Saturday, October 31, 2009

Marcus Miller Master of All Trades - Nikki's Groove

Now I'm on the subject of Marcus Miller, check this out:

Listen to Marcus groovin' starting at 3:42. Great stuff!

Marcus Miller DVD

For Sinterklaas I ordered myself this Marcus Miller DVD. Cool! Now I have to wait until the 5th of December for my gift. Not so cool!

Sunday, October 25, 2009

Wattgate 381 Audio Grade Duplex Socket

A new gizmo for audiophools to spend their money on. An audiograde wall socket... Yup that's right. Yours for only US$ 147. Read the hilarious reviews here.

What's next? I already know what's coming next: audiograde in-wall wiring. That's right folks, remember you read it here first!

mini Aleph - let there be bass

My newly built mini Aleph plays beautifully and keeps us warm at the same time. Still there was something lacking. Bass. Initially there wasn't a decent amount of bass coming out of it. Bass response was a bit "thin". Yet I remembered having read that the mini Aleph produces a decent bass. A quick search on diyAudio.com revealed this bit: "I absolutely LOVE how this little amp sounds. Very tight, controlled bass and silky highs." OK, the silky highs are there but no very tight, controlled bass. Until yesterday afternoon that is. I was playing Erykah Badu's CD Baduizm Live. There's great bass playing on it by Hubert Eaves IV, and suddenly there it was: tight & controlled bass. Must be because it's burning in properly. Can 12-15 Watts per channel ever be enough for a decent bass reproduction? Oh yes, you'd be surprised!

BTW if you haven't heard that CD yet, give it a spin, it's a great CD.

Saturday, October 24, 2009

mini Aleph - burning in

A quick check just now revealed a DC offset of 56 mV for the left and 69 mV for the right channel. That's satisfactory. Yesterday the right channel measured 107 mV, that's a bit too high. I will check the DC offset at intervals to see if there's any change as the amp gets burned in.

Other things to note: this dinky Alpeh runs HOT! After an hour the entire case is pretty warm and the metal mounting disc for the toroid is also pretty warm. Apparently class A amplification puts a lot of stress on the transformer, more than class AB amplifiation.

This morning a funny thing happened. At the moment I use the preamp in my Cambridge Audio 540A amp to drive the mini Aleph. The power amp of the 540A isn't used at all. Yet the protection of the 540A kicked in right at the moment I thought that there really was a decent amount of "ooompf" in this little puppy. Weird kind of protection when the 540A wasn't even asked to deliver any power. All the more reason to build the B1 as soon as I have the B1 PCB in my hands. The B1 doesn't have a protection circuit.

Friday, October 23, 2009

mini Aleph - room for improvement

As much as I like my newly built mini Aleph there's room for improvement. I feel the PSU could be improved by having more capacitance, especially the final electrolytic caps in the CCRC configuration. The final caps form a RC filter with the preceding resistor, it's used to filter mains hum. Right now I have ~0.65 ohm as R and 10000µF for C. If I would increase the capacitance to say 22000µF the resistor could be lowered by a factor of 2.2 and I would still have the same RC filter time constant. It would result in a resistor of ~0.29 ohm, which in turn would lead to less heat coming off of the resistor. Right now they're HOT...

Thursday, October 22, 2009

mini Aleph - up and running

It works! I hooked up the right channel tonight and now both channels are working. Woohoo! I had to add resistors to the CCRC PSU though, as the originally present 3x 3W resistors got very, very hot. How hot? Well how about 91°C and rising... and that was the moment I switched off power. D'oh! With the added resistors the load is now divided by 5x 3W resistors and temperature is about 52°C. Much better. 

How does it sound? Was it worth the money and effort? Sound: very rich in detail, tremendous clarity and depth. It stays that way even at low listening volume. It's no powerhouse with about 12 Watts per channel. Think quality rather than quantity. Was it worth it? Hell yes! Want one too? Build you own, go on!

How much will it cost to build your own? Well it depends on your wishes and wallet. A few items are expensive the rest it relatively cheap, although I must admit all those small amounts add up quikly.

Expensive

  • transformer, don't skimp here - it's the heart of the amp
  • power supply capacitors, don't skimp here either
  • a ready made case with ample heatsinks
  • input and output sockets

Cheap

  • transistors, resistors, diodes, small capacitors, wire, etc.
  • ready made PCB's, given the quality
  • labour, after all this is d.i.y.

Read all about the mini Aleph, or mini-A as it is affectionately known at diyaudio.com.

mini Aleph - tweaking bias

I've been tweaking the bias of the left channel today. The right channel isn't hooked up yet. Currently the bias is at 1.25 amps, I lowered the source resistor to ~0.32 ohms. It's been idling for half an hour like that and heatsink temp is 40°C (104°F) right now. Well that's a very nice stopping point. A bias current of 1.25 amps @ 40°C isn't in the dangerzone. Although the heatsink is warm to the touch it's not that hot you risk burning yourself when you touch it. Touching the heatsink with the inside of my wrist (where the skin is pretty thin) isn't painful of uncomfortable. Also this temp is still well within the SOA (safe operation area) of the IRFP240 power MOSFETs.

mini Aleph - one hour later

After the left channel had been idling for over an hour I took the following measurments:

  • DC offset ~70 mV
  • voltage across source resistor ~400 mV
  • rail voltages ~18.6 V
  • heatsink temperature ~36°C (97°F) or 16°C above ambient.

So nothing really changed much, meaning I'm going to shop for some resistors today.

The really good news is that it works! I hooked up my iPod and there's music coming out of my Monitor Audio Bronze 1. I really like what I hear, I must hookup the right channel too. Hum? A very faint bit with my ear pressed against the speaker grill cloth. Hiss? Read after Hum! Woohoo!

Wednesday, October 21, 2009

mini Aleph - fire in the hole

Right now I have one channel wired up. Because I had already established that the PSU was working properly I flipped the mains switch and then... Nothing happened, no smoke or noises. That's good! After that the left channel heatsink slowly started warming up... Woohoo, it's working right at the first time!

Rail voltages are ~18.3 Volts. Voltage across the source resistors (0.47R) is 0.402 volts meaning a bias current of ~0.86 Amps (V/R = I). A bit too low, a mini Aleph should run at a bias current of at least 1 amp. More amps is better, heatsinks permitting of course. Perhaps it will increase after it's warmed up properly. If not I'll have to increase the bias current by lowering the value of the source resistors by paralleling another resistor. Heatsinks are about 35°C, or ~14 degrees above ambient temperature.

DC offset is ~70 mV, a bit high. Again I will see what it does after an hour or so of warm up time.

I'm really glad I bought the optional perforated base for the casing, it made mounting the PCB's and toroid very easy. Also very convenient for securing wiring to the base using cable ties.

mini Aleph - under construction

Time for a little break. As expected my toroid arrived. A quick hookup revealed that 
  • the toroid works OK
  • the PSU works OK
  • unloaded rail voltages are +21.4 Volts and -21.4 Volts

Rail voltages are a tad high for a mini Aleph but I expect them to drop a bit when I load the PSU and because of the current load a further drop in voltage is to be expected as the Hexfred rectifier diodes I used have a larger forward voltage drop than the standard 0.7 Volts diode loss.

I chose not to use an inrush current limiting NTC for the toroid. Since it's only 160 VA it's not really needed. I did hookup the grounding wires, it's very important not to forget that. I'm dealing with potentially lethal currents here. Safety first! The audio output grounds are connected to the chassis through an NTC to prevent groud loops and then to the IEC earth lug.

Tuesday, October 20, 2009

mini Aleph

If all goes as planned the Amplimo 2x 15 Volts / 160VA toroid transformer for my mini Aleph amplifier will be delivered tomorrow. Woohoo! Then it's time to turn the parts into a working class A amplifier, which will probably take me all day.

What is a mini Aleph you ask? It's a 2x 10~13 Watt power amp running in class A. Class A amps are highly inefficient but have very low distortion levels. I have never heard a class A amp but apparently they are the bees knees. The mini Aleph is derived from the Aleph 3 amp designed by Nelson Pass

For the boffins, read all about it here, and here.

Goodbye MyOpera, hello Blogger!

I've had it! I'm moving blog. I've been blogging on MyOpera for a while now but the server monkeys finally pissed me off for the last time. Goodbye MyOpera.