A Very Compact Hybrid Amp

[cfcubed]

> .. I can't help but wonder what better use the space allocated to these sorts of things (jacks, pots, etc) could be put to.

> ... In this compact amp the front and back panel real estate will have to be used as efficiently as possible. And so it may turn out that everyone will be happy to just take pre-fab'd pieces because there just isn't any other creative way to do it (assuming the Hammond enclosure).

Perhaps best if the general merits of pre-fab pieces & board-mounted accessories should appear in a separate thread.

No need to get ahead of ourselves here... Take another look at the proto PCB PDF of this [trans]portable amp and you'll see there is NO room for jacks, pots, etc anyway

We have put all the space to good use

We think anyway, still have yet to build & hear this PCB version yet.

I'll try to keep quiet now until I've some nice, little 4.7" x 3" x 1.7" thing to talk about

 

[m0b1liz3]

cfcubed, you have built the proof of concept though right? To your ears does it sound as good or better than your existing SOHA?

 

[cfcubed]

Quote:

Originally Posted by m0b1liz3 /img/forum/go_quote.gif cfcubed, you have built the proof of concept though right? To your ears does it sound as good or better than your existing SOHA?

Yes indeed.. Although the POC lacks the improved "pot-less" frontend, I like its sound very much. Didn't want to "tear" myself away from listening to it to inform the development team of the performance of this new design rev. No surprise, really, as it has the combo of tube at better operating point (85V) and discrete buffer. Plan on "re-discovering" the 12AU7 variants I've laying around

Nice with my hi-Z DT-880s and also with my low-Z D2000s, it is likely this will end up the favorite of my tiny stable (now w/SOHA+JISBOS). Maybe it will be the one that stops me from building others, but probably not due to curiosity & builders itch

That said, as a design contributor of this amp, always respected runeight's refrain from hyping his designs. Guess he prefers to let those outside the design team do so. In which case I've gone too far already

 

[runeight]

They have shipped and I will get them on Monday and send to cfcubed and forsakenrider on Tuesday. I'm anxious to see these tiny boards.

I'll post a photo.

 

[m0b1liz3]

This may be a stupid question but...

Is the assumption that with a potless front end you are using your computer or mp3 player to control the volume level?

 

[runeight]

Interesting thought, but no, we were just planning for a small off-board pot.

Nothing but the power jack is on the board. No pot, input or output jacks, power switch or heater switch. To maximize space available for the components.

 

[nsx_23]

hmm, that will make casing a bit tricky.

 

[runeight]

Maybe, but maybe not. cfcubed is already planning how to mount the auxilliary components. We'll see how he does with the proto.

One thing to remember is that while the board is very dense in 2D space there is room in the vertical dimension to fit lots of things.

Nevertheless, a good prototype will tell.

 

[cfcubed]

Quote:

Originally Posted by m0b1liz3 /img/forum/go_quote.gif Is the assumption that with a potless front end you are using your computer or mp3 player to control the volume level?

Oops, my mistake, there is a volume control! I should be saying "trimpot-less" frontend or maybe auto-biasing or whatever runeight may want to call the use of an opamp in the frontend/tube stage (see frontend design). IOW, unlike many other designs, you will not have to fiddle with trimpots & testpoints when rolling tubes.

Don't anticipate casework to be hard, but it's all relative I guess. Will use masking tape templates & center punch. E.g. from the thumbnail below notice:

1. Front panel (plastic) - Gets easy holes for pot & jacks. Since input jack and pot are tied, there are only 6 connections to PCB (IG,IL,IR,OG,OL,OR). I'm using RK097 I have around, but panny EVJ series is fine too.
2. Back panel (plastic) - Round holes for A/C in, fuse & optional power switch. Fuse is recommended to save your $20 wallwarts in case of build error/short. Small rectangle for heater slide switch. Air holes will also happen.
3. Top panel - aluminum (removable in target case) - Hole for tube. I'll use my large $25 Greenlee step drill.
4. Sides (aluminum) - Probably some discrete air holes will be needed.

Deck of playing cards is shown for size comparison... There are alot of parts going in there

But most of the bulk is plastic bags.


Will be following runeight's "a slow and careful build process will be the best way" and no beers during this build

Confident it will be very much worth the effort.

 

[forsakenrider]

NO BEERS! what... i dunno if i can handle that.
I got my DIGI order today, over night shipping for 8 bucks canadian.... wow.

 

[nsx_23]

I can't wait to see the finished prototype!

 

[runeight]

Boards arrived today. Off to cfcubed and forsakenrider tomorrow.

I must admit that I am getting pretty stoked about this little amp. And that's unusual for me.

Boards are very tiny and very tiny to hold an entire tube hybrid amp with discrete output stages and a 95V supply and to run from a walwart.

Good stuff.

 

[digger945]

I guess if your stoked, this must hold a lot of promise.
Impressive looking boards, they will be packed for sure.
I look forward to listening impessions.
If the protos go smoothly, could this be offered pretty soon? A group buy initially?

 

[runeight]

Yes, I think it does have a lot of promise. But, like everyone else, I'll have to wait for our intrepid prototypers to finish and tell us.

I ordered some extra boards this time and if the amps work out well I will make these available to whoever is interested.

After that we can consider group guys along with pre-fab'd casing pieces.

 

[wiatrob]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Boards are very tiny and very tiny to hold an entire tube hybrid amp with discrete output stages and a 95V supply and to run from a walwart.

I was wondering how this was progressing a while back, and missed this thread. Congrats on another unique design - that's a lot of little holes

Looking forward to reports on the first builds. Great gents!