Messages

It's a pitty you couldn't fix that, the board looked so nice.
I never dared to squeeze things like you guys do.
IMHO, a 3 gain stages is too much if you try to push the power section, I prefer just one or two gain stages and some kind of transistor overdrive before.
Cheers.

Got round to building this today, the amp portion works but there's some oscillation issue I think interfering with the SMPS so it's stuck at 300V, I tried a verified standalone PCB to check it wasn't the SMPS layout and the same thing happened as soon as it was hooked up to the amp.

...Then it is the amp section layout?
The image showed 250V caps, so bear it in mind.
One simplistic suggestion, grounding the pots through their metal chassis. The presence circuit is ok?

I saw the answer in the other forum, tubes are 6111 and 6112. Very nice amp!
Cheers.

Impressing Thomasha, as usual.
What kind of tubes did you use this time?
Cheers.

Hi again, Thomas and others, and thanks.
I would say it had more "character" before, but it was just noticeable when I turned up the volume pot. The thing is that, for practising at home, I have enough volume with gain at some point, depending on what I am going to play, and volume control between minimum and first quarter. The first stage draws so much, that you can play with the volume pot all the way down but then, tone stack is useless.
I hope one of this days will get a mic. and time to record some sound samples, painting the box and covering the cabinet with tolex. I don't know where I can get some corners for a so small cab.
Your design is very interesting, although I would prefer a separate SMPS from main board, just because if PSU starts smoking you just have to replace it and if you have ground noises you can find a solution moving a single (or maybe more) cable(s) as I did. But obviously, if everything goes right you'll have a design much more compact.
Good luck and tell us your findings .
Cheers.

Hi all you,
Nice piece of work, Thomasha.
I have been working on the submini head on its ground scheme to remove hums and other noises and finally achieved a quiet amp.
As shown on picture at previous post #100, I have replaced the 1K5 R8 (cathode resistor in output stage) for a 2K2, reducing power dissipation from 0,99W to 0,7W, as I have now B+1=210V and Vk=7,72V. I have an impedance ratio of 8750:8 in my O.T. and tested with the 8750:4 and an 8ohm speaker too, to double its Zpri. but readings didn't changed much.
It would be nice to test it with a hammond 125A transformer with other impedances to see if it really increases output power with higher impedances.
Find below some gutshots and the 6" jensen speaker cabinet.
Cheers.

Hi Thomas,
Sorry, I can not take any pictures right now, but I hope I will have some time one of these day, I'd like to profit when I open the amp to fix the hiss issue, make some more holes and take some temperature readings.
At the moment, I can show you the preamp section I have used, is from a JCM800 series, but I don't know which one.
The power stage is the same schematic as on previous post.
The layout is the same idea as the other amp, but it has two PCB's for pots: gain, vol, sweep and tone stack at the other. All linked by screened cables.   
I like the sweep pot, as it moves all the bands, it is quite useful to change the whole amp tone for different styles.
I also would appreciate suggestions for paintings. I already have some synthetic solvent based painting in spray but last time I used it, it did not last so long, so I am thinking in some primer.
...Whel, that's all for now.
Cheers,
Miquel

Hi all,

I've been working a little on the 3 submini tubes and max1771 smps head, now it sounds quite good but I have the same issue than you, Thomas: hiss at max. gain and max. volume. I like its tone specially for ac-dc, led-zepp rocks.
I need more holes on its top to cool it (about 50ºC after 30') and have to do some tests recording to find changes in tone due to heating, but I´d like to keep its psu without heat sink, if possible. I'll test it with the 4Ohms output as well to listen its changes.
The 2x6n16b, with a NE555, will stay as it is, I know it can cope with its temperature and it has been my test rig for months without issues.
There are some pictures of the 2x6n16b and 2x6n16b+6n17b model.
Cheers,
Miquel

Madbean:My boards look much more shabby!

Thomasha: I haven't used any heat sink that's what surprised me, I have to see what happens with the max1771 smps...but I have enough room inside the case if I need any.
I repaired many 'big' combos with tubes downward mounted and almost all of them had marks of heat in their pcb's if these were above tubes, there's a model I remember, a Crate Vintage Club that had this heating issue in their pots, but I have to admit that your whole amp looks very nice, I would try a fan, as you mentioned.
Cheers,
Miquel

Hi again,
The transformer I use is a 'custom made' model by a local 'trannymaker' it has 8k75 at primary and 4-8 at secondary, 2,5W.
At the moment I am using a 2x12 Celestion Vintage30 cabinet at 8 Ohms and I can say there is very low hum and enough power to annoy my neighbours.
The idea is to build the amp as an aluminium head, with everything inside the box to keep it enough portable to bring it in the guitar cover.
I built its power stage prototype, the schematic is from Dimitry's web page, in a can box of I don't know what, but it is funny because the brand says SOVIET... I forgot to switch it off for two nights and their days and it was still cool enough. When I'll finish the current version I hope I'll be able to make enough holes on its box surface to keep it cool enough as well  ...Then there'll be the nightmare of finding a good painting.
Cheers,
Miquel

Thank you Thomas for all the info. I am still surprised of the primary impedance of your O.T.
I will post some pictures of my submini-amp which is enclosed in a bigger 1590DD box. I got it sounding well until I mounted  inside the box and stopped sounding so I need to do some debugging (probably a broken cable).
My idea is to build a small cabinet with a 6" 12W Jensen speaker as well, but it will take more time as I cannot fill my home with sawdust. I will keep this updated.
Cheers

Really nice amp!!
What high voltages are you using?
Regards

The Max1771 SMPS delivers 240 v from a 12v 1A supply.

The board and schematic are here:
https://dl.dropboxusercontent.com/u/10420127/Superfly%20Project.pdf

Hope you enjoy!

Thanks Thomas,
What I find more intersting is the submini-combo.
I built some subminiamps, using the same schematics from Dimitry but the self-split output stage version, all of them with 6n16b and 6n17b, although I am glad with their sound, now I have bought some 6n21b to try for the preamp.
I mailed him (very kind guy) and he recommended me using any 8~10kOhm  O.T. but with this impedance, and feeding output tubes with the same SMPS than you at 220V, I was running 6n16b out of specs, so I had to lower plate voltages.
I suppose that you can use higher voltages due to the larger impedance of your O.T. Isn't it?
By the way, now I am triying to build a similar boost converter but with a cheaper UC3845 instead of the expensive MAX Ic.

Cheers

Really nice amp!!
What high voltages are you using?
Regards