Toft ATB Power Supply Problem

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Floti

Well-known member
Joined
Feb 20, 2013
Messages
128
Location
Düsseldorf
Hi! I did some changes to the master module in my Toft ATB and by reassembling it I connected it the wrong way. In the master module there is a connector for the optional meterbridge, but there is also a ribbon cable inside that fits that same connector and is actually intented to provide power to the optional digital card. I connected the wrong one (stupid me!) and made a short that led to my PSU fuses blowing. After fixing it the master module is fine and sounds great but there is a constant loud 100 hz hum. So I checked my PSU and the negative rail is stop on, but the positive rail is giving me 29V instead of 17. I have no schematics and forgot to take some pictures, but you guys are really smart and can probably help anyway! The PSU has one secondary per rail that goes to a chasis mount bridge rectifier followed by two tip141 voltage regulators (also per rail). After that there´s a trimpot in both rails. I checked for visibly blown capacitors or burnt components but didn´t see any. Swapped the secondaries to see if the problem was in the transformer and the negative rail was still spot on, so I guess the transformer is fine. Checked for continuity between the capacitors legs to see if there was a short somewhere but there wasn´t. Tried to change the output voltage with the trimpot with no success. Also realized there is one large IC per rail. I thought that had something to do with the LEDs in the frontpanel, but actually I have no clue. So, until now my suspects are the TIP141s, the trimpot, mabe the IC and the caps, even if they look fine. Yesterday I had no time to keep checking and playing around, but I´d like to fix this today after work. Do you guys think know where the problem might be? Have you had something similar??

Btw, the master module sounded really good and I wanted to ask if maybe the higher voltage is the reason why. Is there a way I could hot rod the PSU to work at for example +-18V? Would that be dangerous somehow?

Thanks in advance!
 
Floti said:
but the positive rail is giving me 29V instead of 17.
Seems you have blown the TIP's. Normally, the PSU should work fine after replacing them.
Btw, the master module sounded really good and I wanted to ask if maybe the higher voltage is the reason why. Is there a way I could hot rod the PSU to work at for example +-18V? Would that be dangerous somehow?
It would make most of the IC's working closer to their certified limit, which may or may not be a problem. I've seen several pieces of gear with 5532's and TL072's operating at +/-20V; they were running hot but they worked. I wouldn't do it myself because of the probable reliability issues, AND because the benefits are incredibly small. I'm not sure the perceived improvement is real.
 
Yes, check the TIP power transistors.
Measure the junctions between base/collector and base/emitter.
They should behave like two diodes, but chances are that collector and emitter are now 'shorted'.
 
Thank you guys, I have ordered the TIPs from Farnell, hope they are here tomorrow! In my local store there´s only TIP142 and 147. I read the datasheet and I guess they are not interchangeable..

And about hot-rodding the psu, I guess I´ll leave as it is, thanks for the advice!

 
Floti said:
Thank you guys, I have ordered the TIPs from Farnell, hope they are here tomorrow! In my local store there´s only TIP142 and 147. I read the datasheet and I guess they are not interchangeable..

And about hot-rodding the psu, I guess I´ll leave as it is, thanks for the advice!
TIP142 is perfectly swappable for TIP141; it has a higher voltage rating.
 
I figured that out after I wrote my reply, but they didn't have it too in the local shop. The 141 are cheaper and on their way, hope I can finish this tomorrow. Thanks again!!
 
You need to replace the shorted transistors to give you back your +/-17vdc. Check the lm v-reg chips, there is one per each 17vdc rail.  The chips in the  toft are tl072's except the preamp chip which is either an ina217 or that 1510, depending on manufacturing date. You will find a 2134 for the headphone amp and 5532's on the main out's if it's stock. The benefits of upping the psu from bi-polar 17 to bi-polar 18 would be negligible from a head room point of view
 
> 5532's and TL072's operating at +/-20V

'5532 is rated +/-22V.

'072 is not.

I used to run "28V rated" power chips at 34V. Worked about a decade (maybe 1,000 hours) and failed. Replaced, went another decade, failed. At this point the chip was "last buy", I got two, and retired ASAP.
 
back in the day trident made special tl072's made that ran off +/-20,  at least that is what I have been told.

I used to work as a service tech for toft/trident.
F
or starters aside from the previous post, in the mixer, malcom did a wonderful thing. He had this idea to have a 2trk digital I/O for the stereo buss. However it was too costly to make or have made as he was not designing that, so it never was put in. However they left the ribbon cable that was supposed to be for power to the digital card in case that would ever change.  To further malcom it, they also had a similar ribbon cable coming off the master channel going out of the desk to feed power to the meter bridge.  Where malcom succeeded was he use the same 10 pin head connector  for both connections.  The only way to tell the difference is the one for the digital section is  soldered  to a little power distribution PCB on the side of the frame.  The one for the meter bridge has the 10 pin header on both ends of the ribbon as the mating connector is on the master channel and on the meter bridge.

FWIW  there will never be a digital option, and in the right circumstances the ribbon that was  to providing power for that digital card, can act like a radio antenna.  You would best to remove it all together.

Other things you can do is replace the preamp chips (IC1) with AD ssm2019. it offers a differnt sonic then the INA 217. I won't say better I will say different.

Oh and avoid jim williams mods I find them to be very sterile....
 
Thanks for the comments! I actually did the J. Williams mod to the master module, just the stereo buss. I am not really confortable putting video chips in there, but wanted to try it out. Apart from the horrible hum, I run a mix through it before and after the mod and it actually sounded more open, with better low end and more alive. I didn´t touch anything else. I guess the many electrolitics that are taken away and the dc coupling in the opamps +-V rails are actually not bad. I don´t know about the ic changes. Maybe the TL072 are actually better for audio, do you have an opinion? I actually want character and don´t mind minimal noise or distortion if I can´t hear it in a mix. I suspect the video chips are probably too clinical, too clean. But I truly have no experience with them, so I can´t tell.

My board is a rev3. I haven´t checked the input modules yet. I didn´t want to fully unpatch the board since I wanted to compare the changes in the mix. I actually was planing to make more changes in the board to get it sounding as good as possible, but since you have experience with these thing I´d like to ask you your opinion about it. I like the board and the possibilities it gives me.

I´ll take out that ribbon cable, that´s actually a good idea.

I hope the TIPs arrive today and I can get the board running again tonight.

Thanks again!
 
> trident made special tl072's made that ran off +/-20

Doubt Trident made chips.

For large orders, chip makers will negotiate special specs. Not 80V on 40V parts, but if standard is 36V and the chipmaker knows they try for 40V every day, then for a few bucks more they will watch the process very closely so breakdown is well above 40V and they can promise 40V operation.

(It is not impossible some other customer had an extra-spec part already tested and in occasional production, so Trident got some of those.)
 
PRR said:
> trident made special tl072's made that ran off +/-20

Doubt Trident made chips.

For large orders, chip makers will negotiate special specs. Not 80V on 40V parts, but if standard is 36V and the chipmaker knows they try for 40V every day, then for a few bucks more they will watch the process very closely so breakdown is well above 40V and they can promise 40V operation.

(It is not impossible some other customer had an extra-spec part already tested and in occasional production, so Trident got some of those.)

sorry I ment to say  I had heard trident had tl072 chips  made for them that would do +/-20VDC.  ;)
 
Floti said:
My board is a rev3. I haven´t checked the input modules yet. I didn´t want to fully unpatch the board since I wanted to compare the changes in the mix. I actually was planing to make more changes in the board to get it sounding as good as possible, but since you have experience with these thing I´d like to ask you your opinion about it. I like the board and the possibilities it gives me.



Thanks again!

RE 3 boards,  are real good. They have the balanced outputs and are mechnically sound in the pot department. The original boards did not have bracing for the potentiometers, which caused them to break in shipment as the channels are held to the frame via the pots.  The rev 3 boards are quite nice.

The board itself is a kin to a trident 80B, the eq circuit is a part for part copy as is most of the desk. To save on costs, Malcom made it all transformerless and did a different preamp topology. In this case they went with a monolithic all in one preamp chip, that both the mic in and the line in  on the channel run through it, the monitor path is separate.  Unfortunately there is no way around that.  You can replace the preamp chip with a few pin compatible preamp chips.  They are: that 1510(which were used in the rev 1's and part of rev2 production), INA217(currently in use), and SSM2019 by analog devices. I can't say any are better because my ears are different then yours but they all will work. Jim williams also has some plug in kind of think that can go in place of those but all I ever saw them do was cause more problems for my clients then not.  I have heard the jim williams master channel mods, I am glad you like them. 

As for modding the desk? beyond swapping preamp chips? it's mostly tl072's chips which is not bad. The desk sounds pretty good stock and is quite usable as is.  not quite sure why one would want to mod something that as is, is pretty good.

 
Well, the truth is that it´s almost more about the fun of customizing something and making it unique than anything else. I´d love to add transformers to this board, or replace components that might offer benefits over the stock configuration. It´s not that I´m trying to turn a consumer board into a professional high end thing, it´s that if I have fun doing and troubleshooting AND it can be somehow better, then why not? I noticed I can drive the output harder now without sounding dull (is that the word? I don´t know). It´s nice for me to not have to so anal about levels and actually be able to get a bit into the red. About sterility, that´s not what I´m aiming for, so I won´t follow Jim´s instructions any further, the master module was enough. But I have enough outboard color to allow me a relatively sterile board to mix through.

But I understand your point of view and think that actually you are right, it´s a nice thing for the price, let´s just use it and get the most out of it.

Anyway, if you could help with schematics, I´d be really thankfull. PMI refuse to share them and I´d like to (at least) understand how this all works without having to reverse engineer it myself.
 
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