No more power transformers?

[Cassiel]

Just think about it, SMPS must be the future for tubes.

I would love to know if there is someone who sells a switch-mode power supply designed specifically for tube amps. Let´s say 300 Volts 150mA and 6,3 V 2 amps.

I would built a lot more, especially preams and small stereos.
And according to reports less noise and faster sound.

Tubelab you got some work to do!!!!!
Seriously, if i were an EE i would have started working today after i saw these pictures in another thread.


http://www.hififever.com/forum/viewt...452f3b98a7e9d8

[JPeitzman]

That's a pretty cute little amp you linked to there. Isn't the problem with SMP's the garbage and noise then tend to dump onto the output? I suppose one could experiment with the switching frequencies. I would think that one may still have to worry about oscillations and other anomalies outside the audio band that would effect circuit stability, but I have never played with SMP's on audio circuits. If not properly filtered don't they kick some nastiest back onto the mains too?

On the plus side they are smaller, more efficient, and cooler running. I don't think I would agree though that they "must be the future for tubes". Transformers for linear supplies are not exactly sky rocketing in price, they are a lot easier to build, and (unless you do something really crazy) they work just about every time without fail. Besides if you need quiet and nonfluctuating voltage output you could implement a simple shunt or series regulator. With the proliferation of SMD passives and some really incredible actives available, a voltage regulator can be built on a PCB about the size of a pack of gum.

For now I am going to stick with linear. Rather than compensate for the problems of a new technology (to tubes, not in general), I will stick with old. Though that is just me and my opinions, that cute little SE you linked to builds a strong case for SMP's I think. Outside of the heat from the tubes, we could have 10watt - 20watt EL84 push pull amps the size of DVD boxes. I don't know about others, but I would take about 5 of those little buggers for a small home theater.

Cheers

James

EDIT:

OK, I just saw this, it was linked to in another thread that I just read.

http://www.silvercore.de/index.php?833c-amp&lang=en

They are using SMP's for the heaters on the 833A. Now to me, as long as the garbage on the output can be minimized or eliminated, this makes sense. That massive DHT draws about 100watts just to heat the filament. That is a fairly good sized linear supply considering it has to be quite and able to feed the heaters that 100watts continuously. Maybe this will be the future of SMP's within tube amps, I guess only time will tell. I would be interested to see someone put these supplies to the test though. I only have lower voltage ones (SMP's) laying around, but I could try some on SS line amps or heaters if/when I can find the time.

[nigelwright7557]

Originally posted by JPeitzman
That's a pretty cute little amp you linked to there. Isn't the problem with SMP's the garbage and noise then tend to dump onto the output? I suppose one could experiment with the switching frequencies. I would think that one may still have to worry about oscillations and other anomalies outside the audio band that would effect circuit stability, but I have never played with SMP's on audio circuits. If not properly filtered don't they kick some nastiest back onto the mains too?

I spent 6 months in an EMC testing facility and tested lots of SMPS's.
Yes they do kick back loads of noise onto the mains but this is taken care of by a mains filter to pass EMC regs.

Careful layout of the SMPS can help with noise on the output and so can plenty of filtering.

I have seen SMPS for valve amps but cant remember offhand which SMPS IC they used.

[Wavebourn]

I would never ever use SMPS in the gear that does not have symmetrical well balanced ins/outs (excluding speakers, however).

[BillEpstein]

Phil Marchand makes EL-84 mono blocs with a wall wart power supply that sound terrific! I had a pair for a few months for review and regretted having to return them.

http://www.marchandelec.com/mb26.html

[Wavebourn]

Originally posted by BillEpstein
Phil Marchand makes EL-84 mono blocs with a wall wart power supply that sound terrific! I had a pair for a few months for review and regretted having to return them.

http://www.marchandelec.com/mb26.html

It is a very good way to avoid UL certification troubles and expenses!

[tubelab.com]

Tubelab you got some work to do!!!!! Seriously, if i were an EE i would have started working today after i saw these pictures in another thread.

I have been tinkering with SMPS's on and off for a few years. I even designed one for a product at work (it ran off 12 volts). So far my "off line" (the terminology for a power supply connected directly to the power line) power supplies have resulted in mosfets and magnetics being sacrificed to the fire gods! When I first mentioned the "solid state transformer" on my web site I received a lot of negative email. The tube purists were not ready to have their glass contaminated with sand. Even the PowerDrive was heavilly criticized at first. Perhaps the time is now right for a universal solid state power transformer. Unfortunately I have very limited time now and for the forseable future, so I will be working on some real tube projects.

What do we need? I think that there is a market for an SMPS that accepts any line voltage from 100 to 250 volts. It should provide an adjustable or programmable (25 volt steps via a DIP switch) voltage from 250 to 500 volts at at least 250mA. It should have one or two isolated 6.3 volt DC supplies at several amps, and two that are 2 to 7.5 volts adjustable at at least 3 amps each. These could be DC or high frequency sine wave AC. This would cover 95% of all tube amps made. It must cost the same or less than a comparable power transformer. Since "one size would fit all" and it would weigh much less than a conventional transformer, the volumes would be enough to justify the development and certification costs.

Even If I could design this power supply, I could never afford the testing required to get UL, CE and CSA approval. That is needed to keep the lawyers happy. This box needs to come from a Chinese PC power supply company!

At least one diyAudio forum member has built a DIY amplifier using a DIY SMPS. I couldn't find it with a search but I think that it was Wrenchone.

[Bitrex]

http://www.instructables.com/id/High...ply-SMPSBoost/

Here's a project on a microcontroller-controlled boost converter for nixie tubes; it could probably also put out enough current for a preamp as well. There's another project on Instructables that's a boost converter using a 555 timer and an IGBT that will put out up to 1000 volts! I'm planning on experimenting with that one, I was able to find some of the parts I needed inside a dead computer SMPS. I plan on using some salvaged high voltage MOSFETs instead of the IGBT though, as the IGBTs are expensive and I can't afford to blow too many at $7-8 each. The author thinks that one might need a FET driver if a MOSFET is used instead of an IGBT - I don't know, aren't most 555s good for up to 100ma of output current? If it doesn't work maybe I can repurpose an LM386 as a FET driver - the data sheet shows that it still has good gain at 100khz.

[astouffer]

I've been toying with the idea to use a switching supply to light some 808 filaments because they need 7.5v at 4 amps. With a linear supply the bridge rectifier gets pretty warm, even warmer than the mosfet in the LDO regulator. Large heatsinks and tube amps are not a good mix.

I found a series of SMPS controllers and the company that makes them has a really good design and simulation program.

http://www.powerint.com/en/design-su...esign-software

You give it all your parameters and it gives you exact part numbers and even all the details on winding the transformer. The only drawback is for designs needing a few amps it tells you to wind a secondary with copper foil. Not sure if the software is any good with high voltage designs but maybe someone will give it a try.

[Enzo]

In professional audio we see SMPSs all the time. They are used in very quite preamplifiers and processors all the way up to multi-thousand watt power amps. We also are seeing them more and more in tube based guitar and instrument amps. SMPS noise has not been an issue in the slightest. And if we can eliminate the weight of a power transformer for a 100 watt amplifier, I'm all for iot.

If ther was going to be a problem with noise, it should certainly show up in a screaming high gain overdriving guitar amp or in a mic preamp used for recording.