SuMIX Headphone Amplifier

Tonight I've built the headphone amp, and tweaked the design to achieve lower distortion (noise is now the  dominant factor).  30R headphones you're looking at around 0.01% distortion at 1kHz when pushing 120mW into the headphone (unlikely!). For 600R headphones you can go even louder with even lower THD, and then I'm starting to reach the limits of my HP distortion analyser (below about 0.005%).

--Neil

First panel mock up of SuMIX

As hinted at earlier, the next module I'm working on is an output summing mixer for the Eurorack format.  And here is the first view of the front panel.

Ignore the blobs on the corners, those are just for aligning the artwork with the panel mechanics.
Also this shows representations of the panel furniture (knobs, leds, jacks, switches) to give a better impression of how it might look.
And thanks to Cody for his useful input :)

DuaLFO Goes Even Slower!

After some discussion on muffwiggler I ran a test to see how slow the DuaLFO could really go with a negative CV input.  Internally it is limited to -0.6V, so I applied -3V just to make sure.

Using my Heath-Robinson-style low frequency counter I measured the period to be about 8,833 seconds, or about 2 hours 27 minutes.  Now that's slow!!!

On to the next one

Now that the DuaLFO is finished and shipping it's time to start work on the next module.  This time it's going to be an audio mixer.  And I think it's going to be very interesting.

DuaLFO Now Available

The first (short) run of DuaLFOs is complete and ready to ship.  Get'em while they're hot!

Auxiliary LFO Equally Slow

Last night I ran the same tests on the Auxiliary LFO.  It has the same maximum frequency of 46Hz, but if anything it is slightly slower than the Main LFO.  I recorded a run of 1 hour 35 minutes.

I think that's slow enough....

Main LFO Goes Slow

Last night I finally characterised the frequency range of the Main LFO of the DuaLFO.  And it is quite a range!  Highest frequency was 46Hz.  Pretty good.  The lowest frequency?  Well, probably better to think of the period rather than frequency.  In this case I measured the period to be 1 hour 25 minutes.  Or, in frequency terms, that's 196 micro-Hertz!

SSssssssllllllloooooowwwwwww...................

Next is the Auxiliary LFO, but I'm guessing that it will have similar performance.

DuaLFO #1 Comes Alive

At long last, and after a couple of minor PCB mods (ahem....) the first DuaLFO is completed, tested, and fully operational:

As you can see this first run of modules is using the Cliff KM15B knobs, and in practice they look and feel great.  The SYNC pos/neg edge button has a nice red Rean cap, and the bicolour LEDs sit nicely in the panel.  I think the graphics worked out well too - the MetalPhoto finish is very crisp.

This is an 18HP panel, offering comfortably spaced controls, jacks and indicators.  While I can understand the benefits of squeezing modules into tiny panels to get a lot of functionality into a small space, it actually takes a lot of skill to design a small panel well.  The best examples of this I know of are the Tektronix 7000-series scope and TM500-series test equipment plugin modules.

The last task to do before these modules are ready to ship is to finish the user manual and get it printed.  If that works out as well as the panels then I think its going to look quite good.

Knobs!

Design of the first CESYG module is progressing well.  The PCB is nearing completion, the order for the front panels has been sent off, and most of the parts are in.

One aspect that needs finalising is the choice of knob.  After much searching and comparing, I've whittled the choice down to two options.

Cliff KM15B

This has a very clean black-on-black look, with diamond-cut lines on the top of the knobs.  From the Cliff website:

Knurled aluminium shell on plastic inner. Standard finish is black anodised to a very high standard.

 Nice.

Sifam TP 150 006

 

With a matching red cap with a white dot - continuing the round theme of the panel graphics - this looks very red and demanding attention from the eye!  It is definitely bolder than the Cliff knobs, but is it too bold?

But.... which to choose?  Choices...choices....

Dual LFO Front Panel draft

Time for an update while I'm refining the PCB layout.  Here is the first draft of the front panel.  Its 18HP wide, and I confess I'm not a graphic designer!

The four input jacks are on the left.  Then the CV pots and the Sync mode switch.  Next column we have the Frequency controls, LEDs, and the manual Shape control,  Finally, on the right are the five output jacks.

I need to experiment with knobs and refine the layout, but I think its quite a clean layout.  The intention is to get this screen printed or perhaps Metalphoto'ed.

LFO Prototype on the Bench

Here's a shot for those who like to see prototypes on the bench:

The donor VCLFO PCB is on the left, with various components and wires hanging off it.  The breadboard on the right has a FET follower/buffer for the sync input.

LFO Auxiliary Sine and Sync

Just for the record, here are scope shots of the Aux LFO sine output.  The first shot shows the basic diode-shaped sine wave:

Clearly not a perfect sine, but the distortion is down to around 1% THD.  Not hi-fi grade but certainly useful for modulation purposes.

The second shot shows the same sine wave but sync'ed to the positive edge of an external square wave:

The sync circuit is designed to reset the auxiliary oscillator to the 0 degree starting point.  With the switch in the NEG position the oscillator is reset by the falling edge of the square wave.

LFO Prototype Finished!

At last the prototype of the first module - a dual LFO based on my earlier design - is complete.  The schematic will be finalised in the next day or so and then on to PCB layout.  Specification is firming up, key features including:

• Main LFO:
• Three sine outputs at 0, 120 and 240 degrees
• Frequency range 100Hz down to around 1mHz (16 minutes)
• CV control of frequency, link-selectable normalised to either internal bus or Aux LFO sine
• Auxiliary LFO: 
• Triangle and sine (diode-shaper) outputs
• Frequency range same as for Main LFO
• CV control of frequency
• Sync input, link selectable for positive or negative edges
• Shape control to adjust triangle to rising or falling sawtooth, also CV controllable
• Eurorack format
• Standard 16-pin IDC header power/bus connection, with reverse voltage protection and RFI filtering
• Blinky lights for both LFOs :)

The frequency range of these LFOs is subject to some further thought.  The prototype is currently configured to go from about 22Hz down to about an hour.  The advantage I can see of going for the higher range quoted above is that it makes for a nicer control range (100-10-1-100m-10m-1mHz) for the front panel.  But if I leave off any real-world markings and just have tick marks then the actual range isn't so important, and can be set to something more useful.
Another option would be a range switch as a lot of other LFOs have.  But I prefer having the full range available in one sweep rather than split into overlapping segments.

Target size is 14HP.  Although I'm considering a wider option so I can bring out the sync edge selection to a front panel switch. If I go with the 14HP panel then the five knobs will be in a single vertical column, and with 20mm between the centres I have identified some sexy rubbery 11mm knobs from Sifam.
The wider panel option would allow me to use larger 15mm knobs.  We shall see how this works out when the PCB is finished.  I'll probably knock up a couple of prototype panels in both formats so I can compare the two and get other opinions.

For now, on with the PCB layout!

1st Module Development

The first module in the CESYG range is going to be based on my earlier SSM2164-based dual sine LFO.  I say based as it is going to have some changes made to it both in terms of core functionality, and adding inputs and controls for a Eurorack module (the original PCB was system-agnostic, with only CV inputs).  The target feature set will include a sync input, shape control for the auxiliary LFO, the addition of a couple of LEDs, and some hopefully useful normalising.  Target panel size is 14HP, but this will depend on the graphics.

More to come...

New year, new blog

2012...  should be an interesting year.  Olympics, Synth DIY UK, another birthday (seems to be an annual event).  And the start of my blog, in tandem with my new synth venture CESYG.