BlackStar - HT-DUAL

[Ripthorn]

Okay, this is really cool, I am going to have to follow this closely for progress.

[Ice-9]

I looked at the circuits in my blackstar distx and it seems all the blackstar pedals in this series use the same pcb's, the pcb's look like there designed to have different combinations of components installed to make them into different vers of the pedals, eg, mine has only one footswitch but places for 3 footswitches. (this way they only need to manufacture 1 pcb type for all there pedals.

I can confirm that the HV psu is exactly the same in my pedal, and is of a similar design to other smps using mosfet switching and inductors. Very interesting thread.

[briggs]

Looking at the power supply - it requires 16VAC. Do you reckon you could glean this from a standard laptop supply, like this: http://www.notebook-ac-adapter.com/product_info.php?language=en&currency=GBP&products_id=1119

One other thing - how are they getting power to those heaters? Just tapping straight off of the 16VAC line with a voltage dropping resistor?

[Ice-9]

Looking at the power supply - it requires 16VAC. Do you reckon you could glean this from a standard laptop supply, like this: http://www.notebook-ac-adapter.com/product_info.php?language=en&currency=GBP&products_id=1119

One other thing - how are they getting power to those heaters? Just tapping straight off of the 16VAC line with a voltage dropping resistor?

Yeah ! the heater voltage is taken from the 16V ac input through the negative diode rectifier then dropped with a 16 Ohm resistor.

[Ice-9]

Looking at the power supply - it requires 16VAC. Do you reckon you could glean this from a standard laptop supply, like this: http://www.notebook-ac-adapter.com/product_info.php?language=en&currency=GBP&products_id=1119

One other thing - how are they getting power to those heaters? Just tapping straight off of the 16VAC line with a voltage dropping resistor?

Yeah ! the heater voltage is taken from the 16V ac input through the negative diode rectifier then dropped with a 16 Ohm resistor.

small correction to my post, The 12v for the heater is taken from the output of the 7915 -15v reg and dropped with a 15Ohm resistor. I will try and do a schematic fot the complete psu section and post it up.

[briggs]

Looking at the power supply - it requires 16VAC. Do you reckon you could glean this from a standard laptop supply, like this: http://www.notebook-ac-adapter.com/product_info.php?language=en&currency=GBP&products_id=1119

One other thing - how are they getting power to those heaters? Just tapping straight off of the 16VAC line with a voltage dropping resistor?

Yeah ! the heater voltage is taken from the 16V ac input through the negative diode rectifier then dropped with a 16 Ohm resistor.

small correction to my post, The 12v for the heater is taken from the output of the 7915 -15v reg and dropped with a 15Ohm resistor. I will try and do a schematic fot the complete psu section and post it up.

Thanks, that would be very helpful indeed

[himister]

OK folks.

I know some of us has been waiting and working for a couple of months on this, so here is the PCB layout for the Blackstar HT SMPS
according to Steve's (Bajaman) schematic. Thnx man!!!

I apologize for this kind of layout but I have "extract" it from the other layout I've been made for tube preamp.
Just to say it's unverified and if anyone is eager to try just go for it.

If there are some traces that are not ok, hope someone will point it out.
Suggestions are very welcome!

Hope it will be useful to many of us for other vacuum tube projects!

Cheers

[bajaman]

IMPORTANT - please read

Earlier in this thread i posted a schematic for the Blackstar HT SMPS power supply.
Unfortunately there is an error - The diode SB246 is actually a 2 amp schottky barrier diode SB240.
I have successfully used a 1N5819 1A schottky in a working version of this power supply.
So the schematic (except for this minor typo) is verified and delivers 305v DC unloaded at the output.
I have designed and built a prototype of this supply on a piece of single sided fibreglass PCB.
I shall publish it in the Ready to Build section of the forum in the next few days.
cheers
Steve

[flood]

go steve! love your work!

[teemuk]

Let's keep this one rolling....

Here's the tube board (attachment). Some component values are missing because they couldn't be interpreted from the photos available. Also, I can't quite interprete whether the heaters were wired for 12V or 6,3V.

I'm reverse engineering the control board schematic ATM but I need photos showing how the traces run under the potentiometers (on component side). The whole circuit is kinda odd looking so the ISF patent offers only little help...
Pictures of that small switch board would also help.

Cool forum by the way...

[briggs]

IMPORTANT - please read

Earlier in this thread i posted a schematic for the Blackstar HT SMPS power supply.
Unfortunately there is an error - The diode SB246 is actually a 2 amp schottky barrier diode SB240.
I have successfully used a 1N5819 1A schottky in a working version of this power supply.
So the schematic (except for this minor typo) is verified and delivers 305v DC unloaded at the output.
I have designed and built a prototype of this supply on a piece of single sided fibreglass PCB.
I shall publish it in the Ready to Build section of the forum in the next few days.
cheers
Steve

Did you ever get chance to post this Steve? I'd love to build one up and set to on a new mini amp project later in the year...

[bajaman]

Hi Fred
yes - i have built the switch mode power supply but I have issues with it - it works and I can get over 300v DC from it, and it can power two 12AX7 tubes comfortably, BUT it whistles like a bitch at about 17Khz or thereabouts.
i have shelved it for the moment and have had better luck using the nixie tube power supply that Rick Holt uses in some of his mini tube projects.
I need to revisit the Blackstar power supply and perhaps increase the oscillator frequency above human hearing - i have tried shielding it but cannot reduce that damned whistle completely.
more later
cheers
bajaman

[briggs]

Ahha, okay! What sort of voltages are you getting with the nixie? ~260V is what I'm after?

[bajaman]

Ahha, okay! What sort of voltages are you getting with the nixie? ~260V is what I'm after?

I am getting between 100 - 200v DC at present - I am sure it will go higher although I like how my experimental twin tube circuit sounds with it at the lower voltages.
cheers
bajaman

[frequencycentral]

With that nixie SMPS I've found I can get 300v from it without load. But when I've tried it with a load I find anything much over 210v causes motorboating in the little amp I'm using it with. Not sure why. Maybe a bigger (than the 2.2uF 400v) reservoir cap would help. I do know that the more voltage you ask of it the hungrier it gets for milliampres - and the hotter the MOSFET gets. Even with my 1.5 amp bench supply I have issues over 210v or so.

Also, a key with that nixie SMPS is to keep the IRF740 cool. As it warms up the voltage will decrease. So it really does need a well connected heatsink with thermally conductive compound.

I've come to the conclusion that I'm happiest running the SMPS at 190v. It seems to run happily for hours. I also figure that as I'm using it for tiny amps, there no point having a tiny amp with a huge adapter to feed the SMPS, and I can run two subminis and the SMPS off a 12v/500ma wallwart.

But hey, I just play around with these things, I don't necessarily understand them.

[himister]

...it whistles like a bitch at about 17Khz or thereabouts.
...I need to revisit the Blackstar power supply and perhaps increase the oscillator frequency above human hearing - i have tried shielding it but cannot reduce that damned whistle completely.
bajaman

Well...mine is on the prototype board and the same issues here...
I even tried some "unusual" components like the TURBOSWITCH ULTRA-FAST HIGH VOLTAGE DIODE STTA812D
At the first testing there was no damn whistle and after a changing a 47n cap and back again whistle appears and it's rising pitch with the voltage.

Small input...I've tried it with two different wallwarts, one is DC an one AC and DC was able to push a bigger output voltage through the SMPS even at smaller current so it would be good to use good DC filtering. AC wallwart was buzzing through the SMPS like a big fat bumble bee.
I had a voltages from 166V to 250V but still no 300.

Steve could you give some small insight which components change the frequency of the UC3843, I would like to try helping to debug this "whistle" problem. I hope that operating frequency is not that much dependent on some of the components like the inductor coil. The silicon components should be able to do the switching at very high frequency so they could be adapted accordingly...by silicon I mean fast recovery diode, guess nothing else should be changed!?

One more insight. the PCB layout posted here before by me need some revision 'cause it's to small for some components.
Will change it soon for general purpose.

Cheers

[teemuk]

I have almost traced the control board but I really need some help.

The photos (although there’s a wealth of them) aren’t showing the area around VR1 (Gain 1 & 2 pot) and beneath the CLN/OD switch PC board in enough detail. Basically, in all the photos (which are not too blurry to interpret) the PC board housing the switch is always blocking the view of the most important parts/traces. I need to see how the traces run beneath that switch/board, and especially around the three-pin connector of the said board. There are at least four traces running towards/close the said connector but none of the photos is intelligible enough to show where these traces go.

Secondly, I need to see beneath VR1 to see what pins the various traces connect. Photos from all angles would be extremely helpful. I need to see as much as possible. ...Barata?

If there’s one thing in tracing a circuit completely from photos, it’s that you can’t have too many photos. I would appreciate if you/someone has the time to open this one up and take a few shots.

I could play a guessing game but without the context of the gain stages involving the switch and the dual gain pot there’s too much to go wrong.

This is what I have figured out so far concerning the area of interest:


I need to fill the blanks, please. By the way, everything else on that board I have already managed to trace out.

The solder side photos have so far been detailed enough.

Let's still keep this one rolling.

[Dirk_Hendrik]

Thsi might help:
http://www.dirk-hendrik.com/temp/Blackstar_HT_Dual_Tonecontrol.pdf

[Dirk_Hendrik]

Let's keep this one rolling....

Here's the tube board (attachment). Some component values are missing because they couldn't be interpreted from the photos available. Also, I can't quite interprete whether the heaters were wired for 12V or 6,3V.

I'm reverse engineering the control board schematic ATM but I need photos showing how the traces run under the potentiometers (on component side). The whole circuit is kinda odd looking so the ISF patent offers only little help...
Pictures of that small switch board would also help.

Cool forum by the way...

Here's the component values. Did not check the circuit:

Tube_Board_sch.gif

[Barata]

Hi teemuk,
Please after read the previews comments please PM me with the spots that you want me to take some shots.
Am still enjoying my holidays but in the end of this week i'll be back home
Good look for you all