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Good SMPS for power amplifier.

linnfomaniac83

linnfomaniac83

I bet you can’t wheelie a unicycle!
I’m currently investigating solutions for fixing the amplifier modules in Linn Sizmik subwoofers. The amplifier circuit itself is based on four TDA7293 ICs in parallel and the supply for all the crossover electronics is derived from the split rail supply for the amplifier circuit... unfortunately, that supply is a really flaky switching supply which has resulted in the death of a large number of these otherwise excellent subwoofers.

It looks like I can just pull the transformer and rectifier diodes and wire in another split rail supply, there is some kind of feedback line running through an optocoupler to the original PSU, I suspect that is to put the PSU into a lower power mode when the unit goes into standby mode. I’m just waiting on a schematic from Linn to confirm that and also to confirm the rail voltages needed to power it... so I’m looking for a decent split rail PSU for a power amplifier, there are a few out there but if anyone here has any experience using them and can point me towards a decent one, it’d be appreciated, it obviously needs to be happy driving a very small load when the unit is in standby... it also needs to be capable of delivering peaks of around 1000w to be on the safe side. It’s likely that I’m going to have to house it in a separate enclosure so I’m not really concerned about physical size (there’s not much room in the amplifier enclosure to fit another board in)... I don’t think a linear supply is going to be practical, a regulated supply of that size would be big, expensive and inefficient, all reasons that Linn didn’t used one.

Thanks in advance.
 
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If I was in Europe, this is what I would use (although this is not SMPS) :

http://www.canterburywindings.co.uk/

https://shop.dadaelectronics.eu/quad-405-bhc-aerovox-dual-mono-power-sup-108462939.html

I don’t know much about Canterbury but I’m sure it’s very high quality.

As for the Dada power supplies, I used their 4x15000 uf version several times with very good results. The connectors are easy to remove if you want to solder the wires directly on the board. Their quality is state of the art and built to last.

I never success on the long term with SMPS........all IMHO, of course.
 
Cheers guys, ideally regulated, the original supply is regulated. The onboard Linn SMPS is terribly unreliable and they will all eventually fail. I very much like the idea of a solid linear supply and I could design that myself, but if I’m going to offer it as a repair option for other Linn users, it has to be economically viable... don’t get me wrong, I’m not looking to profit anyway, I just like to help others keep their kit going and I hate seeing stuff go to landfill, but if the power supply costs as much as the sub is worth, it isn’t viable.
 
I use this https://www.minidsp.com/products/plate-amplifiers/pwr-ice250.
I use it to run 2x12" subs. a box is also available.
Several people have commented how well it integrates with my Quad 989's

It gives 500W into 8 Ohm, connection via Ethernet to your laptop gives you full control. Which is a must for subwoofers IMO.

As for needing 1000W peak Linn quotes this 'figure' for both the 10" and 12" models !. They then go on to show distortion at 50 and 150 W, a more realistic power requirement IMO.
 
Arkless Electronics said:
I'd use a linear unregulated supply personally.
Click to expand...
I just need to weigh up the cost, I suppose I could scavenge bits from dead PA amps, provided I get the output voltages close enough, that’d be a cheap enough way of doing it... I need to find out what the output rails of the original power supply were, the TDA7293 chips themselves are good for +/- 60v but I suspect that’s a bit high for other components on the board... looks easy enough to hack in another power supply though so I’ll have a go, nothing to lose.

I also have a plate amp here from BK electronics which I’m going to try, the only reason I haven’t yet is because my back is in bits and I can’t down on the floor to wire it in to my system... I suspect this will work better than the Linn amp module thanks to much finer control over crossover frequency and phase, for my own sub, this is likely what I’ll use... but to fit it in the box means getting the jigsaw out. I’m happy to either do that or to stick the boards out of the plate amp in the box off a Linn Intersekt... but the point of this project is to revive these “unrepairable” Linn modules... I think it’ll be pretty easy.
 
misterdog said:
I use this https://www.minidsp.com/products/plate-amplifiers/pwr-ice250.
I use it to run 2x12" subs. a box is also available.
Several people have commented how well it integrates with my Quad 989's

It gives 500W into 8 Ohm, connection via Ethernet to your laptop gives you full control. Which is a must for subwoofers IMO.

As for needing 1000W peak Linn quotes this 'figure' for both the 10" and 12" models !. They then go on to show distortion at 50 and 150 W, a more realistic power requirement IMO.
Click to expand...

The power figures Linn quote for the original amp module are laughable... 500w continuous (with 1000w peak) from four TDA7293s? No chance, 250 all day long with sufficient cooling but not 500. I think any module that can push 250 watts with low distortion will be plenty for a Sismik, 500 definitely would. I have looked at those Mini DSP modules, and the Hypex and Dayton modules, they all look ideal and would offer comprehensive calibration tools... my original intention was to experiment with these, and the BK module and see which offered best bang for buck as a replacement.

I also wanted to investigate why the Linn power supply fails and see if they could be fixed... well they’re a bit shit and there are multiple failure modes, I have two in front of me, one with a dead VB408 regulator, the other with a shorted fet that has in turn burned several resistors and the PWM driver... so I won’t be investigating that further... but as it happens, it’s really easy to bypass that supply... it’ll be interesting to see what the feedback line that runs through the optocoupler is doing, I’m thinking it could be for overload protection (to cut the rails in the case a a fault in the output stage),if it is I could implement a separately powered latching relay circuit to kill the main supply rails... I just need to question the viability.

PS, this one looks like the one to use from MiniDSP, it’s cheaper and offers 450w into 4r, the nominal DC resistance of the drive unit is 6r so it should be easily up to the job.
 
We have a successful power up!

I am going to build the power supply in an external enclosure I think... I’d thought about putting it in the sealed speaker enclosure, running the wires through to the amplifier cavity and sealing them with a bit of hot glue but if I go with a linear PSU, it’ll be quite big (but won’t be a fire risk)... an SMPS would fit easily without making a notable difference to the air volume, but there’s a load of wadding in there, if it ever fails violently, it could set the wadding alight, which obviously wouldn’t be desirable. I’m sure whatever I put together, it’ll outlive Linn’s effort!



 
Just a tip.
Noise from Flyback PSU and that a no load no work properly do not use.
Push Pull PSU good but choke has to change from low to high vale to get best performance.
Full Bridge PSU better but again you need a choke and to change value as load changes to get best performance.
No isolated BUCK FORGET IT NASTY AND WILL KILL
Full Resonant are fantastic, sin op no nasty square wave less harmonic but cost more.
The biggest FR I made was 150KW for a Xray machine, only 1 amp. And oil filled transformer.
The nicest one was the PSU for the fuel cells in the Space Station got 97% efficiency,

So Flyback constant load , Buck forget it,PP ok,FR perfect, ok I hear what about CUK, well check them out you turn to study he he
 
linnfomaniac83 said:
We have a successful power up!

I am going to build the power supply in an external enclosure I think... I’d thought about putting it in the sealed speaker enclosure, running the wires through to the amplifier cavity and sealing them with a bit of hot glue but if I go with a linear PSU, it’ll be quite big (but won’t be a fire risk)... an SMPS would fit easily without making a notable difference to the air volume, but there’s a load of wadding in there, if it ever fails violently, it could set the wadding alight, which obviously wouldn’t be desirable. I’m sure whatever I put together, it’ll outlive Linn’s effort!



Click to expand...

Hi linnfomaniac83,

also have a dead Sizmik 10.25 Amp with burn diodes under the transformer and interested in how exactly did you bypass the internal PSU with external one.
Please could you share specs and connection points for your external PSU with pics?
Would appretiate your help.
Did you got shematics from support? If so can you share them?
Thank you
 
THX but for now im interested in how exactly to bypass with external PSU.

(Maybe later i will put in a ice 500a modul with minidsp 2x4 i also have.)
 
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