G1176-FET (BF245A or 2N5457) Input HEADROOM & POT too lo

FIY, the R26-mod worked pretty good.

[quote author="enthalpystudios"][quote author="khstudio"]with the inputs @ the same level the units "Should" react the same... I think all of the 1176 side chains are very close if not the same circuit[/quote]

this is true, unless the side chain is built with different parts.[/quote]

This is why I wanted some more voltage measurments. I think I'm going to try the Original Transistors before I do the R26 MOD... I guess if you don't have any more voltage readings I can take some before & afters... but this still leaves me in the dark with refference to the Original 1176's voltages. I'd like to match them (in the sidechain)
Like: @ What voltage SHOULD the sidechain kick in (in the original)

I'm sure it's been asked before but I couldn't find it:
- How well does the Originals input impedence match up (or sound) with Modern 10k equipment... like 10k unbalanced inserts?

Thanks

I did the r26 mod today and it improved the headroom a bunch by making the sidechain less sensitive...

Cheers
Ray

Dudes

We fixed this awhile back with the 100K pot. i've got one inside my 1176 and its great, it works quite nicely.

[quote author="bradb"]Dudes

We fixed this awhile back with the 100K pot. i've got one inside my 1176 and its great, it works quite nicely.[/quote]

That's very cool :thumb:

But I'm trying to figure out WHY it needs the mod in the 1st place :?

Is it the different transistors ?

If it is... I'd rather change them.

And changing R1a to 3k7 (opamp balanced input only!) makes the input similar to the stepdown of the original tranny..both of thesemods together really improve the headroom..I have my input and output pots at 12 o'clock with a pre driving at -3 db and it compresses just right and sounds great..do the mods Kev...don't lose anymore sleep

Ray

OK, OK :green:

I'll do it... but "just for the hell of it" Has anyone TRIED the Original transistors? ...just to see. It would save be the bullshit of ripping them all out to see for myself, that's all.

I'm not too stressed about it...

Has anyone TRIED the Original transistors

Click to expand...

Yup. And chosen the substitutes according to the results.

Jakob E.

[quote author="gyraf"]

Has anyone TRIED the Original transistors

Click to expand...

Yup. And chosen the substitutes according to the results.

Jakob E.[/quote]

Wow..OK.

Thanks Jacob :thumb:

I've had a pretty eye opening day when it comes to these 1176's :shock:

OK... I like the 3.7k mod to match the Originals gain BUT my biggest issue with BOTH of mine (1xIC & 1xTranny input) is the threashold...

OK, I know about the MOD but I wanted to check things out for myself. So I did some research & found (in the UREI 1176 Manual) the threashold levels that the 1176 is suppossed to start compressing at:

20:1 = -24dB
12:1 = -25dB
8:1 = -26dB
4:1 = -30dB

Well, after I made absolutly sure my unit was properly calibrated, I injected these voltages into the input & it was DEAD ON RIGHT :!: :!: :!:
((Measured @ the 10k POT's wiper))

But DAMN... these are some LOW LEVELS It just doesn't make sense... no wonder I feel a loss of headroom.

-30dB = 0.024 Volt RMS / 0.069 PP Volts

... those levels are down there... WTF. None of my meters even go that low. I even tested my DISTRESSORS & they didn't kick in until close to 0dB (or just under depending on the Ratio)

My point is, when I put a mic pre in front, putting out .775 to 1v (or so)... it just KILLS the 1176 threashold level.

But damn, it's just like the manual said :sad:

I should be getting my Purple KIT in this week so we'll see if I'm crazy or not? (when it comes to the threashold, NOT the input level)

Thanks everyone for your input :thumb:
-----------------------------

How does changing the input tranny to 2:1 affect the impedence &/or the 12k loading resistors :?:

matthias - you had mentioned it didn't work our so well... could you give more details WHY?

Thanks

Dude, I feel you. I guess you just want your units to work and act like the original(s), but it might be time to do that R26-mod and just enjoy your compressors.

[quote author="ChrioN"]Dude, I feel you. I guess you just want your units to work and act like the original(s), but it might be time to do that R26-mod and just enjoy your compressors.[/quote]

#1
I AM enjoying them... I'm trying to learn about them a little more so I can make better decisions when it comes to modding, the way I feel they should work best for me... I don't mind if they are different than the originals. When I first built them I just left them alone & never spent time learning about the circuits like I NORMALLY do with ALL my DIY gear.

I will be doing the 3k7 MOD to the input (to lower the gain there) but I'm still unclear about the Tranny input :roll:

I'm going to hold off doing ANY mods until I see (& can measure) my Purple MC76. The low threashold MAY just be the nature of all the 1176's... I won't know til I have the other to compare to.

As soon as I saw the "Threashold points" in the manual I knew they were low & that my units were probably working correctly. (except for the input gain)

Just as a matter of note, it is normal for the input pot on an 1176 to be round about 10 o'clock position for regular compression.
With a 'Black Face' type a typical scenario with an 87 vocal mic. would be: mic gain 30 dB / 1176 on insert point - input pot at 30 position, output pot at 18.
I suppose Urie wanted to make sure they covered all bases when setting thresholds etc. I know that some desks (Harrisons for example) use a lot lower level at insert points (-6dBm), so the Urie settings would be more like 12 o'clock on in and out.
Just as an aside, on the standard Urie LA3A the gain control is normally set ridiculously low and a standard mod to reduce output noise and raise the level at the pot, was to reduce the gain of the output amp. by changing one resitsor.
On my LA3A's I actually replaced the output amp. with a Jensen 990 and used Jensen transformers throughout.

at first i saw your post in the thread 'originals' and then saw it here, but just wanted to say thanks for the comment regarding normal use of the actual units, since I know I've never personally even touched an original or a reissue, so I'm in the dark concerning a lot of the units operation.

the g1176's i've built are awesome, however, and I really love working with them, so I've started on a quest so to speak to find out all i can and to make my units the best they can be, and i'm to cover all the bases, but i've still yet to turn the knobs on an original, so thanks for that, it helps me out until i can get my paws on one.

i just want to try things with all the combinations among the originals and the clones around here.... different input stages, output transformers, and transistors. caps aren't something i'm all that interested in a/b'ing at the moment, i think the input/output stages and original/replacement transistors are probably most of whats going on.

i'm working on some purple units, some gyraf type chip input lundahl output, and some original transistor, chip input, 1:3.5 clone output versions, and I've made all my boards, except purple, with sockets so that once i've decided what i like best and is most useable i can make them the same. 4 combos, aside from the purple, which will be more or less my reference. i'm sure there's a good chance that there will be a 2 iterations that work in different ways for me, and i'll have a couple different flavors, but i'll see when i get there.

the whole point of this stuff, for me, is to have alll custom equipment. which is really why i'm excited to learn more and more, and work towards designing myself for my personal needs and goals.

the XXL 1176 schem on my wall gets a lot of attention, and hopefully i'll 'get it' thoroughly at some point.

The 1176 came in many different versions from the black face to the silver face - input transformer / 5532, Class A output, Class AB etc.
I have been fortunate to try many different versions and when I was rebuilding my own one (which was non-working when I bought it), I tried to incorporate the best things into it.
For my money, I think the input transformer and Class A output sounds the best and I would use the IC meter circuit from the later version as the original 2 transistor one is tricky to set up and drifts all over the place.
joe electro said a very interesting thing which I would also agree with - the original Teledyne FET (U2244) had a more 'musical' character to it than the later 2N5457 or 2N5458, but you would be lucky to find any U2244's in matched pairs. I got a pair of 2N5458's. What are you guys using in your clone versions?
All in all though, any version of the 1176 is a great limiter and testament to the fantastic design by Bill Putnam who was a great recording engineer.

well there seem to be a few with 2n5457's around, from what i read, but i think that most of the gyraf clones have been built with bf245a's. the ones i built with bf245a's weren't 'wrong' so much as i want to try each style of input, fet, signal/sidechain transistors, and output.

so i'm building 4 with 5532 inputs and class a/b output, as follows:

1 with replacements signal/sidechain Q's, and lundahl output
1 with original signal/sidechain q's, and lundahl output
1 with replacement q's and clone rev g output transformer
1 with original q's and clone rev g output transformer.

and then 2 purple kit units, which are kind of a different thing altogether, but i'll use as a reference as far as threshold and how they operate, more so than 'sound'

whew. its coming along fine, just need to do some metalwork really, the wiring is about done as well. everythings socketed, so on top of having 4 versions, i can see which fets work best, so really 8 combinations. whew again. with everything socketed i can make them all consistent or 2 consistent pairs based on what i like and what works for me.

!!!