1176 low gain..

Hi guys, i'm testing my new 1176.
Is it normal a gain of -6 dB at max volume?
when i'm trying to put up the volume it's start a gradually distortion.
it seems that the out gain is -6dB low circa than the original UA 1176.
I checked all the values of the components but i didn't find a solution, can you help me?
any suggest is appreciated..
Thank you in advance.
Corrado

Yes, the G1176 has some 6dB less gain than the original, due to a different output transformer ratio.

You could reverse wire the output transformer, wireing it 1:2 to get higher gain - like the original.

There is a post somewhere about which traces to cut and which to connect in order to do this..

Jakob E.

Lowering R33 will give you some more gain. It's a trick from the old forum and it worked for me.

ThX, now i try, i will try also the trafo connection.. :grin:

I tried to change R33 to 4,7K with no significant changes.
Jacob did you knows where is the notes about trafo wiring changes?
THX

http://www.groupdiy.com/index.php?topic=8180

I know you already found this - just for reference if others are looking..

Jakob E.

Ok, now i solved the gain problem.. :wink:
but like before i feel a strange behavior.
In bypass mode and with low compression 1:4 (attack and rel slow) i have got no distortion, but if i move Att&Rel to the max and also the ratio 1:8, 1:12 and 1:20 the sound is really dirty, distorted.
I have to move down input signal to have a clean sound, of course in this case it will be not compressed..
all the components seems right, i checked again (i've built 2 of these 1176, with the same behaviour).
I'd a reissue of a 1176 in my studio for more than 1 year, but i didn't remember any distortion.
somebody had the same behavior?

Don't worry, this seems to be normal.

Remember, that on the 1176, the attack/release goes "the other way", with fastest setting all the way up. And attack is REALLY fast on 1176.

With fastest attack and release you will have distortion, like on any compressor that is set this fast. Including the original.

Jakob E.

Yes, but i feel a strange operation mood on control pot..
I would to reassume, maybe something is wrong with my pot (Buyed from RS), on the box was written 2 log and 2 lin, but stamped on the pot was all A (mean lin?) and i'm not sure these are ok.
also on BC107, have to be C type or B?
on transistors are not specified, can be a problem?
again, i didn't find BD 517 and BD 518 and i used the BD 135 and BD 136 wired as explained from NRG recording site.
Now i forgot for the BF245..i not remember if is A type..
Sorry Jacob, today is a little bit chaotic..

Which control pot do you feel has a strange behaviour?

BC107 can be B or C type.

BD135 and BD136 should be fine if wired as on Franks site. Also, you said that audio passes fine without higher compression, so output stage is probably okay.

Don't worry, most of my day are chaotic!

:green:

Mark

But BC 107 without any letter is important? what's the difference?
With pots on the middle position i don't have got any Hum..(not @ 50Hz more higher)<70dB, but if i'll move cw or close (in or out pot) i feel a hum that comes up near to 50dB.. open or close..
maybe is a ground problem..

Ah yes,

That's a problem I found when doing the +6dB gain mod! Because the output stage gain is rising +6dB, the noisefloor (including any ground noise) is also raised +6dB. I did a simple fix- I wired a piece of insulated wire diagonally across the board like this:



To find the optimum place to connect the wire, I connected one end to the ground trace where the centre-tap of the transformer enters the board, and with the unit powered up, and monitoring the output with both controls up until I could hear the hum, touched the other end of the wire to parts of the ground trace on the other side of the board. When I touched it onto the far side of the board, the hum reduced significantly (>12dB lower!)

This may not work for your setup, because I have a feeling it depends how you have your other grounds organised in the unit, but this helped my friends unit a great deal- it only needed to be done after the +6dB gain mod.

The "Gain Groups" of the transistors are organised by letter- no letter is unsorted, A is low gain, B is medium gain, and C is high gain (can't remember the actual hfe group ratings...

Handy page explaining transistor markings

...but it's something like A= <100, B= 100 to 500 C= >500

I think I remember Jakob saying that the circuit is designed to work with any hfe range transistors- they're all working at quite low gains anyway, and are all bias stabilised.

(BTW, make sure you don't confuse the hfe gain of an individual transistor with the actual gain of a transistor amplifier stage- the hfe is a measure of current gain Ic/Ib. The AC gain of the transistor is set by the collector load and emitter resistor. Some circuits rely on a higher hfe transistor, but this is often more to do with impedance transformation and current amplification and overcoming feedback than actual "stage gain" and "voltage gain" for AC)

Mark

Thanks, Mark.

There is a confusing way of marking pots.

10KA means 10K Linear
10KB means 10K logarithmic

but

A10K means 10K logarithmic
B10K means 10K Linear

..that is, most of the time. To make sure, set your pot to middle position, and measure resistance to each end. If the two resistances are about the same, it's linear. If one resistance is 1/10 to 1/3 of the other, you have a log pot.

Jakob E.

:grin: wow, i will try ASAP..
i tell you if it's work..except for these small things i'm very proud for these units..

[quote author="gyraf"]Thanks, Mark.

There is a confusing way of marking pots.

10KA means 10K Linear
10KB means 10K logarithmic

but

A10K means 10K logarithmic
B10K means 10K Linear

..that is, most of the time. To make sure, set your pot to middle position, and measure resistance to each end. If the two resistances are about the same, it's linear. If one resistance is 1/10 to 1/3 of the other, you have a log pot.

Jakob E.[/quote]


finished wiring my 1176 and when i turn it on there is a huge amount of hum and buzz. i used the mnats revision j board push switch version. Audio passes through it but cant even hear any compression really. useed shielded cable for all the audio . even buzzez when the power is off and cord is out of it. I just found a problem where i need to attatch the shield from xlr input to the chassis. where should i attatch the ground from the power input module? to the meter pushboard ground?

Ok...Where to start? My 1176 is Mnats version with the output wired 1:2 (Lundahl)..When driving it with an input that approaches -3 db my output knob is set around 2 or 3 (!!) at most regardless of the ratio...So my question to you guys is..are you driving it with a clean, balanced , hot signal either from a pre or a console? I did the mod that made the compression kick in a a higher threshhold and it helped a ton. Did you go with the electronically balanced input or transformer? Are you driving the 1176 output balanced into a balanced input on your DAW, Console or Tape machine? Impedance imbalances can do alot of funky things too.
I do not get much distortion at all unless I clip the inputs of my DAW...Post more details and I am sure we can all help you guys out!

Cheers,
Ray

[quote author="raysolinski"]Ok...Where to start? My 1176 is Mnats version with the output wired 1:2 (Lundahl)..When driving it with an input that approaches -3 db my output knob is set around 2 or 3 (!!) at most regardless of the ratio...So my question to you guys is..are you driving it with a clean, balanced , hot signal either from a pre or a console? I did the mod that made the compression kick in a a higher threshhold and it helped a ton. Did you go with the electronically balanced input or transformer? Are you driving the 1176 output balanced into a balanced input on your DAW, Console or Tape machine? Impedance imbalances can do alot of funky things too.
I do not get much distortion at all unless I clip the inputs of my DAW...Post more details and I am sure we can all help you guys out!

Cheers,
Ray[/quote]

yes running a clean hot signal from great river pre to the 1176 then balanced in to the daw. used the input transformer instead of electronically balanced version. well, I attatched the shield of the input xlr lug to the ground bolt but then all audio including buzz was eliminated. i have the ground wire from the POWER input module to that same bolt. so im thinking if i attatch the ground from the Power input module to the ground on the meter board it wont buzz cuz its one continuous ground from end to end. please tell me if my logic is screwy.

For all projects I simply attach all ground points seperately to the same place on the chassis (a star ground) and also attach the mains ground there from the ac input (NOT the positive or neutral AC..the middle ground pin on an IEC)...Never had a buzz or hum in anything. If attaching the input xlr (pin 1) to ground shorts your audio then you have some wiring issues or what you think is the ground pin on your xlr isn't. I know it is a pain in the a$$ but look at your input section very carefully..sounds like you have on of your hot inputs (2 or 3) grounded. That would explain the shorting when you ground pin 1 and the weak signal input and distortion (you are only getting half the signal)..I am merely guessing this because the same thing happens when I accidentally use an unbalanced cable on my patchbay with my 1176..and I have done that more than a few times!!

Ray

[quote author="raysolinski"]For all projects I simply attach all ground points seperately to the same place on the chassis (a star ground) and also attach the mains ground there from the ac input (NOT the positive or neutral AC..the middle ground pin on an IEC)...Never had a buzz or hum in anything. If attaching the input xlr (pin 1) to ground shorts your audio then you have some wiring issues or what you think is the ground pin on your xlr isn't. I know it is a pain in the a$$ but look at your input section very carefully..sounds like you have on of your hot inputs (2 or 3) grounded. That would explain the shorting when you ground pin 1 and the weak signal input and distortion (you are only getting half the signal)..I am merely guessing this because the same thing happens when I accidentally use an unbalanced cable on my patchbay with my 1176..and I have done that more than a few times!!

Ray[/quote]

So helpfull thanks. I thought that i was going to have to replace my trimpots and all. Ill double check the audio input and output and get back to you with results. Thanks sop much for your fast response. Its my first one and Im proud of the damn thing even it its current state ( shambles)

Derrick

[quote author="raysolinski"]For all projects I simply attach all ground points seperately to the same place on the chassis (a star ground) and also attach the mains ground there from the ac input (NOT the positive or neutral AC..the middle ground pin on an IEC)...Never had a buzz or hum in anything. If attaching the input xlr (pin 1) to ground shorts your audio then you have some wiring issues or what you think is the ground pin on your xlr isn't. I know it is a pain in the a$$ but look at your input section very carefully..sounds like you have on of your hot inputs (2 or 3) grounded. That would explain the shorting when you ground pin 1 and the weak signal input and distortion (you are only getting half the signal)..I am merely guessing this because the same thing happens when I accidentally use an unbalanced cable on my patchbay with my 1176..and I have done that more than a few times!!

Ray[/quote]

tried it and there is still loud hum, audio is distorting, meter isnt even showing signal. the uv lamp brightens up when audio passes through. So frustrating :?