Starving Student

I finished my Starving Student hybrid headphone amp today. I plugged it in and held my breath. Not because of excitement, I just don't want to inhale magic blue smoke... ;)

The heatsinks warm up pretty quick, as do both tubes. OK, now check DC offset at the outputs. Oops, that's ~12.5 VDC. Not good. Check the schematic again. I forgot to add two resistors...

With the resistors installed I get ~3mV of DC offset. That's good. On top of the 2" tall heatsinks I measure ~50°C (122°F), the IRF510 metal tab clocks in at ~63° (145°F). This thing gets bloody HOT. Cool! I plugged in my PX-100's and it works! No hum. Some very faint hiss, hardly worth mentioning. It sounds great already. Plenty of punch, lovely highs. Gotta do some burning in but I really like what I'm hearing already.

I'm a bit disappointed in the Electro-Harmonix 12AU7 tubes: no tube glow as the heaters are enclosed. I might install orange LEDs to light up the tubes. I did prepare the tube sockets for that.

Fashion Trends

Fashion trends come, fashion trends go. Now here's a fashion trend I won't like to see go: nipple enhancers. 

The natural look is back. Nipples are in. From your favourite magazines, to stars gracing the red carpet, women are showing off their breasts with pride. Body Perks nipple enhancers are the latest fashion accessory for your breasts, so take the lead from Sex and the City's Samantha and draw attention to your natural assets. For full effect, wear under a soft cup bra for enhanced, perky appeal.

Available here

Jeff Lorber in concert

A friend of mine mentioned Jeff Lorber is giving a concert in Zoetermeer june 1st. He's bringing Jimmy Haslip (bass), William Kennedy (drums), and Eric Marienthal (sax) with him. Today he left a message on my voicemail, he bought a ticket and he's going.

Count me in! I'm going too.

Cisco PSU

I got my Cisco 48 VDC PSU today. The PSU is new and unused and clocks in at 48.1 volts DC, excellent!

12AU7

I went shopping for two 12AU7 tubes today. I also needed fitting sockets. I came home with two Electro-Harmonix 12AU7/ECC82 tubes and two ceramic tube sockets. The tube sockets have a hole in the center and thus will allow me to glue a 3mm LED underneath the tube to augment "tube-glow". Hmm, what colour should I choose?

CD player mod

My Cambridge Audio 540C CD player is a good CD player and offered very good value for money when I bought it. I couldn't afford the better spec'd 640C at the time. The 540C however truely lived up to its promise. It sounded so much better than my old Kenwood DP-4020. That is until all of a sudden no sound came out of mine. It was diagnosed with a broken DAC chip, something rare apparently. The repair bill was a whopping €150...
This weekend I thought I would swap the opamp in the output stage of the 540C. Originally the 540C sports a NE5532P opamp. A decent opamp that does its job but is far from spectacular. Better opamps however exist and don't have to cost a fortune. A NE5532 costs approx. €0.80 and falls into the "jellybean" category. It's cheap and thus a common opamp to find inside devices.
Today I popped open the 540C and cut out the NE5532P. Next I desoldered its eight pins and used a desoldering pump to suck the holes clear of solder. I popped in a high quality opamp socket and soldered it to the board. In went my AD8066 on a Doc Brown™ adapter. A quick check reveals that it works. Woohoo! Got to do some serious listening tonight, but my first impression is it's highs are much clearer now and the stereo image is wider.
While I was at it I also noticed something unexpected. My 540C doesn't have a WM8716 DAC chip. It has got a WM8740 instead. The WM8740 is a better spec'd DAC and was used in the 640C. When they repaired my 540C they must have put that one in. Lack of WM8716 chips perhaps? I don't know if the sound quality benefits from the WM8740, the electronics that surround it may need upgrading...
Update
A thought entered my mind today. How much voltage does the 540C supply to the opamp and can my AD8066 handle that? The two voltage regulators (7815 & 7915) supply ± 15V to pins 4 and 8 of the opamp. So 30 Volts total (I measured 29.8 Volts). A quick check of the AD8066 datasheet yields 24 Volts as highest safe operating voltage and an absolute maximum of 26.4 Volts. I quickly pulled out the AD8066 and inserted an OPA2134. I'm very lucky that the AD8066 still works...
Next tweak will be a change of a capacitor. C32 is a 47µF cap on the output of a 7805 (U1). U1 supplies the voltage for the clock. A change to OS-CON on the digital power supply line could improve things further. Too bad the DAC is fed from a single 7805 (U4), changing C15 to a Sanyo OS-CON means the power supply to the analog part of the DAC will be fed from the OS-CON too. OS-CONs are less suitable for analog circuits.

Jeff Lorber Fusion

I have a few Jeff Lorber Fusion CDs. My favourite one is Water Sign from 1979. Great album from start to finish. I just love Tune 88. Later on Jeff renamed the Jeff Lorber Fusion to just Jeff Lorber while the music on the subsequent CDs gets progressively smoother. On those CDs there is usually only one track that really interests me.

Today I discover this: Jeff Lorber breathes new life into the Jeff Lorber Fusion! Now this is good news, and good music. 

This new incarnation of the Jeff Lorber Fusion includes luminaries like bassist Jimmy Haslip, saxophonist Eric Marienthal, trumpeter Randy Brecker, guitarist Paul Jackson Jr., and drummers Vinnie Colaiuta and Dave Weckl.

The bits of music here are very promising.

Starving Student

Operation Starving Student is a go! I got lucky on eBay and won the required 48VDC Cisco power supply. Winning bid: €1.16... Let's not discuss shipping costs. I hope it's here soon and that the skies stay clear of volcanic ash. I also bought some resistors and four IRF510's (yes four, so have two spares) for it. 

Millett Starving Student

Yet another DIY project: a Starving Student. Originally designed by Pete Millett the Starving Student is a cheap to make but very good sounding headphone amp. Didn't I make one (Mini³) already? Well yes but this one is different. Whereas the Mini³ is a DC coupled opamp-based headphone amp, the Starving Student is a hybrid design. Hybrid in that it has both tubes and transistors. Pete Millett designed the Starving Student using cheap and freely available 19J6 tubes. Due to the enormous popularity of the Starving Student the availability of the 19J6 tubes has become a problem. What tubes there are still out there now go for a premium price. Basic supply and demand. I tried to find the 19J6 tubes locally. No such luck though.

There's still hope for prospective DIY-ers though. Two DIY-ers modified the original schematic to be able to use the 12AU7 tube. The 12AU7 tube is freely available. Won't it go just like it did with 19J6 tube? No, the 12AU7 tube is still in production today. The 12AU7 and it's cousins the 12AT7 and 12AX7 are still used in amps today. Guitar and bass amps for instance.

I asked about the availability of 12AU7 (AKA ECC82) tubes at two local shops yesterday. No problem, Sovtek's for 10 euro a piece. The other shop sold 12AU7's at 13 euro a piece.

So am I gonna make one? It depends on if I can get the required 48 Volts DC power supply for it. Once I have that, I will make a Starving Student myself.

Mini³ lettering

I just remembered I have a set of paint sticks. I bought these once for filling in the engraved numbers on my Leica lenses. I took out the white paint stick and rubbed it over the engraved lettering on the Mini³ panels. Removed excess paint with some tissues and cleaned up with mineral oil (baby oil). The result is white lettering instead of silver (aluminium). The difference is small but noticeable.

Yesterday I bought a new knob for it. The silver one didn't fit very well visually. I now have a black knob with a white index mark. Looks better.

Mini³ tweak(ed)

I'm gonna tweak the Mini³ a bit... The built-in battery charger to be precise. Built per spec the battery gets charged at ~17mA. I couldn't get the stock 75Ω resistor and bought a 68Ω instead. At 68Ω the charge current is ~18.5mA. This results in a charge time in excess of 15 hours, that's a bit too long to my liking.

A rechargeable battery is usually slowly charged at 0.1C, or at one tenth of its rated capacity. For my 250mAh battery this means a charge current of 25mA. To get 25mA of charge current in my Mini³ that means I need a 50Ω resistor (1.25/R = I). 

For higher capacity batteries lowering the resistor works up to a point. Maximum charge current is ~35mA so as not to overheat the LM317 voltage regulator. A higher charge current could be done though by using a LM317 in a TO-39 package with a heatsink attached. Then getting rid of the built up heat inside the case becomes another problem though.

Just got back from the shop. No 50Ω resistor but a 47Ω resistor instead. A 47Ω resistor makes the charge current a bit higher than the 0.1C or 25mA I was shooting for. I removed the 68Ω resistor and popped-in the 47Ω resistor. Battery charge current should be 26.6mA. In real life it is now 26.3mA. I'm quite happy with that value.

I saw on the shop's site they might have the 2SJ109 dual JFET. At €9.15 each not exactly cheap but not expensive either for such a difficult to source part. One problem: only one in stock. That rules out making an Aleph J.