"Superfly" - submini tube version of Doug H's Firefly

[frequencycentral]

These DM160 are seriously small. Left to right, 12AU7, 6111 submini, DM160, LM324 quad opamp:

[prnet]

standing ovation...

[merlinb]

Merlin, can you explain the heater circuit in your schematic on the previous page please, the two npn transistors. Also, do you think we should start a new thread for the 9v DM160 uFly?

The two transistors are simply a current-limiter, which in this instance will basically act like a constant-current source. The current is 0.6V / R, where R is the base-emitter resistor. So for 30mA:
R = 0.6 / 0.03 = 20 ohms. As for a new thread that's up to you. Probably worth starting one when you actually start fleshing out s proper circuit. Getting the self-split to work would be the first step, IMO.

[prnet]

ok... I'm still trying to fix the amp..
Now I can't get 180v anymore.. maybe the irf is damaged in someway..
Afterwork, I'm going to take another ic, maybe a irf840 (you told me it's ok..)
and some other inductance.. I think I'll solder another breadboard too, to be sure... or maybe I can etch a board from the layout posted in the thread.

I really hope to play with my new amp...

[prnet]

Hi Rick,
I was taking a look at the amp, and I remembered that I used a 1n4007 instead of the ultrafast...
I really wonder if this could be the matter...

[frequencycentral]

Hi Rick,
I was taking a look at the amp, and I remembered that I used a 1n4007 instead of the ultrafast...
I really wonder if this could be the matter...

Oops!  A 1n4007 just isnt going to work. It has to be an ultra fast recovery diode, I use UF4004. Also, another guy who built one ended up simplifying the ground connection by adding a jumper from f8 to n8 instead of having the ground go all the way around the board. On my last two I removed C8, which cut out some whine at high volume, and also allows a direct ground trace from f8 to n8.

[prnet]

yes.. I've noted some differences between your bottom amp photo and the layout.. then I've already seen thatif you  remove the pf cap you can place a trace direct to ground..

[prnet]

hi again.. just to update my experience.. still the same situation..
I tried yesterday an irf840 and another diode BY..(something.. don't remember)
It seemed it worked better, with more volume, but still far from the result..
I think I'll try now to separate the power section and build the smps. uhm...
the inductor is still getting warm too, while the mosfet seems to be more colder respect to 740?!?

it's very difficult to find inductors here, but I don't want to buy one from internet and pay 3€ of shipment for a 1€ component.. damn...
ok, keep the calm... how McGyver would find the solution? (he's got only a knife, a stick, a chewingum, and distilled water) 

[frequencycentral]

Here's one made by Tilly Dog, posted over at AX84:

Well, here's more evidence



I gave up on the tone stack - I could get a weak treble cut/boost with the moonlight stack, but the tone pot on the guitar has much more range. I tried a master volume, and found it *much* more useful. I was only ever going to put two knobs on the box, so went for the gain control and a master volume.

The switch changes the cathode resistor in the 2nd stage from 820R ("Ash") to ~4.7K ("Smoke") - the larger value gives the amp *some* clean headroom and a bit mellower tone, at the expense of some volume. (Centre position of this switch is off).

I had the case a lovely sooth satin black, but the clear-coat I put over the front panel reacted with the paint and crackled it :-(.

Even at 160V B+ this is too loud as a 'bedroom amp' without the MV.

There is still a certain amount of HF noise visible on the scope which is being picked up somewhere in the first stage. I played around with different grounding, etc. but other than moving the input ground as I mentioned before, nothing made much difference - even breaking the ground path to the switching circuit and running a separate ground for it. Nothing is audible, so I decided to leave it alone for now. (I didn't pull the 470p cap).

The guts aren't as neat as Rick's, but then you wouldn't expect that!



It's gone to my 'Official Tone Consultant' (proper guitar player) for a couple of days so I'll let you know what his verdict is when I get it back.

What a fun project, though !

Thanks

Andy

[CynicalMan]

Do you know what the amplification factor of the 7327 is? I've been looking at datasheets but they all seem to be strangely missing that information.

[frequencycentral]

The datasheet says 'a direct replacement for types 6111 and 6021', the 6111 has a gain of 20, the 6021 has a gain of 35, that's all I know. 

[prnet]

today, while i was rebuilding my P1extreme 19w in a new painted case, I etched the pcb for my superfly.
So, I can do another try.. hope this miniamp filnally will work.... tomorrow the response...
Anyway, the pieces are all new..  so if it won't work, maybe i'll start suspect about the tubes... 
maybe i could try with a 12ax7 and a 12au7....

I can always recycle the submini tubes to build a booster, if I'll lost my patience.. But never happened that an fx or an amp has win against me...
with a little of debug everything always worked to me... 

[frequencycentral]

New layout. What's changed:

• 470pF cap removed
• Ground trace simplified
• MOSFET orientation corrected
• Decoupling cap added for preamp supply
• Provision for Tilly Dog's bias mod
• Provision for master volume
• 1n4007 polarity protection added
• Fatter traces for fatter tone!

[prnet]

Here my little DiamondG 1W...

http://www.thepiper.eu/?page_id=129

Finally...
still some little problem to solve but it's ooooook!

[prnet]

Hi again, I'm again a bit confused..

I need to jump back of some posts...
I was still unsure about the transformer pinout..

I found today some files about the original firefly schematic and building guide.
(I uploaded the file at http://www.thepiper.eu/files/firefly.pdf )

the schematic and the build guide uses pins 4-2 that means 22500:8   

[frequencycentral]

I referenced this schematic: http://www.ax84.com/media/ax84_m276.gif which states 2 and 5 transformer pinouts.The Firefly is a 'classic AX84 project'.

Just looked at the chart on a 125A box,

• 2-4 @ 8R = 22500
• 2-5 @ 8R = 8200

The plate resistance of a 12AU7 is 6500 - 7700 ohms, so 8200 is pretty close. The plate resistance of a 6111WA is 4000 - 5000 ohm. So maybe there's a slighly better combination available. I did try different combinations including 2 and 4, with little difference THB.

Just looking at the chart on a 125A box again, 1-5 = 5600 and 2-6 = 4200. Maybe one of those would suit the 6111WA better.

I suspect the answer can be found one one of the many AX84 Firefly threads.

Maybe Doug could shed some light on it?

[sdp1234]

I was wondering if the transformer that Doug Hoffman sells would work for this type build.  It powers two 12AX7's at  240v from a wall wart.

http://www.hoffmanamps.com/MyStore/catalog/images/IMG_2431.jpg

http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=enter&template&thispage=Transformers&ORDER_ID=!ORDERID!
http://www.el34world.com/projects/images/TubePedalSchematic.gif

[zencafe]

Hey Frequency Central! Congrats on the good build, also congratulations to Doug for the great design.

One question, Have you tried 2 similar circuits with both nixie powersupply, and your voltage multipliers (the ones with diodes, caps and a max1044)?
I wanna check hoe the different voltages affect really the sound...

Thanks!

[Scruffie]

If I wanted to... could I build the Superfly Special using normal tubes (The 12AX7 & 12AU7) and use the new MAX1771 charge pump to give it a bit more voltage? Anything need changing or can I just sorta... put them in.

(Tube Newb  )

[Scruffie]

Well... I went over the datasheets of the AX7 & AU7 and other than the pin outs, I see no difference between the schematics apart from dropping the Extra tube and a few minor ammendments... I did draw a schematic but don't really see the point in posting it as i've just changed the pin numbering for the tubes and added the MAX1771 schematic on the same sheet and added a Baxandall Tone Stack rather than big muff... plus it's not really my work.

So unless anyone has any comments on wether it'll work or not and me not wanting to derail this thread from its sub-mini routes, the only question I really have is where can I get a 0R050 1 Watt Resistor? And as the MAX1771 can deliver higher voltages than the 555 is there any harm in upping it to 250V? I see the tubes are rather to 300V on the Plates but only 180V on the Cathodes....