Posted 20th December 2013 at 10:29 AM byrjm (RJM Audio Blog)
Earlier this year I had a really, really bad experience attempting to get a new soldering iron. This time around I made my purchase through a reputable Japanese online retailer, and am now the proud and happy owner of a Hakko FX-950 soldering station.
Its an analog unit, and was discounted quite a bit as a result. Personally I'm happier with a rotary dial temperature control anyway.
This thing rocks! I've dragged my heels on getting a decent iron for so long its ridiculous. In my defense, I could always borrow a semi-decent one from work, so the pressure to buy my own was not as great as it otherwise might have been.
Top five reasons to spend the extra cash:
1. 70W, variable, closed loop temperature control. As much heat as you need, whenever you need it: the feedback loop means that the power is proportional to the conductance load: the tip will not cool down when heating up a large thermal mass.
Posted 17th December 2013 at 10:10 PM byrjm (RJM Audio Blog)
Updated 20th December 2013 at 10:14 AM byrjm
Straightforward transplant. Out with the old (anyone want them?) in with the new. Re-used the OPA134 op amp and my dog-eared pair of 0.47uF Multicaps.
On powering up I discovered that with the specified 10 ohms in R9,10 the output bias current was upwards of 200 mA and things were getting a bit toasty. I paralleled a second 10 ohm resistor, dropping the resistance to 5 ohms and dialing back the output bias current to about 70 mA. Latest schematic revision has R9,10 values edited to match.
Currents stable. Heatsink temperatures around 50 C. Output offsets around 15 mV. No noise or hum.
Posted 21st November 2013 at 11:45 PM byrjm (RJM Audio Blog)
Updated 5th January 2014 at 08:17 AM byrjm(update schematic to 20f4)
Update: I've ordered parts for small number of Sapphire 2.0 kits. The normal price will be $125, but as an introductory offer the first batch will be available for $100. Kit includes a set of boards and all the parts for the board. You need to supply the transformers and diodes, as well as a volume control, and the chassis hardware.
November. That time of year for finally getting around to advancing some of my audio projects a little.
The Sapphire has remained in "rev 1+" for some time now, partly because of time constraints, partly because of the lack of popularity, and partly because it was already a re-spin of the beta version and worked just fine.
There were a few housekeeping things I wanted to add though, which have been included in the 2.0 revision.
- added a dedicated ground (GND) pad to connect to chassis...
Posted 10th November 2013 at 11:00 AM byrjm (RJM Audio Blog)
Updated 10th November 2013 at 01:11 PM byrjm
Last one for today.
I was having problems getting this to work, the key seems to be adjusting R6 to null the voltage offset. Works fine now, but this is just a rough reverse engineer of the diagram, the parts values and the type of transistors are essentially placeholders.
The input jFET is shown as a dual package. The output bias current is most likely much lower than the 100 mA I configured, so the class A output power is proportionately smaller. For the rest of the currents and the types of transistors used, your guess is as good as mine.
edit: R7 should most likely be closer to 47 ohms, while another 5p capacitor should go in parallel with the feedback resistor, R17.
Posted 9th November 2013 at 11:42 PM byrjm (RJM Audio Blog)
Browsing through an old issue of MJ (No. 1076), I found some sketches of the Marantz SA 11S3 SACD player analog circuitry which seemed interesting.
The are two discrete op amp "modules", one is used for the I/V converter and low pass filter, the other design is applied to both the line output and headphone outputs.
The parts and values are not given, so the circuit below is just a working mock up in LTSpice based on the published diagrams.
The output stage from the headphone / line driver op amp is attached below. There's a JFET input and BJT gain stage as well, and the whole thing is wrapped up in a feedback loop. The buffer itself, being unity gain, works just fine as a standalone circuit element.
Posted 3rd June 2013 at 11:28 PM byrjm (RJM Audio Blog)
Updated 3rd June 2013 at 11:32 PM byrjm
In early May Trent Wolbe traveled to the High End trade show in Munich, Germany. This is part one of a two part series exploring the cutting edge of audiophile technology.
By Trent Wolbe, writing for The Verge. A feature on high end audio part 1 and part 2.
It was halfway through the next selection, a quietly seductive 24 / 192 recording of “Cielito Lindo,” that I realized I was enjoying the music quite a lot, not because I particularly enjoy bossanova versions of Mexican classics, but because the Evolution One speakers were recreating one of my favorite things about eating psychedelic mushrooms.
Posted 29th May 2013 at 12:12 PM byrjm (RJM Audio Blog)
Updated 29th May 2013 at 11:59 PM byrjm
Oh, for Heaven's sake...
Just got the FX-888 soldering station I bought on ebay.
It does not power up.
Do you know why it doesn't power up?
So glad you asked...
It does not power up because - pause for effect - the fuse board that fits on the power transformer is inserted the wrong way round. That's right, the full "rotated 180 degrees" deal.
Fortunately I have another soldering iron. You know, so I can fix my soldering iron...
I would just return it, but the shipping would cost me half again what I paid for it. Perhaps ebay will refund me anyway. We'll see.
I think I know what happened: The people selling these are modding them by changing the voltage and power cord. The soldering stations are officially bound for the Chinese domestic market, 220 VAC. The box, when it came, had "110V" hand-written on it, though the instructions...
Posted 28th May 2013 at 12:24 AM byrjm (RJM Audio Blog)
Updated 28th May 2013 at 12:08 PM byrjm
Experimental : For Research Use Only
It's bring-your-own-voltage-gain. This output stage is a unity gain buffer. A sort of diamond-buffer-meets-sziklai-pair hybrid. It lets the driver pair bias the output pair without the complexity of an additional bias network, but, unlike the basic diamond buffer, the output pair can have a much higher bias current than the drivers.
LTspice file attached, if you'd like to play along.
I did my best to shut my eyes and design this just by messing about in LTSpice from the starting idea of a "level-shifted-complementary-sziklai-pair" (i.e. mirrored J-Mo mk II), but I see now a shout-out to 47 Labs is due as the 0247 Treasure uses the same stage.
Ah well, I guess my neat idea isn't new after all.
The general performance is in the order of 0.01% THD for 50 mW / 16-300 ohms at 100 mA bias though the output pair. I've been trying to...