Min's World of Tube Audio: February 2008

1626 Darling Single Ended Triode SET Tube Amplifier V

1626 Darling SET Tube Amplifier

0.75 wpc of pure SET sound

5th Darling on sale on eBay

This amp is headed to Singapore. The guy loves the amp. I do hope that he's got a pair of efficient speakers for this to drive. I never get tired of building Darling amps, especially when they bring in good profits to perpetuate my hobby.

JE Labs 300B SET Amps

JE Labs 300B SET Amplifier with James 6123HS OPTs

Custom ordered

Completed on 2/25/08

This was by far the simplest amp that I've wired so far. It helped to have all the big components mounted on top and to have all that space underneath. The only thing that I would have done differently is to have the OPT where the choke is. Steve Chu, my customer, wanted it this way for looks and I just had to make it work. Well, customers are always right. When I first fired the amp up, I noticed that there was clicking noises coming from the bypass cap for 6SN7. Apparently, the voltage handling on the cap was a bit low and was working to its limit. I replaced them with 47uF 160VDC and the clicking went away.

Under the hood with everything mounted on the top plate. Notice the octopus of wires coming out of those holes off of power tranny.

Voila! The finished amps. I thought my Dynaco MKIIIs were big. They are puny compared to those 300B monoblocks!

Yep, all those irons for glorious 9 watts of SET audio.

These monoblocks weigh at least 40 lbs each.

Size comparison of James 6137HS iron to 6113HS. The 6137HSs are SE 30W 7K primary and 4, 8, 16 ohms secondary taps. I am putting 8 ohms loads to 16 ohms taps to lower the primary Z to 3.5 k for 300Bs. It's all about ratio when it comes to trannies.

How does it sound? I am very happy with these amps. They really groove to the music when listening to rock or pop music. Great textural rendition and rhythmic integrity when listening to complex ensemble. 9 wpc is plenty for my listening level and the efficiency of my speakers, but it's still just 9 watts. They do seem struggle a tiny bit when I try to push the full power of orchestra through them. All in all, their dynamic performance is amazing for most music I have CDs, mp3, and records for.

Will I build these for myself? Probably not, mostly because of its size and the cost of construction. I think the same caliber of sound can be achieved using other designs in stereo at 3/4 of cost or less.

1626 Darling Single Ended Triode SET Tube Amplifier IV

1626 Darling SET Tube Amplifier

0.75 wpc of pure SET sound

4th Darling sold on eBay

Tidy Transmission Line DIY Speakers

Transmission Line Speaker Design by SDS Labs

My first DIY speaker

Completed on 2/10/08

This is my first attempt to build DIY speakers. I have always been curious about how transmission line speakers sound for a long time. It seems to me like there are as many people who are interested in the TL design as there are people who are into tube amps. Being a experimentalist at heart, I had t give this one a try. I used Sheldon Stokes' Tidy TL design. What attracted me to the design is its compactness: most of TL type of designs that I read about are either really complicated folded horns or 6' tall pipes like Voigt Pipes, neither of which had much appeal to me for the lack of WAF (wife acceptance factor) and cost of construction.

I used some 2' x 4' 1/2" MDF boards that I had purchased to build a dog house for Sophie, but I never got around it. The biggest challenge that I faced in making these speakers was cutting. I so wish I had a table saw for this. I just didn't get the most accurate cuts using circular and jig saws. I had to do lots of sanding and patching up with wood filler to hide my mistakes. But it worked out ok in the end. The speakers are veneered in mytrle burl (purchased on eBay for 100 sq/$20) and finished in 3 coats of natural stain, followed by 3 coats of satin polyurethane.

How do they sound? They seem to perform best with vocals and instrumentals. They definitely do lack bass extension (below 80 Hz), but this was to be expected with this design. I have a subwoofer picking up the slack on it, so I don't have any problem with that. One thing that I do want to try next is to use different drivers. The ones in there are 5.5" Dayton PA drivers that I purchased for $22/pr at Partsexpress. They tend to sound more like PA speakers than hi-fi speakers. I am leaning towards any of Fostex 6" 160 series, and I will post the result of that upgrade when it happens.

1626 Darling Single Ended Triode SET Tube Amplifier III

1626 Darling SET Amp

This is my 4th Darling I made to Sell

Sold on eBay in 30 minute!

VTA SP6 Preamp

Roy Mottram's VTA SP6 Preamp

Completed on 1/16/08

PCB available at www.tubes4hifi.com

I guess I got the point where all the tweaking with power amps has been done and it's about time that I looked into preamps and speakers. So far, I have gone through several solid state preamps (NAD, Adcom, etc.). I also tried a passive preamp with a homebrew phono preamp. All these gave me performances a lot to be desired. I have always wanted to try a tube preamp or two, but I was somewhat put off by off-the-wall prices of preamps that were worth considering. I guess the Dynaco PAS-2/3 would have been an option that can be had for under 200 bucks, but some tweaking (PS upgrade, recapping, and tone control removal) would have to be done to make it listenable. I figured that if I were to spend more than $200 on a decent preamp, I might as well built something new. After having done some research, I narrowed it down to Aikido preamp or Roy Mottram VTA SP-6. I settled for the latter, mostly because I had to have a phono stage.

The harware (knobs and RCA inputs) on the chassis is salvaged from my passive preamp. Built on an oak base stained in dark cherry, and finished in high gloss polyurethane. I ended up using a 12x12 lexan polycarbonate as a top plate to showcase all the electronics and glowing tubes inside. The preamp uses 2 NOS RCA 12au7s for the linestage and 2 TAD 12ax7s for the phono stage. This probably is the best sounding preamp that I owned so far. It sounds very neutral and lets all the subtleties in recording pass without any coloration. It's fast, articulate and versatile. I would recommend it to anyone who's serious about their audion stuff.

JE Labs 2A3 SET Amp

JE Labs 2A3 Single Ended Triode

3.5 wpc DHT SET Sound

Finished on 1/5/08

This is my first attempt to handwire a hi-cost SE DHT amp. I have built several Get*Set*Go amps that are SE DHTs, but they were all built using PCBs. As much as I have liked how the GSG amp sounded, I felt like I would never fully appreciate amp building unless I handwired a SE DHT. Since building a hum-free and low-noise SET is often difficult, I welcomed the challenge of building one that was not only hum-free, but one that sounded good.

Since this was going to be a keeper amp, I didn't want to compromise on parts used. I wanted to make sure that the amp was overbuilt with resistors, caps, and irons that were well over the required power rating. I went with James 6123HSs, which BTW was compared quite favorably with Hashimoto OPTs by many fellow amp builders. The schematic I used was JE Labs Simple 45/2A3, with a minor change: instead of 1 k for the 2A3 cathode resistors, I used 900 ohms. I got more out of those Sovtek 2A3s this way. I never really liked the electrolytics in the PS, which I think have a tendency to produce mechanical sound. So I went with all Solens PP caps in the PS section.

Gotta love those gold plated binding posts. Thet are oversized and heavy duty.

Square waves at 40 hz

At 1 kHz

At 10 kHz

At 20 kHz

Wiring was quite easy, but building the chassis was not. I am not going into details of how the chassis was made, but it suffices to say that I could use some good set of tools, including a table saw. So, how does it sound? Simple awesome! The amp is very musical. It has all the excellence and frailties of SE DHT. Very well balanced with tight bass. Mids and highs are very fluid. I love listening to classical music through this amp. I really think that the James OPTs do a great job at frequency response. Will I keep it? 100% yes. I finally found an amp worth of my collection. I hope this will be a family heirloom.