Seck 1882

 Posted by on April 15, 2008  Add comments
Apr 152008
 

Last updated on September 6th, 2011

Hey man, hope all is going well with your visitors this week (editors note: SGI USA visitors to set up SEIN network)

Seck 1882 Mixer Manual I have attached the service manual for the Seck 1882, let me know what you think

Also here is a link for already partially built PSU
https://www.fivefish.net/diy/default.asp
I know there are for outboard, but they seem to have the same voltages, regulated 18+/- & 48 phantom
Would they work if we added a transformer and rectifying

Looked at the transformer on Maplin. How do I choose the right size?
Thanks once again for all info

I’ve added a few books that might build on the knowledge for this post – SP

  6 Responses to “Seck 1882”

  1. Thanks Dave.
    Old Studiotoe is hacking into another mixer now as I think he’s given up on the Seck… Perhaps you could let him know how easy it is to get a PSU going…? !! And how much was the Seck? 😉

  2. Many thanks …. Great site for the old seck I have 2 a 12 and an 18 .. You would not believe how much I got the 18 for …. Making a PSU at the moment ..

  3. Get it Paul. Bid at the very last minute. The parts would cost you about £50 with a box and you’d need a custom connector on top and replace the one in the mixer. I’d go with that one – even it was broken. In fact, get a broken one if you can if you don’t get this one as the parts are dead cheap to replace – the connector and box is a lot of the price and adds to the usability.

    Oh! Also remember that modern parts are generally a bit smaller, especially things like electrolytic capacitors. This has two benefits;

    1. You can fit them into the space easier
    2. There’s more room for air to circulate – hence better cooling

    Strangely Perfect

  4. Hi, I saw this item on eBay and thought you might be interested.
    What do you think?
    How much would the parts cost roughly to build mine?
    Should I get?
    Paul

    ps Hope you are well and enjoying your visitors

  5. Hey man, thanks for all that info
    With my limited knowledge, I have absolutely no idea which way to go from here
    What do you recommend?
    Obviously Id like to keep the £s down, but at the same point I want the best quality that is going to effect performance
    So it’s over to you, when you’ve got time
    Ill just go and and buy it, you tell me how to put it together and then Ill solder
    What do you think?
    Have a good one
    I really appreciate all the time and energy you have been putting in to help me
    How are things going with your visitors
    Are you learning much?
    Any interesting stories?
    Thanks
    Paul

  6. Hi Paul

    Welcome to America!

    Check out https://www.ti.com/lit/ds/symlink/ne5532.pdf This is the spec sheet to the main input op-amps in your mixer from the manual you sent (on page 12). You’ll see that the recommended max voltage (Vcc-+) is 15V which is what we said.
    The EQ section is a standard set up using TL072 op amps. The specs for these can be found here https://www.ti.com/lit/ds/symlink/tl072.pdf You’ll see on page 6 that Vcc max is +-18V which again is like I said it would probably be. This op-amp is a bit noisier but has a higher slew rate, hence it’s choice c.f. the other one in it’s mic input stage.
    You’ll see that the circuits for both in your manual are standard op-amp ones just like in the books!
    The heaphone amp mentioned on page 19 uses two transistors, BC637/8 which can be found here https://www.radiovilag.hu/images/BC639-640.pdf You’ll see the max open circuit voltage of the things (Vceo) is >60V which means that they are getting their electric from the unregulated power supply, which is what I suspected.
    A ZTX212 is mentioned as part of a switching circuit so I think it’s a standard thing as I can’t find much about it.

    For the power supply, which they describe on page 21, circuit on page 55 which is really useful. They use a transformer with two secondary windings which I said, one of which is centre tapped to produce the split power rails. They’ve shown the (industry standard) voltage regulators of 7815 & 7915 which give 15V + and 15V – This explains why the higher rails aren’t regulated but everything comes off the one secondary. There’s a standard little equation that you use to choose the voltage range needed for your transformer. I can’t remember off the top of my head but it’s really easy-peasy. However, they’ve done the work and you need a 16-0-16 secondary capable of delivering 2A (the fuse size!)
    Also, they’ve voltage protected the power supply with a chip controlled SCR (Thyristor). The chip is the MC3423 and details are here https://www.icbase.com/pdf/ONS/ONS09170407.pdf and here https://www.datasheet4u.com/html/M/C/3/MC3423_Motorola.pdf.html This is extra overkill. I never used any of this extra protection stuff with my things I made – I was just very careful to avoid short circuits etc.
    What I did do was oversize the main capacitors for extra smoothing and use power transistor power control from a zener diode (i.e. use the zener to regulate the 2N3055 which can handle 15A !!! The circuit is in my old circuits thing (scan attached). It’s at the bottom right. Page from ETI Magazine: ETI Circuits No.2

    I found that circuit to be the most useful thing.

    Quite often, I never even used a bridge rectifier but used discrete power supply diodes of the right rating as they are cheaper and have nice long stiff leads to be used as part of the wiring. All you then need is a big reel of insulating sleeving (about a quid) to make sure there are no shorts!
    If you can’t get a transformer with the right windings, the 48V phantom supply is really low current so it only needs to be the smallest available. It’s a 40V winding, but you could just get a ready made phantom supply or not use it at all (it depends if you intend to use phantom powered mikes with the mixer – if you never intend for this then it’s needless expense). The 16-0-16 secondary can in actual fact be anything from 12-0-12 to 18-0-18 and everything will be okay. If you are worried, you could regulate the 24V rails and then none of the output transistors would pop and you’d have the benefit of extra smoothing etc. Doing this would allow you to choose transformers like 25-0-25 safely.
    The only things close on the Maplin site are N14CF & N32CF say.
    Otherwise, see places like https://www.theelectronicsshop.co.uk/Spares/transformer%20chassis.htm or https://www.parmeko.co.uk/html/transformers.html who don’t supply direct I suspect, but call them and they’ll tell you a supplier. A twenty quid transformer will be big enough. Don’t spend more unless you have to. https://www.theelectronicsshop.co.uk/Products/Spares.htm is actually pretty good. They’ve got a shed load of stuff buried in their site including 2500W amps!, mixers (neat Behringer with all effects), pots, speakers, case handles and all sorts. They have a little 0-24,0-24 transformer for £2.77 that would series up into 48V ac which you could then regulate down to 48V dc! They’ve even got little boxes, plastic & die-cast suitable to put custom stuff into!

    The fivefish kits look okay but you’d need to tag on some separate rails. Overall, they’d save a lot of fiddling about I suppose but you’ll have import taxes I guess.

    There’s a lot in the SECK manual. It’s a good thing to learn from in combination with other books and stuff.

    TTFN

    Rees

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