PSU for Studiomaster 16-4-8

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dunham91

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Nov 14, 2021
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Hello to everyone! This is my first post here even if I'm reading the forum since a while now! Thanks again for accepting me.

I'm here for asking some advice on what to do with a Studio Master pro-line 16-4-8 I received as pay for a work.

The owner pointed out 2 channels that actually wasn't working, but as everything was working properly i decided to clean it up deeply all, and most everything was working smoothly......
But the day I decided to stress him out a bit a fatal error occurred.. I forgot a cloth directly on the back of the device, where the transformer sit... and it blow up. I really suspect an overeating of the transformer as the toroidal has been shorted and I guess there is no way to fix it (or better, where to find the substitute for the toroidal in germany).

Does anybody think this is a reasonable explanation or should i suspect something more? I was as reparation technician for audio devices but never worked on the part of this circuit.... I mostly work with DC voltages

Reading this forum I found two solutions:

recording.org/index.php?threads/vintage-mixing-console-needs-power-supply-help.52650/


Would be possible building a suitable +-15V PSU out of two of this like it was realized in the second post? would be actually the cheapest solution for me.....
In that case, would just be necessary to wire the +15,-15 and ground directly to the mixer or should i create some kind of protection for the lines first? I could follow the schematics i found.....

MW IRM-60-15ST - Switching Power Supplies Module, 60 W 15 V / 4 A, screw

The soultion of the first post is a bit too expensive for me, would be 200€ more or less... could someone suggest something similar, maybe cheaper?

Please if someone have some hints..... I'm not totally noob about electronics , but pretty new into PSU and things that can actually kill me or damage my house seriously XD

Thanks to everyone that will help!

Cheers :)
 

moamps

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Welcome here.
Are you absolutely sure that the transformer is faulty? Did you measure the windings resistance and possibly the secondary AC voltages? Transformers break down mainly after prolonged overload and short circuit. If this is not the case with you, maybe something else is wrong. It would be useful if you can post a few pictures of the power supply board and transformer here and a schematic of the power supply.
 

dunham91

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Nov 14, 2021
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berlin
first thanks a lot for the reply!

Yea, unfortunately I really suspect the toroidal just blow up.

To be honest, i was repairing this at my place, and i have a on open space and the kitchen and my repair part is separated just from a half wall.... a cloth felt down from that wall and went exactly behind the mixer and covered all the part where the transformer sit down...... I guess this caused an overheating of it till the collapse as was my "stress-test" day. Most pf channels was open and this s**t happened.

I will upload the pictures and also the schematics i found online, Is not the same exat model but i guess they didn't upgraded the PSU.

As you can see the PSU stayed the same for most of the models of that era, so I will not suspect they changed it for this baby!
 

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moamps

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It is obvious from the pictures that your transformer has suffered significant damage and needs to be replaced. The bad thing is that this transformer is not simple because it has 4 secondary windings and it is difficult to find such a transformer as a ready-made product. The good thing is that all the parameters are known (all voltages and associated powers) so that such a transformer can be easily made in a local electrical shop. Or you can ask international suppliers such as Toroidy.pl.
I think that would be the cheapest solution. You also need to check all the parts in the power supply (stabilizers and rectifiers for sure). And replace 317 in phantom power with TL783.
 
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Whoops

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dunham91

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Hello and thanks to everyone who replied! I was damn busy for all this time with the new label and other working projects, Finally I could dedicate some time to this project!

I have already contacted Toroidy.pl. to have an idea what would the price for a custom made transformer...... just to be fancy( but if the price will be too much I will go with the option under).

I have also found a solution on Banzai and the single toroidals price on Toroidy........
The price would be the same (considering I could pick up stuff from banzai directly in Berlin...) But from Toroidy I could order directly +18V, +45V and double +18V in order to have the + and - 15V........ With Banzai I should play with series and parallel....... I think I could stick with this as they aren't super expensive but I have a few questions..... what would be more performing between those two (Toroidy vs Banzai?)
I was thinking to use Banzai and designed a little schematic to help me be sure I really understood how to do it, but maybe having already the right voltages and needing to do only one series would be better.......

Anyway, the 230V of the primary voltage would be connected to the fuse in this way? (see pics) Sorry for the dumb question but this is not exactly my area of competence.... Also the Toroidal I should substitute have a lot of wiring on the primary side I don't really know what they do, I guess its coming from the primary voltage regulation you have with the fuse, but what will I need to do then if I will just stuck with +230? Just connect + and -?

Also, what VA (nominal power) should I look for? Would be 50VA enough? What would you suggest?

I will open again the mixer and check for shorts inside, I did a rapid check but no power lines seems shorted so far..... I will go a little bit more in depth with schematics before having a try with the new PSU.

Thanks again to everyone :)
 

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dunham91

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Actually the preventive from Toroidy was pretty fast and probably the cheapest option....

This is what i got for an option:
Audio grade transformers:
TS 60VA PRI: 230V
SEC I: 17,5-0-17,5V (1A @ 35VA)
SEC II: 17,5V (1A @ 17,5VA)
SEC III: 45V (0,12A @ 5VA)

The price would be basically the same of having all the singles transformer, and would be totally more easy to follow this way. I'm just concerned about the Current they can provide, seems a bit low to me....... would this fit?
 

Matt Syson

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Dec 17, 2005
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Hi
Go with the 'custom' transformer as it's power rating will be fine for what you need.
Just out of curiosity what price were you quoted for the 'custom' transformer?
Although switchmode modules are cheap and plentiful there are very goor reasons why you shouldn't just 'bung them in' to make a repair.
Oh an obvious question, have you checked the proposed dimensions of the replacement transformer? Will it actually fit in the space you have?
Matt S
 

dunham91

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Joined
Nov 14, 2021
Messages
7
Location
berlin
Hi
Go with the 'custom' transformer as it's power rating will be fine for what you need.
Just out of curiosity what price were you quoted for the 'custom' transformer?
Although switchmode modules are cheap and plentiful there are very goor reasons why you shouldn't just 'bung them in' to make a repair.
Oh an obvious question, have you checked the proposed dimensions of the replacement transformer? Will it actually fit in the space you have?
Matt S

Hello there! finally the toroidal has arrived! (yes, took more than a month...)

The price was around 100€ with the shipping, the first preventive was made on a wrong A calculation and the right one was 20€ more pricey, but still quite a cheap and fast solution.

The dimension were a bit bigger than the original, on paper I should have been able to fit it, in reality seems I will need to push it a bit inside, or create a hole and attach it on the bottom of the case or try to enlarge the previous one a bit (its about 0.2 cm larger than expected and not fitting perfectly, but I guess I will find a solution for it, its really not that much more!).

Now i have a bit of a doubt, as the Glass Passivated Bridge Rectifier WL10F is of course not available anymore, I found a substitute with better characteristics, I guess it should work as a drop in replacement but as I have already the topic open I will ask here:

file:///D:/Immagini/synths%20schematics/STUDIOMASTER/WL10F.pdf thats the original part, WL10F the exact model (last column).

https://www.mouser.it/datasheet/2/345/rc201_rc207-1893473.pdf RC207 would be my choice for the replacement (also last column).

What else should I check before switching it of again? Would be recapping the whole power supply a good idea? I was thinking to actually change all the old components in the PSU board, they are very few, most of them I have it in my laboratory so wouldn't be much of a job to me....... any Advice?

Also if I have to hunt for some kind of shorts I could have underestimated in my previous work, where should I start? is there any guide to follow for it?
In my work I'm used to deal repairing hardware with many channels and so, so I guess I will inspect the main power lines and if a short is present I will go deactivating one by one all the channels till finding the short, but maybe someone have a better technique for it!
 

dunham91

Member
Joined
Nov 14, 2021
Messages
7
Location
berlin
It is obvious from the pictures that your transformer has suffered significant damage and needs to be replaced. The bad thing is that this transformer is not simple because it has 4 secondary windings and it is difficult to find such a transformer as a ready-made product. The good thing is that all the parameters are known (all voltages and associated powers) so that such a transformer can be easily made in a local electrical shop. Or you can ask international suppliers such as Toroidy.pl.
I think that would be the cheapest solution. You also need to check all the parts in the power supply (stabilizers and rectifiers for sure). And replace 317 in phantom power with TL783.

Sorry for the noob question, but why not substituting the 317 in the phantom power with a normal lm317? They should be still in production as I can find them pretty easily and cheap. Wouldn't a TL783 need some kind of Resistance adjust? I will anyway order a couple of TL783, I already have the 317 in house.
 

moamps

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The maximum difference between the input and output voltage for the LM317 is about 40V, so in some situations in the power supply for phantom voltage can exceed this value and destroy the stabilizer. Therefore, it is recommended to use TL783 or LM317HVT, which have a higher Vo-Vi voltage. These stabilizers are pin compatible with LM317. If you really can't make that replacement, you can place one zener diode for a voltage of about 30 volts 2W in parallel with the diode 1N4004 which is connected via LM317.
 

dunham91

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Joined
Nov 14, 2021
Messages
7
Location
berlin
The maximum difference between the input and output voltage for the LM317 is about 40V, so in some situations in the power supply for phantom voltage can exceed this value and destroy the stabilizer. Therefore, it is recommended to use TL783 or LM317HVT, which have a higher Vo-Vi voltage. These stabilizers are pin compatible with LM317. If you really can't make that replacement, you can place one zener diode for a voltage of about 30 volts 2W in parallel with the diode 1N4004 which is connected via LM317.
Perfect, I was thinking the same. I will anyway to replace the rectifiers just to be sure and I will buy also a couple of TL783 then , I want this mixer to be operative as soon as possible :) Thanks for the support!
 
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jokeramik

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Sep 28, 2010
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Location
Germany
The LM317 for phantom-power is working in a floating mode. This is possible and not a problem for the IC.
Best regards!
jokeramik
 

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