the filament part of the smps can not handle the cold resistance of the tube filaments, i will put a 10 ohm ntc to mitigate inrush...or another trick do not swatch on the B+ yet until the filaments are all glowing.. or a combination of both...
the trick with smps is not to load it with what the manufacturer tell you...derating by as much as 50%...
not this one, as i have yet to buy....U$50 is not cheap but neither is it prohibitive...i am waiting for our local Lazada or Shopee to offer it then i buy...
i have extensive experience repairing atx psus so i know how they tick,
i have purchased around 35 units of 24vdc 6 ampere smps bricks for twice the number of ACA boards that we built, i have installed the smps very close the ACA boards and there were no issues that others are afraid of...
my recent 48v ACA also used four of these bricks, 48vdc/200 watt rated, so four of them can dish out 800 watts, but used them to deliver about 300 watts only so i have a wider margin of capacity.
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A computer power supply is different ... usually uses a dedicated controller that has multiple and complex protections on all output voltages .
Clasic SMPS don't need reset after a short . But if you buy that chinese supply be ready to replace all electrolytics with good ones , 100% chance that all of them are the cheapest crap you could find
Clasic SMPS don't need reset after a short . But if you buy that chinese supply be ready to replace all electrolytics with good ones , 100% chance that all of them are the cheapest crap you could find
A computer power supply is different ... usually uses a dedicated controller that has multiple and complex protections on all output voltages .
Clasic SMPS don't need reset after a short . But if you buy that chinese supply be ready to replace all electrolytics with good ones , 100% chance that all of them are the cheapest crap you could find
i have seen them all, most of then use the half bridge technology, two stacked capacitors with two switching tranies driven by tl494 thru drive traffos, others use a single Mosfet driven by uca382 pwm chip..
It does power up the heaters to a stable condition all the time, no problem. The problem was just inrush of high voltage, but it have been solved. So actually it is possible to use Switching PSU in tube amp especially if the form factor and weight are playing significant role. However, it is hard to assess how different the same amplifier sounds with switching PSU and traditional one based on kenotron or solid state rectifier.
I much prefer the B+ to come on gradually. One way is to use a mosfet, another way is to use a string of properly sized thermistors (NTC resistors) and then after a little while bypass the thermistors with a time delay relay.
I avoid silicon in a tube amplifier - a rectifier tube with some silicon diodes for rectification I'll live with. Much prefer to have the simplest designs -and no more- and design for longevity/reliability and low distortion.
SMPS was looked at , seen some amplifiers back in 1997 when I was in Hong Kong, but will those parts still be available in 10 year or 20 years for repair? Recently I unearthed a delay relay for a extractor fan - was bought new and sat in a box for 9 years. It worked for 5 weeks and then died.
AM
I avoid silicon in a tube amplifier - a rectifier tube with some silicon diodes for rectification I'll live with. Much prefer to have the simplest designs -and no more- and design for longevity/reliability and low distortion.
SMPS was looked at , seen some amplifiers back in 1997 when I was in Hong Kong, but will those parts still be available in 10 year or 20 years for repair? Recently I unearthed a delay relay for a extractor fan - was bought new and sat in a box for 9 years. It worked for 5 weeks and then died.
AM
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guitar amplifiers can benefit...imagine lugging your gear from gig to gig....
the smps that i use today are small, has passive pfc, and b+ comes on after about 3 secs....they have come very cheap that repairing is no longer practical, buy a new one...
better yet derate them at 50% of capacity...never had any failures yet...
Ulrich Neumann used 2-3 SMPS in his hybrid 'SOLO' PCB-based ~100W guitar amp:
JFET-MOSFET cascode input clean stage, 3-12AX7's for 'color stage' DCCF & PI driving BJT SS output stage. There are LND150's scattered throughout, as well.
Output stage Vcc and 12AX7 filaments in series run on 36VDC (Meanwell 150-200W, higher if you insist on abusing it consistently).
360V B+ comes from a couple conversions using a 36:11 buck converter, then a ~11:360 boost converter, followed by a BJT capacitance multiplier to get rid of ripple from the output of the boost converter. He doesn't specify exactly what those are because he's used a variety of eBay-type no-name PCB's, depending on availability.
I bought the book and PCB initially to study the circuitry, PCB layout etc. but it's become pretty intriguing so I will eventually build it as intended. It may become a kit someday (Weber?).
stringsandfrets - Guitar Amplifier Design: Tubes and Semiconductors Play Together
JFET-MOSFET cascode input clean stage, 3-12AX7's for 'color stage' DCCF & PI driving BJT SS output stage. There are LND150's scattered throughout, as well.
Output stage Vcc and 12AX7 filaments in series run on 36VDC (Meanwell 150-200W, higher if you insist on abusing it consistently).
360V B+ comes from a couple conversions using a 36:11 buck converter, then a ~11:360 boost converter, followed by a BJT capacitance multiplier to get rid of ripple from the output of the boost converter. He doesn't specify exactly what those are because he's used a variety of eBay-type no-name PCB's, depending on availability.
I bought the book and PCB initially to study the circuitry, PCB layout etc. but it's become pretty intriguing so I will eventually build it as intended. It may become a kit someday (Weber?).
stringsandfrets - Guitar Amplifier Design: Tubes and Semiconductors Play Together
Well today I tried it in a preamp. The B+ won't charge 500uF of capacitance through 500R so it makes LV for x seconds, applied B+ and immediately resets. This is my only beef with SMPS - Most have ZERO ability for inrush because of poorly designed "protection" circuits.
If anyone knows how I can disable/remove SS/OC protection, maybe this thing would be useful. As of now, I'm left creating a "soft start" so it will start the caps. Could I not use a CCS as a current limiter? Say set it to 300mA, but the total draw in normal operation is only about 100mA so it won't trip? I think I'll try to use a big Depfet for this.
All this without any tubes in the damned thing so no LV loading either.
If anyone knows how I can disable/remove SS/OC protection, maybe this thing would be useful. As of now, I'm left creating a "soft start" so it will start the caps. Could I not use a CCS as a current limiter? Say set it to 300mA, but the total draw in normal operation is only about 100mA so it won't trip? I think I'll try to use a big Depfet for this.
All this without any tubes in the damned thing so no LV loading either.
Do you need 500uF ?
As a switcher it has less 50(60) hz hum, you should be able to use a dramatically smaller cap and still have B+ in every signal.
The filtering on the preamp PCBs use 620R/220uF per channel, the buffers use 2k/47u, and the phono uses 2k/220u per stage. These are for decoupling otherwise you get crosstalk.
So I rigged a current limiter using a depfet. It would finally start into the load so I plugged in 8 tubes. Won't turn on into them. It might be good for a two tube preamp or something but 250W supply that needs to be derated to 25W is worthless IMHO. Now it seems I need to either add another depfet for the heaters, or bin the POS. What's the point of a 250W supply that can't start up into a 75W total load?
So I rigged a current limiter using a depfet. It would finally start into the load so I plugged in 8 tubes. Won't turn on into them. It might be good for a two tube preamp or something but 250W supply that needs to be derated to 25W is worthless IMHO. Now it seems I need to either add another depfet for the heaters, or bin the POS. What's the point of a 250W supply that can't start up into a 75W total load?
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It just goes to show that a delayed B+ supply can have unintended consequences. Perhaps remove or shorten the delay, so that the valves aren't yet conducting.
Does the B+ hiccup when you indicate the supply 'immediately resets', or does the supply restart the whole sequence of powering up with a delay? If the B+ just hiccups, and if the delay is short enough then B+ may rise up sufficiently by the time the valves are starting to conduct.
Does the B+ hiccup when you indicate the supply 'immediately resets', or does the supply restart the whole sequence of powering up with a delay? If the B+ just hiccups, and if the delay is short enough then B+ may rise up sufficiently by the time the valves are starting to conduct.
With typical Mains → DC converters, there is a strict limit to the amount of external capacitance that can be applied. It's much smaller than expected, for many users.
The data sheet will tell the tale, but if there is no data sheet, or no capacitance specified, you have to assume that even 47-100µF may cause problems.
This is not simply a matter of current limit.
Typical converters do not have low open-loop output impedance, and so adding big caps can rotate phase very steeply, and render the control loop unstable.
Looking at the Listing for that supply, the lack of data sheet is in keeping with the photo of the unit. The badly-mounted power-devices sets my crap-ware detector a-buzzing.
The data sheet will tell the tale, but if there is no data sheet, or no capacitance specified, you have to assume that even 47-100µF may cause problems.
This is not simply a matter of current limit.
Typical converters do not have low open-loop output impedance, and so adding big caps can rotate phase very steeply, and render the control loop unstable.
Looking at the Listing for that supply, the lack of data sheet is in keeping with the photo of the unit. The badly-mounted power-devices sets my crap-ware detector a-buzzing.