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

[jaapie]

another update-

I think the volume control thing is just a quirk of the guitar wiring that i haven't noticed before. I don't usually play with as much gain as I'm able to with this amp, so i think the hum is just more apparent now.

I also added a cobbled-together one-knob BF tonestack to give it more of a midscoop. There's a good bit less gain than there was before, but the tone is spot-on and there's still a good bit of bite, especially on chords. Maybe I should check out adding an opamp recovery stage before the volume control to give it a little more dirt?

[frequencycentral]

I always remove the 470k grid stopper when I add a tonestack. Get you a bit of gain back.

[jaapie]

I pulled the grid stopper out, but it actually sounded cleaner so I put it back in! The more I play around with it, the more I like it even with less gain. I may see about adding a cathode bypass cap to the second gain stage, but it works great just as is! Thanks for a fun, great sounding little circuit dude!

[jaapie]

eh, I just looked at the "Superfly Special" schematic with the tone control, and I see maybe you meant the resistor and capacitor... maybe I'm a bit too literal! I'll try it tomorrow taking both of them out and see what happens.

[iccaros]

Good work Jappie, I found that I like the dual 6011 tubes if I am adding pedals, but the 6112 and 6021 If I am going to use it on its own..

PS I like your bread board..

[iccaros]

Help, I am getting a stutter,
My first try to fix it was to pull and move wiring, but no good, then I soldered the tubes to the board... Nope (it is louder ..  now)

So before I look at the IFR 740, which is what I think it is,
can having the output transformer inside this lunch box (metal) this way cause this problem?



here is a video of the meter, you can not hear the stutter (don't know why?), but you can see it  on the meter. This is reading DC voltage for the B+ off the output transformer
http://dl.dropbox.com/u/14312589/MVI_0256.AVI

If I have my guitar at full volume or no volume its not as noticeable, but when I turn down the guitar it starts to stutter. I would agree that it is oscillation, and I have changed out tubes and lowered voltage.. No joy.  I may try a 1 meg across the input jack.

Any and all suggestions are appreciated, thanks

[jaapie]

All right, I finally finished building everything into the radio chassis last night and got it up and running. I still need to give it a couple tweaks (wired up the tone pots backwards, which is interesting!) but it seems to be working well, with one caveat: The heaters won't heat unless the amp is put into standby before the HV is turned on (I know that this is good practice anyway, but I didn't have this issue on the breadboard. Here's a breakdown of what happens:

When the amp is powered on without being put in standby first, the 12v node of the power supply as well as any node in the circuit that is supposed to be at 12v (i.e. heaters, Nixie supply, even the power switch) drops to 0v. Strangely, however, the HV taps are all about right. This is obviously really screwy and I'm pretty sure it's against the law to make energy from nothing. Anyway, I don't think tubes like that high voltage when they're cold.

If I put the amp in standby as per the mod mentioned a while back in this thread (shorting the emitter and collector of the BJT), the 12v doesn't drop to 0 and the tubes heat up properly. When standby is switched off, the HV comes on as it should and everything works properly.

I'm excited that it works, but I'm curious as to what could be causing this to happen. Does anyone have any ideas?

[frequencycentral]

I think the SMPS draws more current when it starts up than when it's running. So when you turn it on the SMPS is fighting the heaters for ma - and winning, as the heaters heat up relatively slowly. I've never had this issue. What's the ma rating of your PS?

[jaapie]

That's what i thought was happening too, but it's strange that it didn't happen before. The wallwart I'm using is rated 1A, so i should have plenty of current, right?

[Perrow]

Glad to see that someone has use of my stand-by mod :-)

[jaapie]

Here's some more pictures:

http://a4.sphotos.ak.fbcdn.net/hphotos-ak-snc6/223701_10100177480834003_22201673_46747679_3889267_n.jpg
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/263378_10100177481003663_22201673_46747684_1740590_n.jpg
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-ash4/281656_10100177481233203_22201673_46747690_5512925_n.jpg

[iccaros]

Here's some more pictures:

http://a4.sphotos.ak.fbcdn.net/hphotos-ak-snc6/223701_10100177480834003_22201673_46747679_3889267_n.jpg
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-snc6/263378_10100177481003663_22201673_46747684_1740590_n.jpg
http://a2.sphotos.ak.fbcdn.net/hphotos-ak-ash4/281656_10100177481233203_22201673_46747690_5512925_n.jpg

Nice, I like the reuse of radio. 

[Perrow]

BTW: Didn't use the IRF740 but rather an 18N50, the on resistance is 0.22R (18N50) instead of 0.48R (IRF740), meaning lots less heat

Interesting! I await your results with anticipation!

Got mine working at 165V with the 18N50 and Futurlecs 100uH power inductor, on for at least five minutes without heatsink on the 18N50 and it's just warm to the touch 

[iccaros]

Got mine working at 165V with the 18N50 and Futurlecs 100uH power inductor, on for at least five minutes without heatsink on the 18N50 and it's just warm to the touch 

@Perrow
so you used this one ? http://www.futurlec.com/Components_Others/IND100.shtml


Thanks for the updates..

[jaapie]

I think he meant this one
http://www.futurlec.com/Components_Others/PIND100.shtml

i ordered a few of the ones you posted, and they're about the size of a 1/4w resistor-- i seriously doubt that they could withstand the high voltage (I think someone else a few pages back was having problems using that inductor). 

On the other hand, I used the smaller inductors as a filter so i could use a 3.5in full-range speaker with my superfly (to filter out freqencies abouve ~5k and very roughly emulate the rolloff of a guitar speaker).

[iccaros]

cool, Making an order, I plan on making a few of these as Christmas Gifts this year..  I did see the post earlier, but I thought maybe with the MOSFET change it made it work..

Not to sound stupid, I am.. But trying not to be..

I bough a few of those 3 watt 3 something inch full range speakers, Which I am making some small Cabinets for,which size inductor did you use?

Thanks

[Perrow]

I think he meant this one
http://www.futurlec.com/Components_Others/PIND100.shtml

That's the one.

[jaapie]

I wound up using a 190µH because i broke the other ones I had (a couple 100µH and a 120µH) trying to fit them inside the speaker cable plug. I was shooting for 220-250µH to roll off above ~5-6kHz...the 190µH rolls off above 7kHz, which is a little too bright for my taste (especially with the tiny, bassless speaker). As it is it still sounds a lot better than my little Marshall MS-2 with the same sized speaker, but it really sounds great through a full-sized guitar cab. I've been playing it through an ancient 15" Vox closed-back bass cab and I love it...although there is some charm to the rattiness of the tiny speaker.

Here's the calculator i used to figure out what value of inductor to use:
http://www.the12volt.com/caraudio/crosscalc.asp

The inductor goes in series with the speaker. I didn't have space for an extra speaker jack, so I soldered the inductor inside a 1/4" plug and then soldered about 6" of speaker cable to the plug and the terminals of the little speaker. That way I don't have to worry about switching the filter in and out, I leave the little speaker plugged in anytime I'm not using a bigger cab (the main reason I put the speaker in it was to decrease the chances of turning it on without a load...the speaker jack is right next to the power switch).

[iccaros]

thanks,

I have three speakers I tested this with, a 12" Celeston Vintage 30, a Red Coat Wizard 12" and my Marshall 4x12... nice...

[Scruffie]

Quick question... how come you're using taps 2 & 5 on the output transformer but the Firefly build guide uses 2 & 4... i'm connecting this to an 8ohm speaker to test it.

On to that PCB layout I did... got a board kindly donated by Markeebee today (Thanks Mark!) and i'm gunna say not to build it, unless you don't mind offboard wiring. I'm gunna use and verify it (or not as the case may be) but mounting on the back of the PCB just takes up too much depth in an standard enclosure so i'll redesign it with the tubes the right way round this time and pots on the same side.

Thankfullly my enclosure is deeper than most so I can get away with it, but it's an odd enclosure.

Hopefully all being well, i'll have an (out the box at least) 12AX7 & U7 firefly verified by tommorow night!