1176 compressor output transformer alternative - diyAudio
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Old 9th March 2011, 08:11 AM   #1
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Default 1176 compressor output transformer alternative

Hi all,

I've been looking at the urei 1176 compressor schematic and often wonder why this unit must have a output transformer on it. Is there another method in which i could use the output of this circuit without the use of a an output transformer. When you look at the schematic for this essentially it is the most expensive part of it. If you could eliminate the output transformer it would make it more viable to build. So could anyone suggest to me how it could be removed from this circuit. I would appreciate any help i can get as far as i can see before it hits the output transformer it hits 13.7 volts so i assume that it would have to be brought down to about 4 volts peak to peak. cheers http://www.gyraf.dk/gy_pd/1176/1176sch.gif
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Old 9th March 2011, 02:23 PM   #2
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Those are DC voltages, not signal.

I'm sure the trafo is for lowering the output impedance and isolation, but their diagram doesn't match the Lundahl diagram.

The nominal output voltage would be around 5V RMS or less before the trafo.
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Old 9th March 2011, 03:01 PM   #3
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You do not need the output transformer at all. These are useded in professional gear to provide a balanced, floating output of nom. 600 ohms.
If the transformer does not have a 1:1 turns-ratio (I did not look-up the specs) you may need to adjust the gain of the output amp.
But...why would you use a 30+ year old design as a DIY project when modern and better designs are available?
E
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Old 11th March 2011, 09:42 AM   #4
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Thumbs up better designs

Hi thanks for the responses what new designs would you suggest are better than the urei 1176 for some reason all audio engineers seem to put this particular design of compressor on a pedastool. Iam more than happy to try new designs and i have a particular interest in compressors i have been trying a few different ones to see. I have seen the optical designs that are out there such as the what compressor and mnat joe weak optical design haven't seen any other fet designs for diy always nice to find a pcb layout if possible or a vero but not always possible but not a huge problem to make your own if you find a really good schematic that will do a great job. Iam trying my best to work out how to one day design some different components but not at that competency level just yet but love building the different designs that i find around the place. Lots of good stuff out there i take my hat of to some of the guys they do a really good job at what they do in regards to some of the projects very talented. i really enjoy reading about them. If anyone can suggest any good compressors to do for diy yourself i'd love to hear about it and converse on how they go. cheers
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Old 11th March 2011, 02:33 PM   #5
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THAT2181. At THAT Corporation Audio Technology
Check their app notes for lots of usefull info.
E
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Old 12th March 2011, 04:19 AM   #6
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Default can't get that chips

Hi any full projects for compressor like the urei 1176 rather than over priced unavailable chips in australia that is. that are on the the diy plane for compressor there aren't any i know of of i guess it make an old 30 year old design more viable when you take a look at the prices of that chips and that there not easily available still open to other options.
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Old 12th March 2011, 12:54 PM   #7
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The old stuff does have particular sonic signatures that some engineers prefer over the modern stuff, but some of it comes from the output trafos. If you're up to building it you could replace the entire line amp section with a modern output buffer circuit, but it wouldn't be an 1176 any more.

It sounds like you want to build a high quality unit on the cheap, but if you add it all together including high quality switches and such, the trafos don't add that much to the price.
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Old 12th March 2011, 05:49 PM   #8
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seedseed: These ICs ar less than US$5, available through Mouser. I can mail you a bunch of the THAT2151 (predecessor to the 2181 and they needs to be trimmed for min. dist.)
PM me if you are interested. E
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Old 24th April 2011, 08:25 PM   #9
Tajzmaj is offline Tajzmaj  Slovenia
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Hi to all.
This particular circuit of 1176 is LN version with 1:1 output transformer. If you look carefully there is an electrolityc cap between output stage and transformer. There was an earlier version of 1176 with class A output stage where was used special transformer......If you want to build this compressor there is a lot of information on Gyraf's page......Because I build some of these for my use here you got some advice. First of all. This is very good and nice sounding compressor, It can't be compared with chip compressors. It has unique sound and character. If you decide to diy it use newer boards....I think it is rev e or f....if you want to avoid trace cutting to get rid of hummmmm. The most expensive part is enclosure. Than you need some pots and switches...and of course nice analog VU meter. The transformer is ,,standard 600:600e so dont worry. But you need some experience to build it and to calibrate it. At the end there is just minor cost to buy such transformer. But it is also possible to wound it yourself. And there is also a lot of information on ,,prodigy professional,, forum........
Diy transformer.
Core ei42
Primary 500 turns
Secondary 500 turns
If you wound for an example
p1=166 turns
s1=250 turns
p2=166 turns
s2=250 turns
p3=166 turns
you will get good results and frq response.
Of course you need to connect p1,p2,p3 in series and s1,s2 in series.....it is also possible to wound it on some other core but must be very similar in dimensions. I don't know exactly how thick was a package of laminations but I think some 15mm. I can check if you want......
Best regards
Taj
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Old 24th April 2011, 08:27 PM   #10
Tajzmaj is offline Tajzmaj  Slovenia
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Location: Ljubljana
P.S.
It is also possible to change a ,,gear,, slightly because 1176 somehow lack of gain....so my advice is to wound a slight step up.......some 600 turns for secondary should work....
Regards
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