All things G1176 - the new "repost" thread.

[gswan]

Are the DC bias conditions correct?
Is the gain of each amplifier stage correct?
Have you calibrated it correctly yet?

 

[casrec]

Hello all,
    I have a couple of questions about my mnats 1176 I would love some help with. I completed my unit, calibrated and compared to my UA 2-1176 and all is fine and sounds great. IMO I think it sounds pretty near identical and even a little better in extreme settings (all buttons in) for drum Overheads and a like. A little smoother, slightly distorted highs I am guessing due to the Higher THD In the OEPs. But, I want to reverse the input trannie to make more like the original. My question is, how do I reset the Q bias so I can recalibrate the unit. Do I just tighten it all the way in? I guess I am little confused about the fact that you can do it over and over again. Put in signal, adjust in and out to plus one set Q bias for I db drop. Readjust in and out for plus one and set Q bias for I db drop and so on and so on. So where is the staring point or how do you reset the Q bias? My next question is can you use the three deck attenuator with the OEP trannie with the mnats board or do you have to have a UTC or equivalent? Thanks a lot guys!

Brandon 

 

[casrec]

Here is my finished unit, I love the wood but had a few problems and it looks a little homemade.  :-\. I don't think I will ever try to hand stamp again. Front panel express here I come. .

 

[Echo North]

That is VERY cool.

Mike

 

[gswan]

I'd recommend removing any connections from the bolt going through the toroid. In doing so you can create a shorted turn (ie a loop around the toroid) if the other end is also connected to the case.
If you need a chassis earth stud this is not the place to do it. Use a dedicated stud for the earth.

 

[Chrome Heart]

Gotta tell ya casrec, that looks great. Doesnt look "homemade" to me at all. Very classy work.

 

[Echo North]

Holy crap nice catch Geoff!

Yes I would move that ground.

Mike

 

[casrec]

  Thanks guys, I will get on that right away. I am going to flip the in put trannie around and still have to hook up the stereo link so I will do it all at once. I didn't get any hum out of it, and it actually has less line noise than my UA 2-1176 which is pretty stinking low itself, but I will still move the grounds. Thanks for the great knobs mike, i couldn't use your push buttons i got from you because i already made my ratio boards and they didn't fit. But still a great product! Thanks guys,

Brandon 

 

[casrec]

Can anyone tell me what C16 does and if I need it? Thanks a lot guys.

 

[gswan]

C16 is a compensation cap. It's not required if you are using a TL071 device. It can be found on op-amps like the NE5534 etc, which allow for external compensation.

 

[casrec]

C16 is a compensation cap. It's not required if you are using a TL071 device. It can be found on op-amps like the NE5534 etc, which allow for external compensation.

Alright, thanks a lot ;D

Brandon

 

[diyfanatic]

hi guys!

just small questions!

I've got a 1k 1w carbon resistor (instead of 1k1) for R87, as it's more than twice the normal size I plan to solder with heat shrink on the back of the pcb. no issue here?

other thing, I've bought some orange drop 225p and 715, for C1,C10,C17,C5,C27,C22,C28
they are really huge (didn't tought), same plan, no issue?

cheers.
Jr.

great built BTW casrec!

 

[MartyMart]

Jr - well I wouldn't recommend it but you could do that, if you get any "issues" then
you have a lot of components on the back , no access for testing etc etc ... !!

I'd keep them on the top if I were you ....

MM.

 

[bpucekov]

Hi !
My 2-1176 finali finished, el. in, lundahl out. Thanks everybody for this great project and special thanks to my wife for toleration this thing on his kitchen tabel for months.
Branko

 

[casrec]

Hey Looks Great Branko, very nice work. Well, I have another stupid question! At Looking at the Urei Schematic for rev F there is no R84. A 1K  connecting the + and - post output trannie. And the schematic shows no connection taking place. And doing my math, don't know if I am completely right, but the resistor is just balancing itself out. Making .775v, .775v. Can Anyone tell me why this is here and why the + and - are conecting together? Thanks!

Brandon 

 

[onlymeeee]

R84 is for termination of the transformer.
Whether it's needed and the ideal value depends on the transformer you're using and also what's next in the chain.
If it's unterminated it can cause ringing or overshoot. If you add too much, it can reduce the headroom and high freq. Maybe even overload the output.
The best way to decide is to apply a 1khz square wave and observe what happens.

What transformer are you using?

The F version used a B11148 trannie and doesn't have a termination resistor. They changed the trannie on subsequent versions which then had a termination resistor.

 

[casrec]

R84 is for termination of the transformer.
Whether it's needed and the ideal value depends on the transformer you're using and also what's next in the chain.
If it's unterminated it can cause ringing or overshoot. If you add too much, it can reduce the headroom and high freq. Maybe even overload the output.
The best way to decide is to apply a 1khz square wave and observe what happens.

What transformer are you using?

The F version used a B11148 trannie and doesn't have a termination resistor. They changed the trannie on subsequent versions which then had a termination resistor.

I am using the mnats with the Oep. I was just looking at the schematic and noticed it. I am trying to make my own board for the challenge. I want to base it off the early rev F with an Oep on the input with a T attenuator and a carnhill on the out. My electronic skills are very rudimentary so mabye I am in over my head. But i would still like to give it a go. I also don't know how much a T attenuator will help. Even UA just feeds A pot from the Input trannie. So I don't know, will see. Thanks for the help. 

 

[Echo North]

UA just feeds A pot from the Input trannie.

This is true of their early re-issues.  A few years ago they reverted to a rev D type design using a T-pad attenuator and UTC O-12 clone.

Mike

 

[gary o]

Hi I love diy 1176 but when I use my fav pre that has fixed gain output so I have to have my input pot all way down nearly & is compressing all my vocals, sometimes I want this but mostly its too much, I also have to have make up pot on full & level is a little low, I tried a little mod I put a 100K pot between the board & the middle leg of FET Q 1 this seems to change the threashhold ,CW I get usual 1176, CCW I get no compression & anything inbetween I can now fiddle with input & output levels & new ratio pot if thats what its doing to give me gentler compression thus more output level......it was just a quick test really to see if would work & does seem to....as expected tho the meter is now wrong was thinking I could use a daul 100K pot & connect the other 100K pot between middle leg of Q10 and the board where it went, I know daul pots halfs dont track that well tho....was wondering if I could try a single pot between attack & release pots feeding the Q1 Q10 via R7 & R48.....or will that just mess with attack & release times ? trouble is I dont have too much electronics theory in my brain still ....anyway Im not too worried if meter is not accurate   

Cheers

 

[gswan]

Probably not a good idea since it will also alter the bias point of the FET.
You could do it by changing that amount of signal being fed into the GR amp section (ie at point 15), or change the amount of -ve bias summed with the GR rectifier output at point 21.