mike stehr Posted March 10, 2012 Share Posted March 10, 2012 I've never had the need for the extra gain a pre-amp has to offer with the tube amplifiers I use. In the beginning, I used a Carver tubed CD player with a variable output direct to a amplifier with good results. But the CD player broke, and finding a CD player with variable output isn't too easy unless there is money involved. So I was always content with just using a resistive potentiometer or stepped attenuator between the CD player and amplifier. Of course this has it's drawbacks, (noise/hum/frequency loss when pots are scaled lower in volume) and I was getting tired of these drawbacks. The stepped attenuator was best, but it still had issues like noted above to a lesser degree. I've built a couple tube linestages, and while the extra tonality involved was cool, I just didn't feel the need for a linestage. Pondered over AVC/TVC type volume controls for years. I couldn't afford commercial offerings, so it was just pondering... Dave Slagle (Intact Audio) came up with a 200 dollar AVC kit...more or less... I pondered on that over time, and was kinda shy to it because of the wiring involved. A forum member SETI, mentioned getting one of the Slagle Hudson dredged steampunk style AVC controls, reporting good results. So I figured I'll burn 200 bucks and give it a chance. I'm glad I did... Quote Link to comment Share on other sites More sharing options...
Guest " " Posted March 10, 2012 Share Posted March 10, 2012 it's amazing how much the sound differs from resistive volume controls when you use an autoformer volume control. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted March 10, 2012 Author Share Posted March 10, 2012 I found a metal test enclosure for 30 bucks off eBay to use. Maybe someday I'll fab a fancy wood box for them, but I'm not too concerned about it... I didn't want to just mount the autoformers directly to the bottom of the enclosure, so I hand fabbed some aluminum brackets from scrap pieces that already had the bends in them. I didn't want to pay/wait online for purchasing hook up wire of teflon tubing/heatshrink, which is spendy. (teflon heatshrink) So for hook up wire, I have some scrap lengths of 14 AWG Solen litz wire. I unraveled the 14 AWG down to single strands, which comes out to .51mm or 24 AWG, roughly. I have some pinched (22 or 24 AWG?) wire with teflon insulation. Or PETF or whatever the acronym is... I pulled the stranded wire that was in the teflon insulation, and used the insulation to cover the Solen 24 AWG wire. Which has enamel/varnish over the wire anyways. (that's why the fruit stripe colors of the insulation) The autoformers can be taken apart and the laminations restacked, to come up with different inductances to help match to the source load. I didn't want have to unsolder 28 connections to experiment with this process. So I figured out that hoarded female "D" sub connector pins from computer jacks will fit the bobbin pins on the autoformers. They are really no different than phono cartridge pins. You can find the conputer jacks on eBay. I bought one locally, cheap. This way I can swap the autoformers out with minimal soldering. I suppose once I'm happy after experimenting, I can just solder the wires directly to the bobbin pins. I'm not done yet.. I need to pony up for high quality input/output RCA female jacks, and would like to have the aluminum brackets, front and back panels anodized satin black. With the faces of the front and back panels grained. I left the blue plastic protective stuff over the panels for now. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted March 10, 2012 Author Share Posted March 10, 2012 One more. It was a bit of a chore to wire. I wished I had tightened up things a little more, but it'll fly... Quote Link to comment Share on other sites More sharing options...
Plink Posted May 1, 2012 Share Posted May 1, 2012 The Slagle autoformers are simply spectacular. Quote Link to comment Share on other sites More sharing options...
Deang Posted May 1, 2012 Share Posted May 1, 2012 Impressive work Mike. Looks great. I always wanted to try one of those but somehow managed to never get around to it. Quote Link to comment Share on other sites More sharing options...
NCBlueTJ Posted May 3, 2012 Share Posted May 3, 2012 How would you compare the sound to a traditional volume pot or stepped attenuator? Quote Link to comment Share on other sites More sharing options...
NOSValves Posted May 3, 2012 Share Posted May 3, 2012 Really nice work Mike! Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted May 3, 2012 Share Posted May 3, 2012 Cool project and neatly done! I guess you're just a selector and additional RCA inputs away from an awesome low level pre. Quote Link to comment Share on other sites More sharing options...
seti Posted May 3, 2012 Share Posted May 3, 2012 So glad it worked out and superb work btw. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted May 3, 2012 Author Share Posted May 3, 2012 How would you compare the sound to a traditional volume pot or stepped attenuator? Ringy. Quote Link to comment Share on other sites More sharing options...
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