Integrated DC Double Darling

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I don't seem to notice anyone showcasing their Darling amps lately (yeah, right!), so I thought I would show off what I did with mine. I built this as per request of two former customers of mine, but I might just keep it (or not).

I got bored of building cap-coupled Darling amps, so I gave a direct-coupled Darling amp a try. I am using a pair of 3K:8sohms Transcendars powered by a NOS Chicago power tranny with a NOS Triad 4H 90 mA filter choke. I used a combination of Bod Danielak's and Jeremy Epstein's schematics. I guess the 4 inputs and selector make it an integrated amp.

I didn't rectify the heaters at all, and I hear ZERO hum through 98 dB/W/m speakers. It was running so quiet that I thought, on the first fire up, that I forgot to plug in the AC cord.

Loads of details and resolution (slightly more than cap-coupled) with tight bass and flowing mids + highs. Doesn't get driven to clipping easily. It's very loud with my Klipsch Fortes. Should give about 1.5 wpc. I gotta give it up for Transcendars. These are seriously fine sounding OPTs at $100/pr. Here are pics:

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[EWBrown]

Very nice! My supply of 1626s is dwindling down to four NOS and a few well-used ones..., I'll have to get some more, and swapmeet and hamfest season is nearly upon us, up here in the NE frozen wastelands ;-) I've been considering PSET or even PP 1626s sometime.

I've not yet tried the direct coupled route with 1626s, but I've had great results with that circuit approach with 6EM7s / 13EM7s (the circuit is found in Gary Kaufman's Tube Page), here :

http://www.the-planet.org/6EM7.html

I have also finally managed to achieve hum-free AC filaments sonic nirvana, also to the point that tI thought the amp wasn't working, even with good R and V checks, until I put a signal through it.

/ed B in NH

[TomMcNally]

Looking good Min ! I haven't tried the DC or Double DC Darlings yet. What kind of B+ did you come up with ? I was going to try a PPP 1626 amp, but I decided not to waste the now precious (thanks to us) 1626's and will look for something else to mess with.

[EWBrown]

The B+ will be significantly higher, as the 1626s' grids and hence the cathodes are riding at or above the driver's plate voltage.

In teh 6EM7 design, the cathode voltage is around 140VDC, plate current 50 mA and V P-K around 180 to 185VDC, the 6EM7 is being run around 90-95% max PD rating.

/ed B

[TomMcNally]

Do you have a schematic for the 'EM7 version Ed ?
I have a big box of them ... time to do something with them.

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Thanks! The B+ is around 400 VDC and 170 VDC at the cathode (common for four 1626s). I was using 325-0-325 PT and I was worried that the B+ was going to be too high. I was going to use 5U4 to drop as much voltage as I could and use a thermistor if needed, but the voltages checked out even with a GZ34. I am a fan of DC Darling now. There is a noticeable increase in resolution and imaging.

Ed, according to Jeremy Epstein, his PP IT-coupled 1626 amp didn't sound all that great. Since he had four 1626s on the chassis already, he rewired it to PSET with 6SN7 and was happier with it.

-Min