Suggest 1.8K for R12 in mnats and other 1176LN Rev D DIY builds

[Stagefright13]

Wow Great find! I always wondered why my first Mnats rev D worked differently from the other 3. I thought it was the Cinemag out or something I did... I still have 1.8's here. Guess I have to change out 3 of them. Then they should all match.

Thanks,
John

 

[hitchhiker]

I note also that the Purple schematic I have shows a 910 ohm resistor used as well so that might be something worth looking into if you own one of these units...

Wow! I built a Purple kit and now I'll have to check it out.  Is it possible that all the Purple Audio 1176 should receive a service bulletin?  Nice work David

Cheers,
Lance

 

[dandeurloo]

Good catch!  I linked this to the stereo 1176 thread as well. 

Again thanks for sharing the info.

 

[Alistair]

Changing R12 to 1.8k should not affect calibration, audio gain, or sidechain gain at all.

Doh!  Sorry, I guess I missed that post.  Unit is sounding great, much more friendly on bass signals now, and I can start with Input and Output at 12 o clock and work from there, rather than having them both sitting below 9oclock all the time.

 

[envelope]

Thanks David. I bought a used DIY 1176 here, I was told was working as it should but he just didn't like them...after I tried them out, they seemed a little 'off' to me.

now they are working perfectly with R12 changed

 

[ethervalve]

Hey I'd just like to add that I'd had an issue getting the stereo linking board to work with my Rev D's but switching to the 1.8K resistors for R12 fixed the issue--the pair are tracking 10+ dB's of gain reduction accurately now.
Thanks for sharing the info.

 

[canidoit]

I have updated my BOM Excel sheet with this new info for those people downloading it and replacing r12 on my build with the 1.8K resistor.

 

[buildafriend]

The original UREI Rev D and E schematics show 910 ohms for R12, but many examples actually use 1.8K, as do the UREI Rev F version and the UA 1176LN reissues. Basically, I think the 910 ohm value was a mistake that crept into certain D's and E's. (Some D's and E's do use 1.8K, which makes me think UREI had a service bulletin or upgrade procedure that addressed this.)

If you use 910 or 920 ohms instead of 1.8K, DC bias in the Q3 / Q14 section will be incorrect, and you'll lose about 8 dB of headroom in the input section. You'll also have less limiting. (Since Q3 / Q14 precede the sidechain circuit, having less gain before clipping at this point forces you to run the input pot lower, reducing the amount of limiting available.)

The error in the value of R12 is understandable, since 910 ohms is shown on the old schematics. But these units will work and sound much better with 1.8K. I can't imagine any benefit to using 910 but if you disagree, please speak up.

(I wasn't sure whether I should start a new thread or post on the main 1176LN Rev D DIY thread, but decided on a new thread because the topic seemed deserving of attention.)

my rev f mnats (23.05.09) 2009 board asks for a 1M resistor on r12. now I can see this is hitting the collector of q2 and base of q3 where as there is a 22k resistor biasing q3's collector (r18).

 

[poctop]

thanks For catching this ,
i have done the mod here on my 4 units,
one of them had the 1.8K already ,

best,
DAn

 

[Winetree]

Just ran accross this. Does this apply to orginal units?
I have 4 orginal Urei 1176LN blackface "D' versions.
Should I pull them from the rack and check R12.
If so would R12 be labeled on the P.S.B.
Could I leave it in the curcuit and just measure accross it with removing it?

 

[pucho812]

You can't leave a resistor in circuit and measure it as it will never read the correct value. You have to at minimum have one leg of the resistor out of circuit to get a correct value reading.  Now IN IMO if the units were sounding fine to you then why even bother to look unless there is an operational issue.

 

[Winetree]

It's just the Mod-ness in me.

 

[ruairioflaherty]

Well as the lucky owner of four original units there is no one better placed to answer your question than you.  You will be able to read the resistor color code without unsoldering anything.  If indeed your units have the "wrong" resistor in place why not mod one and compare it to an un-modded unit?

 

[Winetree]

Great Idea. I'm in the middle of studio rebuild.
Probably be a couple of months and I'll look and give it a try.

 

[ruairioflaherty]

Excellent.  If you need ears or a great speaker system to compare I am in the neighborhood...

 

[David Kulka]

Just ran across this. Does this apply to original units?
I have 4 original Urei 1176LN blackface "D' versions.
Should I pull them from the rack and check R12.
If so would R12 be labeled on the P.S.B.
Could I leave it in the circuit and just measure across it with removing it?

Yes, as I mentioned in my OP, some original units have this problem. (That's where the error originated.) You can check the resistor value by looking at the color code on it.

 

[mnats]

You can't leave a resistor in circuit and measure it as it will never read the correct value. You have to at minimum have one leg of the resistor out of circuit to get a correct value reading.

I'm not anxious to help the poster who you were replying to but this blanket statement doesn't always apply. It all depends on context; a parallel resistance can cause a reading different from the one marked on the body but in this case there is a capacitor in parallel so you could easily tell if there's a 920 or 1.8k there (if you can't be bothered reading the color code).

In the consumer electronics repair world we don't have the luxury of pulling out every resistor's leg to test its value - maybe it's different in pro audio where they pay you enough to have the time...

 

[pucho812]

that is true but in pro audio land I'm usually not testing every resistor unless absolutely necessary and I haven't had to do that in ages. 

 

[Spadehead]

Changing R12 to 1.8k should not affect calibration, audio gain, or sidechain gain at all.

Doh!  Sorry, I guess I missed that post.  Unit is sounding great, much more friendly on bass signals now, and I can start with Input and Output at 12 o clock and work from there, rather than having them both sitting below 9oclock all the time.

Old thread I know but help! I thought this thread was the answer to my problem - 2 Rev Ds and a Rev A that all seem to have a hot input and I seem to always have to have input and output set around 9 O'clock all the time as well.

I popped open one of the Rev D units, expecting to be able to swap out R12 but I already have the 1.8K resistor there so what else could be causing this? It seems that WAY too much signal is entering my units, meaning lower headroom and generally too much compression going on.......

I've scratched my head about this thinking it could be patchbay issues, balanced/unbalanced or whether I need pads etc but none of my other comps are affected in this way (LA-3As, dbx 160, Xpressor) so I'm not sure what's going on.

All three units are affected in the same way even though they are different designs so maybe I've missed something?

Any help greatly received guys, thanks in advance.....

 

[poctop]

As i understood on this thread it did not seems that a recalibration is necessary but notice that my GR mode odb comprression is now off by at least a 1db or 2 db can somone confirm that the unit do not need recalibration cause my meter now says diefferently or it is just a matter of re-Zeroing the meter in GR mode to zero again ,

Let me know,
Best,
dAN <