Trident Trimix PSU and input module questions

[Brinxter]

Hi guys

I have 12 old Trident Trimix channels that I´m about to rack and I would love some advice from you experts.
I wanted to know if anyone here has done any mods to these channels and what I should maybe look into doing (maybe nothing). I need a power supply to power the channels, I have schematics of the original psu but they were thought to be substandard to drive the whole mixer, do you guys know why?

Best regards
Biggi

 

[Rob Flinn]

I used this PSU design which I nicked from AMEK when I had a trimix with 39 input channels.    It worked really well & has upto 5A capability depending on what secondary voltage your mains transformers you use.    I managed to fit it in the original PSU box by using encapsulated toroidal transformers bolted on the back of the PSU case.    I used T03 package LM338k regulators which fitted in the original heatsinks.  I used the existing 48v & 5v (I think) supplies.  This all allowed me to run the power down the original Power cable to the console.    If you have no 5v you could use half of the same PSU design for the 5v with a different mains transformer.

When I first got this console  I was using the original PSU supplied this desk & I wasn't really noticing a big problem I only changed it because one of the unobtainable regulators blew up.  The one frame 18 channel versions are probably more than fine with the original PSU & if you're only using 12 channels ................

I never modified the channels, they sounded ok once I had recapped them & given them a clean, & I always had a lot more fun doing a recording than using a soldering iron, so prefered to balance my time that way.  If you can get on the YAhoo group Trident users forum there is a load of stuff about swapping op amps out.  The main one was making sure the summing amps weren't using TL071's (mine were 5534's anyway).  In every position for op amps there is the easy potential to change to 5534's since the boards have an unpopulated place for the 22pF compensation capacitor.

 

[pvision]

Before you stuff 25 V AC up that circuit... isn't a rectifier required? Or 25 V DC?

Nick Froome

 

[Rob Flinn]

Before you stuff 25 V AC up that circuit... isn't a rectifier required? Or 25 V DC?

Nick Froome

That's correct.

 

[Brinxter]

Wow great thanks for the response i´ll be sure to check this out Rob

 

[Rob Flinn]

Here's a pic of the extra transformers mounted on the back of the original supply.

 

[Rob Flinn]

Here's a pic of the extra new PSU components.  I mounted them on a turret board since that was an easy way to lay it out & also there would be no issues with current delivery on weedy pcb tracks.  It s mounted on the heatsink that has the 2x  LM338k's on it.  n the bottom left hand corner you can just see part of the original transformer which is still used for the 48v & 5v rails.  I think I bolted some big rectifiers to the box somewhere.

 

[Brinxter]

Nice work Rob I´m also thinking about balancing my direct output by  inserting a 5534 driver amp and 2503/2623 ( they both have 75ohm primary impedance)  transformer, i might even go as far as bypassing the onboard fader booster amp and inserting an Api clone one directly after the fader to drive the direct out, any takers  ;D

 

[abbey road d enfer]

Nice work Rob I´m also thinking about balancing my direct output by  inserting a 5534 driver amp and 2503/2623 ( they both have 75ohm primary impedance)  transformer, i might even go as far as bypassing the onboard fader booster amp and inserting an Api clone one directly after the fader to drive the direct out, any takers  ;D

Beware that a 5534 may not be capable of driving correctly such xfmrs. They are designed with low nominal inductance, resulting in a rather high magnetizing current at low fequencies, even with an (almost) unloaded secondary.
This choice of low inductance is guided by the resulting high frequency extension, at the cost of necessitating a rather strong driver.
Actually, the combination of a 2520 and a 2503 wired as a 1:3 step-up is capable of driing a 600r load at 26+ dBu. Do you need that?

 

[Rob Flinn]

Nice work Rob I´m also thinking about balancing my direct output by  inserting a 5534 driver amp and 2503/2623 ( they both have 75ohm primary impedance)  transformer, i might even go as far as bypassing the onboard fader booster amp and inserting an Api clone one directly after the fader to drive the direct out, any takers  ;D

I understand your keeness to modify the desk.  Personally I would get the channels working first.  You might just like the sound which would save you a whole load of grief.  No point in fixing something that isn't particularly broken.  Then again you might hate the sound ....

 

[Brinxter]

Beware that a 5534 may not be capable of driving correctly such xfmrs. They are designed with low nominal inductance, resulting in a rather high magnetizing current at low fequencies, even with an (almost) unloaded secondary.
This choice of low inductance is guided by the resulting high frequency extension, at the cost of necessitating a rather strong driver.
Actually, the combination of a 2520 and a 2503 wired as a 1:3 step-up is capable of driing a 600r load at 26+ dBu. Do you need that?

Hi and thanks for the reply.
I want to rack these channels so I wanted to balance the direct output, need is maybe a bit strong but more like want. Any suggestions on balancing the outputs are greatly appreciated

 

[Brinxter]

I understand your keeness to modify the desk.  Personally I would get the channels working first.  You might just like the sound which would save you a whole load of grief.  No point in fixing something that isn't particularly broken.  Then again you might hate the sound ....

The channels work, but they are not going to be in a desk, the frame has been scrapped, but I´m going to rack these channels and wanted to balance the direct outs any suggestions  8)

 

[abbey road d enfer]

The channels work, but they are not going to be in a desk, the frame has been scrapped, but I´m going to rack these channels and wanted to balance the direct outs any suggestions  8)

You may use a transformer, one that is rated at about 2.4 kohm. There are several of them available. They should be adequate for driving standard line inputs (not 600 ohm).
Or you may use an active balanced stage; there are several possibilities, but the THAT1646 is the best combo of performance and ease of implementation.
Or you could choose impedance-balanced, that comes at the expense of two resistors and one capacitor.

 

[Brinxter]

Thanks for the replies Greatly appreciated. I was given a 220watt Mackie analog 8-bus power supply, which has +-18 volts, can I use that instead of a +-17volts?

 

[Rob Flinn]

Probably.  Depending on the regulators used, you may be able to dial the voltage down a bit.   

 

[anders]

I am feeding the direct outputs into Jensen 123-S output transformers. Jensen secondary/output is strapped to edge connector 19&20, factory hardwired to motherboard Molex B, 3&4. Those points makes for an additional/optional  balanced output. The stock TL071 direct output /fader buffer (IC3) should not have any problems driving modern 10-20 kOhm impedance line inputs, at least not over "reasonable" cable lengths. If you still want to swap those ICs, the OPA 134 is regarded as a "stiffer" line driver. TL071 and OPA134 will be fully compatible, as neither offset trimming pins 1,5,8 are connected in this circuit. Of course the OPA will draw some more current, but you avoid the NE5534-style compensation cap.