Presonus M80 Power Supply Transformer Specs?

[Pat Maki]

The toroid on my M80 power supply let the smoke out after many years of service. Need to replace it but not sure what the specs are. Anyone know what the voltages out are? It's got dual windings. Thx, Pat

 

[Bo Deadly]

Don't know but once you figure out what the voltages are I would convert to SMPS. The only real negative of an SMPS is EMI radiating to nearby circuits. Since the M80 supply is external, it's ideal for upgrading to SMPS. However, there are rules for building SMPS supplies for audio that must be followed carefully. So it's not a trivial build. You would need to make a PCB. If that's not your thing, then just find a replacement torriod.

 

[Pat Maki]

Thanks for the idea Bo. This sounds really interesting. Comfortable etching PCBs/building from scratch, so if I can't find the replacement toroid, will study up on this. Also, i created a ticket on the Presonus site last night, so will see if they have any spares/provide specs. BR, Pat

 

[Khron]

I'd be skeptical about that - they were unwilling to even provide the (ready-compiled) firmware contents for one of their older interfaces...

 

[john12ax7]

Might have the MP20 info if that helps.

 

[Pat Maki]

I'd be skeptical about that - they were unwilling to even provide the (ready-compiled) firmware contents for one of their older interfaces...

Hey @Khron , me thinks you have the right take...still not a peep from them. That's ok, who needs presonus when you have sisu?! (-;

 

[Pat Maki]

Might have the MP20 info if that helps.

Hi @john12ax7 , that would most appreciated if it's not to much of a hassle. I've got a broken MP20 coming in the mail and that would come in most handy! Btw: have you done any modding to the MP20? I've done quite a bit to half the channels in the M80 and curious about others' experiences with these units.

 

[john12ax7]

MP20 schematic is here, seems 18V rails but no transformer specs
https://groupdiy.com/threads/presonus.44834/#post-1001210

 

[john12ax7]

I replaced the generic transformers with the Jensen equivalent. And also replaced the NE5534 opamps. Both made an improvment imo. You could also try and bypass some of the mixing circuitry and get a more direct output.

 

[dom]

Going from the schematic, it looks like you'll need a multi-tap secondary with roughly 16V RMS (center tapped) and 40 V RMS windings. Might be tricky to find. The majority of off the shelf toroidals only have a single output voltage. For primary current ratings, check the mains fuse value, or the maximum power draw listed at the mains input connector as a starting point.

You're positive the transformer is bad right? Should be easy to confirm by disconnecting the secondary connector to the PCB. Confirm AC presence and fuse continuity at the primary, then check for at AC presence at the secondary winding connector.

 

[Mixermend]

It will be difficult/impossible to get a multi secondary transformer - but assuming that there is room, two separate transformers could be used.

The Phantom supply transformer can be quite small, but first check that the existing transformer is indeed faulty. Toroids invariably fail with shorted turns, blowing the mains fuse, check this with a lamp limiter, with the secondary disconnected - which is easy as it is on a connector.

If it is indeed faulty - we can suggest suitable alternative transformers.

The maker is visible on the Presonus transformer - find out is they are still trading and can supply information - or even a replacement?

 

[Bo Deadly]

Going from the schematic, it looks like you'll need a multi-tap secondary with roughly 16V RMS (center tapped) and 40 V RMS windings.

I think you mean two 18V or one 36V center tapped and one 48V. I think with some digging you could probably find that. But you don't know the current. You could probably get away with guesstimating based on the physical dimensions and perhaps more accurately by weight. Of course it would have to be a torriod and it would have to be for audio where the 48V was the right current (which is a lot less than the other windings). You can figure that out based on the number of phantoms. Or cut the BS and go SMPS.

 

[dom]

I think you mean two 18V or one 36V center tapped and one 48V

Nope, I meant 16V (32V) and 40V.

18V (36V) and 48V would be a bit too high for the rectifier capacitor voltage ratings, especially at high-line.

That's not to say the caps can't be swapped out for higher voltage ones. That might not be a bad idea either way (I would, personally). But, as-is 16V and 40V seems like the sweet spot in the middle of the tolerance stack up between cap ratings at high-line while still maintaining about a 3V minimum drop across the regulators at low line and max tolerance of 18V.

Of course you can run the caps at a bit higher than their ratings, and it'd probably be fine for some time. But, it makes analyzing lifetime of the caps impossible since you're operating them outside of spec.

 

[Pat Maki]

MP20 schematic is here, seems 18V rails but no transformer specs
https://groupdiy.com/threads/presonus.44834/#post-1001210

Thanks @john12ax7 !

 

[Pat Maki]

I replaced the generic transformers with the Jensen equivalent. And also replaced the NE5534 opamps. Both made an improvment imo. You could also try and bypass some of the mixing circuitry and get a more direct output.

I'm sure that was a nice enhancement. Will def bypass the mix circuitry on the MP20. The M80 is nice since you can go direct out per channel. Mine came stock with Jensens. When the MP20 arrives, if it has the generic trafos, then I'll order some Jensen's (they still sell these last time I checked a year ago). I tried 4 of the opamps that Jim Williams suggested and they all sound better than the NE5534 imo. All quite different. My favorite is the LT1357...very clear and accurate.

 

[MisterCMRR]

If the MP20 were mine, I'd replace the power transformer with one having only a 32 VAC center-tapped secondary. That works out to a about 22 VDC inputs for the 18 VDC regulators. And, for the phantom supply, I'd stack a voltage doubler (2 rectifiers, which could be ones in D10, and another electrolytic cap) on top of the +22 VDC. This would produce a nominal +66 VDC to feed the +48 regulator. Replace the LM317HV with the Texas Inst TL783 (rated for up to 125 V input) and you're there ... without another transformer secondary. The rating on C156, at 63 V, would be marginal (especially at high AC line and no loading of the phantom), so I'd replace it with a 100 V version. C156 also seems very large for a supply that only puts out 20 mA worst-case, but keeping it at 1000 µF won't do any harm (I'd suggest 330 µF @ 100 V for that and the added cap in the doubler. If you like this idea, I'll post a partial schematic. Other manufacturers commonly use doublers in their phantom supplies - to avoid a custom power transformer.

 

[dom]

Here's a voltage tripler scheme to generate +66V (What misterCMRR is describing):


Basically it's three extra parts, C3, D5, D6.

Lots of transformer options available with this approach because you only need a single, center-tapped output.

Talema 62063 is probably in the right ballpark (though you may need to go a bit up or down in turns ratio or power rating).

 

[Pat Maki]

Going from the schematic, it looks like you'll need a multi-tap secondary with roughly 16V RMS (center tapped) and 40 V RMS windings. Might be tricky to find. The majority of off the shelf toroidals only have a single output voltage. For primary current ratings, check the mains fuse value, or the maximum power draw listed at the mains input connector as a starting point.

You're positive the transformer is bad right? Should be easy to confirm by disconnecting the secondary connector to the PCB. Confirm AC presence and fuse continuity at the primary, then check for at AC presence at the secondary winding connector.

Sounding like a drop in replacement may not be in the cards. Will need to get creative. Don't have the PSU in front of me, but recall the fuse was 2 or 3A (since the M80 is 8 channels). I disconnected the PSU unit from the preamp and upon plugging it into 115V, it blows a fuse, so that isolates the issue to the PSU. Only visually inspected the other components within the PSU and nothing looks out of sorts, but whew the smell coming off that trafo isn't pleasent! So only used the sniff test so to speak.

 

[Pat Maki]

It will be difficult/impossible to get a multi secondary transformer - but assuming that there is room, two separate transformers could be used.

The Phantom supply transformer can be quite small, but first check that the existing transformer is indeed faulty. Toroids invariably fail with shorted turns, blowing the mains fuse, check this with a lamp limiter, with the secondary disconnected - which is easy as it is on a connector.

If it is indeed faulty - we can suggest suitable alternative transformers.

The maker is visible on the Presonus transformer - find out is they are still trading and can supply information - or even a replacement?

I'd done some digging around to find that company, but all dead ends their website is no longer. I found them on Duns and Bradstreet and the owner's name was listed, so push come to shove I could try to track him down. But I doubt I'll need to given all the great input from you and the others here. I think your prognosis is spot on...a short within the toroid would seem to explain the fuse popping every time. I'll find a lamp limiter to do a proper test and report back. Thanks!

 

[Pat Maki]

It will be difficult/impossible to get a multi secondary transformer - but assuming that there is room, two separate transformers could be used.

The Phantom supply transformer can be quite small, but first check that the existing transformer is indeed faulty. Toroids invariably fail with shorted turns, blowing the mains fuse, check this with a lamp limiter, with the secondary disconnected - which is easy as it is on a connector.

If it is indeed faulty - we can suggest suitable alternative transformers.

The maker is visible on the Presonus transformer - find out is they are still trading and can supply information - or even a replacement?

A kind tech at Presonus eventually shared the schemos for the M80. I would like to take the two trafo approach. Based on this image, are you able to suggest values for the two? Looks like one will be C.T.