Darling Amp, JE Labs Style

It's been 20 years since jc morrison started hosting the new york noise audio design exhibition at his Hoboken, NJ loft. One of the highlights of that year's exhibit was Darlingfest '99 as reported by Jeremy Epstein in the final issue of Sound Practices. The Darling amp was the brainchild of Bob Danielak and was published in Sound Practices Issue 15.

Jeremy's octal driven Darling amp made a lasting impression on me but I never got a chance to build my own version due to a busy performing schedule.

While I was organizing my workshop in the basement this past winter, I found power and output transformers from a Sony TC500A tape recorder + other parts to build a Darling amp.  

The chassis cleaned up nicely with a wire brush. Then I drilled, cut and punched the necessary holes before spraying a fresh coat of silver Hammerite.

I chose the 6F5 hi-mu triode with a cool grid cap as the input/driver tube.

To qualify as a Darling amp, the indirectly heated 1626 transmitting triode  output tube is de rigueur.

The TC500A donated a healthy 6CA4 rectifier.

!!!WARNING!!! 

The voltages found in this circuit can be lethal, build at your own risk!!!

My interpretation of a Darling amp is ready for testing and listening!

Bench Testing

Both channels driven

P = V²/L

2.415 x 2.415 = 5.832/8 = .729 or 729mW per channel

Hum and Noise = 1.8mV

100Hz

1kHz

10kHz

I did not expect this level of performance from the cheap looking Sony OPTs, which I also verified while listening to the amp!

Bass extension is surprising from this 3/4 watter! It is deeper and tighter compared to my Tango'ed SE171A amp. However, in the midrange, the true Directly Heated Triode shines. The 1626 was just a touch veiled in comparison. Although it sounds more powerful than the similarly rated SE171A, it also doesn't overload as gracefully. I remember hearing a similar phenomenon when Steve @ Angela Instruments asked me to build the Simple 5691 > EL34 SE amplifier. The Simple 45/2A3 clips with more finesse. Is the cathode causing the relative lack of transparency and harder clipping?

The days of $5 Type 45s and 2A3s are long gone. But NOS 1626 tubes can still be acquired for under $10 a piece. Since it has a cathode, with careful wiring less than 2mV noise is achievable on AC heating which is quiet enough for me even on headphones. There's no need to hunt for hard to find 25-75 ohm, 2W hum nulling pots. That's just a couple of reasons as to why a Darling amp derivative is one of the cheapest and easiest routes to a DIY SET amp nowadays.

Did I mention that it also does a great job driving headphones?

headphone adapter/attenuator schematic for 
efficient headphones ex: Grado SR80, Koss KPH30i/Porta Pro
Lower efficiency/high impedance classic headphones like the 600 ohm AKG K240 Monitor, 
Sennheiser HD420, HD6xx and Orthodynamic/Planar magnetic: Echo TDS-16, 
Fostex T10 and Yamaha YH-1, can be driven directly from the speaker terminals

Happy listening!