The Sukuma Darling Amp
UPDATE : The Sakuma Darling is currently torn apart. I never could get the last bit of humm out of it and it was quite frustrating. I NEEDED to move ahead and work with my 12B4 tubes for a headphone amp, and (hopefully) my 813 powered amp for my living room. The Sakuma Darling will have to wait a little bit. Here is a picture of it in its almost final form.
The Sukuma Darling was designed by Bob Danielak. Check out his site.
Basically the Sukuma Darling is a variant of the DC Darling using tranformer coupling and similar tubes. Normally one would use a different tube driving the output tube. In this case we use a 1626 to drive another 1626 thru an interstage transformer. The now discontinued P-157 "nickle wonder" couples the audio signal to the input tube and a Hammond Universal OPT handles the output to the speaker.
No pictures yet, the chassis is not finished yet and I am embarrased at the way it looks so far. Right now there is a good bit of hum which should disappear once I fix my crummy grounding scheme (dont ask!). Bass is a bit rolled off too, thats got me curious. I'm thinking the interstage transformer is responsible for this but I will wait for things to burn in before I start yanking parts. One tube is gassy, so I am happy I purchased extra tubes. Finally I am still playing with loading on the output transformer. Going from 4800k to 5200k really improved the sound. I'll step up the load till it starts to sound bad and step back. More details and pictures soon.
Update 18 Dec 2000
After some thought, I totally rewired my little Sakuma Darling. I discovered the holes drilled for input jacks were tight, something I like to do, yet this caused the inputs to be grounded to the chassis and not my isolated wiring. After isolating the input jacks from the chassis things got a bit quieter, still not perfect. I added a ground from the voltage doubler and a chassis ground to psu ground. Total silence!
The amp plays the mid/high range quite well, bass is nice and solid now with some material. Lisa Ekdahl sounds incredable, so does Holly Cole and Eminem. Music with much more complexity or lots of energy tends to get muddy, congested and somewhat distorted. I assume i'm running into issues relating to the interstage transformer. I have read some tricks to improve the performance somewhat so I will see what I can do.
Update 02 Apr 2001
Finally the Sakuma Darling is done. All that is left is a nice base for the unit. So what has happened in the some 3 months? Quite a bit. I had taken a break from it for a bit but then jumped back in determined to resolve my sound issues. Totally rewired, I played with grounding a good deal. This amp has some slam. It will not drive my current speaker setup but thats okay. I am using it as a headphone amp at work to drive some grado headphones. Big time impedence mismatch given the grado's 32ohm vs the OPT's strapped at 16ohm. No clue what my operating point is with that setup. The poor power tranny gets a tad warm. I ended up redesigning the PSU a good deal. I feel it could be even better with more time and effort but I have other projects in the wings which I would rather fiddle with. My PSU looks like this:
PST->180uf cap->5h Choke->100uf cap->100ohm wirewound->50uf cap->100ohm wirewound->15uf cap.
The 180uf and 100uf caps are crummy electrolytics scavanged from a powersupply I had. Used beyond belief but still good. The 50uf and 15uf are big ass paper in oils. A voltage doubler with less than perfect parts supplies the filements. Personally I would have redone that first but I lazy like that. I think its the source of the last bit of noise I have not been able to exorcise out. Given the noize is lower in db than tube hiss I am not concerned.
Tips For Building
- Build a beefy beefy PSU.
- Build a beefy beefy PSU with excellent parts.
- Breadboard this before you commit
- Parts quality is important but not critical
- Enjoy the music