Lets´try these pictures regarding spectrum analysis, upper one a peep at the noise floor but ignoring the LHS side arbitary audio levels.. Note there are no switching 75Khz harmonics f-x on the output at full power. I assumed any signal harmonics created by the HP339A signal source (-100 dB) is so low by comparison with the tube amp, it can be ignored. Tube amp 120W
Next at 100W power level, thd 0.2% as stated on lower left.
Keep at it, next more on the switcher. This the most dangerous part.
It can be done !
Bench Baron
Next at 100W power level, thd 0.2% as stated on lower left.
Keep at it, next more on the switcher. This the most dangerous part.
It can be done !
Bench Baron
I tried using a Mean Well SMPS for the filaments of a DHT in filament bias and the result was horrible. Not a fan myself.
I looked into using a 100v Meanwell SMPS for the HT of my X10 preamps but the switching frequencies were too low (in the audio band).
Otherwise I now use a common mode choke and low ESR caps either side to clean up the output when using one for triode heaters.
Using one with DHTs would be a challenge, but a CMC and LM 350T voltage regulator may clean it up.
Otherwise I now use a common mode choke and low ESR caps either side to clean up the output when using one for triode heaters.
Using one with DHTs would be a challenge, but a CMC and LM 350T voltage regulator may clean it up.
Using the basic variants of SMPS, Buck, Boost, Flybacks etc are actually quite easy and reliable to design, but where it goes adrift is the amount of interference supression with the expensive achilles heel of EMC compliance.
These add considerable filter bulk and often ruin the space required, but the power to weight ratio is still better.. Going into the Resonant and exotic types then the learning curve and the design issues go exponentially upward, with expensive test equipment . Two decades ago I designed a resonant 4 quadrant design producing very low interference levels but at that time the UC3875 ic wasn´t stable under certain light load conditions. Reliability came into question. There are SMPS from Asia & FE being imported without compliance certs.....check the spec statements if they have any !
Bench Baron
These add considerable filter bulk and often ruin the space required, but the power to weight ratio is still better.. Going into the Resonant and exotic types then the learning curve and the design issues go exponentially upward, with expensive test equipment . Two decades ago I designed a resonant 4 quadrant design producing very low interference levels but at that time the UC3875 ic wasn´t stable under certain light load conditions. Reliability came into question. There are SMPS from Asia & FE being imported without compliance certs.....check the spec statements if they have any !
Bench Baron
Lots of commercial equipment contains SMPSs these days and they have to pass rigorous efficiency and EMC requirements - EVs, hybrids, PHEVs, TVs, monitors, LED lighting systems, chargers of all sorts of different kinds and lots of things I don't even know about.
Some of the equipment is light weight, small and often, thin in the case of TVs and monitors. It must be possible to meet the EMC requirements in cost-effective ways.
As you say, the secret is fancy test equipment. And also, amortizing the development cost across tens of thousands or millions of units.
Some of the equipment is light weight, small and often, thin in the case of TVs and monitors. It must be possible to meet the EMC requirements in cost-effective ways.
As you say, the secret is fancy test equipment. And also, amortizing the development cost across tens of thousands or millions of units.
In my day job, I once designed a monitor for a transport application, that required proof of EMC compliance.
After a run in the EMC chamber, one of the non-compliances that emerged was LF (150-300kHz) conducted emissions (noise sent up the mains cable by SMPS units). The emissions came from two 50W units, made by TDK-Lambda (so, at least half-decent reputation). The manufacturer will say that it's because there were two of them; but there's nothing very unusual about that. It wasn't too tough to fix (CMC, DMC, X and Y caps) but the cost was non negligible, once PCB for the input connector was accounted for.
IME, noise injected into the mains suppy is bad news for audio. I mentioned earlier that below 150kHz, there are no limits for EMC (IT or transport equipment reguations, at least) and mains→DC converter units ("SMPS") have high emissions there. You can apply an SMPS to an amplifier, and finds that it degrades your MC cartridge amp, or DAC.
Those thinking of SMPS apps in low noise pre-amps and even main amps wanting a noise ceiling better than -80dB noise and under, take note of all comments! Even with careful calculation, design and using pricy chokes, I find getting better than -70dB down S/N ratio with any SMPS in the chassis is hard to achieve. My power amp has an SMPS rated 1kW, and co nforms to the EN 50xx spec, I can mitigate around some of the issues by going to balanced inputs, so if the problems occur at only 100W...Beware ! Of course one can cheat and switch in that 20Khz filter on the analyser and say you dooone´it ! but that switching noise is still lurking out there. That AM/FM tuner lurking nearby is bound to pick up something, If your design is good then maybe it´s picking up next doors warbling solar PV converter. I´m afraid worse is to come !
As dch53 rightly mentions, big lab projects, typ in my days doing tram, train & escalator SS designs around EN 50155 spec, new lab equipment was often hossed out after only a years service, and new purchased; some on hire but other written off against juicy corporate tax relief, and it goes on.
Being in a plucky R&D position, for 2nd hand it was easy to settle for nominal and get equipment in good serviceable condition....I still have the 1976 Tekt 2445A analog scope which was a top flight tool for it´s day. The Hameg not far behind. The cue to longevity on expired/written off equipment is switch it on once a couple of days for 1/4 hr to keep the electrolytic cap films and others in order. Viva
Bench B
As dch53 rightly mentions, big lab projects, typ in my days doing tram, train & escalator SS designs around EN 50155 spec, new lab equipment was often hossed out after only a years service, and new purchased; some on hire but other written off against juicy corporate tax relief, and it goes on.
Being in a plucky R&D position, for 2nd hand it was easy to settle for nominal and get equipment in good serviceable condition....I still have the 1976 Tekt 2445A analog scope which was a top flight tool for it´s day. The Hameg not far behind. The cue to longevity on expired/written off equipment is switch it on once a couple of days for 1/4 hr to keep the electrolytic cap films and others in order. Viva
Bench B
I'm facing a Quandary with a Crown SXA amplifier... they did a lot of cutting of corners to make the thing fit into the small rack mound amp space back in the 50s, but still managed to build a pretty good Tube Amp using EL37s... i've taken the chassis down to the Transformers again. To start over and try and separate the two power supply transformers to create dual mono blocks within the same chassis. The original design saw the 2 power Transformers coupled for the B+. But if i'm going through the trouble of rebuilding it, I would like to have it be discreet and separate topology on both sides. It's not that big of a push, because I believe either the output Transformers will put out 300V AC... but I believe that they want the system to run at 410V DC loaded... and then there's the issues of the preamp tubes and the bias supply. I have no qualms with putting solid state regulator of some sort in there... as long as it was noise free and maybe saved a little bit of space, and of course made it sound nice! Ideally, I'm just trying to find something that will turn that 300V. Ac into usable, dc and ideally be mounted on a single pcb. I have a recording studio here and I also have some speakers that I'm building specifically for this project. Just to have something cool to a/b with my larger speakers. The crown puts out a solid thirty watts per channel... and I imagine that is capable of much higher transients... i've been trying to get an idea of what's out there and what could be built to do this and how complex it would be if I could do it myself or should I just hire somebody to print up a board and populated it myself? Attaching a schematic and a pic of the unit.I don´t like the idea that the HV is dependent on the heater current, it tells me that the regulation is only on the LV output. Swap tubes, i-e heater current and all HV havoc voltage prevails, No! unless after post-regulation is used which would seem a waste.
Regulation seems typical of a switching topology having poor cross-output regulation, and it looks there is no coupled filter inductor used on each switching output. That rules out forward topology. Also, on paper there is no emissions compliance regulation that interference produced could play havoc with nearby radio etc. Switchmodes are designed to run hot to limit core size, power losses roughly 50% ferrite and 50% copper. Running temp on full load 30°C over 25°Cambient isn´t unusual. That implies 55°C to touch, requiring min F or H grade UL listed insulated copper wire.
Of course only my view;
By all means proceed, but use an isolating transformer, but take care and don´t get stung. Keep loads connected !
Over the decades I have designed several 1kW PFC 450V 2A, versions and higher volts for tube amps but using a mains transformer for the heater supply. Also mention that any seriousswitchmode design requires dramatic knowledge and experience bumps, way upward of Tube amps. However, once the subject is mastered, there are negligable voltage droops on transients with excellent regulation benefits. There is also more to go wrong.
Viva SMPS
Bench Baron
I'm using the same switcher the OP posted for a SEUL EL-34 amp I'm building
The original builder bread boarded this amp and the SMPS doesn't get too hot just mounted on a piece of wood mounted on short stand offs.
I'll be building the amp on a 1/8" thick aluminum plate with thermal grease between the switcher and aluminum chassis.
Here is the schematic below. I had all the tubes, resistors, caps, etc on hand.
The SMPS and OPT's will be here in a few days.
I payed around $40 for the switcher, so I bought a second one and may use it for another project.
The original builder bread boarded this amp and the SMPS doesn't get too hot just mounted on a piece of wood mounted on short stand offs.
I'll be building the amp on a 1/8" thick aluminum plate with thermal grease between the switcher and aluminum chassis.
Here is the schematic below. I had all the tubes, resistors, caps, etc on hand.
The SMPS and OPT's will be here in a few days.
I payed around $40 for the switcher, so I bought a second one and may use it for another project.
Attachments
I looked at it for heater supply (4x6c33) and bought one.
https://www.tigerpowersupplies.com/...ower-supply/fanless-power-supply-500w-series/
Yes worked fine but you need twice the rating for the start up current. Then you need to de-rate it for the hot temperatures the valve amp runs at unless you add fans. So in the end a simple (250W) toroidal was a better option.
As far as EMC I could not fault it - but that's probably why it costs. If you do use SMPS make sure you load them to 30% or more so that they don't go discontinuous and generate in band audio tones.
https://www.tigerpowersupplies.com/...ower-supply/fanless-power-supply-500w-series/
Yes worked fine but you need twice the rating for the start up current. Then you need to de-rate it for the hot temperatures the valve amp runs at unless you add fans. So in the end a simple (250W) toroidal was a better option.
As far as EMC I could not fault it - but that's probably why it costs. If you do use SMPS make sure you load them to 30% or more so that they don't go discontinuous and generate in band audio tones.
Last edited:
For a 6C33C with heaters in series you could use an ATX power supply. The 12V rail can supply plenty of power. Very bulky though.
I haven't used any "modules" as of yet, but I have designed my own AC-DC and DC-DC converters to power my own tube creations. I am in the throes of laying out a 5X feedback-based lineamp using the 6N3P-EV, and that one will be powered by a 150V linear regulator driven by a little Antek 50VA toroid with 140V and 6.3V outputs.
I've since decided i will use the transformers provided in the amp, but instead of their original wiring, wire it up with full wave rectification and make it a dual monoblock. I believe this is probably the best thing. I would really like to go DC with the heater voltage though. I think that would help a lot and also make it sound a lot cleaner.
Just to round off this thread, it's worth appreciating the risk anyone takes in using an off-line switchmode power supply that has no safety compliance rating - for AC mains connection safety. Without that compliance, you take on the risk that some aspect of safety is deficient - the list of corner cutting or inferior design can be very long - and the risk matrix extends to death of the user (or the unfortunate person that gets the amp in a few years time).
I have a PP 6p15p amp running off one of those. Near 40 mA idle per tube, and about 14 mA per front end. Total heater is 5A, and the two channels are rigged in series across the 12.6V output. Outputs are stolen from a Sherwood S-5000 carcass. I think it works quite well.
Am going to use a pair for 600V and run a 6CK4 off each 6.3. The amp is PP, A2 so current will be relatively constant. The finals are DH, and run on 7.5V so they'll get AC/60cps.
Douglas
Am going to use a pair for 600V and run a 6CK4 off each 6.3. The amp is PP, A2 so current will be relatively constant. The finals are DH, and run on 7.5V so they'll get AC/60cps.
Douglas
Attachments
I tried using SMPS for heater and HV Boost converter for tube preamps and they work good, just add additional filtering if you want.
Hello,
If anyone wants to try it, I spotted this power supply.
PSV68-420/-100 [Dual Voltage] [100-240VAC – +420V/-100V, 68W]
https://gra-afch.com/catalog/power-supplies/power-supply-for-vacuum-tubes-amplifier-psv68-420-100/
Regards,
Stef.
If anyone wants to try it, I spotted this power supply.
PSV68-420/-100 [Dual Voltage] [100-240VAC – +420V/-100V, 68W]
https://gra-afch.com/catalog/power-supplies/power-supply-for-vacuum-tubes-amplifier-psv68-420-100/
Regards,
Stef.
Attachments
What I would like is a bit of an improvement in selection. Heater voltage ones, and B+ ones, so the regulation loops don't have to be shared. Adjustability on them would be great.
Douglas
Douglas
I used SMPS to power filaments of GK-71 tubes, 120W total. Directly heated. To start it, I added a bridge from 12V secondary that did initial heating, then SMPS catch up. It reduced weight and size of the amp.
Before that, I used a 240V inverter removing 50 Hz chopper from it, to power a guitar amp from 12V.
In both cases there were no interference, since I always keep in mind currents that flow through ground connections, as well as capacitive parasitic couplings.
Before that, I used a 240V inverter removing 50 Hz chopper from it, to power a guitar amp from 12V.
In both cases there were no interference, since I always keep in mind currents that flow through ground connections, as well as capacitive parasitic couplings.
Last edited:
I would not mind high frequency AC heaters for DH tubes, in 7.5V/3.5A capacity right off the rack either. 200kHz should leave things quite quiet.
Douglas
Douglas