For most of my audio projects I’ve been working with linear supplies. Convenient, easy to calculate and regulate. Never cheap or flexible though.
For a new preamp project I’m looking for a power supply that is able to deliver 20 mA at 420V to 5 12ax7’s. Two triodes will be cathode followers with the cathodes at 180 V. The heaters probably need to be elevated. The best transformer I could find in The Netherlands is a Hammond 369bx. 300 Vct and enough heater current. Antek is much cheaper, but shipping is around 40 bucks.
So I started looking for cheaper options. Found some China made dc-dc converters capable of 450V and looked at some offerings of LT (lt3757 as flyback controller). I could drive them of a 12 V transformer, maybe regulated. Problem is: how do I elevate the heaters in that case? Not possible I think. I could use a separate fly back converter for the heaters, but then which one and how do I regulate the output of the 12 V converter while floating?
All in all a linear supply looks like a much easier option, but maybe you guys see other options I just totally miss?
For a new preamp project I’m looking for a power supply that is able to deliver 20 mA at 420V to 5 12ax7’s. Two triodes will be cathode followers with the cathodes at 180 V. The heaters probably need to be elevated. The best transformer I could find in The Netherlands is a Hammond 369bx. 300 Vct and enough heater current. Antek is much cheaper, but shipping is around 40 bucks.
So I started looking for cheaper options. Found some China made dc-dc converters capable of 450V and looked at some offerings of LT (lt3757 as flyback controller). I could drive them of a 12 V transformer, maybe regulated. Problem is: how do I elevate the heaters in that case? Not possible I think. I could use a separate fly back converter for the heaters, but then which one and how do I regulate the output of the 12 V converter while floating?
All in all a linear supply looks like a much easier option, but maybe you guys see other options I just totally miss?
I use these... DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay
For 420V use the 220V AC output and a voltage doubler using 10u-22u caps and HER208 (or equivelent) for the diodes. The output is isolated from the input, and you should still be able to elevate the heaters. I power it from a 12V SMPS but you could use a linear 12V supply. You could also use 2 SMPS 12V supplies, one for the heaters, and one for the boost converter.
A pair of these would work: 6A-8A Unit For 12V 100W Switching Power Supply Board AC-DC Circuit Module | eBay
For 420V use the 220V AC output and a voltage doubler using 10u-22u caps and HER208 (or equivelent) for the diodes. The output is isolated from the input, and you should still be able to elevate the heaters. I power it from a 12V SMPS but you could use a linear 12V supply. You could also use 2 SMPS 12V supplies, one for the heaters, and one for the boost converter.
A pair of these would work: 6A-8A Unit For 12V 100W Switching Power Supply Board AC-DC Circuit Module | eBay
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How hard do you want to play? Google "Current Fed Buck Converter". For example...
UC3827-1 Buck Current/Voltage Fed Push-Pull PWM Controllers | TI.com
If you want multiple isolated outputs, high and low voltage, that track each other then the above is the topology to go for.
Not that hard haha. However, you are correct. This is perhaps the way to go when using one controller. But why not use two, e.g. EC3843's. One for HV, one for LV. There are loads of information to be found on the PWM controllers, not so much for the UC3827. I mean, I can read app notes and data sheets, but I'm not an EE. Working with a UC3827 probably requires a bit more than my basic SMPS knowledge.
12V 30 VA into reversed 6V 15VA would do the job quite well. Buying new trannies (toroids) would probably set me back 50 to 55 Euros ex. shipping though. Will have to see what I've got lying around in the house.
EDIT: Got a 2x12V 50VA toroid around!
Still I wonder, where are the people that actually build a switching power supply for tube amps. Should be doable right? Würth offers some nice offline flyback transformers with a HV winding. 90-265 VAC to 285 V @ 70 kHz for example.
Yes... Not for the faint hearted. I would not suggest you try to implement an off-line power supply using this method but it might fall into your comfort zone if you consider using a 50Hz lump of iron to give you an isolated 15V supply with which to feed the chip.
http://www.farnell.com/datasheets/312001.pdf
http://citeseerx.ist.psu.edu/viewdo...65A63A4?doi=10.1.1.362.4613&rep=rep1&type=pdf
Second link is to SLUP117.pdf which TI do not appear to wish to give you unless you create an account with them. Unfortunately it is a bit overboard in that it goes into a great level of detail for most available topologies before settling on the UC3827. Then it still tries too hard...
If you have basic SMPS knowledge, you mention the peak current mode UC3843, then getting your head around the UC3827 should not cause too much stress. Using a lump of iron to supply things simplifies your feedback, no need for opto-couplers or similar.
Once you get the idea behind average current mode control and slope matching then design of the internal current loop and external voltage loop is a veritable pleasure. None of this slope compensation to avoid subharmonic oscillation as with peak current mode control.... not strictly true because you still need it for a stable peak current limit.
If you want I can slap together an idealised LTSPice model of the beast so you can have a practice. How many 6V3 Heater Supplies do you need and at what current? How many High Voltage Supplies do you need and at what voltages and currents?
I can take you through the compensation of the thing and you might be pleasantly at the level of performance that should be possible. <50uS[20uS] response times to step levels in load and other nice numbers.
Biggest fear would be that you probably should not knock one up on a bit of Vero Board. It might work but a PCB is recommended. Depends on your resources.
Iron to a dc-dc converter was my first idea actually. Some nice converters on fleabay. 12V 24V to DC 200-450V 70W High Voltage Boost Converter Step Up converter New | eBay
Good for up to 40W continuously, although I have no idea what the resulting dc looks like. I also don't know if different filtering with an additional LC would improve matters if needed. It looks like a flyback converter, so diode -> C.
Then again, how can I elevate the preceding 12V supply without affecting the DC-Dc converter? Can that even be done?
Now if I could find me a 12V to 12V isolated DC converter, the problem would be solved. Power the whole thing - separate DC-DC converters for LV and HV that is - with the 12V toroid I was mentioning earlier and elevate the output of the 12V converter via a divider form the HV. Done.
Or power two offline flyback converters and use off the shelf Würth transformers. Will post a schematic next, to clarify.
I'm just looking for a single 12.6V @ 750ma heater supply. Or 6.3V but double the current. I'm not sure how much current the tubes draw when cold. Cold resistance is 14 Ohms for 12.6V.
It would be great if you could make an idealised model, but please remember that it might just be for educational purposes.
I use vero just for low frequency setups and even then I almost never use it. I can build single sided photo's, although i generally prefer to outsource for more permanent setups/work. For small boards I send my stuff to OSHpark for example.
Good for up to 40W continuously, although I have no idea what the resulting dc looks like. I also don't know if different filtering with an additional LC would improve matters if needed. It looks like a flyback converter, so diode -> C.
Then again, how can I elevate the preceding 12V supply without affecting the DC-Dc converter? Can that even be done?
Now if I could find me a 12V to 12V isolated DC converter, the problem would be solved. Power the whole thing - separate DC-DC converters for LV and HV that is - with the 12V toroid I was mentioning earlier and elevate the output of the 12V converter via a divider form the HV. Done.
Or power two offline flyback converters and use off the shelf Würth transformers. Will post a schematic next, to clarify.
I'm just looking for a single 12.6V @ 750ma heater supply. Or 6.3V but double the current. I'm not sure how much current the tubes draw when cold. Cold resistance is 14 Ohms for 12.6V.
It would be great if you could make an idealised model, but please remember that it might just be for educational purposes.
I use vero just for low frequency setups and even then I almost never use it. I can build single sided photo's, although i generally prefer to outsource for more permanent setups/work. For small boards I send my stuff to OSHpark for example.
Iron to a dc-dc converter was my first idea actually. Some nice converters on fleabay. 12V 24V to DC 200-450V 70W High Voltage Boost Converter Step Up converter New | eBay
I used one of those to power B+ to a se EL84 stereo amp. Tranny for heaters. Worked like a charm!
I used one of those to power B+ to a se EL84 stereo amp. Tranny for heaters. Worked like a charm!
I've used these. They are isolated, however they are adjustable which causes instabilities and oscillation if used with a choke input/crappy load.
I have used:
DC-DC 8-32V to 45-390V Step Up Power Supply Module High Voltage ZVS Boost Module | eBay
Not isolated, single ended design. I use one for powering a phono stage. More stable than the above.
DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay
I prefer this design. It's isolated. I use them with a voltage doubler on the AC output to get 420V.
MINI DC-AC Inverter 12V to 18V220V/380V 500W Boost Step UP Power Module New Hot | eBay
I use these for power amplifiers. I'm using one to power a PP 6550 Amp. Runs with a 10 - 15 degree rise at 150W output.
I have used:
DC-DC 8-32V to 45-390V Step Up Power Supply Module High Voltage ZVS Boost Module | eBay
Not isolated, single ended design. I use one for powering a phono stage. More stable than the above.
DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay
I prefer this design. It's isolated. I use them with a voltage doubler on the AC output to get 420V.
MINI DC-AC Inverter 12V to 18V220V/380V 500W Boost Step UP Power Module New Hot | eBay
I use these for power amplifiers. I'm using one to power a PP 6550 Amp. Runs with a 10 - 15 degree rise at 150W output.
Take an AC to 12V converter that can handle your preamp's total power consumption. Tweak it to get 12.6 Vdc and feed the tubes' heaters and a DC to DC converter with isolated output for HV supply. Elevate your 12.6 Vdc by means of a voltage divider at the HV side. That's all. I can't see any problems with this, given that the HV converter is isolated.
Best regards!
Best regards!
What got me confused is how feedback from the HV supply would work. The output is isolated from a floating input via a fly back transformer. But the feedback path might or might not be isolated (if there is any feedback at all). I guess I will have to see how the feedback is done on an actual supply.
Apologies for the delay. Education is good. I'm getting some as I try to get the beast to work whilst dealing with competing issues.
I've assumed 1 X 420V@ 50mA and 2 X 12.6V @ 750mA. About 40W. I have also assumed that you might use a Laptop brick. You can get 70W ones with 19V out and they are cheap.
That takes care of your mains isolation but you should still be concerned about safety in respect of your 420V.
The following #CODE is the LTSpice model. Save as an .asc file and LTSpice should load it and let you poke about and play. Again this is not final but a closest best and possibly realisable guess.
Pictures are circuit, circuit in regulation, circuit with a 20mA/50mA load transient on the 420V rail and start up as things come into regulation.
There are reasons why it behaves the way it does and other than a load of other headaches some anomalous behaviour that could need chasing down.
I'll try some more words later.
Code:
Version 4
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WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName VCLK
SYMATTR Value PULSE(0 15 10u 1n 1n 500n 10u)
SYMBOL sw 1552 864 R0
WINDOW 0 8 -12 Left 2
WINDOW 3 7 8 Left 2
SYMATTR InstName PWM
SYMATTR Value CMP
SYMBOL res 1536 592 R0
WINDOW 0 37 44 Left 2
WINDOW 3 38 71 Left 2
SYMATTR InstName RDD
SYMATTR Value 1K
SYMBOL voltage 1648 1072 R0
WINDOW 0 37 41 Left 2
WINDOW 3 36 70 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName VDD
SYMATTR Value 15V
SYMBOL Digital\\dflop 1952 624 R0
WINDOW 0 48 -19 Left 2
SYMATTR InstName A1
SYMATTR SpiceLine Vhigh=15V Vlow=0V Td=10n
SYMBOL res 1264 560 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R15
SYMATTR Value 30K
SYMBOL res 1120 560 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 10K
SYMBOL voltage 384 1072 R0
WINDOW 0 46 47 Left 2
WINDOW 3 49 74 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName VREF
SYMATTR Value 5V
SYMBOL res 272 560 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R5
SYMATTR Value 330K
SYMBOL cap 352 560 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C2
SYMATTR Value 82p
SYMBOL cap 352 656 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 22p
SYMBOL res 0 1072 R0
WINDOW 0 40 45 Left 2
WINDOW 3 38 70 Left 2
SYMATTR InstName R4
SYMATTR Value 2K155
SYMBOL res 224 368 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 18K
SYMBOL cap 320 368 R90
WINDOW 0 7 61 VBottom 2
WINDOW 3 -17 -6 VTop 2
WINDOW 123 38 34 VTop 2
SYMATTR InstName C1
SYMATTR Value 3n3
SYMATTR Value2 IC=420
SYMBOL Digital\\or 2512 576 R0
SYMATTR InstName A3
SYMATTR SpiceLine Vhigh=15V Vlow=0V
SYMBOL Digital\\or 2512 688 R0
SYMATTR InstName A4
SYMATTR SpiceLine Vhigh=15V Vlow=0V
SYMBOL res 2288 128 R0
WINDOW 0 42 44 Left 2
WINDOW 3 38 66 Left 2
SYMATTR InstName RLB
SYMATTR Value 16R8
SYMBOL res 928 560 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R11
SYMATTR Value 22K
SYMBOL res 784 768 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R9
SYMATTR Value 1K6
SYMBOL res 784 560 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R8
SYMATTR Value 1K6
SYMBOL res 816 1184 R180
WINDOW 0 47 66 Left 2
WINDOW 3 48 45 Left 2
SYMATTR InstName R10
SYMATTR Value 22K
SYMBOL Digital\\or 1760 912 M180
SYMATTR InstName A5
SYMATTR SpiceLine Vhigh=15V Vlow=0V
SYMBOL ind2 2496 48 R180
WINDOW 0 -64 74 Left 2
WINDOW 3 -75 50 Left 2
SYMATTR InstName LSC
SYMATTR Value 355µ
SYMATTR Type ind
SYMATTR SpiceLine Rser=10m
SYMBOL diode 2560 -144 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName DRI
SYMATTR Value DID
SYMBOL diode 2624 -96 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName DRJ
SYMATTR Value DID
SYMBOL diode 2624 48 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName DRK
SYMATTR Value DID
SYMBOL diode 2560 160 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName DRL
SYMATTR Value DID
SYMBOL cap 2720 -48 R0
WINDOW 0 40 22 Left 2
WINDOW 3 43 46 Left 2
WINDOW 123 44 72 Left 2
SYMATTR InstName CFC1
SYMATTR Value 1000µ
SYMATTR Value2 IC=12.6
SYMBOL res 2720 128 R0
WINDOW 0 39 45 Left 2
WINDOW 3 40 71 Left 2
SYMATTR InstName RESRC
SYMATTR Value 10m
SYMBOL res 2992 128 R0
WINDOW 0 40 46 Left 2
WINDOW 3 40 72 Left 2
SYMATTR InstName RLC
SYMATTR Value 16R8
SYMBOL Opamps\\LT1677 208 848 R0
WINDOW 0 19 2 Left 2
WINDOW 3 22 28 Left 2
SYMATTR InstName VEA
SYMBOL Opamps\\LT1677 864 704 R0
WINDOW 0 18 4 Left 2
WINDOW 3 20 28 Left 2
SYMATTR InstName CDA
SYMBOL Opamps\\LT1677 1200 832 R0
WINDOW 0 16 4 Left 2
WINDOW 3 16 29 Left 2
SYMATTR InstName CEA
SYMBOL voltage 528 1072 R0
WINDOW 0 46 47 Left 2
WINDOW 3 49 74 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName VCC
SYMATTR Value 3.5V
SYMBOL res 272 1040 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 22K
SYMBOL res 160 1184 R180
WINDOW 0 -68 70 Left 2
WINDOW 3 -80 44 Left 2
SYMATTR InstName R7
SYMATTR Value 22K
SYMBOL res 1088 896 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R13
SYMATTR Value 22K
SYMBOL res 1152 1184 R180
WINDOW 0 -59 71 Left 2
WINDOW 3 -59 45 Left 2
SYMATTR InstName R14
SYMATTR Value 22K
SYMBOL res 224 464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R3
SYMATTR Value 180K
SYMBOL res 336 464 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R2
SYMATTR Value 180K
SYMBOL current 1632 144 R0
WINDOW 3 24 80 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR Value PULSE(50mA 50mA 0 100n 100n 1m 2m)
SYMATTR InstName I1
SYMBOL cap 1344 560 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C4
SYMATTR Value 390p
SYMBOL ind 2048 -144 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName LFB
SYMATTR Value 100µ
SYMATTR SpiceLine Rser=10m
SYMBOL ind 2752 -144 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName LFC
SYMATTR Value 100µ
SYMATTR SpiceLine Rser=10m
SYMBOL cap 2160 -32 R0
WINDOW 0 43 8 Left 2
WINDOW 3 45 30 Left 2
WINDOW 123 45 55 Left 2
SYMATTR InstName CFB2
SYMATTR Value 330n
SYMATTR Value2 IC=12.6
SYMBOL cap 2864 -32 R0
WINDOW 0 43 8 Left 2
WINDOW 3 45 30 Left 2
WINDOW 123 45 55 Left 2
SYMATTR InstName CFC2
SYMATTR Value 330n
SYMATTR Value2 IC=12.6
SYMBOL ind 1248 -144 R270
WINDOW 0 32 56 VTop 2
WINDOW 3 5 56 VBottom 2
SYMATTR InstName LFA
SYMATTR Value 100µ
SYMATTR SpiceLine Rser=10m
SYMBOL cap 1360 -32 R0
WINDOW 0 41 6 Left 2
WINDOW 3 43 32 Left 2
WINDOW 123 44 58 Left 2
SYMATTR InstName CFA2
SYMATTR Value 330n
SYMATTR Value2 IC=420
SYMBOL cap 1488 -32 R0
WINDOW 0 41 6 Left 2
WINDOW 3 43 32 Left 2
WINDOW 123 44 58 Left 2
SYMATTR InstName CFA3
SYMATTR Value 1µ
SYMATTR Value2 IC=420
SYMBOL res 1488 128 R0
WINDOW 0 39 45 Left 2
WINDOW 3 40 71 Left 2
SYMATTR InstName RDA2
SYMATTR Value 18R
TEXT 1536 336 Left 2 !K1 LPA LPB LSA LSB LSC 1
TEXT 1528 408 Left 2 !.MODEL DID D(Ron=10m Roff=1E7)
TEXT 1528 360 Left 2 !.MODEL MSW SW(Ron=10m Roff=1E7 Vt=7V5)
TEXT 1528 456 Left 2 !.LIB OPAMP.SUB
TEXT 1528 480 Left 2 !.tran 0 10m 5m uic
TEXT 1528 432 Left 2 !.MODEL ZID D(Ron=10m Roff=1E9 VRev=5V)
TEXT 1528 384 Left 2 !.MODEL CMP SW(Ron=10m Roff=1E7 Vt=0V)
LINE Normal 928 32 928 -48 2
LINE Normal 944 32 944 -48 2
LINE Normal 608 48 608 -48 2
LINE Normal 624 48 624 -48 2
LINE Normal 1728 32 1728 -48 2
LINE Normal 1744 32 1744 -48 2
LINE Normal 2432 32 2432 -48 2
LINE Normal 2448 32 2448 -48 2Attachments
I haven't thanked you yet MorbidFractal, so thank you.
In the end I took the easy way out. I ordered a 12V @ 5A Meanwell smps and a 12 to 200-450V converter from eBay. Together they should be up to the task. The high voltage converter easily does 20mA at 440V. That's all I need. I probably need some more filtering in the B+ supply to filter out high frequency content. I was thinking about adding a LC filter, something like 330uH and 4u7. Does that seem right?
In the end I took the easy way out. I ordered a 12V @ 5A Meanwell smps and a 12 to 200-450V converter from eBay. Together they should be up to the task. The high voltage converter easily does 20mA at 440V. That's all I need. I probably need some more filtering in the B+ supply to filter out high frequency content. I was thinking about adding a LC filter, something like 330uH and 4u7. Does that seem right?
The experiment did not work as good as intended.
Firstly the dc/dc converter for the HV was not isolated. There seems to be a resistive path form the - at the secondary side to the - at the primary side. My guess: a simple adjustable resistive divider. Hence lifting the 12V supply to 70/80V did not work as expected (read: not at all). With cathodes of 12ax7 cathode followers at 200V I can't get away with a normal ground connected faux centre tap on the heaters.
What did work, was supplying the heaters with a separate 12V smps and lifting just that one and use the other 12V smps to power the DC/DC converter. I think this is far from ideal.
Secondly there was a lot of switching garbage on the HV that I just could not get rid of. The supplies were rather far away from the test preamp board I made, not likely to be EMF products being the culprit. The only way to tame the hum generated by the DC/DC converter was adding a RC filter behind it. Still to much garbage on the PSU to sound clean. There was a constant faint 250 Hz tone hearable.
What makes it difficult to address the problems is that the DC/DC converter is a black box. No schematic, no name on the control IC (other than some Chinese signs), no data sheet for the MOSFETS. Construction seems good but engineering is a bit sub par. No snubber over the single output diode, just one C filter at the output, no input filtering that I could see. I guess I could say not up to the task of supplying B+ to a highly sensitive guitar preamp.
So, back at square one!
I'd still like to go the route of an smps. Size does matter as the preamp must fit in a 1U rack enclosure (40mm internal height). I'm open to the option of a transformer too as long as it does a rectified 430 and 12.6 V.
Firstly the dc/dc converter for the HV was not isolated. There seems to be a resistive path form the - at the secondary side to the - at the primary side. My guess: a simple adjustable resistive divider. Hence lifting the 12V supply to 70/80V did not work as expected (read: not at all). With cathodes of 12ax7 cathode followers at 200V I can't get away with a normal ground connected faux centre tap on the heaters.
What did work, was supplying the heaters with a separate 12V smps and lifting just that one and use the other 12V smps to power the DC/DC converter. I think this is far from ideal.
Secondly there was a lot of switching garbage on the HV that I just could not get rid of. The supplies were rather far away from the test preamp board I made, not likely to be EMF products being the culprit. The only way to tame the hum generated by the DC/DC converter was adding a RC filter behind it. Still to much garbage on the PSU to sound clean. There was a constant faint 250 Hz tone hearable.
What makes it difficult to address the problems is that the DC/DC converter is a black box. No schematic, no name on the control IC (other than some Chinese signs), no data sheet for the MOSFETS. Construction seems good but engineering is a bit sub par. No snubber over the single output diode, just one C filter at the output, no input filtering that I could see. I guess I could say not up to the task of supplying B+ to a highly sensitive guitar preamp.
So, back at square one!
I'd still like to go the route of an smps. Size does matter as the preamp must fit in a 1U rack enclosure (40mm internal height). I'm open to the option of a transformer too as long as it does a rectified 430 and 12.6 V.
Then I still suggest you use one of these. It is isolated and so shouldn't mind it's 12V being referenced to 80V. Use the square wave 220V AC output and a voltage doubler to get 440VDC. You must use ultrafast diodes such as HER108 or UF4007.
I use one for a four tube 6SN7 based Williamson front end, another for an Aikido 6N3P/6N6P headphone amp. No measurable noise with my scope, either. DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay
I use one for a four tube 6SN7 based Williamson front end, another for an Aikido 6N3P/6N6P headphone amp. No measurable noise with my scope, either. DC-AC Converter 12V to 110V 200V 220V 280V 150W Inverter Boost Board Transformer | eBay