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D3 A Darling Amplifier Variation
Revised 1-10-2005 |
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 This amp represents yet another design from scratch. I've studied this tube vis a vis the various efforts of others as well as my own past efforts and concluded this tube would sound better with a slightly higher impedance load. I feel 5K is too demanding and cuts off the plate swing extension too soon. (I'm open to comments on this.) With a higher Z, I can deliver more voltage to the tube and get a better positive plate swing and end up at the same - or more - power output. The tube ends up biased at -31V and 25.8mA. Net result: Better than 750mW output/ch. The vintage RCA trannies were pulled from a stereo SE 6V6 console unit. I've had VERY good experience with these trannies: they have a nice open sound. Therefore at 7.5K they will be the units for this Darling variation. Below is a "before" shot of the trannies as pulled from the console.  Nice, fat oversized OPT Trannys  Good shot of relative OPT size. I decided I wanted to try another "theme" color for this unit. Again I picked a metallic paint. (Your comments on the color and paint would be greatly appreciated.) I don't know WHY I do this. It looks great but metallic is such a mess to work with. The 1626's are NOS RCA that had never been opened until I opened them. The boxes had the original rusty staple in each. The 5965 is the large plate GE 5-star. 
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I did the breadboard thing and experimented before settling into the final design. A lot of listening, parts changes etc. as is our usual practice. The amp consists hand selected new, NOS and Vintage parts. Except for the MF resistors in the plate cicuit of the 5965's and the power supply caps, everything is vintage NOS. An vintage German made cap bypasses the nice ceramic cathode resistor in the output stage. I got a batch of these caps from Walter and I think they work and sound great. The bypass caps are further bypassed by some film caps.
  Power Supply The input stage is simplicity itself. I'm using the 5965 here; a well established combination with the 1626. I ran a lot of biasing schemes to try to complement the 1626 characteristics at my chosen operating point. I didn't want to give up too much of the 1626 sound, nor did I want to hamper the 5965 with too little plate current, but I prefer the lower distortion a properly aligned input stage can provide. I got a nice compromise which ended up with hand selected the resistors for this stage.  Amp Section In my previous Darlings, I complained I couldn't get enough gain. That complaint comes because I don't like to bypass in the input stage. That's why I tried a 6SL7 in my previous version. It was a good choice at it really let the 1626 sound come through. But since gain was an issue for me, I decided to bypass in the input stage in this version. After trying about 20 caps and not liking many, I hit on the Vintage Sprague that is in the unit now. So now with the bypass, I can operate the input stage exactly as I want AND provide enough gain for almost any line level input device. The wiring is solid copper for the power and ground runs, stranded for the AC power and heater runs and silver and/or silver plated mil spec on the input runs. All the soldering uses silvered solder except the heavier connections where I needed a better flux flow. Power runs are in star mode and the ground is in buss mode as usual for me. All the stuff is mounted in my .063 clear anodized alum chassis. You're not looking a bare alum here as in all my amps.  The speaker connectors 5-way binding posts are high quality vintage NOS types. They will accept 16 ga. wire or a pin plug via the hole. Otherwise you can wrap a larger wire, use a spade terminal or a banana connector.
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 How does it sound? With apologies to those who bought my previous efforts, this one may be the best to date. What's the difference? This one seems to have more "air". Now I am saying this on my recollection ... and as you know, you just cannot truly remember what an amp sounded like a month or two ago. Maybe I just miss having the Darling sound around. (Although my BX7 amp has been keeping me pretty happy.) This amp is everything I've come to expect from a Darling style and I will be glad to have one for my own soon. I feel this one might have a tad better bass detail as well. My first impression was a lack of deep bass. However, I now realize that when the bass is in the recording, the amp plays it without adding. This seems to bring the detail forward. There is an overall sense of "presence" and clear sound. Vocals sound natural and without ssssibilants. Wide imaging and depth are the de-rigor of this amp as in the previous ones. I think the RCA trannys have proven out here as well as going to a higher output Z. I recommend others might try this approach and will provide my output stage setup to those who are interested. 
Thanks for looking. |