1176 Rev D cap BS

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soundguy

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Joined
Jun 4, 2004
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Location
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looking at the Rev D schematic, it looks like C14 is a .033 cap. Looking at the circuit board, theres a silk screen for an electrolytic and all the pics of 1176's Ive seen have electrolytics there. Is that just a mistake on the schematic or what? What does that cap do exactly? If you were building one from scratch, what would you do? If I use a poly cap in there, will the supreme being come down and demand to get his map back?

dave
 
If I use a poly cap in there, will the supreme being come down and demand to get his map back?

I'd be more afraid of all the singers whining about not sounding good.

:guinness:
 
Hey Soundguy. is that for that blank Urei PCB that you have?

BTW. I emailed Purple Audio about parts and PCBs and stuff for 1176s. They said they'll be making DIY kits and parts available soon.
 
For what good it's worth I have a real 1176 (silver face, so a later one) in my studio, if anyone needs me to look at anything for them or take a photo.
 
The C14 on the rev#D (Class A-circuit!) shunts the primary of the output transformer. Make this capacitor anything near electrolytic values, and you'll short your output signal. Larger than the recommended 33nF makes no sense here.

On the other hand, the C14 on later 1176 models (Class AB circuits) has an entirely different function. Here it acts like a bootstrapping cap, allowing the driver transistors to swing further out to supply rails. This definitely requires a electrolytic - not smaller than the used 22uF.

So C14 is not always just C14..

Jakob E.
 
[quote author="ytrehalf"]BTW. I emailed Purple Audio about parts and PCBs and stuff for 1176s. They said they'll be making DIY kits and parts available soon.[/quote]Is Purple Audio's 1176 a faithfull clone the original circuit or is it a new take on a classic circuit?
Kelley
 
its based off the class A o/p stage... 600 Tatten on the front end. The hardest part about this comp is getting those Tatten..

quality is better IMHO.. full ground plane on the top layer of the board. only issue I have is for it to be a "modern" deign it would have been nice to see the board compacted into a smaller space.
 
kelly-

the mc76 is an 1176. Wether or not it is a "faithful clone" IMO is a pretty subjective thing considering Urei has had several different versions of the 1176 as well as the UA reissue gone through different changes. The purple has a lot of bypass caps in it, which Ive never seen in an older 1176. The transformers are mounted off the board, LED's instead of incandescent lights on the meter, lots of little stuff like that, PCB mounted on the switch bank, etc. They sound very good. They are a lot cleaner sounding than what I expect from an 1176, but Ive always credited that more to their choice of components rather than the little changes in design they've made.

jakob- thanks for clearing up the differences between the two!

dave
 

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