New low voltage tube amp project. Runs on 12v walwart 62v inside. not to scary.

[zambo]

http://i1108.photobucket.com/albums/h408/7Ambo707/HPIM14051_zpsf27732c2.jpg
http://i1108.photobucket.com/albums/h408/7Ambo707/HPIM14071_zps9764c030.jpg

Schematic and layout are in the description of the video as well. If you feel like building it yourself please do. Its great for room volume noodling. about like a tv at normal volume. you can still talk and have a conversation while playing. Just thought some of the low voltage tube peeps on here might like it. I dont have a bom drawn up or detailed instructions but will have them posted soon. I plan on doing a construction vid of this kit this week sometime.

Cheers,

Greg

[psychedelicfish]

That sounds pretty damn good to me...

Some suggestions:

Use a "proper" SMPS, something like this. It gives the option for higher voltage (more output, more clean headroom) and is regulated (note the feedback with the voltage divider to the base of the transistor).

If you have a 12AT7 lying around, give that a try in place of the 12AU7. You'll get slightly less output but more distortion and the distortion will sound different

Bypass the cathode resistor of the 12AU7 with a capacitor, say 47uF. You'll get more output and more distortion.

[zambo]

All of the above are true, however, I was trying to make an amp that was quieter than normal for indoor, late night use. Also wanted to keep the voltage low for first timer tube folks. something like a step up after the valvecaster. Nothing to advanced or scary. I also wanted it to be a bit more on the clean/break up cranked old school sound. I figure everyone has a tube screamer or some boost pedal that will make it distort if they want. I get the most comments and requests for this type of amp and had never put it into kit form or offered it before. I finally caved in and this is what I settled on. I just wanted to make the schem etc. available here for the diy crowd thats helped me get started. I use the 1363/4 smps when i want higher voltage and some 30 to 50 ma. any more than that I just use a power xformer.

[zambo]

And btw thank you! I hope I didnt sound snooty or anything 

[Shoeman]

That's great!  I already have a Firefly but building one of these seriously tempts me.

[GibsonGM]

Well done, Zambo!  Sounds nice!    I love those little tubey projects...each one seems to come with its own personality, and yours does too! 

Shoeman, you north, mid or southern Maine?  I'm over in the mountains near NH....cold winter, isn't it?  ;o)

[Renegadrian]

Nice! What's the name of the project?! It has to have one!!! is that a 1054 as a multiplier!?

[Shoeman]

I've never studied that sort of PS design.  Any threads here we could reference?    GibsonGM, I'm in Bangor, and yeah, it's been cold.  Best time of year for electronics projects though.

[zambo]

I always called this amp The Gooneybird .... long story... Still open for names lol!!  This is a LT1054 voltage multiplier that I borrowed from The Murder One by Frequency Central. It puts out the right amount of voltage and  the 1054 puts out a lot of milliamps . Ive had one up around 120 volts with no issues. Its more sturdy than the max1044. To be honest I only half understand how it works. I believe Frequency Central (aka Rick Holt) designed it. Many thanks to you FC!! I have used this on so many different tube projects its silly. I built 2 or 3 just to use as prototype power supplies.

[jubal81]

Any problem with just plugging in some headphones?

[zambo]

I tried it and it was remarkably underwhelming. the headphones lived though. I would think some dropping resistors and a headphone jack would be good though. Like a 47k in series from + lead on the speaker jack to the + headphone jack and a 1k pot from + headphone to ground lug on the head phone jack. that would give you a reduced signal to headphones with a volume control. I dont know what actual value the series resistor would need to be and you would also need a dummy load for the speaker jack while its un plugged. I think a 10 ohm 5 watt resistor would do the trick without getting to hot. Ideas anyone?

[kingswayguitar]

that sounds really good man
keep it up

[psychedelicfish]

Ideas anyone?

Plugging ordinary headphones into a scaled down guitar amp output isn't going to sound at all the same as having the amp plugged directly in to the speaker. The headphones, to start with, don't have the same frequency response as a guitar speaker, so will sound very  different. Also, a speaker is an inductive load, and has an impedance that rises with frequency. This also means that the output valve sees an impedance that rises with frequency, which is an effect you won't get as much of loading the output with just a plain resistor.

Your idea with a dummy load+series resistor would work fine, if you really wanted a headphone output. A 10 ohm, 5 watt (1 watt would probably be fine with an amp this size) resistor would work well as a dummy load, but 47k in series with the headphones would be WAY too high. Don't forget that the resistor and the impedance of the headphones (32 ohms is pretty common, IIRC) form a voltage divider, and the output of your amp is not particularly high to begin with. Try 33 ohms in series with the headphones, and if it's too loud, increase the value, if it's too quiet decrease the value. You could also consider adding 330uH or so inductors in series with the dummy load and the headphone+resistor string. The inductor would make the headphone load "look" a little more like a speaker to the amp.

You might consider adding something like this rather than/as well as a headphone output.

[zambo]

Yeah the Firzog is perfect for that! Thanks phsycedelicfish!! I forgot about that one. Will it still drive headphones? I guess it would and if it was lacking volume you could start changing the 150k series resitor? I still think someone needs to develop guitar specific headphones. dont know what it would take but I think you could sell a but load of them instantly and every christmas after that!! Maybe I will take some cheap ones and cover the speakers with light glue or something. I wonder......

[psychedelicfish]

150k is way too high for a series resistor, and a 1M pot won't be much use anywhere below max.

When you tried headphones before, was the volume level OK? If the volume was fine, or slightly too loud, try running the headphones in parallel with a 10 ohm or so dummy load. If you want it to sound more similar to a speaker, then connect the line out of the firezog to a cabinet simulator and then into a headphone amp. For cabinet simulators, try this.

PS: a 240V:5V mains transformer can also be used for the output transformer, if anyone is wondering

[zambo]

The volume seemed pk but my headphones have a volume control. not sure how it works on those. sound was blah though. Love the cab sim you mentioned. Might have to build a pcb. it would be nice if someone built a reactive dummy load with cab sim and headphone out all in one box. that would solve a bunch of problems all at once.

[psychedelicfish]

It would be nice, but it would be incredibly  difficult to do from a design perspective without active circuitry. If you wanted it to be nice and small, you'd need the active circuitry to be solid state. This sort of thing has been done with valves, but all the designs I've seen have been big and expensive.

[sajy_ho]

Thank you Greg, brilliant as always! I only have a PP OPT around, can I use a PP design for output?

[smurfedelic smurfberry]

I like the sound of this, and happens to have a 12au7 and a 12ax7 tube lying around, so I might get to it eventually.

I look forward to some more instructions and advice. Would love hi-res gut shots too.

[zambo]

@ Sajy - yes you can. and it sounds great as a push pull. you build it the same except for the opt you put one wire on plate a and the other on plate b. voltage goes to the middle. also instead of hooking the grids toigether one gets grounded. its just like the firefly at that point. http://ax84.com/media/ax84_m276.gif Learned most of what I know playing with firefly schematics. Long live DougH! Let me knbow if you get stuck, glad to help