NuTube preamp concept

happyrabbit · « **on:** 18 Apr 2018, 12:54 am »

Just a thought. Design not finalized.

Jensen 1:1 transformer coupled input
NuTube using a 100k ladder attenuator as the plate load.
LSK489 output buffer.

Adjustable plate, grid , filament (ccs) based on the lt3082

Startup/Shutdown muting.

6 layer pcb - S/G/P/P/G/S

See attached images

Speedskater · « **Reply #1 on:** 18 Apr 2018, 04:39 am »

Schematic?

Folsom · « **Reply #2 on:** 18 Apr 2018, 05:21 am »

Quote from: Speedskater on 18 Apr 2018, 04:39 am

Schematic?

That would be nice.

Folsom · « **Reply #3 on:** 18 Apr 2018, 05:26 am »

Also, what about running it balanced ? If you had transformer in and out, that'd be possible.

happyrabbit · « **Reply #4 on:** 18 Apr 2018, 07:32 pm »

+ Schematic - very similar to designs shown on http://www.nutube.us
+ Transformer Coupled Output (gain stage is single ended & buffered by a Sonic Imagery Op Amp)
+ Load Line

Dwight

happyrabbit · « **Reply #5 on:** 29 Jun 2018, 12:51 am »

Finalized the layout. Updated the start-up/ shutdown with a 1C reed relay. Ordered a couple shunt based ps pcb’s from hotshotaudio. Picked the lsk489 in a simple voltage follower for the output buffer. Also ordered a couple khozmo 100k ladder attenuators. See attached.

Dwight

happyrabbit · « **Reply #6 on:** 26 Aug 2018, 01:59 am »

Ok... almost finalized. This pcb layout uses both channels instead of one

happyrabbit · « **Reply #7 on:** 12 Nov 2018, 12:19 am »

Can’t seem to let this project die..

mono channel with jfet(w/o protection)

Dwight

happyrabbit · « **Reply #8 on:** 26 Dec 2018, 03:23 pm »

Pic of the shunt based ps with the latest pcb concept. Going to order enclosures from this company. Watched the videos on using their software. Seems simple enough..

https://www.protocasedesigner.com

Dwight

happyrabbit · « **Reply #9 on:** 20 Mar 2019, 06:23 pm »

randytsuch · « **Reply #10 on:** 20 Mar 2019, 07:39 pm »

I've used these guys before, for custom front panels
https://www.frontpanelexpress.com/

I also just bought a nutube PWB, should be getting it in about a week.
Its from a diyaudio group buy.
Now have to decide if I want to build it lol

Randy

happyrabbit · « **Reply #11 on:** 21 Mar 2019, 12:46 am »

R ,

Thanks for the insight on frontpanelexpress. I will down load it and give it a spin. I would build the diyaudio pcb. It’s a solid design and 100% functional

Dwight

randytsuch · « **Reply #12 on:** 21 Mar 2019, 02:45 pm »

Quote from: happyrabbit on 21 Mar 2019, 12:46 am

R ,

Thanks for the insight on frontpanelexpress. I will down load it and give it a spin. I would build the diyaudio pcb. It’s a solid design and 100% functional

Dwight

I didn't buy the one from the store, bought this one
https://www.diyaudio.com/forums/group-buys/334216-gb-b1-nutube-pcb-integrated-ps.html

Has a PS built in to make it easier. It was a limited group buy, so I joined.
I have a backlog of projects, need to finish and case up my headphone tube amp as my highest priority.

I used FPE a long, long time ago, but it was pretty intuitive and easy. If you can design PWB's, I'd expect you'll have no problems with this.
Not sure about the costs these days, it seemed reasonable at the time to get a custom front panel. I added engraved lettering which makes a nice touch.

Randy

tubesguy2 · « **Reply #13 on:** 27 Mar 2019, 04:02 pm »

Quote from: randytsuch on 20 Mar 2019, 07:39 pm

I also just bought a nutube PWB, should be getting it in about a week.
Its from a diyaudio group buy.
Now have to decide if I want to build it lol

You should definitely give it a shot. I've always been in the "ruthlessly revealing" and "vanishingly low distortion" camps, but, golly, music sounds great coming out of the B1 Korg.

happyrabbit · « **Reply #14 on:** 5 Jul 2019, 11:40 pm »

Mono 100k ladder attenuators from Khozmo

happyrabbit · « **Reply #15 on:** 13 Sep 2019, 03:34 pm »

Changed design to thru hole. Prototype SMT is expensive !

hopefully ordering a couple pcb’s this weekend

happyrabbit · « **Reply #16 on:** 25 Sep 2019, 07:28 pm »

Norman Tracy · « **Reply #17 on:** 26 Sep 2019, 08:33 pm »

Dwight,

About your case:

So ~~pretty~~ expertly styled and tastefully designed, can't stop
Is that the product of www.protocasedesigner.com mentioned above?

About your project:

Details on the shunt based power supply please.
You will find the NU-TUBE very much worth the efforts you are expending.

happyrabbit · « **Reply #18 on:** 26 Sep 2019, 09:44 pm »

Norman Hey !

Thanks for the kind words

I ended up using protocasedesigner. I would rather design the case using Alibre but custom case prototypes are silly expensive. To be honest , the case turned out lovely.. I did not have high hopes for it when I hit the ‘buy’ button. I attached another pic next to a Schiit amp for reference.

The shunt power supply was from eBay but i cannot seem to locate seller anymore

Also , the pcb’s arrived today ! My 1st 6 layer PCB. This design is a bit more elaborate than the reference design. Fingers Crossed.. The devil is in the details

Dwight

Norman Tracy · « **Reply #19 on:** 27 Sep 2019, 07:50 pm »

Dwight,

All the more impressive seeing your case next to a sublimely designed piece from Schiit. I call their work ‘sublime’ (perhaps a slight exaggeration for effect) because the result is functional, cool, interesting, and lust inducing while also being elegantly simple and relatively easy to manufacture. Both designs use the fact CNC controlled sheet metal punches can make holes in a flash to their advantage. Schiit’s has all those little holes for ventilation but also to portray a sense of technology at work. Dwight chose a wide ‘C’ shape in a very interesting organic pattern nicely contrasting the straight linear case edges and surfaces.

I am very curious what Dwight does for a living and would not be at all surprised if it involves some aspects of product and/or industrial design.

I make a living as an electrical design engineer and with PCB layout one of the favorite aspects of my job some comments on your PCB.

Six layers is a bit extravagant for a circuit of this complexity. I like it high-end audio is all about the subtle (and at times far from subtle) extravagances. Excellent design practice adding all the stich vias connecting the copper pour to ground. As I expect you know that will really help in the last degree of noise reduction.

Next you matched the fonts on the PCB to the ‘dht Luv’ on the front panel!?!?!?!!!!! Please take this as a complement but when we change the fonts on a PCB CAD system to an artistically selected typeface matching and front panel we have well and truly crossed the Rubicon to Industrial Design Geek 1st Class. I’m jealous due to still being stuck at 2nd class ranking.

Finally I have never seen anything like and really love the subtle detail on parts like C2, C9, C10 calling out their insertion polarity. Normally we use the ‘+’ sign or fill in part of the outline circle with a boring straight line fill. The subtle crescent moon thickening of one side of the circles on your electrolytic cap footprints just made me grin (because such-a-sad-but-happy-geek).

A closing question. Have you noted Korg’s warning the NuTube is microphonic? The taut wire that forms the control grid elements has a high-Q ringing in the kilo-Hz range. Decoupled PCB mounting and soft feet for the enclosure are your friends.