors on channel 2 and it wasn't the only work on that channel. One of the ICs had been replaced at some point, but typically it was one of the few that were not socketed, which is itself odd as I had thought all E II's had every IC socketed. The replacement IC had been socketed, but it looks as though whoever did the work lifted a pad on the top side of the board and attempted to get the pin in contact with the remains of the track by applying a huge amnount of solder - which ended up shorting two pins - between -15v and AGND.

Previous "repairs" circled

Removing and replacing the socket resulted in me lifting another pad, but I fixed this and the first one with a pair of wires under the board. The short is gone and everything that should be connected is. I'm want to test it, but as I managed to destroy some of the capacitors that I removed trying to trace the problem, I am now waiting for parts. Some of the other ceramic capacitors are visibly cracked and although they have not gone short yet, they likely will in time, so I intend to replace every bypass capacitor on both PCBs - about 150 of them. Oh and that nasty replacement jack just has to go.

Part 3 to follow once I have the parts...

Emulator II Repair Part 1

As mentioned in the last post, I have acquired some new toys. The DEP-3 looks band new despite being 25 years old, works perfectly and sounds great. The early '80s Soundtracs mixer has some dead op amps, including one that appears to have got hot enough to scorch the inside of the front panel. The other item is an E-MU Emulator II. With problems....

I knew the E II was dead before buying it. The power supply had failed (a common problem) and supposedly one of the voices had also expired prior to this. The first thing to do was get the power supply working.

The PSU in the E II was not designed by E-MU. It is an early switch mode supply made by a company called Compower and supplies 5v for the digital circuitry, 12v for disk drive motors (although this isn't actually used in my early E II, they share the 13.4v rail), +13.4v and -15v for the analogue circuitry. The latter two rails are linear regulated after the switch mode supply.

PSU before

and after

Initially the PSU was completely dead and blew the fuse on switch on. A couple of resistors were scorched and one tantalum capacitor had pretty much vaporised. The chopper transistor was shorted and I suspected that most of the electrolytic capacitors were past their prime. As such, I replaced the damaged components and all capacitors. This had no effect on operation - the fuse blew again on power being applied.

I had intended to replace various other aged components later on o make an effectively new PSU and as such had replacements for the various rectifier diodes. This lead me to remove and test the diodes on the mains input on the off chance that they were the problem. Two of them turned out to be shorted! Replacing these solved the fuse blowing issue, but the output rails were still dead. Replacement of the remaining transistors solved this and I now have a working E II PSU.

I still intend to replace the remaining rectifier diodes and also the two linear voltage regulators, but that can wait for another day. Unfortunately I have found an unexpected problem on the E II itself - a short from -15v to ground on the (huge) output PCB. This board is covered in tantalum capacitors and these are my initial suspects. Time to dig out the desoldering gun again...

Repairs

Long time no post! I have been meaning to post something for a while, but I didn't realise that it had been quite that long.

So what have I been up to? I have built a MIDIbox Seq V4 and MIDIbox CV. Neither are completely finished, but they are usable. I have also acquired some more retro toys in varying states of (dis)repair....

Only one of these actually works, so lots to do. Oh and my Juno 106 is now suffering from the dreaded 80017A VCA/VCF plague. I have removed these and will be giving them the acetone bath treatment in due course.

Shruthi-1 Build

Another day, another build. The Shruthi-1 4 Pole Mission kit arrived from Mutable Instruments a few days ago and the remaining parts (resistors, capacitors, etc) turned up yesterday. Too inpatient to wait for the latter, I soldered anything I could as soon as I had the kit.

By the time the remaining parts arrived, it looked like this:

Shruthi-1 PCBs partially populated

A couple of hours later it looked like this:

Analogue board

Digital board (top)

Digital board (bottom)

A quick test before putting it in the enclosure and then the most awkward part - putting the case together.

Done!

A final addition was the LEDs for the dog's eyes. These had to wait until this morning when I found some header connectors. The filters still needs tuning, but other than that, it works.

Effects

I still haven't got around to doing a video of the MIDIpal, but the effects PCBs finally arrived a few days ago. I brought the boards for a Gristleizer and an EchoBase delay from http://musicpcb.com. Prior to this and in need of something to occupy me, I drilled a case for the Gristleizer, mounted the pots on a piece of stripboard and did some of the wiring. I opted for small desktop format cases rather than stomp boxes.

Prepared case

Once the PCB arrived, it was quickly populated and wired up. I ordered the wrong trim pots, but they fit with some leg-bending and the LFO speed pot has the wrong taper. Anyhow, it works and I'll change the pots at some point.

The Gristleizer PCB

PCB mounted and wired

"Completed" Gristleizer. Yes I drilled a hole in the wrong place.

Having completed the Gristleizer and before starting on the EchoBase, I decided that laser cut front bezels would look good. I designed one, along with a drill template for the EchoBase in Inkscape and will do also design a new front panel for the Gristleizer.

Initial EchoBase drill template

I built and tested the EchoBase outside the case as there are several mods available that I wanted to experiment with before modifying the panel (see http://musicpcb.com/pcbs/echo-base-delay/). I went with a diode lift switch, along with substituting the value of one resistor to cope better with "hot" signals as I will be running synths through this.

EchoBase guts

Finally, the case was drilled (with the deletion of the effect LED as the LFO LED is dual purpose) and the internals mounted within.

The completed units

I intend to do several more effects and also build a power supply for them in a matching case, rather like a DIY version of the Boss Micro Rack series from the 1980s. In the meantime I'll get the bezels made and build the Shruthi-1.

Shruthi-1 coming

I have ordered a Shruthi-1 - more precisely the limited edition Shruthi-1 4 Pole Mission. Hopefully I'll get a chance to build it next weekend.

In other news. I now have all the parts for the Gristleizer and Echo Base - except the PCBs. <rant> Deliveries from the US to UK seem to be getting slower - and more expensive what with the post office's "admin fee" for paying import duty that is often several times the cost of the duty itself........ </rant>

MIDIpal

This wasn't supposed to be my next project, but I am still waiting on parts for the audio effects units.

I have intended to get a MIDIpal for a while now, but was put off by the surface-mount soldering involved. I finally bit the bullet and ordered one and built it over the last few evenings.

The MIDIpal is a tiny MIDI processor, which can serve as an arpeggiator, a simple step sequencer and delay, among other functions. It is Open Source hardware and available as a kit from Mutable Instruments.

This was my first experience of surface-mount soldering and it actually turned out easier than expected, though I applied too much solder to the ATMega328p MCU, resulting in a short between VCC and ground. Solder wick fixed the short, but left rather a lot of burnt flux behind. As for the resistors, LEDs, diodes and capacitors - soldering was actually quicker than with through-hole parts.

The completed MIDIpal in it's transparent case. Despite the mess around the MCU, it works!

Uploading the firmware using a USBtiny ISP.

I'll post a video once I have had a chance to play with it.

Next up

I should have started writing this blog some time ago. I have a few more pretty much complete projects to post and I will endeavour to put them up in the next week or so.

They are:

MB6582 - MIDIbox SID synth
MIDIbox Seq V4L
MFOS Sound Lab Ultimate - In a similar state to the 9090.....

Future planned builds will be:

Gristleizer and EchoBase effects units - I am awaiting the final parts for these.
MB-9090 sequencer
MIDIbox Seq V4
SammichFM - MIDIbox FM synth

....and possibly:
A Roland CR-78 clone, if I can find schematics that are actually readable!

x0xb0x.

I built this in a few days, whilst waiting to acquire some rare transistors to finish the 9090. The 9090 took weeks.

The x0xb0x is a clone of the infamous Roland TB-303 "Transistor Bassline", designed by Adafruit Industries and originally supplied by them. Kits are currently available from several sources. I got mine from http://www.x0xsh0p.de.

The underside of the main PCB. This is split into two sections - towards the front is the synthesiser, using mainly original '80s "rare parts" and at the back is the sequencer. The ATmega for the latter is missing in this shot.

The top of the same PCB, with buttons and LEDs for the sequencer in the foreground and potentiometers for the synth at the back.

The main PCB mounted in the case, and wired to the IO board which contains the MIDI, DINSYNC and USB interfaces, CV and Gate out and the audio jacks. The power supply is also on this board.

The completed x0xb0x.

9090

A few photos and a brief (and bad) video of my 9090 drum machine. This is a clone of the Roland TR-909 voices, without the sequencer, designed by Trevor Page. Yes it is attached to a piece of cardboard, but this is temporary! For more information on the 9090 see: http://www.introspectiv.org/

I intend to build a sequencer, based on the MidiBox Seq V4. For more on this visit: http://www.ucapps.de/ (MidiBox) and http://www.synthage.com/ (the sequencer control surface).

Board 1 part completed. This contains the power supply, noise generator, bass, snare, low tom and mid tom drums.

Completed board 1

Completed board 2 comprising high tom, rim shot, hand clap, hi-hats and cymbals, plus the MIDI interface. The three large ICs are EPROMs containing the samples for crash and ride cymbals and hi-hats. All other voices are analogue.

The rather temporary card panel with potentiometers attached.

Close up of the EPROMs on board 2, also showing some of the rare parts - three types of long discontinued Japanese transistors.

The 9090 in action.

Hello

Hello and welcome to yet another blog.

I intend to post details of the various electronic synths, drum machines and other noise makers that I have built, as well as anything else that takes my fancy......