The MAX1771 SMPS Development Thread

[zambo]

run the 1363 into a reservoir cap. it works like a charm now and no whine to it. I used a cap---resistor ( 1 ohm) cap---b+ and it works great now.

[cfcubed]

run the 1363 into a reservoir cap. it works like a charm now and no whine to it. I used a cap---resistor ( 1 ohm) cap---b+ and it works great now.

It's funny, I was just thinking about this.  I've a 1364 in hand I was thinking of trying the 130R thing on, but if a C-R-C like that fixes it that'd be great.
BTW what cap values did you use & what are you driving with this (e.g. tube/topology/B+/current if you know 'em)?

[zambo]

I am driving a whole amp. 2 x 22uf 350v caps and 10ohm resistor.   http://www.youtube.com/embed/rkhOqfyzdN4  i show it at the end of the vid if you skip the playing parts.

[cfcubed]

I am driving a whole amp. 2 x 22uf 350v caps and 10ohm resistor.   http://www.youtube.com/embed/rkhOqfyzdN4  i show it at the end of the vid if you skip the playing parts.

Like your playing:)  

Well I've tried filtering circuits incl CLC & CRC in my application (headamp discussed previously) with the 1393/1394 and could not eliminate the high-pitched squeal entirely.
Using a Simple R-C filter calc ( http://www.muzique.com/schem/filter.htm ) it seems your filters corner freq is about 700hz, which appears to block the high-freq oscillations from passing to your tube B+ in your application.  But are you saying this filter also stopped the high-pitch noise from emanating from the unit itself too?  This would be curious as it would then have affected the switchers operation as well (such that it stopped oscillating).

Last night I dove into this once more 1st adding your filter (have 22uf/250v caps around) & it may have help a bit in the headamp's output but did not change the emanating oscillation (which may be creeping other parts of the circuit as my 1394 is not yet shielded).  Then I suffered through adding a 120R resistor at pin #5 as discussed before & bridged the other pins w/wire-wrap wires.  It was hell.  Took several tries & an hour or so w/my equipment.  But it was worth it as it entirely eliminated the high-pitch noise - both that emanating from the unit & downstream in the headphone output.



The only noise left is a very, very low-level hum that goes away when I place a finger on the 1394's coil spool OR better place a simple grounded shield over it.
If we could get Taylor Electronics Services to include the 130R SMD resistor for pin #5 for 1393 and/or 1394 (with optional pins/jumper to bypass providing original operation) I think the 1393/1394 could be a low-cost HV SMPS solution for lots of projects. I'll email taylotjpt about this & if others did too maybe they'd consider it.
The whole thing would likely perform even better w/o the wire hackery I had to botch in to do it.  

BTW Don't even think about doing the hack above w/o very tiny soldering tip, steady hands, a few 139Xs to kill, a smaller resistor than mine, wire-wrap, time & patience.

BTW I'll be building this proto headamp out with a simple open-ended grounded sheet-metal cover over the switcher & a 2nd order LP filter using 47R/100uf/470R/10uf (e.g. http://www.electronics-tutorials.ws/filter/filter_2.html ).

[iccaros]

I am not getting any noise from the unit its self?

.

[zambo]

Wow that is some seriouse micro soldering Cfcubed! I am glad it worked out finaly. I have never used the 1364 you show pictured but only the 1363. It may be that i am pulling as many ma as possible through the tubes and that seems to quiet them down as well. You are using it to power a couple preamp tubes i think right? I think they dont pull as many ma and the switcher works in the sonic range without the max load on it if that makes sense. Either way, I am glad its working now!

[cfcubed]

I have never used the 1364 you show pictured but only the 1363. It may be that i am pulling as many ma as possible through the tubes and that seems to quiet them down as well. You are using it to power a couple preamp tubes i think right? I think they dont pull as many ma and the switcher works in the sonic range without the max load on it if that makes sense.

Yep pre-amp tubes & their lower draw was probably causing the squeal due to:

... this switcher uses a PFM control scheme that skips cycles when the load does not pull the output down below the recycle threshold resulting in a "frequency" of operation less than the 300kHz internal setting.  The core can emit sound via magnetostriction if the PFM beat frequency is in the audio range.

BTW 1393 & 1394 share the same datasheet & parts look identical so I think they are the same thing packaged in different ways.

I am not getting any noise from the unit its self?

Are you telling me you've used these switchers & gotten no squeal OR are you asking me whether I'm getting noise from the unit itself?
As I said in my last post, with the crazy mod I did, inserting the resistor under pin # 5 as taylotjpt mentioned, I do not get any high-pitched noise/squeal at all anymore.  Not from the unit itself & not in its output.   I only get a barely audible, low-freq hum that goes away with a grounded metal shield (esp. over the coil bobbin (or place a finger on it)).

Bottom line tho w/the experiences we've had think its hard to recommend these switchers for use in audio, at least w/o on-board support of that resistor (and users adding a shield).  Except maybe for specific schematics in which the 1393/1394 has proven to behave well (e.g. perhaps zambo's design).

[cfcubed]

I only get a barely audible, low-freq hum that goes away with a grounded metal shield (esp. over the coil bobbin (or place a finger on it)).  <<<  The low-freq hum went away in the (more proper) buildup, its working well w/no noise of any kind.  So a shield should be unnecessary & wouldn't want one close to the bobbin anyway (re: shorted turn/specsheet)

Bottom line tho w/the experiences we've had think its hard to recommend these switchers for use in audio, at least w/o on-board support of that resistor (and users adding a shield).  Except maybe for specific schematics in which the 1393/1394 has proven to behave well (e.g. perhaps zambo's design).  <<<  PM'd taylotjpt about possibility of on-board support for the resistor & haven't heard back.  May try a direct email to TES before giving up on it.

[iccaros]

I think I know my issue but I am looking for suggestions

So I have one of these SMPS with the output going to a 33u cap with a 5k 5watt to a 33uf cap where I then connect my small amp (I build a AX84 HO with submin tubes)
I want to pull my heaters from the 12 volt supply but it looks to my wall adapter like a dead short and it will not power..
I had before 2 meg going to ground from the last cap and the heaters worked, but the the 5K was dropping 151 volts across it.

So I think the 5K is so high compared to the heaters causing the power supply to think its shorted. .

[papasteack]

Hi,

As max1771 seems to have some instability issues, and 555 seems to have too low current, what do you think about the cheap cicuit used here, with a lm393 here ?
http://threeneurons.wordpress.com/dekatron-stuff/variable-dekatron-spinner-kit/
It would be to power two a 12ax7 preamp, with lr8 linear regulator for each ones...

[iccaros]

the 555 does not sink current and is not the limiter of current in most designs, the IRF 740 has too high of an turn on resistance, but replacing with and 840 which has a lower turn on resistance can allow upwards to 150ma, by some reports.

But to your post, it looks like a good design, low MA range >15ma, which is OK for preamps, and some small amps. Merlin Posted a simpler version in one of the threads, the only way to know is to try, I find that a lot of SMPS made for Nixie's are noisy on audio CKT.. 

[jazbo8]

SMT... Fogetaboutit... For relatively light load, one of these cheapo inverter does the trick.

More discussions here.



Jaz

[zambo]

1363 se 2 watts.

[iccaros]

awesome Greg.. tone is in the fingers, and yours has it in spades.. share your design?

[zambo]

lol, thanks man. Design is dead simple. Gain stage one is 100k plate / 1.5k cathode / .022 cap out to 1 meg volume / gain stage 2 is the same / 220k grid leak and 5k grid stop on the 6v6 power tube/ 400R cathode. power supply is 47uf cap / 10R / 22uf / 100r/ 22uf . heaters run on 6 volts dc. just took a lead off of the power in and dropped it over 4 diodes. ( in4007 ) to get to 6 volts. wire them just like 6v ac. 4,5 hot 9 grounded on the 12ax7. 2 hot 7 grounded on the 6v6. works with 6k6 as well and is a bit quieter. OT is 5k primary single ended to 8 ohm speaker.

Bypass caps on all the cathodes of 22uf on the pre and 220uf on the power will make this thing bark. If I did that mod i would change the first coupling cap from .022 to .0022 and see how that sounds. If that wasnt good I would switch it with the second coupling cap. Thanks for looking!

[blackcorvo]

SMT... Fogetaboutit... For relatively light load, one of these cheapo inverter does the trick.

More discussions here.



Jaz

This has really peaked my interest.
I'm gonna see if I can find one of those and get something workable out of it. Would be super neat to get a compact, high-voltage supply that could allow the use of either an external DC adapter, or a gel battery, to go "Tubbin' on the road".