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compasspnt

Diamond Forever

Posts: 21,216 Member Since: 08/01/2011

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Jan 29 11 1:23 PM

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Hey Keith,

I know you are somewhat of an expert on the innards of the venerable 1176 compressor.

Would you mind explaining in general the differences in the various revisions, I think they had A through G?

Also, I have seen a couple of people say that the 1176 was the "transistor version of the 176."  In my mind they are nowhere near each other.

Thanks!

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ssltech

Aqua Marine

Posts: 4,058 Member Since:22/01/2011

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Jan 29 11 3:01 PM

Near each other? -perhaps neighbours in the same solar system! one is a variable-mu element, the other is a FET. -If they can be considered very "similar" then it shoudl be possible to make a FET version of a Fairchild... (I think not!)

The 176 ...and 175, and -rarest of all the 177 are OPERATIONALLY similar to the  1176 et all, insofar as the threshold is fixed, and the input gain drives the compression. (Unlike other units which have a threshold control for example). (the 177 had no metering, and the 175 I think had no 'trim' controls (labeled "Vernier"); just the stepped input and output levels)

This is somewhat timely, because last week I dropped off a newly-completed 'Bloo' 1176 type unit to a local studio owner for his opinions. -I'd built it specifically to investigate why my OTHER bloo units sounded 'hairy'. -People LIKE the way they sound, and everyone told me that the units did NOT sound like Purples or UA's when you pushed them hard. -I wanted to find out why, but nobody wanted me to 'change' anything, in case it lost the 'mojo'!

-So I built a third, and -surpise surprise- NO MOJO!

I ended up with the lids off of all three, probing around and looking at all of the revisions, and I discovered where I'd used a 'wrong' value resistor in the output stage. -This was biasing the output to run MUCH hotter, and causing some power rail 'sag', which was fuzzing the output stage (and others, probably!) somewhat.

So I made the 'effect' switchable, and have dropped it off with a trustwirthy engineer, for evaluation. -Also last weekend, I dropped the original two off for Colin Richardson to use on a project... Again, I'll hear back on how they were perceived.

SO... Revisions:

The first ones were Blue-Stripe and Revision A. Only about 25 were made.

There was a interim Revision 'AB' which had minor resistor and capacitor changes, I understand.

Revision B followed shortly, still blue-stripe. This used FETs ONLY for the gain reductionand metering bridge elements... Two FETs per unit. (Revisions A and AB had used FETs in the input stage as part of the signal amplification path).

Revision C was the first black-face, and the first to bear the 'LN' mod from the factory. -Earlier 'B' versions were able to be retrofitted with "the blob", which was an epoxified lump of circuitry designed by Brad Plunkett (later designer of the LA-3) to reduce noise and control distortion around the FET.

Revision D re-laid out the main board to include the blob components on the board, but apart from the layout, nothing changed.

Revsion E also nothing in the circuit changed... just a slide-switch added to the transformer primary winding to allow switchable AC voltages.

Revision F saw the output stage changed from a tertiary-wound transformer driven by a class-A all-discrete signal path, to an IC driving a simple primary/secondary output transformer. This was capable of driving higher loads with less distortion, but is less loved.

Revision G saw the INPUT transformer eliminated and replaced by a differential IC front end. (The input transformer had changed from a 'Peerless' in the earliest blue-stripe models to a UTC "ouncer" by the start of the black-face 'C' revisions). By now, the gain reduction meter-drive circuitry was also an op-amp, and units were cheaper to manufacture, though less loved. MOST of these last units were silver-face, but black-face versions exist. NEVER judge a unit by its front panel!

Note: Revisions C, D and E were all the same in terms of circuitry, -Any B units which have "the blob' inside were ALSO the same circuit. Revisions A, AB, F and G and B without 'the blob' inside are all different from one another, and from the "golden" period from C to E'.



On a related note: I was rummaging the other day, and delighted myself to discover TWO new-old-stock 0-12 "ouncer" transformers in a box I'd forgotten about. -Guess who's going to build a couple more 1176 replicas? -Maybe I'll have a crack at the version 'A' this time?

Keith

-Keith Andrews -If I can't fix it, I can fix it so [i]NOBODY[/i] can fix it!

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ampman1961

Silverado

Posts: 90 Member Since:29/01/2011

#3 [url]

Jan 29 11 5:15 PM

Keith...
Thank you. Finally, I understand why my friend's Blue Stripe sounds different from his E and purple units.
It feels and sounds like THE GO TO guitar compressor/limiter. He now owns 2 Bloos.

"Life is too short for Solid State" Billy Yates Red Jones Amplification Venice California 310-425-2566

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trock

Platinum Blonde

Posts: 1,073 Member Since:21/01/2011

#4 [url]

Jan 29 11 6:22 PM

seriously, thanks for that info keith. i am always wondering about the different versions when i read about who has what and used what etc

thats fantastic

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ssltech

Aqua Marine

Posts: 4,058 Member Since:22/01/2011

#6 [url]

Jan 29 11 8:41 PM

No, I'm afraid that's true... The last one which I built was when my assistant at the time -Carlos- brought me his kit which he simply never built up or finished.

I gave him what he paid for all the parts, and slowly pieced it together.

As of right now, the best kits are Hairball Audio. They offer revision A, D and G I think.

The only bits that one might do well to upgrade would be the input and output transformers. -There are probably a couple of non-authentic bits in the power supply regulation, but if you're looking to do one yourself, they;re "close enough" and at least offer revision A type cases.

Of course, if David Kulka  corrects me on any of this, I defer to his close ties with Universal Audio and hie deep familiarity with a good number of historic units.

The next couple I might build may be Hairball audios with a blue stripe case... the case looks pretty good, but makes no claims to be the genuine article (i.e. no "UREI" or "Universal Audio" branding).

See what I mean:
http://hairballaudio.com/shop/product_info.php?cPath=31&products_id=56

Keith

-Keith Andrews -If I can't fix it, I can fix it so [i]NOBODY[/i] can fix it!

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LeforaGuest

New Forum Friend

Posts: 0 Member Since:24/06/2017

#7 [url]

Jan 29 11 9:18 PM

Thanks, Keith.

I've been eyeing the Hairball stuff for a while actually. I've been itching for a little project, and that seems like something I could manage.

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philip

Silverado

Posts: 96 Member Since:29/01/2011

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Jan 30 11 11:18 AM

I have a pair of orignal E revisions, I also have a UA 2-1176 which I like just as much.

However I see a lot comments that the UA re-issue(the single and the twin version) compared to the original. doesn't sound very good compared to the original.

If actually true, why is this the case? Since so many seem to be doing DIY versions and some even copying the less respected F/G revisions like the Mohog guy (which seem to have a good rep),

what are they all doing that even UA seemingly cannot do themselves, or is this just the usual internet BS?

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ssltech

Aqua Marine

Posts: 4,058 Member Since:22/01/2011

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Jan 30 11 11:40 AM

There have been a few things which have been tricky to replicate: the original input was ALL passive up to the FET, and this comprised a constant-impedance attenuator, a transformer, a resistor and then the FET. The input attenuator was expensive, the transformer was expensive. When they were replaced by active circuitry and a simple pot, the way in which the units react to the SOURCE impedance changes... so units which sounded very similar when connected to one insert send (for example) reacted somewhat differently to one another when following the output of a Neve preamp, for a random example... It's not just the compressor sounding different, it's how it loads the preceding device which can make THAT sound a little different...

Cost of manufacture was WAY lower, and the attenuators were getting difficult to source. -Lord knows, I struggled to find them with my first units! -So low-cost and availability probably drove the changes.

In any piece of gear, the transformers will have subtle effects varying with source and load, and just copying the turns ratio and the laminations/wind structure simply doesn't always produce an identical result... this is why the Pultec Peerless output transformer is going for mega-bucks these days.

So if you can't get an ouncer at the input, and a properly wound output transformer, things might be slightly different. -I haven't had to look at any of the 2-1176's, even though we have a dozen or so of them at work. None the less, I seem to recall that in the LA-610 for a comparative example, Universal audio skipped a couple of transformer stages, to keep costs down. -Also, the board layout is VERY different, and that tends to spook people.

The DC voltage regulation may be different... I'd be surprised if they still used the "heat-the-resistor-and-zener-up-until-you-can-roast-wieners-on-them" approach on such a crowded layout... That might make a pronounced difference in terms of how the output 'sags' under high output loads. -Mind you, I'm not 100% certain that the Hairball/Mnats kits don't also use the active DC regulation... Later 1176's (the class A/B output versions) also used the same regulation, and people didn't like them so much... Who knows which parts are responsible for what part of the mojo?

Keith

-Keith Andrews -If I can't fix it, I can fix it so [i]NOBODY[/i] can fix it!

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ssltech

Aqua Marine

Posts: 4,058 Member Since:22/01/2011

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Jan 30 11 11:51 AM

Oh, here's a complete pdf with schematics of all the varions versions towards the end. It's almost 13Meg, so why not right-click-and-save while you're at it.

http://www.jblproservice.com/pdf/Vintage%20JBL-UREI%20Electronics/UREI-1176LNmanual.pdf

it also shows revision 'K', and uses a slightly different labeling for the first three... what I'm calling revision'A' it gives no revision letter, to, what I'm calling AB, it calls 'A', and then we agree from 'B' onwards.

Note the +30V regulator changes in revisions G, H and K, compared to the earlier "heat it all up" crude zener regulation.

Keith

-Keith Andrews -If I can't fix it, I can fix it so [i]NOBODY[/i] can fix it!

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yz

Aqua Marine

Posts: 2,831 Member Since:26/01/2011

#11 [url]

Jan 30 11 3:38 PM

Hey Keith,

I have a basic question...  in technical terms, what exactly happens when in 'all buttons in' mode?

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gregdixon

Gold Finger

Posts: 484 Member Since:30/01/2011

#12 [url]

Feb 5 11 5:34 PM

Keith, The Hairball/Mnats versions do use the power supply from one of the latter revisions. No idea how his transformers compare to the originals, but they sound fantastic. I built a pair of Rev Ds and a Rev A last year. Both designs have more 'personality' than the ones I built from the earlier Mnats boards, using OEP transformers.

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bob olhsson

Aqua Marine

Posts: 3,343 Member Since:25/01/2011

#13 [url]

Feb 6 11 12:19 PM

...It's not just the compressor sounding different, it's how it loads the preceding device which can make THAT sound a little different...

-ssltech

How devices react to different loads can be a major part of how they sound. This is why well respected people can have such vastly differing opinions about the merits of a given box.

www.audiomastery.com Bob's room 615 562-4346 georgetownmasters.com Georgetown Masters 615 254-3233 www.thewombforums.com

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volki

Tin Man

Posts: 21 Member Since:06/02/2011

#14 [url]

May 13 11 7:27 PM

After having digested the schematics of all those revisions, I'm wondering about the sonic relevances of some smaller, less discussed changes (some of which have been hinted at) which happened through the years.
To aviod confusion, I'll be referring to the revisions as indicated in the manual linked in Keith's post above, where the original circuit has no revision marking, the first revision being A, then B (bearing in mind that the original circuit is alternatively called "A", with first actual revision being named "AB").

The big differences obviously are:
- original circuit and Rev. A ==> T600 attenuator + Xformer front end / 2-transistor preamp / 3-transistor Class A output amp + 5002 Xformer
- Rev. D/E ==> changed preamp to 3-transistor circuit incl. LN mod (revised coupling to the gain reduction FET)
- Rev. F ==> changed o/p amp to Class AB +11148 Xformer
- Rev. G ==> changed front-end to bridging active I/P stage


Now which of the following, less discussed changes, would also affect sonic differences to a notable degree?

- different Attack time constants: R54 changed in Rev. A and B, C27 added in Rev. A and changed in B
- Changes in the associated network for Q-Bias Adjust (R35,59,60,85) in Rev. A and B

- (if minor) resistor value changes / additions on the Ratio switches in Rev. A, B, C, E and F

- Different coupling of base of GR FET to the I/P signal: Before the preamp I/P through C1/R6, as per Original & Rev. A, or tapped off the preamp NFB loop through R6/C3/C9, as per Rev. B and onwards. (actually, I'm not even sure why the GR FET is fed forward / fed back a portion of the I/P signal in the first place, anyone care to fill me in?)

- Original & Rev. A: both preamp and o/p amp have an FET in their 1st stage, from Rev. B onwards they're changed to all BJT circuits

- Rev. A: additional Feedback path from Q6 emitter through o/p Xformer primary back to source of Q4
- Rev. B: Bootstrap from Q3 back to Q2 in the preamp (said to reduce 3rd harmonic distortion... by a noticeable amount?)
- Rev. E: Resistor value changes (and tolerance restricted to 1%) around Q9 in the S/C amp
- Rev. F: "Output" pot changed from 250K to 100K
- Rev. G: switch from Zener to Voltage Regulator IC for the +30 rail (might result in different performance at high o/p levels?)
- Rev. H: change O/P xformer to 12614


I'm definitely going to build at least one version, maybe even incorporating alternative switching between different topologies within the circuit, but just out of curiousity I was also thinking about breadboarding several versions including those "minor" changes... which I wouldn't bother to do if there are no significant sonic differences.

Thanks a bunch for any input!


Volker Meitz

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mdm

Platinum Blonde

Posts: 1,736 Member Since:27/01/2011

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May 30 12 5:23 PM

I built one but prefer tube compressors..sold it.

One thing that Keith mentioned but perhaps is not fully explained is that the 1176 does change the threshold, depending on the ratio, so that at 4:1 you would get a lower threshold than at 20:1

the reasoning behind these 'presets' is quite good IMO:  at 20:1 you are limiting and therefore you want the the threshold high to attenuate just the peaks.

at 4:1 you are compressing the dynamic range so you want the threshold lower.  This way, since the ratio is low, you can also have a similar output for all 4 presets.. if it were not so you would get a louder output on the low ratios.

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ssltech

Aqua Marine

Posts: 4,058 Member Since:22/01/2011

#18 [url]

May 30 12 6:41 PM

A few other people actually do the same trick Max... SSL buss compressors being one example which springs to mind.

What's 'funny' about that is that while the UREI just has input and output gain controls, and doesn't specify anywhere where the onset of limiting is supposed to happen, the SSL actually has a threshold control marked in dB... which amuses me a little, since the actual threshold of limiting onset 'shifts' depending on the selected ratio... basically doing what Max describes.

However, I did explain it here... -Two paragraphs after the subtitle "sensitivity training".

-Keith Andrews -If I can't fix it, I can fix it so [i]NOBODY[/i] can fix it!

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mdm

Platinum Blonde

Posts: 1,736 Member Since:27/01/2011

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Jun 1 12 8:47 AM

Yes, I was just expanding on that.

I wonder how much of the percieved 'sound' of these compressors is actually due to a fixed and 'technically correct' threshold setting for each ratio? ..as opposed to placing the threshold level too high or too low and then playing with the volume controls too much.


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ssltech

Aqua Marine

Posts: 4,058 Member Since:22/01/2011

#20 [url]

Jun 1 12 11:04 AM

I don't believe that they owe much of their 'sound' to that; -It's a nicety of convenience. but I'd prefer to steer away from sonic preferences and musings, and concentrate on definite information, I think.

-Keith Andrews -If I can't fix it, I can fix it so [i]NOBODY[/i] can fix it!

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