Welcome baby Sofia

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On Sunday 19th our lovely baby girl Sofia arrived in St George’s Hospital in London. Both mum and  baby girl are doing fine and we are trying to adjust to the new lifestyle.

SofiaShe’s a musical baby. In fact, back in the operations theatre room I sung to her “Rocky Racoon” to sooth her once the medical team gave it to me for the first time. We used to play the Beatles’ white album frequently during her pregnancy and am sure she recognised the tune.

She loves “Ella Fitzgerald” and it’s one of my favourite records to play on at 2 or 3 in the morning to get her back to sleep

I’m still enjoying playing the valve amps whilst it last. It will be probably for another 4 months so best to get the most out of them

I’m a happy dad…

Ale

  

Sound Card interface (revisited)

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For  measuring my system, I was struggling with not having a floating USB sound card to use with Pete Millett’s interface. I found a cheap alternative (Focusrite Scarlett 2i2) which can do ASIO 96kHZ and 24-bit.

focusrite loopback FR

Above is the response with internal loopback at 1Vrms on the 2Vrms scale of the SC interface.The distortion is really good below 0.01% just above 25Hz:

focusrite loopback THD

With the balanced input and outputs the noise level is really low. Below -120dB mostly across the entire 20Hz – 50kHz band. Inband noise level is below 100uV when the DAC volume is at highest level and the ASIO generator is muted:focusrite no signal

For distortion testing this USB audio interface has a very good oscillator output performance. Check out the 100mV level below:
focusrite loopback 100mV

  

AVC finished

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Today I soldered the remaining connections to get the second channel up and running. The result is impressive. The AVC project is now finished. And I’m a happy bunny.

IMG_0674.JPG

 

The sound is stunning. As good as I was expecting to be. Very detailed and no loss at bass or treble. The combination of 4P1L driving the AVC and the 814 input step-up transformer seems to work much better this way. The 4P1L preamp has no challenges in driving the AVC, however the full signal swing from the 4P1L step-down via by the AVC seems to sound extremely well.

Thanks to Dave Slagle for such a wonderful AVC. I measured the AVC and matching with a FR sweep and the scope. I was pleased to see the matching between channels and also the nice response 10Hz up to 30-40kHz.

Hard work to wire but it’s worth every penny, trust me…

I have also tried a new set of interconnect cables I made using PTFE shielded RF coaxial. Very simple to build and with nice performance.

The AVC is placed very closed to the power supplies (as you can see on the picture below). The AVC is still very quiet and there is no hum picked up due to the system layout.  Lucky me.

IMG_0676.JPG         

  

Slagle’s AVC project

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It’s been a long time since I had the chance to do any work on audio. I’m working on my solid state amp albeit very slowly. I need a volume control before I get the opportunity to install the new solid state system.

The Slagle’s AVC have been waiting for more than 6 months. I’ve been put off by the milling and woodwork involved. I simply don’t like that work. I found time and energy today to get started and managed to make very good progress.

I used existing 4mm aluminium top plates I had at hand, hence the layout of this box. The hardwood frame has a first coat of wax. Need to add a second to reinforce the tone and make it slightly darker. The rotary switch is a  Russian 28-step military unit. Way more cheaper than the expensive hi-fi ones. The AVCs are from Dave Slagle. They have a fantastic reputation and having heard them before there is no doubt this will be a great addition to my system.

I had to build a mounting frame for the AVCs. This support unit will hold the AVCs to the top plate. I have also added a mute switch which is quite handy.

Soldering the AVC is a daunting task. Something I will do another day.

Happy Easter!

  

Transistor Curve Tracer

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Finally I’ve had the chance to test Locky’s Intelligent Curve Tracer. This is a great piece of testing gear if you’re looking to match transistors or derive some curves for solid state amps. Great for FET matching in RIAA stages as well.

Here are some quick tests I performed after installing the software:

LND150 transfer curve

LND150 transfer curve

 

 

 

2SK170BL Id / Vds

2SK170BL Id / Vds

Matching 2SK1530 for the LME Amplifier

Matching 2SK1530 for the LME Amplifier