Slagle’s AVC project

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!

Custom Transformer Supplier in Europe

Custom transformer supplier

Given I had several emails asking about the output transformers I used in the recent upgrade of the 814 SE Amp, I asked Mr. Vincenzo to kindly provide an email address so you can reach directly to him. You can send your request via the form below which protects his email address from internet SPAM :).

Alternatively, if you don’t want to use the form below you can browse his website (in italian only sorry).

I hate metalwork

Don’t you?

Building your own interconnect cables

I’ve been struggling for some time to find an affordable interconnect cable choice without falling into the trap of the ultra-expensive hi-fi commercial cables. In the end, an interconnect cable has to provide low capacitance, low resistance and proper shielding to protect our desired signal from external noise. We don’t need exotic cables or connectors to achieve this. Ideal dielectric is air, but is not practical build cable using air as dielectric 🙂

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Fixed bias regulator

Testing the Rod Coleman Fixed Regulator

As part of my 300B SE project design, I looked into various fixed bias arrangements and regulators. Rod Coleman has developed another fantastic circuit after the success of his DHT filament regulator which is now the preferred filament supply kit within the DIY audio community. After many years of refining the DC filament regulator, Rod came up with a clever design for fixed bias using the same concept: a gyrator and a temperature-compensated CCS. Instead of feeding a current through the DHT filaments, in this case the current is used to generate a clean bias voltage across a “bias resistor”. The bias resistor is bypassed by a capacitor as the high impedance loop formed by the regulator and the bias resistor is sensitive to pick up HF noise which could be amplified by our system.

The kit is of the same quality you would expect from Rod’s boards and very easy to build. It takes less than an hour to build the boards:

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Refurbishing an LCR bridge

Recently I acquired a second-hand and untested TF2700 LCR bridge from Marconi. This is a fantastic piece of engineering and a superb LCR bridge that can only be beaten by an expensive impedance analyser, something I can clearly not afford.

This bridge is perfect for selecting accurately capacitors for a RIAA network with extreme accuracy. In fact, the 1% precision can be improved down to 0.25% by replacing the main bridge 0.5% resistors with 0.1% ones as suggested by Morgan Jones in his “Building Valve Amplifiers” (Second Edition) page 330 and 331.

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Customised Potentiometers

I was looking to repair my LCR bridge and found that a 2k5/25k ganged potentiometer was needed. I found this great supplier of potentiometer that can provide you with a customised ganged potentiometer at a very competitive cost. Worth considering this great Welsh company!

Ale